Sonneberg plate photometry for Boyajian's Star in two passbands

Abstract: The F3 main sequence star KIC 8462852 (Boyajian's Star) showed deep (up to 20 mission. A 0.164 mag (16 the analysis of photographic plates from the Harvard Observatory. We have gathered an independent set of historic plates from Sonneberg Observatory, Germany, covering the years 1934-1995. With 861 magnitudes in B, and 397 magnitudes in V, we find the star to be of constant brightness within 0.03 mag per century (3 best 119 plates. Results are supported by data from Sternberg Observatory, Moscow, which show the star as constant between 1895 and 1995. The previously claimed century-long dimming is inconsistent with our results at the 5-sigma level, however the recently reported modest dimming of 3 not inconsistent with our data. We find no periodicities or shorter trends within our limits of 5 Oct 1978.

star
sonneberg observatory
constant brightness


Non-standard Models and the Sociology of Cosmology

Abstract: I review some theoretical ideas in cosmology different from the standard "Big Bang": the quasi-steady state model, the plasma cosmology model, non-cosmological redshifts, alternatives to non-baryonic dark matter and/or dark energy, and others. Cosmologists do not usually work within the framework of alternative cosmologies because they feel that these are not at present as competitive as the standard model. Certainly, they are not so developed, and they are not so developed because cosmologists do not work on them. It is a vicious circle. The fact that most cosmologists do not pay them any attention and only dedicate their research time to the standard model is to a great extent due to a sociological phenomenon (the "snowball effect" or "groupthink"). We might well wonder whether cosmology, our knowledge of the Universe as a whole, is a science like other fields of physics or a predominant ideology.

cosmology
cosmologist
standard model
sociological phenomenon
snowball effect


CLASS: The Cosmology Large Angular Scale Surveyor

Abstract: The Cosmology Large Angular Scale Surveyor (CLASS) is an experiment to measure the signature of a gravita-tional-wave background from inflation in the polarization of the cosmic microwave background (CMB). CLASS is a multi-frequency array of four telescopes operating from a high-altitude site in the Atacama Desert in Chile. CLASS will survey 70% of the sky in four frequency bands centered at 38, 93, 148, and 217 GHz, which are chosen to straddle the Galactic-foreground minimum while avoiding strong atmospheric emission lines. This broad frequency coverage ensures that CLASS can distinguish Galactic emission from the CMB. The sky fraction of the CLASS survey will allow the full shape of the primordial B-mode power spectrum to be characterized, including the signal from reionization at low ℓ. Its unique combination of large sky coverage, control of systematic errors, and high sensitivity will allow CLASS to measure or place upper limits on the tensor-to-scalar ratio at a level of r=0.01 and make a cosmic-variance-limited measurement of the optical depth to the surface of last scattering, τ.

cosmic microwave background
array
reionization
upper limit


Bayesian Methods for Analysis and Adaptive Scheduling of Exoplanet Observations

Abstract: We describe work in progress by a collaboration of astronomers and statisticians developing a suite of Bayesian data analysis tools for extrasolar planet (exoplanet) detection, planetary orbit estimation, and adaptive scheduling of observations. Our work addresses analysis of stellar reflex motion data, where a planet is detected by observing the "wobble" of its host star as it responds to the gravitational tug of the orbiting planet. Newtonian mechanics specifies an analytical model for the resulting time series, but it is strongly nonlinear, yielding complex, multimodal likelihood functions; it is even more complex when multiple planets are present. The parameter spaces range in size from few-dimensional to dozens of dimensions, depending on the number of planets in the system, and the type of motion measured (line-of-sight velocity, or position on the sky). Since orbits are periodic, Bayesian generalizations of periodogram methods facilitate the analysis. This relies on the model being linearly separable, enabling partial analytical marginalization, reducing the dimension of the parameter space. Subsequent analysis uses adaptive Markov chain Monte Carlo methods and adaptive importance sampling to perform the integrals required for both inference (planet detection and orbit measurement), and information-maximizing sequential design (for adaptive scheduling of observations). We present an overview of our current techniques and highlight directions being explored by ongoing research.

adaptive scheduling
planet
velocity
importance


Rescuing Quartic and Natural Inflation in the Palatini Formalism

Abstract: When considered in the Palatini formalism, the Starobinsky model does not provide us with a mechanism for inflation due to the absence of a propagating scalar degree of freedom. By (non)–minimally coupling scalar fields to the Starobinsky model in the Palatini formalism we can in principle describe the inflationary epoch. In this article, we focus on the minimally coupled quartic and natural inflation models. Both theories are excluded in their simplest realization since they predict values for the inflationary observables that are outside the limits set by the Planck data. However, with the addition of the R^2 term and the use of the Palatini formalism, we show that these models can be rendered viable.

palatini formalism
inflationary model
non-minimal coupling
gravity


Statistically Anisotropic Tensor Modes from Inflation

Abstract: We consider the inflationary universe with a spectator scalar field coupled to a U(1) gauge field and calculate curvature perturbation and gravitational waves (GWs). We find that the sourced GWs can be larger than the one from vacuum fluctuation and they are statistically anisotropic as well as linearly polarized. The GW power spectrum acquires higher multipole moments as 𝒫_h ∝ (1-cos^2θ+cos^4θ-cos^6θ) irrespective of the model parameters.

scalar field
gravitational wave
anisotropic inflation


Polycyclic aromatic hydrocarbons in the dwarf galaxy IC 10

Abstract: Infrared observations from the Spitzer Space Telescope archive are used to study the dust component of the interstellar medium in the IC 10 irregular galaxy. Dust distribution in the galaxy is compared to the distributions of Hα and [SII] emission, neutral hydrogen and CO clouds, and ionizing radiation sources. The distribution of polycyclic aromatic hydrocarbons (PAH) in the galaxy is shown to be highly non-uniform with the mass fraction of these particles in the total dust mass reaching 4 regions and correlate well with atomic and molecular gas. This pattern suggests that PAHs form in the dense interstellar gas. We propose that the significant decrease of the PAH abundance at low metallicity is observed not only globally (at the level of entire galaxies), but also locally (at least, at the level of individual HII regions). We compare the distribution of the PAH mass fraction to the distribution of high-velocity features, that we have detected earlier in wings of Hα and SII lines, over the entire available galaxy area. No conclusive evidence for shock destruction of PAHs in the IC 10 galaxy could be found.

aromatic hydrocarbon
galaxy
mass fraction
metallicity


Understanding higher-order nonlocal halo bias at large scales by combining the power spectrum with the bispectrum

Abstract: Understanding the relation between underlying matter distribution and biased tracers such as galaxy or dark matter halo is essential to extract cosmological information from ongoing or future galaxy redshift surveys. At sufficiently large scales such as the BAO scale, a standard approach for the bias problem on the basis of the perturbation theory (PT) is to assume the `local bias' model in which the density field of biased tracers is deterministically expanded in terms of matter density field at the same position. The higher-order bias parameters are then determined by combining the power spectrum with higher-order statistics such as the bispectrum. As is pointed out by recent studies, however, nonlinear gravitational evolution naturally induces nonlocal bias terms even if initially starting only with purely local bias. As a matter of fact, previous works showed that the second-order nonlocal bias term, which corresponds to the gravitational tidal field, is important to explain the characteristic scale-dependence of the bispectrum. In this paper we extend the nonlocal bias term up to third order, and investigate whether the PT-based model including nonlocal bias terms can simultaneously explain the power spectrum and the bispectrum of simulated halos in N-body simulations. We show that the power spectrum, including density and momentum, and the bispectrum between halo and matter in N-body simulations can be simultaneously well explained by the model including up to third-order nonlocal bias terms up to k 0.1h/Mpc. Also, the results seem in a good agreement with theoretical predictions of a simple coevolution picture, although the agreement is not perfect. These demonstration clearly shows a failure of the local bias model even at such large scales, and we conclude that nonlocal bias terms should be consistently included in order to model statistics of halos. [abridged]

bispectrum
biased tracer
galaxy
matter halo
perturbation theory


Can Late Dark Energy Transitions Raise the Hubble constant?

Abstract: Late times dark energy transitions at redshifts z ≪ 0.1 can raise the predicted value of the Hubble constant to the SH0ES value, 74.03± 1.42 (km s^-1 Mpc^-1) or more, while providing an equally good fit as ΛCDM at 67.73 ± 0.41 to higher redshift data, in particular from the cosmic microwave background and baryon acoustic oscillations. These models however do not fully resolve the true source of tension between the distance ladder and high redshift observations: the local calibration of supernovae luminosities well out into the Hubble flow. When tested in this manner by transferring the SH0ES calibration to the Pantheon supernovae dataset, the ability of such transitions to raise the Hubble constant is reduced to 69.17 ± 1.09. Such an analysis should also be used when testing any dynamical dark energy model which can produce similarly fine features in redshift or local void models.

dark energy
energy transition
late time
baryon acoustic oscillation
gravitational theory


Field sources for Simpson-Visser space-times

Abstract: Simpson-Visser (SV) space-times are the simplest globally regular modifications of the Schwarzschild, Reissner-Nordstrom and other blak-hole solutions of general relativity. They smoothly interpolate between these black holes and traversable wormholes. After a brief presentation of the Schwarzschild-like and Reissner-Nordstrom-like SV geometries, including their Carter-Penrose diagrams, we show that any static, spherically symmetric SV metric can be obtained as an exact solution to the Einstein field equations sourced by a combination of a minimally coupled phantom scalar field with a nonzero potential V(ϕ) and a magnetic field in the framework of nonlinear electrodynamics with the Lagrangian ℒ(ℱ), ℱ = F_μν F^μν (in standard notations). Explicit forms of V(ϕ) and ℒ(ℱ) are presented for the cases of Schwarzschild-like and Reissner-Nordstrom-like SV metrics.

static
scalar field
electrodynamic
field source


Analytic calculations of the spectra of ultra-high energy cosmic ray nuclei. I. The case of CMB radiation

Abstract: We present a systematic study of different methods for the analytic calculation of ultra-high energy nuclei diffuse spectra. Nuclei propagating in the intergalactic space are photo-disintegrated and decrease their Lorentz factor due to the interaction with cosmic microwave background and extragalactic background light. We calculate the evolution trajectories in the backward time, that describe how atomic mass number A and Lorentz factor Γ change with redshift z. Three methods of spectra calculations are investigated and compared: (i) trajectory method, (ii) kinetic equation combined with trajectory calculations and (iii) coupled kinetic equations. We believe that these three methods exhaust at least the principal possibilities for any analytic solution of the problem. In the most straightforward method (i) only trajectory calculations are used to connect the observed nuclei flux with the production rate of primary (accelerated) nuclei A_0. In the second method (ii) the flux (space density) of primary nuclei, and secondary nuclei and protons are calculated with the help of kinetic equation and trajectories are used only to determine the generation rates of these nuclei. The third method (iii) consists in solving the complete set of coupled kinetic equations, written starting with primary nuclei A_0, then for A_0-1 etc down to the A of interest. The solution of the preceding equation gives the generation rate for the one which follows. An important element of the calculations for all methods is the systematic use of Lorentz factor instead of energy. We consider here the interaction of nuclei only with the cosmic microwave background, this case is particularly suitable for understanding the physical results.

analytic calculation
high energy
astrophysical background
observed spectrum


Generalised DBI-Quintessence

Abstract: We investigate the phase space of a quintessence theory governed by a generalised version of the DBI action, using a combination of numeric and analytic methods. The additional degrees of freedom lead to a vastly richer phase space structure, where the field covers the full equation of state parameter space; -1 ≤ω≤ 1. We find many non-trivial solution curves to the equations of motion which indicate that DBI quintessence is an interesting candidate for a viable k-essence model.


Selecting microscopic Equations of State

Abstract: We compare a set of equations of state derived within microscopic many-body approaches, and study their predictions as far as phenomenological data on nuclei from heavy ion collisions, and astrophysical observations on neutron stars are concerned. We find that all the data, taken together, put strong constraints not easy to be fulfilled accurately. However, no major discrepancies are found among the selected equations of state and with respect to the data. The results provide an estimate of the uncertainty on the theoretical prediction at a microscopic level of the nuclear equation of state.

large masse
particle density
nucleonic degree


Fifth force constraints from galaxy warps

Abstract: Intra-galaxy signals contain a wealth of information on fundamental physics, both the dark sector and the nature of gravity. While so far largely unexplored, such probes are set to rise dramatically in importance as upcoming surveys provide data of unprecedented quantity and quality on galaxy structure and dynamics. In this paper, we use warping of stellar disks to test the chameleon- or symmetron-screened fifth forces which generically arise when new fields couple to matter. We take r-band images of mostly late-type galaxies from the Nasa Sloan Atlas and develop an automated algorithm to quantify the degree of U-shaped warping they exhibit. We then forward-model the warp signal as a function of fifth-force strength Δ G/G_N and range λ_C, and the gravitational environments and internal properties of the galaxies, including full propagation of the non-Gaussian uncertainties. Convolving this fifth-force likelihood function with a Gaussian describing astrophysical and observational noise and then constraining Δ G/G_N and λ_C by Markov Chain Monte Carlo, we find the overall likelihood to be significant increased (Δlog(ℒ) ≃ 20) by adding a screened fifth force with λ_C ≃ 2 Mpc, Δ G/G_N ≃ 0.01. The variation of Δlog(ℒ) with λ_C is quantitatively as expected from the correlation of the magnitude of the fifth-force field with the force's range, and a similar model without screening achieves no increase in likelihood over the General Relativistic case Δ G=0. Although these results are in good agreement with a previous analysis of the same model using offsets between galaxies' stellar and gas mass centroids (Desmond et al. 2018), we caution that the effects of confounding baryonic and dark matter physics must be thoroughly investigated for the results of the inference to be unambiguous.


Exoplanet Chemistry

Abstract: The terrestrial and gas-giant planets in our solar system may represent some prototypes for planets around other stars; the exoplanets because most stars have similar overall elemental abundances as our sun. The solar system planets represent at least four chemical planet types, depending on the phases that make them: Terrestrial-like planets made of rock (metal plus silicates), Plutonian planets made of rock and ice, Neptunian giant planets of rocky, icy with low H and He contents, and Jovian gas-giant planets of rocky, icy planets with near-solar H and He contents. The planetary compositions are linked to the chemical fractionation in the planetary accretion disks. Chemical tracers of these fractionations are described. Many known exoplanets are gas-giant planets with up to several Jupiter-masses and their atmospheric chemistry is compared to that of brown dwarfs. Exoplanets in close orbits around their host stars may resemble hot brown dwarfs (L-dwarfs). Planets receiving less radiation form their host may compare more to the methane-rich T dwarfs. The cloud layers resulting from condensation of oxides, metal, sulfides, and salts in these hot and cool gas giant planets and their chemical tracers are described.

chemistry
composition
atmospheric chemistry
exoplanet


Relativistic Stars in Beyond Horndeski Theories

Abstract: This work studies relativistic stars in beyond Horndeski scalar-tensor theories that exhibit a breaking of the Vainshtein mechanism inside matter, focusing on a model based on the quartic beyond Horndeski Lagrangian. We self-consistently derive the scalar field profile for static spherically symmetric objects in asymptotically de Sitter space-time and show that the Vainshtein breaking branch of the solutions is the physical branch thereby resolving several ambiguities with non-relativistic frameworks. The geometry outside the star is shown to be exactly Schwarzschild-de Sitter and therefore the PPN parameter β_ PPN=1, confirming that the external screening works at the post-Newtonian level. The Tolman-Oppenheimer-Volkoff (TOV) equations are derived and a new lower bound on the Vainshtein breaking parameter Υ_1>-4/9 is found by requiring the existence of static spherically symmetric stars. Focusing on the unconstrained case where Υ_1<0, we numerically solve the TOV equations for polytropic and realistic equations of state and find stars with larger radii at fixed mass. Furthermore, the maximum mass can increase dramatically and stars with masses in excess of 3M_⊙ can be found for relatively small values of the Vainshtein breaking parameter. We re-examine white dwarf stars and show that post-Newtonian corrections are important in beyond Horndeski theories and therefore the bounds coming from previous analyses should be revisited.

horndeski theory
scalar-tensor theory
post-newtonian correction
relativistic star
gravity


Effective metric outside bootstrapped Newtonian sources

Abstract: We determine the complete space-time metric from the bootstrapped Newtonian potential generated by a static spherically symmetric source in the surrounding vacuum. This metric contains post-Newtonian parameters which can be further used to constrain the complete underlying dynamical theory. For values of the post-Newtonian parameters within experimental bounds, the reconstructed metric appears very close to the Schwarzschild solution of General Relativity in the whole region outside the event horizon. The latter is however larger in size for the same value of the mass compared to the Schwarzschild case.

bootstrapped newtonian potential
vacuum
general relativity


Core-Collapse Supernova Explosion Theory

Abstract: Most supernova explosions accompany the death of a massive star. These explosions give birth to neutron stars and black holes and eject solar masses of heavy elements. However, determining the mechanism of explosion has been a half-century journey of great complexity. In this paper, we present our perspective of the status of this theoretical quest and the physics and astrophysics upon which its resolution seems to depend. The delayed neutrino-heating mechanism is emerging as a robust solution, but there remain many issues to address, not the least of which involves the chaos of the dynamics, before victory can unambiguously be declared. It is impossible to review in detail all aspects of this multi-faceted, more-than-half-century-long theoretical quest. Rather, we here map out the major ingredients of explosion and the emerging systematics of the observables with progenitor mass, as we currently see them. Our discussion will of necessity be speculative in parts, and many of the ideas may not survive future scrutiny. Some statements may be viewed as informed predictions concerning the numerous observables that rightly exercise astronomers witnessing and diagnosing the supernova Universe. Importantly, the same explosion in the inside, by the same mechanism, can look very different in photons, depending upon the mass and radius of the star upon explosion. A 10^51-erg (one "Bethe") explosion of a red supergiant with a massive hydrogen-rich envelope, a diminished hydrogen envelope, no hydrogen envelope, and, perhaps, no hydrogen envelope or helium shell all look very different, yet might have the same core and explosion evolution.

explosion
star
black hole
core-collapse supernovae


Cosmological Parameter Estimation with Large Scale Structure Observations

Abstract: We estimate the sensitivity of future galaxy surveys to cosmological parameters, using the redshift dependent angular power spectra of galaxy number counts, C_ℓ(z_1,z_2), calculated with all relativistic corrections at first order in perturbation theory. We pay special attention to the redshift dependence of the non-linearity scale and present Fisher matrix forecasts for Euclid-like and DES-like galaxy surveys. We compare the standard P(k) analysis with the new C_ℓ(z_1,z_2) method. We show that for surveys with photometric redshifts the new analysis performs significantly better than the P(k) analysis. For spectroscopic redshifts, however, the large number of redshift bins which would be needed to fully profit from the redshift information, is severely limited by shot noise. We also identify surveys which can measure the lensing contribution and we study the monopole, C_0(z_1,z_2).

large scale
galaxy survey
angular power spectra
cosmological parameter


Bispectrum Supersample Covariance

Abstract: Modes with wavelengths larger than the survey window can have significant impact on the covariance within the survey window. The supersample covariance has been recognized as an important source of covariance for the power spectrum on small scales, and it can potentially be important for the bispectrum covariance as well. In this paper, using the response function formalism, we model the supersample covariance contributions to the bispectrum covariance and the cross covariance between the power spectrum and the bispectrum. The supersample covariances due to the long wavelength density and tidal perturbations are investigated, and the tidal contribution is a few orders of magnitude smaller than the density one because in configuration space the bispectrum estimator involves angular averaging and the tidal response function is anisotropic. The impact of the super-survey modes is quantified using numerical measurements with periodic box and subbox setups. For the matter bispectrum, the ratio between the supersample covariance correction and the small scale covariance, which can be computed using a periodic box, is roughly an order of magnitude smaller than that for the matter power spectrum. This is because for the bispectrum, the small scale non-Gaussian covariance is significantly larger than that for the power spectrum. For the cross covariance, the supersample covariance is as important as for the power spectrum covariance. The supersample covariance prediction with the halo model response function is in good agreement with numerical results.


Tidal Love Numbers of Kerr Black Holes

Abstract: The open question of whether a Kerr black hole can become tidally deformed or not has profound implications for fundamental physics and gravitational-wave astronomy. We consider a Kerr black hole embedded in a weak and slowly varying, but otherwise arbitrary, multipolar tidal environment. By solving the static Teukolsky equation for the gauge-invariant Weyl scalar ψ_0, and by reconstructing the corresponding metric perturbation in an ingoing radiation gauge, for a general harmonic index ℓ, we compute the linear response of a Kerr black hole to the tidal field. This linear response vanishes identically for a Schwarzschild black hole and for an axisymmetric perturbation of a spinning black hole. For a nonaxisymmetric perturbation of a spinning black hole, however, the linear response does not vanish, and it contributes to the Geroch-Hansen multipole moments of the perturbed Kerr geometry. As an application, we compute explicitly the rotational black hole tidal Love numbers that couple the induced quadrupole moments to the quadrupolar tidal fields, to linear order in the black hole spin, and we introduce the corresponding notion of tidal Love tensor. Finally, we show that those induced quadrupole moments are closely related to the well-known physical phenomenon of tidal torquing of a spinning body interacting with a tidal gravitational environment.


New Scalar Field Quartessence

Abstract: We propose a cosmological scenario involving a scalar field, φ, that is a source of Dark Matter as well as of Dark Energy. Besides φ, the Lagrangian of the field theory envisaged in our scenario contains a second field χ, for simplicity assumed to be a scalar, too. For fixed values of χ, the potential term decays exponentially at large positive values of φ. While φ is not coupled to Standard Model fields, χ is assumed to be coupled to them, and the Green functions of χ depend on the cosmological redshift in the expanding universe. We assume that the term in the Lagrangian coupling χ to φ is such that, at redshifts z larger than some critical redshift z_c, φ is trapped near φ=0, and oscillations of φ about φ=0 describing massive scalar particles give rise to Dark Matter. At redshifts below z_c, the field φ is no longer trapped near the origin and starts to `roll' towards large field values. A homogenous component of φ emerges that acts as Dark Energy. Within over-dense regions, such as galaxies and galaxy clusters, the redshifting of χ stops, and φ therefore remains trapped near φ=0 as long as z_c is smaller than the redshift when structures on galactic scales decouple from the Hubble flow. Thus, at the present time, φ describes both Dark Energy and Dark Matter.


Cosmic Strings and the Origin of Globular Clusters

Abstract: We hypothesize that cosmic string loops are the seeds about which globular clusters accrete. Fixing the cosmic string tension by demanding that the peak in the distribution of masses of objects accreting onto string loops agrees with the peak in the observed mass distribution of globular clusters in our Milky Way galaxy, we then compute the expected number density and mass function of globular clusters, and compare with observations. Our hypothesis naturally explains why globular clusters are the oldest and most dense objects in a galaxy, and why they are found in the halo of the galaxy.

globular cluster
cosmic string loop
mass distribution


An Ignoble Approach to Large Field Inflation

Abstract: We study an inflationary model developed by Kaloper and Sorbo, in which the inflaton is an axion with a sub-Planckian decay constant, whose potential is generated by mixing with a topological 4-form field strength. This gives a 4d construction of "axion monodromy inflation": the axion winds many times over the course of inflation and draws energy from the 4-form. The classical theory is equivalent to chaotic inflation with a quadratic inflaton potential. Such models can produce "high scale" inflation driven by energy densities of the order of (10^16 GeV)^4, which produces primordial gravitational waves potentially accessible to CMB polarization experiments. We analyze the possible corrections to this scenario from the standpoint of 4d effective field theory, identifying the physics which potentially suppresses dangerous corrections to the slow-roll potential. This yields a constraint relation between the axion decay constant, the inflaton mass, and the 4-form charge. We show how these models can evade the fundamental constraints which typically make high-scale inflation difficult to realize. Specifically, the moduli coupling to the axion-four-form sector must have masses higher than the inflationary Hubble scale (10^14 GeV). There are also constraints from states that become light due to multiple windings of the axion, as happens in explicit string theory constructions of this scenario. Further, such models generally have a quantum-mechanical "tunneling mode" in which the axion jumps between windings, which must be suppressed. Finally, we outline possible observational signatures.

axion
effective field theory
fundamental constraint
high-scale inflation
flux


Higgs G-inflation

Abstract: A new class of inflation models within the context of G-inflation is proposed, in which the standard model Higgs boson can act as an inflaton thanks to Galileon-like non-linear derivative interaction. The generated primordial density perturbation is shown to be consistent with the present observational data. We also make a general discussion on potential-driven G-inflation models, and find a new consistency relation between the tensor-to-scalar ratio r and the tensor spectral index n_T, r = -32 √(6)n_T / 9, which is crucial in discriminating the present models from standard inflation with a canonical kinetic term.

g-inflation
new class
derivative interaction
tensor-to-scalar ratio


Variations of Infinite Derivative Modified Gravity

Abstract: We consider nonlocal modified Einstein gravity without matter, where nonlocal term has the form P(R) F() Q(R). For this model, in this paper we give the derivation of the equations of motion in detail. This is not an easy task and presented derivation should be useful to a researcher who wants to investigate nonlocal gravity. Also, we present the second variation of the related Einstein-Hilbert modified action and basics of gravity perturbations.

cosmological constant
differentiable function
ricci scalar


A cluster finding algorithm based on the multiband identification of red sequence galaxies

Abstract: We present a new algorithm, CAMIRA, to identify clusters of galaxies in wide-field imaging survey data. We base our algorithm on the stellar population synthesis model to predict colours of red-sequence galaxies at a given redshift for an arbitrary set of bandpass filters, with additional calibration using a sample of spectroscopic galaxies to improve the accuracy of the model prediction. We run the algorithm on 11960 deg^2 of imaging data from the Sloan Digital Sky Survey (SDSS) Data Release 8 to construct a catalogue of 71743 clusters in the redshift range 0.1<z<0.6 with richness after correcting for the incompleteness of the richness estimate greater than 20. We cross-match the cluster catalogue with external cluster catalogues to find that our photometric cluster redshift estimates are accurate with low bias and scatter, and that the corrected richness correlates well with X-ray luminosities and temperatures. We use the publicly available Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) shear catalogue to calibrate the mass-richness relation from stacked weak lensing analysis. Stacked weak lensing signals are detected significantly for 8 subsamples of the SDSS clusters divided by redshift and richness bins, which are then compared with model predictions including miscentring effects to constrain mean halo masses of individual bins. We find the richness correlates well with the halo mass, such that the corrected richness limit of 20 corresponds to the cluster virial mass limit of about 1 ×10^14 M_Sun/h for the SDSS DR8 cluster sample.

cluster
red-sequence galaxy
redshift range


Observational constraints to a unified cosmological model

Abstract: We propose a phenomenological unified model for dark matter and dark energy based on an equation of state parameter w that scales with the arctan of the redshift. The free parameters of the model are three constants: Ω_b0, α and β. Parameter α dictates the transition rate between the matter dominated era and the accelerated expansion period. The ratio β / α gives the redshift of the equivalence between both regimes. Cosmological parameters are fixed by observational data from Primordial Nucleosynthesis (PN), Supernovae of the type Ia (SNIa), Gamma-Ray Bursts (GRB) and Baryon Acoustic Oscillations (BAO). The calibration of the 138 GRBs events is performed using the 580 SNIa of the Union2.1 data set and a new set of 79 high-redshift GRBs is obtained. The various sets of data are used in different combinations to constraint the parameters through statistical analysis. The unified model is compared to the ΛCDM model and their differences are emphasized.

phenomenological unified model
cosmological parameter
supernovae


The universal rotation curve of low surface brightness galaxies IV: the interrelation between dark and luminous matter

Abstract: We investigate the properties of the baryonic and the dark matter components in low surface brightness (LSB) disc galaxies, with central surface brightness in the B band μ_0 ≥ 23 mag arcsec^-2. The sample is composed by 72 objects, whose rotation curves show an orderly trend reflecting the idea of a universal rotation curve (URC) similar to that found in the local high surface brightness (HSB) spirals in previous works. This curve relies on the mass modelling of the coadded rotation curves, involving the contribution from an exponential stellar disc and a Burkert cored dark matter halo. We find that the dark matter is dominant especially within the smallest and less luminous LSB galaxies. Dark matter halos have a central surface density Σ _0 ∼ 100 M_⊙ pc^-2, similar to galaxies of different Hubble types and luminosities. We find various scaling relations among the LSBs structural properties which turn out to be similar but not identical to what has been found in HSB spirals. In addition, the investigation of these objects calls for the introduction of a new luminous parameter, the stellar compactness C_* (analogously to a recent work by Karukes & Salucci), alongside with the optical radius and the optical velocity in order to reproduce the URC. Furthermore, a mysterious entanglement between the properties of the luminous and the dark matter emerges.

low surface brightness
galaxy
dark matter


Minimal Inflation

Abstract: Using the universal X superfield that measures in the UV the violation of conformal invariance we build up a model of multifield inflation. The underlying dynamics is the one controlling the natural flow of this field in the IR to the Goldstino superfield once SUSY is broken. We show that flat directions satisfying the slow roll conditions exist only if R-symmetry is broken. Naturalness of our model leads to scales of SUSY breaking of the order of 10^11-13 Gev, a nearly scale-invariant spectrum of the initial perturbations and negligible gravitational waves. We obtain that the inflaton field is lighter than the gravitino by an amount determined by the slow roll parameter eta. The existence of slow-roll conditions is directly linked to the values of supersymmetry and R-symmetry breaking scales. We make cosmological predictions of our model and compare them to current data.

universe
superfield
goldstino
minimal-inflation
low energy


When Matter Matters

Abstract: We study a recently proposed scenario for the early universe: Subluminal Galilean Genesis. We prove that without any other matter present in the spatially flat Friedmann universe, the perturbations of the Galileon scalar field propagate with a speed at most equal to the speed of light. This proof applies to all cosmological solutions – to the whole phase space. However, in a more realistic situation, when one includes any matter which is not directly coupled to the Galileon, there always exists a region of phase space where these perturbations propagate superluminally, indeed with arbitrarily high speed. We illustrate our analytic proof with numerical computations. We discuss the implications of this result for the possible UV completion of the model.


CNN Architecture Comparison for Radio Galaxy Classification

Abstract: The morphological classification of radio sources is important to gain a full understanding of galaxy evolution processes and their relation with local environmental properties. Furthermore, the complex nature of the problem, its appeal for citizen scientists and the large data rates generated by existing and upcoming radio telescopes combine to make the morphological classification of radio sources an ideal test case for the application of machine learning techniques. One approach that has shown great promise recently is Convolutional Neural Networks (CNNs). Literature, however, lacks two major things when it comes to CNNs and radio galaxy morphological classification. Firstly, a proper analysis of whether overfitting occurs when training CNNs to perform radio galaxy morphological classification using a small curated training set is needed. Secondly, a good comparative study regarding the practical applicability of the CNN architectures in literature is required. Both of these shortcomings are addressed in this paper. Multiple performance metrics are used for the latter comparative study, such as inference time, model complexity, computational complexity and mean per class accuracy. As part of this study we also investigate the effect that receptive field, stride length and coverage has on recognition performance. For the sake of completeness, we also investigate the recognition performance gains that we can obtain by employing classification ensembles. A ranking system based upon recognition and computational performance is proposed. MCRGNet, Radio Galaxy Zoo and ConvXpress (novel classifier) are the architectures that best balance computational requirements with recognition performance.

recognition performance
radio galaxy zoo
computational requirement
cnns


Two-portal Dark Matter

Abstract: We propose a renormalizable dark matter model in which a fermionic dark matter (DM) candidate communicates with the standard model particles through two distinct portals: Higgs and vector portals. The dark sector is charged under a U(1)' gauge symmetry while the standard model has a leptophobic interaction with the dark vector boson. The leading contribution of DM-nucleon elastic scattering cross section begins at one-loop level. The model meets all the constraints imposed by direct detection experiments provided by LUX and XENON100, observed relic abundance according to WMAP and Planck, and the invisible Higgs decay width measured at the LHC. It turns out that the dark matter mass in the viable parameter space can take values from a few GeV up to 1 TeV. This is a new feature which is absent in the models with only one portal. In addition, we can find in the constrained regions of the parameter space a DM mass of ∼ 34 GeV annihilating into b quark pair, which explains the Fermi-LAT gamma-ray excess.


Dynamics of a lattice Universe

Abstract: We find a solution to Einstein field equations for a regular toroidal lattice of size L with equal masses M at the centre of each cell; this solution is exact at order M/L. Such a solution is convenient to study the dynamics of an assembly of galaxy-like objects. We find that the solution is expanding (or contracting) in exactly the same way as the solution of a Friedman-Lemaître-Robertson-Walker Universe with dust having the same average density as our model. This points towards the absence of backreaction in a Universe filled with an infinite number of objects, and this validates the fluid approximation, as far as dynamics is concerned, and at the level of approximation considered in this work.

universe
einstein field equation
toroidal lattice


Large-Scale Structure Observables in General Relativity

Abstract: We review recent studies that rigorously define several key observables of the large-scale structure of the Universe in a general relativistic context. Specifically, we consider i) redshift perturbation of cosmic clock events; ii) distortion of cosmic rulers, including weak lensing shear and magnification; iii) observed number density of tracers of the large-scale structure. We provide covariant and gauge-invariant expressions of these observables. Our expressions are given for a linearly perturbed flat Friedmann-Robertson-Walker metric including scalar, vector, and tensor metric perturbations. While we restrict ourselves to linear order in perturbation theory, the approach can be straightforwardly generalized to higher order.

redshift-space distortion
matter density fluctuation
velocity effect
magnification bias


Variable gravity Universe

Abstract: For variable gravity models the strength of gravity, as measured by Newton's “constant” or the Planck mass, depends on the value of a scalar field, the cosmon. We discuss two simple four-parameter models with a quadratic or constant cosmon potential. They are compatible with all presently available cosmological observations, including inflation. The inflaton and the scalar field of quintessence are the same cosmon field. Dark Energy constitutes a small, almost constant fraction of the energy density during the radiation and matter dominated epochs (Early Dark Energy). In the present epoch we witness a transition to a new Dark Energy dominated epoch. Our models are free of a big bang singularity. The stability of solutions generates an arrow of time. Our picture of the Universe is unusual, with a shrinking or static scale factor, while the masses of particles increase and the size of atoms shrinks. The evolution of the universe can be very slow for all cosmological epochs including inflation, with typical time scale 10^10 yr, and in sharp contrast to the usual big bang picture. The map to the equivalent Einstein frame with constant particle masses and expanding scale factor can be singular at the big bang.

energy density
big bang picture
massive neutrino matter


Spectator Dark Matter

Abstract: The observed dark matter abundance in the Universe can be fully accounted for by a minimally coupled spectator scalar field that was light during inflation and has sufficiently strong self-coupling. In this scenario, dark matter was produced during inflation by amplification of quantum fluctuations of the spectator field. The self-interaction of the field suppresses its fluctuations on large scales, and therefore avoids isocurvature constraints. The scenario does not require any fine-tuning of parameters. In the simplest case of a single real scalar field, the mass of the dark matter particle would be in the range 1 GeV≲ m≲ 10^8 GeV, depending on the scale of inflation, and the lower bound for the quartic self-coupling is λ≳ 0.45.

dark matter
scalar field
spectator field
matter particle
era


Relativistic Corrections to the Growth of Structure in Modified Gravity

Abstract: We present a method to introduce relativistic corrections including linear dark energy perturbations in Horndeski theory into Newtonian simulations based on the N-body gauge approach. We assume that standard matter species (cold dark matter, baryons, photons and neutrinos) are only gravitationally-coupled with the scalar field and we then use the fact that one can include modified gravity effects as an effective dark energy fluid in the total energy-momentum tensor. In order to compute the scalar field perturbations, as well as the cosmological background and metric perturbations, we use the Einstein-Boltzmann code . As an example, we study the impact of relativistic corrections on the matter power spectrum in k-essence, a subclass of Horndeski theory, including the effects of massless and massive neutrinos. For massive neutrinos with ∑ m_ν = 0.1 eV, the corrections due to relativistic species (photons, neutrinos and dark energy) can introduce a maximum deviation of approximately 7% to the power spectrum at k ∼ 10^-3 Mpc^-1 at z=0, for a scalar field with sound speed c_s^2∼ 0.013 during matter domination epoch. Our formalism makes it possible to test beyond ΛCDM models probed by upcoming large-scale structure surveys on very large scales.

n-body gauge approach
gravity effect
large scale


The Baryon Cycle of Dwarf Galaxies: Dark, Bursty, Gas-Rich Polluters

Abstract: We present results from a fully cosmological, very high-resolution, LCDM "zoom-in" simulation of a group of seven field dwarf galaxies with present-day virial masses in the range M_vir=4.4e8-3.6e10 Msun. The simulation includes a blastwave scheme for supernova feedback, a star formation recipe based on a high gas density threshold, metal-dependent radiative cooling, a scheme for the turbulent diffusion of metals and thermal energy, and a uniform UV background that modifies the ionization and excitation state of the gas. The properties of the simulated dwarfs are strongly modulated by the depth of the gravitational potential well. All three halos with M_vir < 1e9 Msun are devoid of stars, as they never reach the density threshold for star formation of 100 atoms/cc. The other four, M_vir > 1e9 Msun dwarfs have blue colors, low star formation efficiencies, high cold gas to stellar mass ratios, and low stellar metallicities. Their bursty star formation histories are characterized by peak specific star formation rates in excess of 50-100 1/Gyr, far outside the realm of normal, more massive galaxies, and in agreement with observations of extreme emission-line starbursting dwarfs by the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey. Metal-enriched galactic outflows produce sub-solar effective yields and pollute with heavy elements a Mpc-size region of the intergalactic medium, but are not sufficient to completely quench star formation activity and are not ubiquitous in our dwarfs. Within the limited size of the sample, our simulations appear to simultaneously reproduce the observed stellar mass and cold gas content, resolved star formation histories, stellar kinematics, and metallicities of field dwarfs in the Local Volume.

field dwarf galaxy
present-day virial masse
cold gas content


Bar formation in the Milky Way type galaxies

Abstract: Many barred galaxies, possibly including the Milky Way, have cusps in the centres. There is a widespread belief, however, that usual bar instability taking place in bulgeless galaxy models is impossible for the cuspy models, because of the presence of the inner Lindblad resonance for any pattern speed. At the same time there are numerical evidences that the bar instability can form a bar. We analyse this discrepancy, by accurate and diverse N-body simulations and using the calculation of normal modes. We show that bar formation in cuspy galaxies can be explained by taking into account the disc thickness. The exponential growth time is moderate for typical current disc masses (about 250 Myr), but considerably increases (factor 2 or more) upon substitution of the live halo and bulge with a rigid halo/bulge potential; meanwhile pattern speeds remain almost the same. Normal mode analysis with different disc mass favours a young bar hypothesis, according to which the bar instability saturated only recently.

bar instability
different disc mass
young bar hypothesis


Cosmic Curvature Tested Directly from Observations

Abstract: Cosmic spatial curvature is a fundamental geometric quantity of the Universe. We investigate a model independent, geometric approach to measure spatial curvature directly from observations, without any derivatives of data. This employs strong lensing time delays and supernova distance measurements to measure the curvature itself, rather than just testing consistency with flatness. We define two curvature estimators, with differing error propagation characteristics, that can crosscheck each other, and also show how they can be used to map the curvature in redshift slices, to test constancy of curvature as required by the Robertson-Walker metric. Simulating realizations of redshift distributions and distance measurements of lenses and sources, we estimate uncertainties on the curvature enabled by next generation measurements. The results indicate that the model independent methods, using only geometry without assuming forms for the energy density constituents, can determine the curvature at the ∼6×10^-3 level.

spatial curvature
universe
independent method


An Improved Calculation of the Non-Gaussian Halo Mass Function

Abstract: The abundance of collapsed objects in the universe, or halo mass function, is an important theoretical tool in studying the effects of primordially generated non-Gaussianities on the large scale structure. The non-Gaussian mass function has been calculated by several authors in different ways, typically by exploiting the smallness of certain parameters which naturally appear in the calculation, to set up a perturbative expansion. We improve upon the existing results for the mass function by combining path integral methods and saddle point techniques (which have been separately applied in previous approaches). Additionally, we carefully account for the various scale dependent combinations of small parameters which appear. Some of these combinations in fact become of order unity for large mass scales and at high redshifts, and must therefore be treated non-perturbatively. Our approach allows us to do this, and to also account for multi-scale density correlations which appear in the calculation. We thus derive an accurate expression for the mass function which is based on approximations that are valid over a larger range of mass scales and redshifts than those of other authors. By tracking the terms ignored in the analysis, we estimate theoretical errors for our result and also for the results of others. We also discuss the complications introduced by the choice of smoothing filter function, which we take to be a top-hat in real space, and which leads to the dominant errors in our expression. Finally, we present a detailed comparison between the various expressions for the mass functions, exploring the accuracy and range of validity of each.

halo mass function
perturbative expansion
non-gaussianitie


Cosmology with matter diffusion

Abstract: We construct a viable cosmological model based on velocity diffusion of matter particles. In order to ensure the conservation of the total energy-momentum tensor in the presence of diffusion, we include a cosmological scalar field ϕ which we identify with the dark energy component of the Universe. The model is characterized by only one new degree of freedom, the diffusion parameter σ. The standard ΛCDM model can be recovered by setting σ=0. If diffusion takes place (σ >0) the dynamics of the matter and of the dark energy fields are coupled. We argue that the existence of a diffusion mechanism in the Universe can serve as a theoretical motivation for interacting models. We constrain the background dynamics of the diffusion model with Supernovae, H(z) and BAO data. We also perform a perturbative analysis of this model in order to understand structure formation in the Universe. We calculate the impact of diffusion both on the CMB spectrum, with particular attention to the integrated Sachs-Wolfe signal, and on the matter power spectrum P(k). The latter analysis places strong constraints on the magnitude of the diffusion mechanism but does not rule out the model.

cosmological model
scalar field
dark energy
diffusion model


Cosmological Perturbations from the Standard Model Higgs

Abstract: We propose that the Standard Model (SM) Higgs is responsible for generating the cosmological perturbations of the universe by acting as an isocurvature mode during a de Sitter inflationary stage. In view of the recent ATLAS and CMS results for the Higgs mass, this can happen if the Hubble rate during inflation is in the range (10^10- 10^14) GeV (depending on the SM parameters). Implications for the detection of primordial tensor perturbations through the B-mode of CMB polarization via the PLANCK satellite are discussed. For example, if the Higgs mass value is confirmed to be m_h=125.5 GeV and m_t, α_s are at their central values, our mechanism predicts tensor perturbations too small to be detected in the near future. On the other hand, if tensor perturbations will be detected by PLANCK through the B-mode of CMB, then there is a definite relation between the Higgs and top masses, making the mechanism predictive and falsifiable.

universe
primordial higgs condensate
primordial perturbation
new physics
inflationary fluctuation


Composition of the Fermi-LAT isotropic gamma-ray background intensity: Emission from extragalactic point sources and dark matter annihilations

Abstract: A new estimation of the isotropic diffuse gamma-ray background (IGRB) observed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi) has been presented for 50 months of data, in the energy range 100 MeV-820 GeV and for different modelings of the Galactic foreground. We attempt here the interpretation of the Fermi-LAT IGRB data in terms of the gamma-ray unresolved emission from different extragalactic populations. We find very good fits to the experimental IGRB, obtained with theoretical predictions for the emission from active galactic nuclei and star-forming galaxies. In addition, we probe a possible emission coming from the annihilation of weakly interacting dark matter (DM) particles in the halo of our Galaxy. We set stringent limits on its annihilation cross section into gamma rays, which are about the thermal relic value for a wide range of DM masses. We also identify regions in the DM mass and annihilation cross section parameter space which can significantly improve the fit to the IGRB data. Our analysis is conducted within the different IGRB data sets obtained from different models for the Galactic emission, which is shown to add a significant ambiguity on the IGRB interpretation.

gamma-ray background
star-forming galaxy
active galactic nucleus


Parametrising non-linear dark energy perturbations

Abstract: In this paper, we quantify the non-linear effects from k-essence dark energy through an effective parameter μ that encodes the additional contribution of a dark energy fluid or a modification of gravity to the Poisson equation. This is a first step toward quantifying non-linear effects of dark energy/modified gravity models in a more general approach. We compare our N-body simulation results from k-evolution with predictions from the linear Boltzmann code , and we show that for the k-essence model one can safely neglect the difference between the two potentials, Φ -Ψ, and short wave corrections appearing as higher order terms in the Poisson equation, which allows us to use single parameter μ for characterizing this model. We also show that for a large k-essence speed of sound the results are sufficiently accurate, while for a low speed of sound non-linearities in matter and in the k-essence field are non-negligible. We propose a tanh-based parameterisation for μ, motivated by the results for two cases with low (c_s^2=10^-7) and high (c_s^2=10^-4) speed of sound, to include the non-linear effects based on the simulation results. This parametric form of μ can be used to improve Fisher forecasts or Newtonian N-body simulations for k-essence models.


Constraining Thawing Dark Energy using Galaxy Cluster Number Counts

Abstract: We study the formation of galaxy clusters in the presence of thawing class of scalar field dark energy. We consider cases where the scalar field has canonical as well non canonical kinetic term in its action. We also consider various form for the potential of the scalar field e.g, linear, quadratic, inverse quadratic, exponential as well as Pseudo-Nambu-Goldstone Boson (PNGB) type. Moreover we investigate situation where dark energy is homogeneous as well as the situation where dark energy takes part in virialization process. We use the Sheth-Tormen formalism while calculating the number density of galaxy clusters. Our results show that cluster number density for different dark energy models have significant deviation from the corresponding value for the ΛCDM case. The deviation is more for higher redshifts. Moreover the tachyon type scalar field with linear potential has the highest deviation from the ΛCDM case. For the total cluster number counts, different dark energy models can have substantial deviation from ΛCDM and this deviation is most significant around z ∼ 0.5 for all the models we considered. We also constrain thawing class of models using the presently available data for number counts of massive X-ray clusters. The results show that current cluster data is not suitable enough for constraining potentials for the thawing scalar fields as well as for other cosmological parameters like n_s. But one can get significant constraint for the parameter σ_8 and a lower bound on Ω_m0.

dark energy
galaxy cluster
number density


The First Stars

Abstract: The first stars to form in the Universe – the so-called Population III stars – bring an end to the cosmological Dark Ages, and exert an important influence on the formation of subsequent generations of stars and on the assembly of the first galaxies. Developing an understanding of how and when the first Population III stars formed and what their properties were is an important goal of modern astrophysical research. In this review, I discuss our current understanding of the physical processes involved in the formation of Population III stars. I show how we can identify the mass scale of the first dark matter halos to host Population III star formation, and discuss how gas undergoes gravitational collapse within these halos, eventually reaching protostellar densities. I highlight some of the most important physical processes occurring during this collapse, and indicate the areas where our current understanding remains incomplete. Finally, I discuss in some detail the behaviour of the gas after the formation of the first Population III protostar. I discuss both the conventional picture, where the gas does not undergo further fragmentation and the final stellar mass is set by the interplay between protostellar accretion and protostellar feedback, and also the recently advanced picture in which the gas does fragment and where dynamical interactions between fragments have an important influence on the final distribution of stellar masses.


Models of Interacting Dark Energy

Abstract: Any non-gravitational coupling between dark matter and dark energy modifies the cosmological dynamics. Interactions in the dark sector are considered to be relevant to address the coincidence problem. Moreover, in various models the observed accelerated expansion of the Universe is a pure interaction phenomenon. Here we review recent approaches in which a coupling between both dark components is crucial for the evolution of the Universe.

coincidence problem
universe
dark energy model


Scaling laws in chiral hydrodynamic turbulence

Abstract: We study the turbulent regime of chiral (magneto)hydrodynamics for charged and neutral matter with chirality imbalance. We find that the chiral magnetohydrodynamics for charged plasmas possesses a unique scaling symmetry, only without fluid helicity under the local charge neutrality. We also find a different type of unique scaling symmetry in the chiral hydrodynamics for neutral matter with fluid helicity in the inertial range. We show that these symmetries dictate the self-similar inverse cascade of the magnetic and kinetic energies. Our results imply the possible inverse energy cascade in core-collapse supernovae due to the chiral transport of neutrinos.

chiral magnetohydrodynamic
scaling symmetry
neutrino


Statistical dynamo theory: Mode excitation

Abstract: We compute statistical properties of the lowest-order multipole coefficients of the magnetic field generated by a dynamo of arbitrary shape. To this end we expand the field in a complete biorthogonal set of base functions, viz. B = sum_k a^k(t) b^k(r). We consider a linear problem and the statistical properties of the fluid flow are supposed to be given. The turbulent convection may have an arbitrary distribution of spatial scales. The time evolution of the expansion coefficients a^k(t) is governed by a stochastic differential equation from which we infer their averages <a^k>, autocorrelation functions <a^k(t) a^k*(t+tau)>, and an equation for the cross correlations <a^k a^l*>. The eigenfunctions of the dynamo equation (with eigenvalues lambda_k) turn out to be a preferred set in terms of which our results assume their simplest form. The magnetic field of the dynamo is shown to consist of transiently excited eigenmodes whose frequency and coherence time is given by Im(lambda_k) and -1/(Re lambda_k), respectively. The relative r.m.s. excitation level of the eigenmodes, and hence the distribution of magnetic energy over spatial scales, is determined by linear theory. An expression is derived for <|a^k|^2> / <|a^0|^2> in case the fundamental mode b^0 has a dominant amplitude, and we outline how this expression may be evaluated. It is estimated that <|a^k|^2>/<|a^0|^2> 1/N where N is the number of convective cells in the dynamo. We show that the old problem of a short correlation time (or FOSA) has been partially eliminated. Finally we prove that for a simple statistically steady dynamo with finite resistivity all eigenvalues obey Re(lambda_k) < 0.

statistical property
multipole coefficient
magnetic field


Masses, Radii, and Equation of State of Neutron Stars

Abstract: We summarize our current knowledge of neutron star masses and radii. Recent instrumentation and computational advances have resulted in a rapid increase in the discovery rate and precise timing of radio pulsars in binaries in the last few years, leading to a large number of mass measurements. These discoveries show that the neutron star mass distribution is much wider than previously thought, with 3 known pulsars now firmly in the 1.9-2.0 Msun mass range. For radii, large, high quality datasets from X-ray satellites as well as significant progress in theoretical modeling led to considerable progress in the measurements, placing them in the 9.9-11.2 km range and shrinking their uncertainties due to a better understanding of the sources of systematic errors. The combination of the massive neutron star discoveries, the tighter radius measurements, and improved laboratory constraints of the properties of dense matter has already made a substantial impact on our understanding of the composition and bulk properties of cold nuclear matter at densities higher than that of the atomic nucleus, a major unsolved problem in modern physics.

neutron star
pulsar
dense matter
electromagnetic spectrum


Stellar Accelerations and the Galactic Gravitational Field

Abstract: Typical stars in the Milky Way galaxy have velocities of hundreds of kilometres per second and experience gravitational accelerations of ∼ 10^-10 m s^-2, resulting in velocity changes of a few centimetres per second over a decade. Measurements of these accelerations would permit direct tests of the applicability of Newtonian dynamics on kiloparsec length scales and could reveal significant small scale inhomogeneities within the galaxy, as well increasing the sensitivity of measurements of the overall mass distribution of the galaxy. Noting that a reasonable extrapolation of progress in exoplanet hunting spectrographs suggests that centimetre per second level precision will be attainable in the coming decade(s), we explore the possibilities such measurements would create. We consider possible confounding effects, including apparent accelerations induced by stellar motion and reflex velocities from planetary systems, along with possible strategies for their mitigation. If these issues can be satisfactorily addressed it will be possible to use high precision measurements of changing stellar velocities to perform a "blind search" for dark matter, make direct tests of theories of non-Newtonian gravitational dynamics, detect local inhomogeneities in the dark matter density, and greatly improve measurements of the overall properties of the galaxy.

star
gravitational acceleration
dark matter


New Q-ball Solutions in Gauge-Mediation, Affleck-Dine Baryogenesis and Gravitino Dark Matter

Abstract: Affleck-Dine (AD) baryogenesis along a d=6 flat direction in gauge-mediated supersymmetry-breaking (GMSB) models can produce unstable Q-balls which naturally have field strength similar to the messenger scale. In this case a new kind of Q-ball is formed, intermediate between gravity-mediated and gauge-mediated type. We study in detail these new Q-ball solutions, showing how their properties interpolate between standard gravity-mediated and gauge-mediated Q-balls as the AD field becomes larger than the messenger scale. It is shown that E/Q for the Q-balls can be greater than the nucleon mass but less than the MSSM-LSP mass, leading to Q-ball decay directly to Standard Model fermions with no MSSM-LSP production. More significantly, if E/Q is greater than the MSSM-LSP mass, decaying Q-balls can provide a natural source of non-thermal MSSM-LSPs, which can subsequently decay to gravitino dark matter without violating nucleosynthesis constraints. The model therefore provides a minimal scenario for baryogenesis and gravitino dark matter in the gauge-mediated MSSM, requiring no new fields.

gravitino
dark matter
gauge-mediated q-balls


On The Maximum Mass of Stellar Black Holes

Abstract: We present the spectrum of compact object masses: neutron stars and black holes that originate from single stars in different environments. In particular, we calculate the dependence of maximum black hole mass on metallicity and on some specific wind mass loss rates (e.g., Hurley et al. and Vink et al.). Our calculations show that the highest mass black holes observed in the Galaxy M_bh = 15 Msun in the high metallicity environment (Z=Zsun=0.02) can be explained with stellar models and the wind mass loss rates adopted here. To reach this result we had to set Luminous Blue Variable mass loss rates at the level of about 0.0001 Msun/yr and to employ metallicity dependent Wolf-Rayet winds. With such winds, calibrated on Galactic black hole mass measurements, the maximum black hole mass obtained for moderate metallicity (Z=0.3 Zsun=0.006) is M_bh,max = 30 Msun. This is a rather striking finding as the mass of the most massive known stellar black hole is M_bh = 23-34 Msun and, in fact, it is located in a small star forming galaxy with moderate metallicity. We find that in the very low (globular cluster-like) metallicity environment the maximum black hole mass can be as high as M_bh,max = 80 Msun (Z=0.01 Zsun=0.0002). It is interesting to note that X-ray luminosity from Eddington limited accretion onto an 80 Msun black hole is of the order of about 10^40 erg/s and is comparable to luminosities of some known ULXs. We emphasize that our results were obtained for single stars only and that binary interactions may alter these maximum black hole masses (e.g., accretion from a close companion). This is strictly a proof-of-principle study which demonstrates that stellar models can naturally explain even the most massive known stellar black holes.


Cosmological parameter fittings with the BICEP2 data

Abstract: Combining the latest Planck, Wilkinson Microwave Anisotropy Probe (WMAP), and baryon acoustic oscillation (BAO) data, we exploit the recent cosmic microwave background (CMB) B-mode power spectra data released by the BICEP2 collaboration to constrain the cosmological parameters of the ΛCDM model, esp. the primordial power spectra parameters of the scalar and the tensor modes, n_s,α_s, r, n_t. We obtained constraints on the parameters for a lensed ΛCDM model using the Markov Chain Monte Carlo (MCMC) technique, the marginalized 68% bounds are r = 0.1043±_0.0914^0.0307, n_s = 0.9617±_0.0061^ 0.0061, α_s = -0.0175±_0.0097^0.0105, n_t = 0.5198±_0.4579^0.4515. We found that a blue tilt for n_t is favored slightly, but it is still well consistent with flat or even red tilt. Our r value is slightly smaller than the one obtained by the BICEP team, as we allow n_t as a free parameter without imposing the single-field slow roll inflation consistency relation. If we impose this relation, r=0.2130±_0.0609^0.0446. For most other parameters, the best fit values and measurement errors are not altered much by the introduction of the BICEP2 data.

free parameter
cosmological model
tensor spectrum


Fine Tuning May Not Be Enough

Abstract: We argue that the fine tuning problems of scalar-driven inflation may be worse than is commonly believed. The reason is that reheating requires the inflaton to be coupled to other matter fields whose vacuum fluctuations alter the inflaton potential. The usual response has been that even more fine-tuning of the classical potential V(φ) can repair any damage done in this way. We point out that the effective potential in de Sitter background actually depends in a complicated way upon the dimensionless combination of φ/H. We also show that the factors of H which occur in de Sitter do not even correspond to local functionals of the metric for general geometries, nor are they Planck-suppressed.

sitter
complicated way
local functional
counterterm


Magnetic Fields from QCD Phase Transitions

Abstract: We study the evolution of QCD phase transition-generated magnetic fields in freely decaying MHD turbulence of the expanding Universe. We consider a magnetic field generation model that starts from basic non-perturbative QCD theory and predicts stochastic magnetic fields with an amplitude of the order of 0.02 μG and small magnetic helicity. We employ direct numerical simulations to model the MHD turbulence decay and identify two different regimes: "weakly helical" turbulence regime, when magnetic helicity increases during decay, and "fully helical" turbulence, when maximal magnetic helicity is reached and an inverse cascade develops. The results of our analysis show that in the most optimistic scenario the magnetic correlation length in the comoving frame can reach 10 kpc with the amplitude of the effective magnetic field being 0.007 nG. We demonstrate that the considered model of magneto-genesis can provide the seed magnetic field for galaxies and clusters.

turbulence
universe
helicity
magnetic field


Modified Gravity (MOG) fits to observed radial acceleration of SPARC galaxies

Abstract: The equation of motion in the generally covariant modified gravity (MOG) theory leads, for weak gravitational fields and non-relativistic motion, to a modification of Newton's gravitational acceleration law. In addition to the metric g_μν, MOG has a vector field ϕ_μ that couples with gravitational strength to all baryonic matter. The gravitational coupling strength is determined by the MOG parameter α, while parameter μ is the small effective mass of ϕ_μ. The MOG acceleration law has been demonstrated to fit a wide range of galaxies, galaxy clusters and the Bullet Cluster and Train Wreck Cluster mergers. For the SPARC sample of rotationally supported spiral and irregular galaxies, McGaugh et al. [24] (MLS) have found a radial acceleration relation (RAR) that relates accelerations derived from galaxy rotation curves to Newtonian accelerations derived from galaxy mass models. Using the same SPARC galaxy data, mass models independently derived from that data, and MOG parameters α and μ that run with galaxy mass, we demonstrate that adjusting galaxy parameters within ± 1-sigma bounds can yield MOG predictions consistent with the given rotational velocity data. Moreover, the same adjusted parameters yield a good fit to the RAR of MLS, with the RAR parameter a_0=(5.4± .3)× 10^-11 m/s^2.

gravity
baryonic matter
galaxy rotation curve


Magnetar superconductivity versus magnetism: neutrino cooling processes

Abstract: We describe the microphysics, phenomenology, and astrophysical implication of a B-field induced unpairing effect that may occur in magnetars, if the local B-field in the core of a magnetar exceeds a critical value H_c2. Using the Ginzburg-Landau theory of superconductivity, we derive the H_c2 field for proton condensate taking into the correction (≤ 30%) which arises from its coupling to the background neutron condensate. The density dependence of pairing of proton condensate implies that H_c2 is maximal at the crust-core interface and decreases towards the center of the star. As a consequence, magnetar cores with homogenous constant fields will be partially superconducting for "medium-field" magnetars (10^15≤ B≤ 5 × 10^16 G) whereas "strong-field" magnetars (B>5× 10^16 G) will be void of superconductivity. The neutrino emissivity of a magnetar's core changes in a twofold manner: (i) the B-field assisted direct Urca process is enhanced by orders of magnitude, because of the unpairing effect in regions where B≥ H_c2; (ii) the Cooper-pair breaking processes on protons vanish in these regions and the overall emissivity by the pair-breaking processes is reduced by a factor of only a few.

superconductivity
proton condensate
neutrino emissivity


Understanding the WMAP Cold Spot mystery

Abstract: The first and third year data releases from the WMAP provide evidence of an anomalous Cold Spot (CS) at galactic latitude b=-57deg and longitude l=209deg. We have examined the properties of the CS in some detail in order to assess its cosmological significance. We have performed a cluster analysis of the local extrema in the CMB signal to show that the CS is actually associated with a large group of extrema rather than just one. In the light of this we have re-examined the properties of the WMAP ILC and co-added "cleaned" WCM maps, which have previously been used for the analysis of the properties of the signal in the vicinity of the CS. These two maps have remarkably similar properties on equal latitude rings for |b|>30deg, as well as in the vicinity of the CS. We have also checked the idea that the CMB signal has a non-Gaussian tail, localized in the low multipole components of the signal. For each ring we apply a linear filter with characteristic scale R, dividing the CMB signal in two parts: the filtered part, with characteristic scale above that of the filter R, and the difference between the initial and filtered signal. Using the filter scale as a variable, we can maximize the skewness and kurtosis of the smoothed signal and minimize these statistics for the difference between initial and filtered signal. We have discovered that the shape of the CS is formed primarily by the components of the CMB signal represented by multipoles between 10<=L<=20, with a corresponding angular scale about 5-10 degs. This signal leads to modulation of the whole CMB sky, clearly seen at |b|>30deg in both the ILC and WCM maps, rather than a single localized feature. After subtraction of this modulation, the remaining part of the CMB signal appears to be consistent with statistical homogeneity and Gaussianity.


IR Divergences in Inflation and Entropy Perturbations

Abstract: We study leading order perturbative corrections to the two point correlation function of the scalar field describing the curvature perturbation in a slow-roll inflationary background, paying particular attention to the contribution of entropy mode loops. We find that the infrared divergences are worse than in pure de Sitter space: they are power law rather than logarithmic. The validity of perturbation theory and thus of the effective field theory of cosmological perturbations leads to stringent constraints on the coupling constants describing the interactions, in our model the quartic self-interaction coupling constant of the entropy field. If the self coupling constant is larger than some critical value which depends in particular on the duration of the inflationary phase, then perturbation theory breaks down. Our analysis may have implications for the stability of de Sitter space: the quantum effects which lead to an instability of de Sitter space will be larger in magnitude in the presence of entropy fluctuations.

entropy perturbation
scalar field
infrared divergence


Optimal Time-Series Selection of Quasars

Abstract: We present a novel method for the optimal selection of quasars using time-series observations in a single photometric bandpass. Utilizing the damped random walk model of Kelly et al. (2009), we parameterize the ensemble quasar structure function in Sloan Stripe 82 as a function of observed brightness. The ensemble model fit can then be evaluated rigorously for and calibrated with individual light curves with no parameter fitting. This yields a classification in two statistics — one describing the fit confidence and one describing the probability of a false alarm — which can be tuned, a priori, to achieve high quasar detection fractions (99 acceptable rate of false alarms. We establish the typical rate of false alarms due to known variable stars as <3 we increase the sample of potential quasars relative to those known in Stripe 82 by as much as 29 2.5<z<3, where selection by color is extremeley inefficient. This represents 1875 new quasars in a 290 deg^2 field. The observed rates of both quasars and stars agree well with the model predictions, with >99 the expected variability profile. We discus the utility of the method at high-redshift and in the regime of noisy and sparse data. Our time series selection complements well independent selection based on quasar colors and has strong potential for identifying high redshift quasars for BAO and other cosmology studies in the LSST era.

selection
quasar
time-series observation


Calibrating the Baryon Oscillation Ruler for Matter and Halos

Abstract: We characterize the nonlinear evolution of the baryon acoustic feature as traced by the dark matter and halos, using a combination of perturbation theory and N-body simulations. We confirm that the acoustic peak traced by the dark matter is both broadened and shifted as structure forms, and that this shift is well described by second-order perturbation theory. These shifts persist for dark matter halos, and are a simple function of halo bias, with the shift (mostly) increasing with increasing bias. Extending our perturbation theory results to halos with simple two parameter bias models (both in Lagrangian and Eulerian space) quantitatively explains the observed shifts. In particular, we demonstrate that there are additional terms that contribute to the shift that are absent for the matter. At z=0 for currently favored cosmologies, the matter shows shifts of 0.5 halos shift it by 0.5 factor at higher redshifts. These results are easily generalized to galaxies within the halo model, where we show that simple galaxy models show marginally larger shifts than the correspondingly biased halos, due to the contribution of satellites in high mass halos. While our focus here is on real space, our results make specific predictions for redshift space. For currently favored cosmological models, we find that the shifts for halos at z=0 increase by 0.3 these theoretical systematics are smaller than the statistical precision of upcoming surveys, even if one ignored the corrections discussed here. Simple modeling, along the lines discussed here, has the potential to reduce these systematics to below the levels of cosmic variance limited surveys.


Lepton asymmetry growth in the symmetric phase of an electroweak plasma with hypermagnetic fields versus its washing out by sphalerons

Abstract: We study lepton asymmetry evolution in plasma of the early Universe before the electroweak phase transition (EWPT) accounting for chirality flip processes via Higgs decays (inverse decays) entering equilibrium at temperatures below T_RL 10 TeV, T_EW < T < T_RL. We solve appropriate kinetic equations for leptons and Higgs bosons taking into account the lepton number violation due to Abelian anomalies for right and left electrons and neutrinos in the self-consistent hypercharge field obeying Maxwell equations modified by the contribution of the Standard Model of electroweak interactions. The violation of left lepton numbers and the corresponding violation of the baryon number due to sphaleron processes in symmetric phase is taken into account as well. Assuming the Chern-Simons wave configuration of the seed hypercharge field, we get the estimates of baryon and lepton asymmetries evolved from the primordial right electron asymmetry existing alone as partial asymmetry at T > T_RL. One finds a strong dependence of the asymmetries on the Chern-Simons wave number. We predict a nonzero chiral asymmetry Δμ= μ_e_R - μ_e_L ≠0 in this scenario evolved down to the EWPT moment that can be used as an initial value for the Maxwellian field evolution after EWPT.

electroweak phase transition
left lepton doublet
baryogenesis


Cosmological constraints on exotic injection of electromagnetic energy

Abstract: We compute cosmic microwave background (CMB) anisotropy constraints on exotic forms of energy injection in electromagnetic (e.m.) channels over a large range of timescales. These constraints are very powerful around or just after recombination, although CMB keeps some sensitivity e.g. to decaying species with lifetimes as long as 10^25s. We review here complementary with CMB spectral distortions and primordial nucleosynthesis bounds, which dominate at earlier timescales. For the first time, we describe the effects of the e.m. energy injection on the CMB power spectra as a function of the injection epoch, using the lifetime of a decaying particle as proxy. We identify a suitable on-the-spot approximation. Our results are of interest not only for early universe relics constituting (a fraction of) the dark matter, but also for other exotic injection of e.m. radiation. For illustration, we apply our formalism to: i) Primordial black holes of mass ∈ [10^13.5,10^16.8] g, showing that the constraints are comparable to the ones obtained from gamma-ray background studies and even dominate below ∼ 10^14g. ii) To a peculiar mass-mixing range in the sterile neutrino parameter space, complementary to other astrophysical and laboratory probes. iii) Finally, we provide a first estimate of the room for improvement left for forthcoming 21 cm experiments, comparing it with the reach of proposed CMB spectral distortion (PiXiE) and CMB angular power spectrum (CORE) missions. We show that the best and most realistic opportunity to look for this signal (or to improve over current constraints) in the 21 cm probe is to focus on the Cosmic Dawn epoch, 15≲ z≲30, where the qualitatively unambiguous signature of a spectrum in emission can be expected for models that evade all current constraints.

energy injection
early universe
dark matter
black hole


The Observational Status of Simple Inflationary Models: an Update

Abstract: We provide an update on five relatively well motivated inflationary models in which the inflaton is a Standard Model singlet scalar field. These include i) the textbook quadratic and quartic potential models but with additional couplings of the inflaton to fermions and bosons, which enable reheating and also modify the naive predictions for the scalar spectral index n_s and r, ii) models with Higgs and Coleman-Weinberg potentials, and finally iii) a quartic potential model with non-minimal coupling of the inflaton to gravity. For n_s values close to 0.96, as determined by the WMAP9 and Planck experiments, most of the considered models predict r≳0.02. The running of the scalar spectral index, quantified by |d n_s/dln k|, is predicted in these models to be of order 10^-4–10^-3.

inflationary model
gravity
chaotic inflation
standard cosmology
simple model


The K2 Mission: Characterization and Early results

Abstract: The K2 mission will make use of the Kepler spacecraft and its assets to expand upon Kepler's groundbreaking discoveries in the fields of exoplanets and astrophysics through new and exciting observations. K2 will use an innovative way of operating the spacecraft to observe target fields along the ecliptic for the next 2-3 years. Early science commissioning observations have shown an estimated photometric precision near 400 ppm in a single 30 minute observation, and a 6-hour photometric precision of 80 ppm (both at V=12). The K2 mission offers long-term, simultaneous optical observation of thousands of objects at a precision far better than is achievable from ground-based telescopes. Ecliptic fields will be observed for approximately 75-days enabling a unique exoplanet survey which fills the gaps in duration and sensitivity between the Kepler and TESS missions, and offers pre-launch exoplanet target identification for JWST transit spectroscopy. Astrophysics observations with K2 will include studies of young open clusters, bright stars, galaxies, supernovae, and asteroseismology.


On the Dynamics and Evolution of Gravitational Instability-Dominated Disks

Abstract: We derive the evolution equations describing a thin axisymmetric disk of gas and stars with an arbitrary rotation curve that is kept in a state of marginal gravitational instability and energy equilibrium due to the balance between energy released by accretion and energy lost due to decay of turbulence. Rather than adopt a parameterized alpha prescription, we instead use the condition of marginal gravitational instability to self-consistently determine the position- and time-dependent transport rates. We show that there is a steady-state configuration for disks dominated by gravitational instability, and that this steady state persists even when star formation is taken into account if the accretion rate is sufficiently large. For disks in this state we analytically determine the velocity dispersion, surface density, and rates of mass and angular momentum transport as a function of the gas mass fraction, the rotation curve, and the rate of external accretion onto the disk edge. We show that disks that are initially out of steady state will evolve into it on the viscous timescale of the disk, which is comparable to the orbital period if the accretion rate is high. Finally, we discuss the implications of these results for the structure of disks in a broad range of environments, including high redshift galaxies, the outer gaseous disks of local galaxies, and accretion disks around protostars.

star
marginal gravitational instability
energy equilibrium
orbital period


Testing Fundamental Physics with Astrophysical Transients

Abstract: Explosive astrophysical transients at cosmological distances can be used to place precision tests of the basic assumptions of relativity theory, such as Lorentz invariance, the photon zero-mass hypothesis, and the weak equivalence principle (WEP). Signatures of Lorentz invariance violations (LIV) include vacuum dispersion and vacuum birefringence. Sensitive searches for LIV using astrophysical sources such as gamma-ray bursts, active galactic nuclei, and pulsars are discussed. The most direct consequence of a nonzero photon rest mass is a frequency dependence in the velocity of light propagating in vacuum. A detailed representation of how to obtain a combined severe limit on the photon mass using fast radio bursts at different redshifts through the dispersion method is presented. The accuracy of the WEP has been well tested based on the Shapiro time delay of astrophysical messengers traveling through a gravitational field. Some caveats of Shapiro delay tests are discussed. In this article, we review and update the status of astrophysical tests of fundamental physics.

fundamental physic
lorentz invariance violation
photon mass


Escape probability of the super-Penrose process

Abstract: We consider a head-on collision of two massive particles that move in the equatorial plane of an extremal Kerr black hole, which results in the production of two massless particles. Focusing on a typical case, where both of the colliding particles have zero angular momenta, we show that a massless particle produced in such a collision can escape to infinity with arbitrarily large energy in the near-horizon limit of the collision point. Furthermore, if we assume that the emission of the produced massless particles is isotropic in the center-of-mass frame but confined to the equatorial plane, the escape probability of the produced massless particle approaches 5/12 and almost all escaping massless particles have arbitrarily large energy at infinity and an impact parameter approaching 2GM/c^2, where M is the mass of the black hole.


Observed galaxy number counts on the lightcone up to second order: II. Derivation

Abstract: We present a detailed derivation of the observed galaxy number over-density on cosmological scales up to second order in perturbation theory. We include all relativistic effects that arise from observing on the past lightcone. The derivation is in a general gauge, and applies to all dark energy models (including interacting dark energy) and many modified gravity models. The result will be important for accurate cosmological parameter estimation, including non-Gaussianity, since all projection effects need to be taken into account. It also offers the potential for new probes of General Relativity, dark energy and modified gravity. This paper accompanies Paper I which presents the key results for the concordance model in Poisson gauge.

projection effect
galaxy clustering
bispectrum
second-order relativistic description
correction


Hubble trouble or Hubble bubble?

Abstract: The recent analysis of low-redshift supernovae (SN) has increased the apparent tension between the value of H_0 estimated from low and high redshift observations such as the cosmic microwave background (CMB) radiation. At the same time other observations have provided evidence of the existence of local radial inhomogeneities extending in different directions up to a redshift of about 0.07. About 40% of the Cepheids used for SN calibration are directly affected because are located along the directions of these inhomogeneities. We derive a new simple formula relating directly the luminosity distance to the monopole of the density contrast, which does not involve any metric perturbation. We then use it to develop a new inversion method to reconstruct the monopole of the density field from the deviations of the redshift uncorrected observed luminosity distance respect to the Λ CDM prediction based on cosmological parameters obtained from large scale observations. The inversion method confirms the existence of inhomogeneities whose effects were not previously taken into account because the 2M++ density field maps used to obtain the peculiar velocity for redshift correction were for z≤ 0.06, which is not a sufficiently large scale to detect the presence of inhomogeneities extending up to z=0.07. The inhomogeneity does not affect the high redshift luminosity distance because the volume averaged density contrast tends to zero asymptotically, making the value of H_0^CMB obtained from CMB observations insensitive to any local structure. The inversion method can provide a unique tool to reconstruct the density field at high redshift where only SN data is available, and in particular to normalize correctly the density field respect to the average large scale density of the Universe.

apparent tension
hubble parameter
outer denser region


Updating constraints on inflationary features in the primordial power spectrum with the Planck data

Abstract: We present new constraints on possible features in the primordial inflationary density perturbations power spectrum in light of the recent Cosmic Microwave Background Anisotropies measurements from the Planck satellite. We found that the Planck data hints for the presence of features in two different ranges of angular scales, corresponding to multipoles 10< l <60 and 150< l < 300, with a decrease in the best fit chi^2 value with respect to the featureless "vanilla" LCDM model of Delta chi^2 around 9 in both cases.

primordial power spectrum
inflationary model
smooth power-law spectrum


The dipole anisotropy of AllWISE galaxies

Abstract: We determine the dipole in the WISE galaxy catalogue. After reducing star contamination to <0.1 close to the Galactic plane, we eliminate low redshift sources to suppress the non-kinematic, clustering dipole. We remove sources within ±5 of the super-galactic plane, as well as those within 1” of 2MRS sources at redshift z < 0.03. We enforce cuts on the source angular extent to preferentially select distant ones. As we progress along these steps, the dipole converges in direction to within 5 of the CMB dipole and its magnitude also progressively reduces but stabilises at ∼0.012, corresponding to a velocity >1000 km/s if it is solely of kinematic origin. However, previous studies have shown that only ∼70 inferred from the CMB dipole is due to sources at z < 0.03. We examine the Dark Sky simulations to quantify the prevalence of such environments and find that <2.1 bulk flow (> 240 km/s extending to z > 0.03) that we do. We construct mock catalogues in the neighbourhood of such peculiar observers in order to mimic our final galaxy selection and quantify the residual clustering dipole. After subtracting this the remaining dipole is 0.0048 ± 0.0022, corresponding to a velocity of 420 ± 213 km/s which is consistent with the CMB. However the sources (at z > 0.03) of such a large clustering dipole remain to be identified.


Perturbative Quantum Gravity Comes of Age

Abstract: I argue that cosmological data from the epoch of primordial inflation is catalyzing the maturation of quantum gravity from speculation into a hard science. I explain why quantum gravitational effects from primordial inflation are observable. I then review what has been done, both theoretically and observationally, and what the future holds. I also discuss what this tells us about quantum gravity.

quantum
gravitational effect
precision cosmology


Cataloging the radio-sky with unsupervised machine learning: a new approach for the SKA era

Abstract: We develop a new analysis approach towards identifying related radio components and their corresponding infrared host galaxy based on unsupervised machine learning methods. By exploiting PINK, a self-organising map algorithm, we are able to associate radio and infrared sources without the a priori requirement of training labels. We present an example of this method using 894,415 images from the FIRST and WISE surveys centred towards positions described by the FIRST catalogue. We produce a set of catalogues that complement FIRST and describe 802,646 objects, including their radio components and their corresponding AllWISE infrared host galaxy. Using these data products we (i) demonstrate the ability to identify objects with rare and unique radio morphologies (e.g. 'X'-shaped galaxies, hybrid FR-I/FR-II morphologies), (ii) can identify the potentially resolved radio components that are associated with a single infrared host and (iii) introduce a "curliness" statistic to search for bent and disturbed radio morphologies, and (iv) extract a set of 17 giant radio galaxies between 700-1100 kpc. As we require no training labels, our method can be applied to any radio-continuum survey, provided a sufficiently representative SOM can be trained.

machine learning method
infrared source
astronomical survey


More on Universal Superconformal Attractors

Abstract: We define a general class of superconformal inflationary attractor models studied in our previous papers [1,2], which include, among others, inflationary models of 'induced gravity' which were argued to retain perturbative unitarity up to the Planck scale [3]. The choice of the function f(ϕ) in superconformal attractors for the models introduced in [3] is f(ϕ)= ϕ^n - ξ^-1. We present both superconformal and supergravity versions of these models, which were derived in [1,2] for arbitrary f(ϕ), together with the universal conditions required for stabilization of the extra three moduli present in the superconformal attractors, in addition to the inflaton.


Phases of New Physics in the CMB

Abstract: Fluctuations in the cosmic neutrino background are known to produce a phase shift in the acoustic peaks of the cosmic microwave background. It is through the sensitivity to this effect that the recent CMB data has provided a robust detection of free-streaming neutrinos. In this paper, we revisit the phase shift of the CMB anisotropy spectrum as a probe of new physics. The phase shift is particularly interesting because its physical origin is strongly constrained by the analytic properties of the Green's function of the gravitational potential. For adiabatic fluctuations, a phase shift requires modes that propagate faster than the speed of fluctuations in the photon-baryon plasma. This possibility is realized by free-streaming relativistic particles, such as neutrinos or other forms of dark radiation. Alternatively, a phase shift can arise from isocurvature fluctuations. We present simple models to illustrate each of these effects. We then provide observational constraints from the Planck temperature and polarization data on additional forms of radiation. We also forecast the capabilities of future CMB Stage IV experiments. Whenever possible, we give analytic interpretations of our results.

free-streaming neutrino
photon-baryon plasma
relativistic particle
cmb experiment