ShantanuT01/DACTYL-Pretraining huggingface dataset:
We study the linear and nonlinear structure formation in the dilaton and symmetron models of modified gravity using a generic parameterisation which describes a large class of scenarios using only a few parameters, such as the coupling between the scalar field and the matter, and the range of the scalar force on very large scales. For this we have modified the N-body simulation code ECOSMOG, which is a variant of RAMSES working in modified gravity scenarios, to perform a set of 110 simulations for different models and parameter values, including the default LCDM. These simulations enable us to explore a large portion of the parameter space. We have studied the effects of modified gravity on the matter power spectrum and mass function, and found a rich and interesting phenomenology where the difference with the LCDM template cannot be reproduced by a linear analysis even on scales as large as k~0.05 h/Mpc. Our results show the full effect of screening on nonlinear structure formation and the associated deviation from LCDM. We also investigate how differences in the force mediated by the scalar field in modified gravity models lead to qualitatively different features for the nonlinear power spectrum and the halo mass function, and how varying the individual model parameters changes these observables. The differences are particularly large in the nonlinear power spectra whose shapes for f(R), dilaton and symmetron models vary greatly, and where the characteristic bump around 1 h/Mpc of f(R) models is preserved for symmetrons, whereas an increase on much smaller scales is particular to symmetrons. No bump is present for dilatons where a flattening of the power spectrum takes place on small scales. These deviations from LCDM and the differences between modified gravity models, such as dilatons and symmetrons, could be tested with future surveys.
This article, dedicated to Herbert Saul Wilf on the occaison of his forthcoming 80-th birthday, describes two complementary approaches to enumeration, the "positive" and the "negative", each with its advantages and disadvantages. Both approaches are amenable to automation, and when applied to the currently active subarea, initiated in 2003 by Sergi Elizalde and Marc Noy, of enumerating consecutive-Wilf classes (i.e. consecutive pattern-avoidance) in permutations, were successfully pursued by DZ's two current PhD students, Andrew Baxter and Brian Nakamura. The Maple packages SERGI and ELIZALDE, implementing the algorithms enable the computer to "do research" by deriving, "all by itself", functional equations for the generating functions that enable polynomial-time enumeration for any set of patterns. In the case of ELIZALDE (the "negative" approach), these functional equations can be sometimes (automatically!) simplified, and imply "explicit" formulas, that previously were derived by humans using ad-hoc methods. We also get lots of new "explicit" results, beyond the scope of humans, but we have to admit, that we still need humans to handle "infinite families" of patterns, but this too, no doubt, will soon be automatable, and we leave it as a challenge to the (human and/or computer) reader. The Maple packages, and lots of sample output, is available from the webpage of this article: http://www.math.rutgers.edu/~zeilberg/mamarim/mamarimhtml/auto.html
We undertake the first comprehensive and quantitative real-space analysis of the cosmological information content in the environments of the cosmic web (voids, filaments, walls, and nodes) up to non-linear scales, $k = 0.5$ $h$/Mpc. Relying on the large set of $N$-body simulations from the Quijote suite, the environments are defined through the eigenvalues of the tidal tensor and the Fisher formalism is used to assess the constraining power of the power spectra derived in each of the four environments and their combination. Our results show that there is more information available in the environment-dependent power spectra, both individually and when combined all together, than in the matter power spectrum. By breaking some key degeneracies between parameters of the cosmological model such as $M_\nu$--$\sigma_\mathrm{8}$ or $\Omega_\mathrm{m}$--$\sigma_8$, the power spectra computed in identified environments improve the constraints on cosmological parameters by factors $\sim 15$ for the summed neutrino mass $M_\nu$ and $\sim 8$ for the matter density $\Omega_\mathrm{m}$ over those derived from the matter power spectrum. We show that these tighter constraints are obtained for a wide range of the maximum scale, from $k_\mathrm{max} = 0.1$ $h$/Mpc to highly non-linear regimes with $k_\mathrm{max} = 0.5$ $h$/Mpc. We also report an eight times higher value of the signal-to-noise ratio for the combination of spectra compared to the matter one. Importantly, we show that all the presented results are robust to variations of the parameters defining the environments hence suggesting a robustness to the definition we chose to define them.
We study a granular gas heated by a stochastic thermostat in the dilute limit. Starting from the kinetic equations governing the evolution of the correlation functions, a Boltzmann-Langevin equation is constructed. The spectrum of the corresponding linearized Boltzmann-Fokker-Planck operator is analyzed, and the equation for the fluctuating transverse velocity is derived in the hydrodynamic limit. The noise term (Langevin force) is thus known microscopically and contains two terms: one coming from the thermostat and the other from the fluctuating pressure tensor. At variance with the free cooling situation, the noise is found to be white and its amplitude is evaluated.
We construct modular compactifications of the universal Jacobian stack over the moduli stack of reduced curves with marked points depending on stability parameters obtained out of fixing a vector bundle on the universal curve. When restricted to the locus of stable marked curves, our compactifications are Deligne-Mumford irreducible smooth stacks endowed with projective moduli spaces and, following Esteves approach to the construction of fine compactifications of Jacobians, they parametrize torsion-free rank-1 simple sheaves satisfying a stability condition with respect to the fixed vector bundle. We also study a number of properties of our compactifications as the existence of forgetful and clutching morphisms and as well of sections from the moduli stack of stable curves with marked points. We conclude by indicating a number of different possible applications for our constructions.
Galaxy cluster merger statistics are an important component in understanding the formation of large-scale structure. Unfortunately, it is difficult to study merger properties and evolution directly because the identification of cluster mergers in observations is problematic. We use large N-body simulations to study the statistical properties of massive halo mergers, specifically investigating the utility of close halo pairs as proxies for mergers. We examine the relationship between pairs and mergers for a wide range of merger timescales, halo masses, and redshifts (0<z<1). We also quantify the utility of pairs in measuring merger bias. While pairs at very small separations will reliably merge, these constitute a small fraction of the total merger population. Thus, pairs do not provide a reliable direct proxy to the total merger population. We do find an intriguing universality in the relation between close pairs and mergers, which in principle could allow for an estimate of the statistical merger rate from the pair fraction within a scaled separation, but including the effects of redshift space distortions strongly degrades this relation. We find similar behavior for galaxy-mass halos, making our results applicable to field galaxy mergers at high redshift. We investigate how the halo merger rate can be statistically described by the halo mass function via the merger kernel (coagulation), finding an interesting environmental dependence of merging: halos within the mass resolution of our simulations merge less efficiently in overdense environments. Specifically, halo pairs with separations less than a few Mpc/h are more likely to merge in underdense environments; at larger separations, pairs are more likely to merge in overdense environments.
A collective vector-boson model with broken SU(3) symmetry is applied to several deformed even-even nuclei. The model description of ground and $\gamma$ bands together with the corresponding B(E2) transition probabilities is investigated within a broad range of SU(3) irreducible representations (irreps) $(\lambda ,\mu )$. The SU(3)-symmetry characteristics of rotational nuclei are analyzed in terms of the bandmixing interactions.
The purpose of this note is to give a linear algebra algorithm to find out if a rank of a given tensor over a field $\F$ is at most $k$ over the algebraic closure of $\F$, where $k$ is a given positive integer. We estimate the arithmetic complexity of our algorithm.
Aims. We aim to contribute to the identification of unassociated gamma-ray sources in the galactic plane in order to enlarge the currently known population of gamma-ray binaries and related systems, such as radio emitting X-ray binaries and microquasars. These objects are currently regarded as excellent test beds for the understanding of high energy phenomena in stellar systems. Methods. Potential targets of study are selected based on cross-identification of the 3rd Fermi Large Area Telescope catalogue with historical catalogues of luminous stars often found as optical counterparts in known cases. Follow-up observations and analysis of multi-wavelength archival data are later used to seek further proofs of association beyond the simple positional agreement. Results. Current results enable us to present here the case of the Fermi source 3FGL J0133.3+5930 where two peculiar objects have been discovered inside its region of uncertainty. One of them is the star TYC 3683-985-1 (LS I +59 79) whose eclipsing binary nature is reported in this work. The other one is the X-ray source SWIFT J0132.9+5932, that we found to be a likely low-power Active Galactic Nucleus at z = 0:1143 \pm 0:0002. If this second object is of blazar type, it could easily account for the observed gamma-ray photon flux. However, this is not confirmed at present, thus rendering still open the star system TYC 3683-985-1 as an alternative counterpart candidate to the Fermi source.
We report the evidence for the anti-correlation between pulsed fraction (PF) and luminosity of the X-ray pulsar SXP 1323, found for the first time in a luminosity range $10^{35}$--$10^{37}$ erg s$^{-1}$ from observations spanning 15 years. The phenomenon of a decrease in X-ray PF when the source flux increases has been observed in our pipeline analysis of other X-ray pulsars in the Small Magellanic Cloud (SMC). It is expected that the luminosity under a certain value decreases as the PF decreases due to the propeller effect. Above the propeller region, an anti-correlation between the PF and flux might occur either as a result of an increase in the un-pulsed component of the total emission or a decrease of the pulsed component. Additional modes of accretion may also be possible, such as spherical accretion and a change in emission geometry. At higher mass accretion rates, the accretion disk could also extend closer to the neutron star (NS) surface, where a reduced inner radius leads to hotter inner disk emission. These modes of plasma accretion may affect the change in the beam configuration to fan-beam dominant emission.
In this article we have investigated the Thomas-Fermi model for the electron gas in Rindler space. We have found that if the uniform acceleration is along $+x$-direction, then there is $y-z$-symmetry in space. For the sake of mathematical simplicity, we have assumed two dimensional spatial structure ($x-y$) in Rindler space. It has been observed that in two dimensional spatial coordinates the electrons are distributed discontinuously but in a periodic manner in a number of rectangular strips like domain along $\pm y$-direction. Some of them are having void structure, with no electrons inside such rectangular strips, while some are filled with electrons. We call the later type domain as the normal zone. We have also given physical interpretation for such exotic type electron distribution in Rindler space.
Observations of helium and hydrogen emission lines from metal-poor extragalactic H II regions provide an independent method for determining the primordial helium abundance, Y_p. Traditionally, the emission lines employed are in the visible wavelength range, and the number of suitable lines is limited. Furthermore, when using these lines, large systematic uncertainties in helium abundance determinations arise due to the degeneracy of physical parameters, such as temperature and density. Recently, Izotov, Thuan, & Guseva (2014) have pioneered adding the He 10830 infrared emission line in helium abundance determinations. The strong electron density dependence of He 10830 makes it ideal for better constraining density, potentially breaking the degeneracy with temperature. We revisit our analysis of the dataset published by Izotov, Thuan, & Stasinska (2007) and incorporate the newly available observations of He 10830 by scaling them using the observed-to-theoretical Paschen-gamma ratio. The solutions are better constrained, in particular for electron density, temperature, and the neutral hydrogen fraction, improving the model fit to data, with the result that more spectra now pass screening for quality and reliability, in addition to a standard 95% confidence level cut. Furthermore, the addition of He 10830 decreases the uncertainty on the helium abundance for all galaxies, with reductions in the uncertainty ranging from 10-80%. Overall, we find a reduction in the uncertainty on Y_p by over 50%. From a regression to zero metallicity, we determine Y_p = 0.2449 +/- 0.0040, consistent with the BBN result, Y_p = 0.2470 +/- 0.0002, based on the Planck determination of the baryon density. The dramatic improvement in the uncertainty from incorporating He 10830 strongly supports the case for simultaneous (thus not requiring scaling) observations of visible and infrared helium emission line spectra.
We derive the exact asymptotics of $P(\sup_{u\leq t}X(u) > x)$ if $x$ and $t$ tend to infinity with $x/t$ constant, for a L\'{e}vy process $X$ that admits exponential moments. The proof is based on a renewal argument and a two-dimensional renewal theorem of H\"{o}glund (1990).
The first part of the paper reviews applications of 2-spinor methods to relativistic qubits (analogies between tetrads in Minkowski space and 2-qubit states, qubits defined by means of null directions and their role for elimination of the Peres-Scudo-Terno phenomenon, advantages and disadvantages of relativistic polarization operators defined by the Pauli-Lubanski vector, manifestly covariant approach to unitary representations of inhomogeneous SL(2,C)). The second part deals with electromagnetic fields quantized by means of harmonic oscillator Lie algebras (not necessarily taken in irreducible representations). As opposed to non-relativistic singlets one has to distinguish between maximally symmetric and EPR states. The distinction is one of the sources of `strange' relativistic properties of EPR correlations. As an example, EPR averages are explicitly computed for linear polarizations in states that are antisymmetric in both helicities and momenta. The result takes the familiar form $\pm p\cos 2(\alpha-\beta)$ independently of the choice of representation of harmonic oscillator algebra. Parameter $p$ is determined by spectral properties of detectors and the choice of EPR state, but is unrelated to detector efficiencies. Brief analysis of entanglement with vacuum and vacuum violation of Bell's inequality is given. The effects are related to inequivalent notions of vacuum states. Technical appendices discuss details of the representation I employ in field quantization. In particular, M-shaped delta-sequences are used to define Dirac deltas regular at zero.
We use the nonstandard Fourier transform method, along with an established nonstandard approach to ODE's, to find a solution to the heat equation, on $(0,\infty)\times\mathcal{R}$, with a given boundary condition $g$ at $t=0$. We use this result to find an algorithm, converging to a solution of this equation, with applications to derivatives pricing in finance.
Recent theoretical and experimental studies of the exotic atoms with Z=1 are reviewed. An interplay between the atomic internal and external degrees of freedom is essential for a good description of the atomic cascade. The perspective of ab initio cascade calculations is outlined.
Kaiser & Squires have proposed a technique for mapping the dark matter in galaxy clusters using the coherent weak distortion of background galaxy images caused by gravitational lensing. We investigate the effectiveness of this technique under controlled conditions by creating simulated CCD frames containing galaxies lensed by a model cluster, measuring the resulting galaxy shapes, and comparing the reconstructed mass distribution with the original. Typically, the reconstructed surface density is diminished in magnitude when compared to the original. The main cause of this reduced signal is the blurring of galaxy images by atmospheric seeing, but the overall factor by which the reconstructed surface density is reduced depends also on the signal-to-noise ratio in the CCD frame and on both the sizes of galaxy images and the magnitude limit of the sample that is analysed. We propose a method for estimating a multiplicative compensation factor. We test our technique using a lensing cluster drawn from a cosmological N-body simulation with a variety of realistic background galaxy populations and observing conditions. We find that typically the compensation factor is appreciable, 1.4<f<2.2, and varies considerably depending on the observing conditions and sample selection. Our method yields a compensation factor which when used to correct the surface density estimates produces values that are in good agreement with those of the original cluster. Thus weak lensing observations when calibrated using this method yield not only accurate maps of the cluster morphology but also quantitative estimates of the cluster mass distribution.
Magnetic fields influence the formation and evolution of stars and impact the observed stellar properties. Ap stars (magnetic A-type stars) are a prime example of this. Access to precise and accurate determinations of their stellar fundamental properties, such as masses and ages, is crucial to understand the origin and evolution of fossil magnetic fields. We propose using the radii and luminosities determined from interferometric measurements, in addition to seismic constraints when available, to infer fundamental properties of 14 Ap stars pr\'eviously characterised. We used a grid-based modelling approach, employing stellar models computed with the \textsc{cestam} stellar evolution code, and the parameter search performed with the \textsc{aims} optimisation method. The stellar model grid was built using a wide range of initial helium abundances and metallicities in order to avoid any bias originating from the initial chemical composition. The large frequency separations ($\Delta\nu$) of HR\,1217 (HD\,24712) and $\alpha$~Cir (HD\,128898), two rapidly oscillating Ap stars of the sample, were used as seismic constraints. We inferred the fundamental properties of the 14 stars in the sample. The overall results are consistent within $1\sigma$ with previous studies, however, the stellar masses inferred in this study are higher. This trend likely originates from the broader range of chemical compositions considered in this work. We show that the use of $\Delta\nu$ in the modelling significantly improves our inferences, allowing us to set reasonable constraints on the initial metallicity which is, otherwise, unconstrained. This gives an indication of the efficiency of atomic diffusion in the atmospheres of roAp stars and opens the possibility of characterising the transport of chemical elements in their interiors.
Theoretical prediction of Curie temperature (TC) is of vital importance for designing the spintronic devices in two-dimensional (2D) ferromagnetic materials. Herein, based on the extensive investigation of Monte Carlo simulations, we summary and propose an improved method to estimate TC more precisely, which includes the different contributions of multiple near-neighbor interactions. Taking monolayer CrI3 as an example, the trends of TC with biaxial strain are investigated via Monte Carlo simulations, mean-field formulas and our method. Besides, our method is not only accurate and convenient to predicting the TC in 2D ferromagnetic honeycomb lattice CrI3 but it can be extended for predicting the TC of other 2D lattices. Our work paves the way to accelerate the prediction and discovery of novel 2D ferromagnets for spintronic applications.
The Relativistic Hartree-Fock-Bogoliubov model for axially deformed nuclei (RHFBz) is introduced. The model is based on an effective Lagrangian with density-dependent meson-nucleon couplings in the particle-hole channel, and the pairing part of the Gogny force is used in the pairing channel. The RHFBz quasiparticle equations are solved by expansion in the basis of a deformed harmonic oscillator. Illustrative RHFBz calculations are performed for Carbon, Neon and Magnesium isotopes. The effect of the explicitly including the pion field is investigated for binding energies, deformation parameters, and charge radii.
We discuss upper bounds on the rate at which unitary evolution governed by a non-local Hamiltonian can generate entanglement in a bipartite system. Given a bipartite Hamiltonian H coupling two finite dimensional particles A and B, the entangling rate is shown to be upper bounded by c*log(d)*norm(H), where d is the smallest dimension of the interacting particles, norm(H) is the operator norm of H, and c is a constant close to 1. Under certain restrictions on the initial state we prove analogous upper bound for the ancilla-assisted entangling rate with a constant c that does not depend upon dimensions of local ancillas. The restriction is that the initial state has at most two distinct Schmidt coefficients (each coefficient may have arbitrarily large multiplicity). Our proof is based on analysis of a mixing rate -- a functional measuring how fast entropy can be produced if one mixes a time-independent state with a state evolving unitarily.
We report the discovery of 70.5 ms pulsations from the X-ray source AX J1838.0-0655 using the Rossi X-ray Timing Explorer (RXTE). PSR J1838-0655 is a rotation-powered pulsar with spin-down luminosity Edot = 5.5e36 ergs/s, characteristic age tau = P/2Pdot = 23 kyr, and surface dipole magnetic field strength Bs = 1.9e12 G. It coincides with an unresolved INTEGRAL source and the extended TeV source HESS J1837-069. At an assumed distance of 6.6 kpc by association with an adjacent massive star cluster, the efficiency of PSR J1838-0655 converting spin-down luminosity to radiation is 0.8% for the 2-10 keV ASCA flux, 9% for the 20-300 keV INTEGRAL flux and ~3% for the >200 GeV emission of HESS J1837-069, making it a plausible power source for the latter. A Chandra X-ray observation resolves AX J1838.0-0655 into a bright point source surrounded by a ~2' diameter, centrally peaked nebula. The spectra of the pulsar and nebula are each well fitted by power laws, with photon indices Gamma = 0.5(0.3-0.7) and Gamma = 1.6(1.1-2.0), respectively. The 2-10 keV X-ray luminosities of the pulsar and nebula are L(PSR) = 4.6e34 d(6.6)^2 ergs/s and L(PWN) = 5.2e33 d(6.6)^2 ergs/s. A second X-ray source adjacent to the TeV emission, AX J1837.3-0652, is resolved into an apparent pulsar/PWN; it may also contribute to HESS J1837-069. The star cluster RSGC1 may have given birth to one or both pulsars, while fueling TeV emission from the extended PWN with target photons for inverse Compton scattering.