ShantanuT01/DACTYL-Pretraining huggingface dataset:
The standard model for GRB afterglow emission treats the accelerated electron population as a simple power law, $N(E) \propto E^{-p}$ for $p \gtrsim 2$. However, in standard Fermi shock acceleration a substantial fraction of the swept-up particles do not enter the acceleration process at all. Additionally, if acceleration is efficient then the nonlinear backreaction of accelerated particles on the shock structure modifies the shape of the non-thermal tail of the particle spectra. Both of these modifications to the standard synchrotron afterglow impact the luminosity, spectra, and temporal variation of the afterglow. To examine the effects of including thermal particles and nonlinear particle acceleration on afterglow emission, we follow a hydrodynamical model for an afterglow jet and simulate acceleration at numerous points during the evolution. When thermal particles are included, we find that the electron population is at no time well-fitted by a single power law, though the highest-energy electrons are; if the acceleration is efficient, then the power law region is even smaller. Our model predicts hard-soft-hard spectral evolution at X-ray energies, as well as an uncoupled X-ray and optical light curve. Additionally, we show that including emission from thermal particles has drastic effects (factors of 100 and 30, respectively) on the observed flux at optical and GeV energies. This enhancement of GeV emission makes afterglow detections by future $\gamma$-ray observatories, such as CTA, very likely.
The k.p perturbation method for determination of electronic structure first pioneered by Kohn and Luttinger continues to provide valuable insight to several band structure features. This method has been adopted to heterostructures confined up to three directions. In this paper, numerical details of setting up a k.p Hamiltonian using the finite difference approximation for such confined nanostructures is explicitly demonstrated. Nanostructures belonging to two symmetry classes namely cubic zincblende and rhombohedral crystals are considered. Rhombohedral crystals, of late, have gained prominence as candidates for the recently discovered topological insulator (TI) class of materials. Lastly the incorporation of strain field to the k.p Hamiltonian and matrix equations for computing the intrinsic and externally applied strain in heterostructures within a continuum approximation is shown. Two applications are considered 1)Computation of the eigen states of a multi-million zincblende InAs quantum dot with a stress-reducing InGaAs layer of varying Indium composition embedded in a GaAs matrix and 2)Dispersion of a rhombohedral topological insulator Bi$_{2}$Se$_{3}$ film.
All quadratic translation- and gauge-invariant photon operators for Lorentz breakdown are included into the Stueckelberg Lagrangian for massive photons in a generalized \xi-gauge. The corresponding dispersion relation and tree-level propagator are determined exactly, and some leading-order results are derived. The question of how to include such Lorentz-violating effects into a perturbative quantum-field expansion is addressed. Applications of these results within Lorentz-breaking quantum field theories include the regularization of infrared divergences as well as the free propagation of massive vector bosons.
Frustrated spin systems generically suffer from the negative sign problem inherent to Monte Carlo methods. Since the severity of this problem is formulation dependent, optimization strategies can be put forward. We introduce a phase pinning approach in the realm of the auxiliary field quantum Monte Carlo algorithm. If we can find an anti-unitary operator that commutes with the one body Hamiltonian coupled to the auxiliary field, then the phase of the action is pinned to $0$ and $\pi$. For generalized Kitaev models, we can successfully apply this strategy and observe a remarkable improvement of the average sign. We use this method to study thermodynamical and dynamical properties of the Kitaev-Heisenberg model down to temperatures corresponding to half of the exchange coupling constant. Our dynamical data reveals finite temperature properties of ordered and spin-liquid phases inherent to this model.
We present a pedagogical study of the commonly employed Speed-Plot (SP) and Time-delay (TD) methods for extracting the resonance parameters from the data of two particle coupled-channels reactions. Within several exactly solvable models, it is found that these two methods find poles on different Riemann sheets and are not always valid. We then develop an analytic continuation method for extracting the nucleon resonances within a dynamical coupled-channel formulation of the $\pi N$ and $\gamma N$ reactions. The main focus is on resolving the complications due to the coupling with the unstable $\pi \Delta, \rho N, \sigma N$ channels which decay into $\pi \pi N$ states. By using the results from the considered exactly solvable models, explicit numerical procedures are presented and verified. As a first application of the developed analytic continuation method, we present the nucleon resonances in the $S_{11}$ and $S_{31}$ partial waves extracted within a recently developed coupled-channels model of $\pi N$ reactions. The results from this realistic $\pi N$ model, which includes $\pi N$, $\eta N$, $\pi\Delta$, $\rho N$, and $\sigma N$ channels, also show that the simple pole parametrization of the resonant propagator using the poles extracted from SP and TD methods works poorly.
In this paper we present a new catalogue of Chemically Peculiar (CP) stars obtained by compiling publications in which abundances of metals are provided. Our catalogue includes 428 stars for which the data were obtained through spectroscopic observations. Most of them (416) are AmFm, HgMn and ApBp stars. We have used this compilation to proceed to a statistical overview of the abundance anomalies versus the physical parameters of the stars. The Spearman's rank correlation test has been applied, and a significant number of correlations of abundance peculiarities with respect to effective temperature, surface gravity and rotation velocity have been found. Four interesting cases are discussed in details: the Mn peculiarities in HgMn stars, the Ca correlation with respect to effective temperature in AmFm stars, the case of helium and iron in ApBp stars. Furthermore, we checked for ApBp stars using Anderson-Darling test wether the belonging to a multiple system is a determinant parameter or not for abundance peculiarities.
The analysis of the APOGEE data suggests the existence of a clear distinction between two sequences of disc stars in the [$\alpha$/Fe] vs. [Fe/H] abundance ratio space. We aim to test if the two-infall chemical evolution models designed to reproduce these two sequences in the solar neighbourhood are also capable to predict the disc bimodality observed in the vertical distribution of [Mg/Fe] in APOGEE DR16 data. Along with the predicted chemical composition of SSPs born at different Galactic times in the solar vicinity, we provide their maximum vertical height |zmax| above the Galactic plane computed assuming the relation between the vertical action and stellar age in thin disc stars. The predicted vertical distribution of the [Mg/Fe] abundance ratio is in agreement with the one observed combining the APOGEE DR16 data and the astroNN catalogue (stellar ages, orbital parameters) for stars younger than 8 Gyr (only low-$\alpha$ sequence stars). Including the high-$\alpha$ disc component, the dichotomy in the vertical [Mg/Fe] abundance distribution is reproduced considering the observational cut in the Galactic height of |z| < 2 kpc. However, our model predicts a too flat growth of the |zmax| as a function of [Mg/Fe] for high-$\alpha$ objects in contrast with the median values from APOGEE data. Possible explanations for such a tension are: i) the data sample with |z| < 2 kpc is more likely contaminated by halo stars, causing the median values to be kinematically hotter, ii) external perturbations such as minor mergers could have heated up the disc, and the heating of the orbits cannot be modelled by only scattering processes. Assuming for the data a disc dissection based on chemistry, the observed |zmax| distributions for high-$\alpha$ and low-$\alpha$ sequences are in good agreement with our model predictions if we consider in the calculation the errors in the vertical action estimates.
The pressure dependence of the Fermi surface of arsenic is examined using the technique of Wannier interpolation, enabling a dense sampling of the Brillouin zone and the ability to capture fine features within it. Focusing primarily on the A7 to simple-cubic phase transition, we find that this semimetal to metal transition is accompanied by the folding of Fermi surfaces. The pressure dependence of the density of states (DOS) of arsenic indicates that the onset of the Peierls-type cubic to rhombohedral distortion is signified by the appearance of emerging van Hove singularities in the DOS, especially around the Fermi level. As we noted in an earlier study, high levels of convergence are consequently required for an accurate description of this transition.
This paper describes joint work with Oded Schramm and Wendelin Werner establishing the values of the planar Brownian intersection exponents from which one derives the Hausdorff dimension of certain exceptional sets of planar Brownian motion. In particular, we proof a conjecture of Mandelbrot that the dimension of the frontier is 4/3. The proof uses a universality principle for conformally invariant measures and a new process, the stochastic Loewner evolution ($SLE$), introduced by Schramm. These ideas can be used to study other planar lattice models from statistical physics at criticality. I discuss applications to critical percolation on the triangular lattice, loop-erased random walk, and self-avoiding walk.
It is shown, that the presently accepted value for b-quark mass can be obtained from the requirement of the exact b-$\tau$ unification in the both non-SUSY and SUSY non-chiral extended GUTs.
A long-standing paradigm in astrophysics is that collisions- or mergers- of two neutron stars (NSs) form highly relativistic and collimated outflows (jets) powering gamma-ray bursts (GRBs) of short (< 2 s) duration. However, the observational support for this model is only indirect. A hitherto outstanding prediction is that gravitational wave (GW) events from such mergers should be associated with GRBs, and that a majority of these GRBs should be off-axis, that is, they should point away from the Earth. Here we report the discovery of the X-ray counterpart associated with the GW event GW170817. While the electromagnetic counterpart at optical and infrared frequencies is dominated by the radioactive glow from freshly synthesized r-process material in the merger ejecta, known as kilonova, observations at X-ray and, later, radio frequencies exhibit the behavior of a short GRB viewed off-axis. Our detection of X-ray emission at a location coincident with the kilonova transient provides the missing observational link between short GRBs and GWs from NS mergers, and gives independent confirmation of the collimated nature of the GRB emission.
We report on near-infrared J- and H-band linear polarimetric photometry of eight ultracool dwarfs (two late-M, five L0-L7.5, and one T2.5) with known evidence for photometric variability due to dust clouds, anomalous red infrared colors, or low-gravity atmospheres. The polarimetric data were acquired with the LIRIS instrument on the William Herschel Telescope. We also provide mid-infrared photometry in the interval 3.4-24 micron for some targets obtained with Spitzer and WISE, which has allowed us to confirm the peculiar red colors of five sources in the sample. We can impose modest upper limits of 0.9% and 1.8% on the linear polarization degree for seven targets with a confidence of 99%. Only one source, 2MAS, J02411151-0326587 (L0), appears to be strongly polarized (P ~ 3%) in the J-band with a significance level of P/sigma_P ~ 10. The likely origin of its linearly polarized light and rather red infrared colors may reside in a surrounding disk with an asymmetric distribution of grains. Given its proximity (66 +/- 8 pc), this object becomes an excellent target for the direct detection of the disk.
The exchange of two massless neutrinos gives rise to a long range force which couples to weakly charged matter. As has been noted previously in the literature, the potential for this force is $\VN \propto G_{F}^2 / r^5$ with monopole-monople, spin-spin and more complicated interactions. Unfortunately, this is far too small to be observed in present day experiments. We calculate $\VN$ explicitly in the electroweak theory, and show that under very general assumptions forces arising from the exchange of two massless fermions can at best yield $1 / r^5$ potentials.
We report for the first time a parametric fit to the pattern of the \ell = 1 mixed modes in red giants, which is a powerful tool to identify gravity-dominated mixed modes. With these modes, which share the characteristics of pressure and gravity modes, we are able to probe directly the helium core and the surrounding shell where hydrogen is burning. We propose two ways for describing the so-called mode bumping that affects the frequencies of the mixed modes. Firstly, a phenomenological approach is used to describe the main features of the mode bumping. Alternatively, a quasi-asymptotic mixed-mode relation provides a powerful link between seismic observations and the stellar interior structure. We used period \'echelle diagrams to emphasize the detection of the gravity-dominated mixed modes. The asymptotic relation for mixed modes is confirmed. It allows us to measure the gravity-mode period spacings in more than two hundred red giant stars. The identification of the gravity-dominated mixed modes allows us to complete the identification of all major peaks in a red giant oscillation spectrum, with significant consequences for the true identification of \ell = 3 modes, of \ell = 2 mixed modes, for the mode widths and amplitudes, and for the \ell = 1 rotational splittings. The accurate measurement of the gravity-mode period spacing provides an effective probe of the inner, g-mode cavity. The derived value of the coupling coefficient between the cavities is different for red giant branch and clump stars. This provides a probe of the hydrogen-shell burning region that surrounds the helium core. Core contraction as red giants ascend the red giant branch can be explored using the variation of the gravity-mode spacing as a function of the mean large separation.
The first Fermi-LAT High-energy source catalog (1FHL), containing gamma-ray sources detected above 10 GeV, is an ideal sample to characterize the physical properties of the most extreme gamma-ray sources. We investigate the pc scale properties of a sub-sample of radio faint 1FHL sources with the aim to confirm the proposed blazar associations, by revealing a compact high brightness temperature radio core, and we propose new low-frequency counterparts for the unassociated gamma-ray sources (UGS). Moreover, we increase the number of 1FHL sources with high resolution observations to explore the possible connection between radio and gamma rays at E >10 GeV. We observed 84 1FHL sources, mostly blazars of High Synchrotron Peaked (HSP) type, in the northern sky with the Very Long Baseline Array (VLBA) at 5 GHz. These sources lack high resolution radio observations and have at least one NVSS counterpart within the 95% confidence radius. For those sources without a well identified radio counterpart we exploit the VLBA multiple phase-center correlation capability to discern among the possible low-frequency candidates. For about 93% of the sources of our sample we reveal a compact high brightness temperature radio core, supporting their proposed blazar association. The vast majority of the detected sources are radio weak, with a median VLBI flux density value of 16.3 mJy. For the detected sources we obtain an average brightness temperature of the order of $2\times10^{10} \, \rm{K}$. We find a compact component for 16 UGS, for which we propose a new low-frequency association. We find brightness temperature values which do not require high Doppler factors, and are in agreement with the expected values for the equipartition of energy between particles and magnetic field. We find strong indications about the blazar nature of all of the detected UGS, for which we propose new low-frequency associations.
We explore the theoretical feasibility of extracting V_ub from two ratios built from B meson inclusive partial decays,   R_1 = Gamma(b-> u cbar s)/3Gamma(b -> c l nu), and   R_2 = [Gamma(b -> c X) - Gamma(b -> cbar X)]/Gamma(b -> c ubar d).   We discuss contributions to these quantities from perturbative and nonperturbative physics, and show that they can be computed with overall uncertainties at the level of 10%.
In this paper we report the results about the synthesis and characterization of optimally doped La1-xNaxMnO3 thin films grown onto SrTiO3 (100), NdGaO3 (100) and NdGaO3 (110) for thickness ranging from 11 to 82 nm. The effect of substrate nature and orientation, film thickness and annealing procedure was investigated in order to optimize their magnetoresistance (MR). We obtained very smooth films displaying MR values greater than 70%, near to room temperature.
We consider a Schr\"odinger-Poisson system involving a general nonlinearity at critical growth and we prove the existence of positive solutions. The Ambrosetti-Rabinowitz condition is not required. We also study the asymptotics of solutions with respect to a parameter.
We investigate the dependance of galaxy sizes and star-formation rates (SFRs) on environment using a mass-limited sample of quiescent and star-forming galaxies with M>10^9.5 at z=0.92 selected from the NMBS survey. Using the GEEC2 spectroscopic cluster catalog and the accurate photometric redshifts from NMBS, we select quiescent and star-forming cluster (sigma=490 km/s) galaxies within two virial radius, Rvir, intervals of 0.5<Rvir<2 and Rvir<0.5. Galaxies residing outside of 2 Rvir of both the cluster centres and additional candidate over-densities are defined as our field sample. Galaxy structural parameters are measured from the COSMOS legacy HST/ACS F814W image. The sizes and Sersic indices of quiescent field and cluster galaxies have the same distribution regardless of Rvir. However, cluster star-forming galaxies within 0.5 Rvir have lower mass-normalised average sizes, by 16${\pm}7\%$, and a higher fraction of Sersic indices with n>1, than field star-forming galaxies. The average SFRs of star-forming cluster galaxies show a trend of decreasing SFR with clustocentric radius. The mass-normalised average SFR of cluster star-forming galaxies is a factor of 2-2.5 (7-9 sigma) lower than that of star-forming galaxies in the field. While we find no significant dependence on environment for quiescent galaxies, the properties of star-forming galaxies are affected, which could be the result of environment acting on their gas content.
Supersymmetric models provide very interesting scenarios to account for the dark matter of the Universe. In this talk we discuss scenarios with gravitino dark matter in R-parity breaking vacua, which not only reproduce very naturally the observed dark matter relic density, but also lead to a thermal history of the Universe consistent with the observed abundances of primordial elements and the observed matter-antimatter asymmetry. In this class of scenarios the dark matter gravitinos are no longer stable, but decay with very long lifetimes into Standard Model particles, thus opening the possibility of their indirect detection. We have computed the expected contribution from gravitino decay to the primary cosmic rays and we have found that a gravitino with a mass of 150 GeV and a lifetime of 10^26 s could simultaneously explain the EGRET anomaly in the extragalactic gamma-ray background and the HEAT excess in the positron fraction.
We are concerned with the two-power nonlinear Schr\"odinger-type equations with non-local terms. We consider the framework of Sobolev-Lorentz spaces which contain singular functions with infinite-energy. Our results include global existence, scattering and decay properties in this singular setting with fractional regularity index. Solutions can be physically realized because they have finite local $L^2$-mass. Moreover, we analyze the asymptotic stability of solutions and, although the equation has no scaling, show the existence of a class of solutions asymptotically self-similar w.r.t. the scaling of the single-power NLS-equation. Our results extend and complement those of [F. Weissler, ADE 2001], particularly because we are working in the larger setting of Sobolev-weak-$L^p$ spaces and considering non-local terms. The two nonlinearities of power-type and the generality of the non-local terms allow us to cover in a unified way a large number of dispersive equations and systems.
Graph pebbling considers the problem of transforming configurations of discrete pebbles to certain target configurations on the vertices of a graph, using the so-called pebbling move. This paper provides counterexamples to a monotonicity conjecture stated by Hurlbert et al. concerning the pebbling number compared to the pebbling threshold.
It is shown theoretically that a one-dimensional crystal with time reversal symmetry is characterized by a Z_{2} topological invariant that predicts the existence or otherwise of edge states. This is confirmed experimentally through the construction and simulation of a photonic crystal analogue in the microwave regime.
A randomly interacting N-species Lotka-Volterra system in the presence of a Gaussian multiplicative noise is analyzed. The investigation is focused on the role of this external noise into the statistical properties of the extinction times of the populations. The distributions show a Gaussian shape for each noise intensity value investigated. A monotonic behavior of the mean extinction time as a function of the noise intensity is found, while a nonmonotonic behavior of the width of the extinction time probability distribution characterizes the dynamical evolution.
Electron paramagnetic resonance studies of the impurity Fe$^{3+}$ and Mn$^{4+}$ centers indicate that the symmetry of the crystal structure of millimeter-scale strontium titanate plates above 105 K lowers in the bulk from cubic to tetragonal, different from that of the conventional low-temperature antiferrodistortive phase. It is shown that the effect does not originate from the residual stress; its magnitude (observed tetragonal distortion) and particular manifestations depend on plate orientation, surface quality and the geometry of a sample. Peculiarities of the observed phenomenon are presented and possible scenario of its realization is discussed.