ShantanuT01/DACTYL-Pretraining huggingface dataset:
Impact of induced strain on charge carrier mobility is investigated for a monolayer graphene sheet. Mobility is computed within Born approximation by including impurity scattering, surface roughness effects and interaction with lattice phonons. Unlike its sSi counterpart, strained graphene shows a drop in mobility with increasing strain. Main reason for this effect is decrease in Fermi velocity due to induced distortions in the graphene honeycomb.
The derivation of the Demianski-Newman solution within the framework of the Ernst complex formalism is considered. We show that this solution naturally arises as a two-soliton specialization of the axisymmetric multi-soliton electrovacuum metric, and we work out the full set of the corresponding metrical fields and electromagnetic potentials. Some limits and physical properties of the DN space-time are briefly discussed.
Recent cosmic-ray measurements have found an anomaly in the cosmic-ray energy spectrum at GeV-TeV energies. Although the origin of the anomaly is not clearly understood, suggested explanations include effect of cosmic-ray source spectrum, propagation effects, and the effect of nearby sources. In this paper, we propose that the spectral anomaly might be an effect of re-acceleration of cosmic rays by weak shocks in the Galaxy. After acceleration by strong supernova remnant shock waves, cosmic rays undergo diffusive propagation through the Galaxy. During the propagation, cosmic rays may again encounter expanding supernova remnant shock waves, and get re-accelerated. As the probability of encountering old supernova remnants is expected to be larger than the younger ones due to their bigger sizes, re-acceleration is expected to be mainly due to weaker shocks. Since weaker shocks generate a softer particle spectrum, the resulting re-accelerated component will have a spectrum steeper than the initial cosmic-ray source spectrum produced by strong shocks. For a reasonable set of model parameters, it is shown that such re-accelerated component can dominate the GeV energy region while the non-reaccelerated component dominates at higher energies, explaining the observed GeV-TeV spectral anomaly.
The cross-correlation of Sunyaev-Zel'dovich effect (SZ) and weak-lensing imaging surveys can be used to test how well hot baryons trace dark matter in clusters of galaxies. We examine this concept using mock SZ and weak-lensing surveys based on the forthcoming AMiBA experiment and generated from a pre-heated cosmological N-body/hydrodynamic simulation. A cross-correlation diagram between matched lensing convergence and Compton y maps exhibits butterfly-wing-like structures, corresponding to individual clusters, that encode rich information about the distributions of hot gas and dark matter. When the cluster redshift and temperature are available the slope of a wing reveals the cluster gas fraction and the width of the wing indicates how badly the hot gas traces dark matter. On the basis of simulated data we discuss systematic errors in the projected gas fraction estimates that would be obtained from such survey comparisons.
Let $\sum\_{n=0}^\infty a\_n z^n\in \overline{\mathbb Q}[[z]]$ be a $G$-function, and, for any $n\ge0$, let $\delta\_n\ge 1$ denote the least integer such that $\delta\_n a\_0, \delta\_n a\_1, ..., \delta\_n a\_n$ are all algebraic integers. By definition of a $G$-function, there exists some constant $c\ge 1$ such that $\delta\_n\le c^{n+1}$ for all $n\ge 0$. In practice, it is observed that $\delta\_n$ always divides $D\_{bn}^{s} C^{n+1}$ where $D\_n=lcm\{1,2, ..., n\}$, $b, C$ are positive integers and $s\ge 0$ is an integer. We prove that this observation holds for any $G$-function provided the following conjecture is assumed: {\em Let $\mathbb{K}$ be a number field, and $L\in \mathbb{K}[z,\frac{d }{d z}]$ be a $G$-operator; then the generic radius of solvability $R\_v(L)$ is equal to 1, for all finite places $v$ of $\mathbb{K}$ except a finite number.} The proof makes use of very precise estimates in the theory of $p$-adic differential equations, in particular the Christol-Dwork Theorem. Our result becomes unconditional when $L$ is a geometric differential operator, a special type of $G$-operators for which the conjecture is known to be true. The famous Bombieri-Dwork Conjecture asserts that any $G$-operator is of geometric type, hence it implies the above conjecture.
We evaluate the relaxation time to equilibrium, and especially show that it is almost independent from the system size for macroscopic isolated quantum systems. It at most polynomially depends on the system size. This estimation holds when the Hamiltonian is non-integrable, the initial deviation of the quantity of interest is of order its spectral norm, and the relaxation process is monotonic.
The interaction of high energy cosmic rays with the Earth's atmosphere produces extensive air showers of secondary particles with a large muon component. By exploiting the sensitivity of neutrino telescopes to high energy muons, it is possible to use these detectors for precision cosmic ray studies. The high rate of cosmic-ray muon events provides a high-statistics data sample that can be used to look for anisotropy in the arrival directions of the parent particles at the per-mille level.   This paper reports on the observation of anisotropy in the cosmic ray data collected with the IceCube neutrino telescope in the 20-400 TeV energy range at multiple angular scales. New data from the IceTop air shower array, located on the ice surface above IceCube, shows an anisotropy that is consistent with the high-energy IceCube results. The sensitivity of IceTop to all the components of the extensive air shower will allow us to explore in more detail the characteristics of the primary cosmic rays associated with the observed anisotropy.
We present a mini-review of the problem of evaluating the energy loss of a ultrarelativistic charged particle crossing a thermally equilibrated high temperature e+e- or quark-gluon plasma.
In this paper, we treat moduli spaces of parabolic connections. We take \'etale coverings of the moduli spaces, and we construct a Hamiltonian structure of an algebraic vector field determined by the isomonodromic deformation for each \'etale morphism.
We find a consistency between two different approaches of hard diffraction, namely the QCD dipole model and the Soft Colour Interaction approach. A theoretical interpretation in terms of S-Matrix and perturbative QCD properties in the small $x_{Bj}$ regime is proposed.
Recently, in Phys. Rev. D 98, 084002 (2018), an investigation was carried out on the gravitational radiation from binary systems in conformal gravity and massive conformal gravity. According to the authors of the paper, these two theories differ only by the sign of a parameter in the matter action of a general conformal theory. For a negative parameter the general conformal theory indeed corresponds to conformal gravity. However, here, we argue that for a positive parameter the general conformal theory does not correspond to massive conformal gravity.
The Gamma-ray burst (GRB) database based on the data by the RHESSI satellite provides a unique and homogeneous database for future analyses. Here we present preliminary results on the duration and hardness ratio distributions for a sample of 228 GRBs observed with RHESSI.
We report on NuSTAR observations of the Intermediate Polar GK Persei which also behaves as a Dwarf Nova. It exhibited a Dwarf Nova outburst in 2015 March-April. The object was observed in 3-79 keV X-rays with NuSTAR, once at the outburst peak, and again in 2015 September during quiescence. The 5-50 keV flux during the outburst was 26 times higher than that during the quiescence. With a multi-temperature emission model and a reflection model, we derived the post-shock temperature as 19.2 +/- 0.7 keV in the outburst, and 38.5 +4.1/-3.6 keV in the quiescence. This temperature difference is considered to reflect changes in the radius at which the accreting matter, forming an accretion disk, is captured by the magnetosphere of the white dwarf (WD). Assuming that this radius scales as the power of -2/7 of the mass accretion rate, and utilizing the two temperature measurements, as well as the standard mass-radius relation of WDs, we determined the WD mass in GK Persei as 0.90 +/- 0.06 solar masses. The magnetic field is estimated as 4*10^5 G.
We consider linear spectral statistics built from the block-normalized correlation matrix of a set of $M$ mutually independent scalar time series. This matrix is composed of $M \times M$ blocks that contain the sample cross correlation between pairs of time series. In particular, each block has size $L \times L$ and contains the sample cross-correlation measured at $L$ consecutive time lags between each pair of time series. Let $N$ denote the total number of consecutively observed windows that are used to estimate these correlation matrices. We analyze the asymptotic regime where $M,L,N \rightarrow +\infty$ while $ML/N \rightarrow c_\star$, $0<c_\star<\infty$. We study the behavior of linear statistics of the eigenvalues of this block correlation matrix under these asymptotic conditions and show that the empirical eigenvalue distribution converges to a Marcenko-Pastur distribution. Our results are potentially useful in order to address the problem of testing whether a large number of time series are uncorrelated or not.
We prove It{\^o}'s formula for the flow of measures associated with a jump process defined by a drift, an integral with respect to a Poisson random measure and with respect to the associated compensated Poisson random measure. We work in $\mathcal{P}_{\beta}(\mathbb{R}^d)$, the space of probability measures on $\mathbb{R}^d$ having a finite moment of order $\beta \in (0, 2]$. As an application, we exhibit the backward Kolmogorov partial differential equation stated on $[0,T] \times \mathcal{P}_{\beta}(\mathbb{R}^d)$ associated with a McKean-Vlasov stochastic differential equation driven by a Poisson random measure. It describes the dynamics of the semigroup associated with the McKean-Vlasov stochastic differential equation, under regularity assumptions on it. Finally, we use the semigroup and the backward Kolmogorov equation to prove new quantitative weak propagation of chaos results for a mean-field system of interacting Ornstein-Uhlenbeck processes driven by i.i.d. $\alpha$-stable processes with $\alpha \in (1,2)$.
Let X_g=C^{(2)}_g be the second symmetric product of a very general curve of genus g. We reduce the problem of describing the ample cone on X_g to a problem involving the Seshadri constant of a point on X_{g-1}. Using this we recover a result of Ciliberto-Kouvidakis that reduces finding the ample cone of X_g to the Nagata conjecture when g\ge 9. We also give new bounds on the the ample cone of X_g when g=5.
Binary stars play a critical role in determining both the dynamical evolution and the observational appearance of globular star clusters. We present a summary of three talks presented at IAU JD15, reviewing the current observational and theoretical status of binaries and related ``exotic'' stars in the Galactic globular cluster system.
We propose a new spin squeezing criterion for arbitrary multi-qubit states that is invariant under local unitary operations. We find that, for arbitrary pure two-qubit states, spin squeezing is equivalent to entanglement, and multi-qubit states are entangled if this new spin squeezing parameter is less than 1.
We derive an energy-dependent decay-time distribution function from the multi-exponential decay of the ensemble photoluminescence (PL) of InGaN/GaN quantum dots (QDs), which agrees well with recently published single-QD time-resolved PL measurements. Using eight-band k.p modelling, we show that the built-in piezo- and pyroelectric fields within the QDs cause a sensitive dependence of the radiative lifetimes on the exact QD geometry and composition. Moreover, the radiative lifetimes also depend heavily on the composition of the direct surrounding of the QDs. A broad lifetime distribution occurs even for moderate variations of the QD structure. Thus, for unscreened fields a multi-exponential decay of the ensemble PL is generally expected in this material system.
Multi-hydrogenated species with proper symmetry properties can present different spin configurations, and thus exist under different spin symmetry forms, labeled as para and ortho for two-hydrogen molecules. We investigated here the ortho-to-para ratio (OPR) of H$_2$Cl$^+$ in the light of new observations performed in the z=0.89 absorber toward the lensed quasar PKS 1830-211 with the Atacama Large Millimeter/submillimeter Array (ALMA). Two independent lines of sight were observed, to the southwest (SW) and northeast (NE) images of the quasar, with OPR values found to be $3.15 \pm 0.13$ and $3.1 \pm 0.5$ in each region, respectively, in agreement with a spin statistical weight of 3:1. An OPR of 3:1 for a molecule containing two identical hydrogen nuclei can refer to either a statistical result or a high-temperature limit depending on the reaction mechanism leading to its formation. It is thus crucial to identify rigorously how OPRs are produced in order to constrain the information that these probes can provide. To understand the production of the H$_2$Cl$^+$ OPR, we undertook a careful theoretical study of the reaction mechanisms involved with the aid of quasi-classical trajectory calculations on a new global potential energy surface fit to a large number of high-level ab initio data. Our study shows that the major formation reaction for H$_2$Cl$^+$ produces this ion via a hydrogen abstraction rather than a scrambling mechanism. Such a mechanism leads to a 3:1 OPR, which is not changed by destruction and possible thermalization reactions for H$_2$Cl$^+$ and is thus likely to be the cause of observed 3:1 OPR ratios, contrary to the normal assumption of scrambling.
We report the discovery of burst oscillations at the spin frequency in ten thermonuclear bursts from the accreting millisecond X-ray pulsar (AMXP) IGR J17511-3057. The burst oscillation properties are, like those from the persistent AMXPs SAX J1808.4-3658 and XTE J1814-338, anomalous compared to burst oscillations from intermittent pulsars or non-pulsing LMXBs. Like SAX J1808.4-3658 they show frequency drifts in the rising phase rather than the tail. There is also evidence for harmonic content. Where IGR J17511-3057 is unusual compared to the other two persistent pulsars is that oscillations are not detected throughout all bursts. As accretion rate drops the bursts get brighter and their rise/decay time scales become shorter, while the oscillation amplitude falls below the detection threshold: first in the burst peak and then also in the rise. None of the bursts from IGR J17511-3057 show evidence for photospheric radius expansion (which might be expected to suppress oscillation amplitude) which allow us to set an upper limit to the distance of 6.9 kpc. We discuss the implications of our results for models of the burst oscillation mechanism.
For any complex number $c$, let $\sigma_c\colon\mathbb N\rightarrow\mathbb C$ denote the divisor function defined by $\sigma_c(n)=\displaystyle{\sum_{d|n}d^c}$ for all $n\in\mathbb N$, and define $R(c)=\{\sigma_c(n)\in\mathbb C\colon n\in\mathbb N\}$ to be the range of $\sigma_c$. We study the basic topological properties of the sets $R(c)$. In particular, we determine the complex numbers $c$ for which $R(c)$ is bounded and determine the isolated points of the sets $R(c)$. In the third section, we find those values of $c$ for which $R(c)$ is dense in $\mathbb C$. We also prove some results and pose several open problems about the closures of the sets $R(c)$ when these sets are bounded.
We report several new transformation theorems that map perfect fluid spheres into perfect fluid spheres. In addition, we report new ``solution generating'' theorems for the TOV, whereby any given solution can be ``deformed'' to a new solution.
Low-dimensional copper oxide lattices naturally manifest electronic states with strong short range quantum entanglement, which are known to lead to remarkable emergent material properties. However the nanometer scale many-body wavefunction is challenging to measure or manipulate in a simple way. In this study, X-ray induced $dd$ electronic transitions are used to suppress spin entanglement across a single lattice site in the spin-1/2 antiferromagnetic chain compound SrCuO$_2$, revealing a class of cuprate magnetic excitations that result from breaking the spin chain. These measurements are the first to employ two closely spaced X-ray resonances of copper (M$_2$ and M$_3$) as a form of natural 2-slit interferometer to distinguish between different types of electronic transition and resolve how they influence the dynamics of nearby spin-entangled electrons.
We discuss the relation between self-organized criticality and depinning transitions by mapping sandpile models to equations that describe driven interfaces in random media. This equivalence yields a continuum description and gives insight about various ways of reaching the depinning critical point: slow drive (self-organized criticality), fixed density simulations, tuning the interface velocity (extremal drive criticality), or tuning the driving force. We obtain a scaling relation for the correlation length exponent for sandpiles.
Consider a single hyperbolic PDE $u_{xy}=f(x,y,u,u_x,u_y)$, with locally prescribed data: $u$ along a non-characteristic curve $M$ and $u_x$ along a non-characteristic curve $N$. We assume that $M$ and $N$ are graphs of one-to-one functions, intersecting only at the origin, and located in the first quadrant of the $(x,y)$-plane. It is known that if $M$ is located above $N$, then there is a unique local solution, obtainable by successive approximation. We show that in the opposite case, when $M$ lies below $N$, the uniqueness can fail in the following strong sense: for the same boundary data, there are two solutions that differ at points arbitrarily close to the origin. In the latter case, we also establish existence of a local solution (under a Lipschitz condition on the function $f$). The construction, via Picard iteration, makes use of a careful choice of additional $u$-data which are updated in each iteration step.
We present an investigation of the influence of structural distortions in charge-carrier doped \lmco by substituting La$^{3+}$ with alkaline earth metals of strongly different ionic sizes, that is M = Ca$^{2+}$, Sr$^{2+}$, and Ba$^{2+}$, respectively. We find that both, the magnetic properties and the resistivity change non-monotonously as a function of the ionic size of M. Doping \lmco with M = Sr$^{2+}$ yields higher transition temperatures to the ferromagnetically ordered states and lower resistivities than doping with either Ca$^{2+}$ or Ba$^{2+}$ having a smaller or larger ionic size than Sr$^{2+}$, respectively. From this observation we conclude that the different transition temperatures and resistivities of \lmco for different M (of the same concentration $x$) do not only depend on the varying chemical pressures. The local disorder due to the different ionic sizes of La$^{3+}$ and M$^{2+}$ play an important role, too.
We study the statistical properties of turbulence driven by structure formation in a massive merging galaxy cluster at z=0. The development of turbulence is ensured as the largest eddy turnover time is much shorter than the Hubble time independent of mass and redshift. We achieve a large dynamic range of spatial scales through a novel Eulerian refinement strategy where the cluster volume is refined with progressively finer uniform nested grids during gravitational collapse. This provides an unprecedented resolution of 7.3 h^{-1} kpc across the virial volume. The probability density functions of various velocity derived quantities exhibit the features characteristic of fully developed compressible turbulence observed in dedicated periodic-box simulations. Shocks generate only 60% of the total vorticity within \rvir/3 region and 40% beyond that. We compute second and third order, longitudinal and transverse, structure functions for both solenoidal and compressional components, in the cluster core, virial region and beyond. The structure functions exhibit a well defined inertial range. The injection scale is comparable to the virial radius but increases towards the outskirts. Within \rvir/3, the spectral slope of the solenoidal component is close to Kolmogorov's, but for the compressional component is substantially steeper and close to Burgers'; the flow is mostly solenoidal and statistically rigorously consistent with fully developed, homogeneous and isotropic turbulence. Small scale anisotropy appears due to numerical artifact. Towards the virial region, the flow becomes compressional, the structure functions flatter and modest genuine anisotropy appear. In comparison, mesh adaptivity based on Lagrangian refinement and the same finest resolution, leads to lack of turbulent power on small scale and excess thereof on large scales, and unreliable density weighted structure functions.
This paper presents a stochastic approach to the clustering evolution of dark matter haloes in the Universe. Haloes, identified by a Press-Schechter-type algorithm in Lagrangian space, are described in terms of `counting fields', acting as non-linear operators on the underlying Gaussian density fluctuations. By ensemble averaging these counting fields, the standard Press-Schechter mass function as well as analytic expressions for the halo correlation function and corresponding bias factors of linear theory are obtained, thereby extending the recent results by Mo and White. The non-linear evolution of our halo population is then followed by solving the continuity equation, under the sole hypothesis that haloes move by the action of gravity. This leads to an exact and general formula for the bias field of dark matter haloes, defined as the local ratio between their number density contrast and the mass density fluctuation. Besides being a function of position and `observation' redshift, this random field depends upon the mass and formation epoch of the objects and is both non-linear and non-local. The latter features are expected to leave a detectable imprint on the spatial clustering of galaxies, as described, for instance, by statistics like bispectrum and skewness. Our algorithm may have several interesting applications, among which the possibility of generating mock halo catalogues from low-resolution N-body simulations.
We consider the inverse boundary value problem for the steady state convection diffusion equation. We prove that a velocity field $V$, is uniquely determined by the Dirichlet-to-Neumann map, when $V \in C^{0,\gamma} (\Omega)$, $2/3< \gamma \leq 1$, i.e. when $V$ is a H\"older continuous vector field with $2/3< \gamma \leq 1$.
We analyse supersymmetric models augmented by an extra $U(1)$ gauge group. To avoid anomalies in these models without introducing exotics, we allow for family-dependent $U(1)^\prime$ charges, and choose a simple form for these, dependent on one $U(1)^\prime$ charge parameter only. With this choice, $Z^\prime$ decays into di-taus but not di-leptons, weakening considerably the constraints on its mass. In the supersymmetric sector, the effect is to lower the singlino mass, allowing it to be the dark matter candidate. We investigate the dark matter constraints and collider implications of such models, with mostly singlino, or mostly higgsinos, or a mixture of the two as lightest supersymmetric particles. In these scenarios, $Z^\prime$ decays significantly into chargino or neutralino pairs, and thus indirectly into final state leptons. We devise benchmarks which, with adequate cuts, can yield signals visible at the high-luminosity LHC.