ShantanuT01/DACTYL-Pretraining huggingface dataset:
We present results of two-dimensional fully kinetic Particle-In-Cell simulation in order to shed light on the role of whistler waves in the scattering of strahl electrons and in the heat flux regulation in the solar wind. We model the electron velocity distribution function as initially composed of core and strahl populations as typically encountered in the near-Sun solar wind as observed by Parker Solar Probe. We demonstrate that, as a consequence of the evolution of the electron velocity distribution function, two branches of the whistler heat flux instability can be excited, which can drive whistler waves propagating in the direction oblique or parallel to the background magnetic field. First, oblique whistler waves induce pitch-angle scattering of strahl electrons, towards higher perpendicular velocities. This leads to the broadening of the strahl pitch angle distribution and hence to the formation of a halo-like population at the expense of the strahl. Later on, the electron velocity distribution function experiences the effect of parallel whistler waves, which contributes to the redistribution of the particles scattered in the perpendicular direction into a more symmetric halo, in agreement with observations. Simulation results show a remarkable agreement with the linear theory of the oblique whistler heat flux instability. The process is accompanied by a significant decrease of the heat flux carried by the strahl population.
The monitor of all-sky X-ray image (MAXI) Gas Slit Camera (GSC) on the International Space Station (ISS) detected a gamma-ray burst (GRB) on 2009, September 26, GRB\,090926B. This GRB had extremely hard spectra in the X-ray energy range. Joint spectral fitting with the Gamma-ray Burst Monitor on the Fermi Gamma-ray Space Telescope shows that this burst has peculiarly narrow spectral energy distribution and is represented by Comptonized blackbody model. This spectrum can be interpreted as photospheric emission from the low baryon-load GRB fireball. Calculating the parameter of fireball, we found the size of the base of the flow $r_0 = (4.3 \pm 0.9) \times 10^{9} \, Y^{\prime \, -3/2}$ cm and Lorentz factor of the plasma $\Gamma = (110 \pm 10) \, Y^{\prime \, 1/4}$, where $Y^{\prime}$ is a ratio between the total fireball energy and the energy in the blackbody component of the gamma-ray emission. This $r_0$ is factor of a few larger, and the Lorentz factor of 110 is smaller by also factor of a few than other bursts that have blackbody components in the spectra.
The equipartition or minimum-energy calculation is a well-known procedure for estimating magnetic field strength and total energy in the magnetic field and cosmic ray particles by using only the radio synchrotron emission. In one of our previous papers we have offered a modified equipartition calculation for supernova remnants (SNRs) with spectral indices 0.5<\alpha <1. Here we extend the analysis to SNRs with \alpha =0.5 and \alpha =1.
We discuss the temperature correction to the Casimir force between nonideal metallic bodies which caused disagreement in the literature. A general method to find the troubling term is proposed that does not require a direct reference to the Lifshitz formula. The linear in temperature correction is shown to survive for nonideal metals. It is important for small separations between bodies tested in the recent experiments.
The prospects for a determination of the strong coupling constant $\alpha_s$ via scaling violations of fragmentation functions in deeply inelastic scattering are studied. The statistical error in the case of an integrated luminosity of $250 pb^{-1}$, and the theoretical errors due to the various parton density parametrizations and to the factorization scale dependence are estimated.
We study a complete, colour-selected sample of double-degenerate binary systems containing extremely low mass (ELM) <0.25 Msol white dwarfs (WDs). We show, for the first time, that Milky Way disk ELM WDs have a merger rate of approximately 4 x 10^(-5)/yr due to gravitational wave radiation. The merger end-product depends on the mass ratio of the binary. The ELM WD systems that undergo stable mass transfer can account for >3% of AM CVn stars. More importantly, the ELM WD systems that may detonate merge at a rate comparable to the estimated rate of underluminous SNe, rare explosions estimated to produce only ~0.2 Msol worth of ejecta. At least 25% of our ELM WD sample belong to the old thick disk and halo components of the Milky Way. Thus, if merging ELM WD systems are the progenitors of underluminous SNe, transient surveys must find them in both elliptical and spiral galaxies.
Hafner and Stopple proved a conjecture of Zagier, that the inverse Mellin transform of the symmetric square $L$-function associated to the Ramanujan tau function has an asymptotic expansion in terms of the non-trivial zeros of the Riemann zeta function $\zeta(s)$. Later, Chakraborty, Kanemitsu and the second author extended this phenomenon for any Hecke eigenform over the full modular group. In this paper, we study an asymptotic expansion of the Lambert series \begin{equation*} y^k \sum_{n=1}^\infty \lambda_{f}( n^2 ) \exp (- ny), \quad \textrm{as}\,\, y \rightarrow 0^{+}, \end{equation*} where $\lambda_f(n)$ is the $n$th Fourier coefficient of a Hecke eigen form $f(z)$ of weight $k$ over the full modular group.
A general theory is derived for the moments of the first passage time of a one-dimensional Markov process in presence of a weak time-dependent forcing. The linear corrections to the moments can be expressed by quadratures of the potential and of the time-dependent probability density of the unperturbed system or equivalently by its Laplace transform. If none of the latter functions is known, the derived formulas may still be useful for specific cases including a slow driving or a driving with power at only small or large times. In the second part of the paper, explicite expressions for mean and variance of the first passage time are derived for the cases of a linear or a parabolic potential and an exponentially decaying driving force. The analytical results are found to be in excellent agreement with computer simulations of the respective first-passage processes. The particular examples furthermore demonstrate that already the effect of a simple exponential driving can be fairly involved implying a nontrivial nonmonotonous behavior of mean and variance as functions of the driving's time scale.
We present constraints on variations in the initial mass function (IMF) of nine local early-type galaxies based on their low mass X-ray binary (LMXB) populations. Comprised of accreting black holes and neutron stars, these LMXBs can be used to constrain the important high mass end of the IMF. We consider the LMXB populations beyond the cores of the galaxies ($>0.2R_{e}$; covering $75-90\%$ of their stellar light) and find no evidence for systematic variations of the IMF with velocity dispersion ($\sigma$). We reject IMFs which become increasingly bottom heavy with $\sigma$, up to steep power-laws (exponent, $\alpha>2.8$) in massive galaxies ($\sigma>300$km/s), for galactocentric radii $>1/4\ R_{e}$. Previously proposed IMFs that become increasingly bottom heavy with $\sigma$ are consistent with these data if only the number of low mass stars $(<0.5M_{\odot}$) varies. We note that our results are consistent with some recent work which proposes that extreme IMFs are only present in the central regions of these galaxies. We also consider IMFs that become increasingly top-heavy with $\sigma$, resulting in significantly more LMXBs. Such a model is consistent with these observations, but additional data are required to significantly distinguish between this and an invariant IMF. For six of these galaxies, we directly compare with published IMF mismatch parameters from the Atlas3D survey, $\alpha_{dyn}$. We find good agreement with the LMXB population if galaxies with higher $\alpha_{dyn}$ have more top-heavy IMFs -- although we caution that our sample is quite small. Future LMXB observations can provide further insights into the origin of $\alpha_{dyn}$ variations.
Observables from parity violation in elastic electron-nucleon scattering and neutral current quasi-elastic neutrino-nucleus scattering are employed as tools to improve the current knowledge on the strangeness content in the nucleon.
It is well believed that Transformer performs better in semantic segmentation compared to convolutional neural networks. Nevertheless, the original Vision Transformer may lack of inductive biases of local neighborhoods and possess a high time complexity. Recently, Swin Transformer sets a new record in various vision tasks by using hierarchical architecture and shifted windows while being more efficient. However, as Swin Transformer is specifically designed for image classification, it may achieve suboptimal performance on dense prediction-based segmentation task. Further, simply combing Swin Transformer with existing methods would lead to the boost of model size and parameters for the final segmentation model. In this paper, we rethink the Swin Transformer for semantic segmentation, and design a lightweight yet effective transformer model, called SSformer. In this model, considering the inherent hierarchical design of Swin Transformer, we propose a decoder to aggregate information from different layers, thus obtaining both local and global attentions. Experimental results show the proposed SSformer yields comparable mIoU performance with state-of-the-art models, while maintaining a smaller model size and lower compute.
We derive the Fermat potential for a spherically symmetric lens embedded in an FLRW cosmology and use it to investigate the late-time integrated Sachs-Wolfe (ISW) effect, i.e., secondary temperature fluctuations in the cosmic microwave background (CMB) caused by individual large scale clusters and voids. We present a simple analytical expression for the temperature fluctuation in the CMB across such a lens as a derivative of the lens' Fermat potential. This formalism is applicable to both linear and nonlinear density evolution scenarios, to arbitrarily large density contrasts, and to all open and closed background cosmologies. It is much simpler to use and makes the same predictions as conventional approaches. In this approach the total temperature fluctuation can be split into a time-delay part and an evolutionary part. Both parts must be included for cosmic structures that evolve and both can be equally important. We present very simple ISW models for cosmic voids and galaxy clusters to illustrate the ease of use of our formalism. We use the Fermat potentials of simple cosmic void models to compare predicted ISW effects with those recently extracted from WMAP and \emph{Planck} data by stacking large cosmic voids using the aperture photometry method. If voids in the local universe with large density contrasts are no longer evolving we find that the time delay contribution alone predicts values consistent with the measurements. However, we find that for voids still evolving linearly, the evolutionary contribution cancels a significant part of the time delay contribution and results in predicted signals that are much smaller than recently observed.
Nonequilibrium electronic transport through a polymer chain is investigated by the scattering state operator method. The polymer chain is described by an electron-lattice coupling model and its two ends are connected with metal electrodes of different chemical potentials. The scattering states are shown to be a set of complete eigenstates of electrons in the system at nonequilibrium steady state. With the method, we show that the nonequilibrium Peierls transition (NEPT) does not survive the lattice relaxation and the soliton-antisoliton pair excitations. Furthermore the electronic transport though the chain is shown to be accomplished through the soliton-lattice energy band.
In the paper by M. Hotta and M. Morikawa [Phys. Rev. A 69, 052114 (2004)] the non-existence of the quantum Zeno effect caused by indirect measurements has been claimed. It is shown here that the pertinent proof is incorrect, and the claim unfounded.
Voltage modulation of yttrium iron garnet (YIG) with compactness, high speed response, energy efficiency and both practical/theoretical siginificances can be widely applied to various YIG based spintronics such as spin Hall, spin pumping, spin Seeback effects. Here we initial an ionic modulation of interfacial magnetism process on YIG/Pt bilayer heterostructures, where the Pt capping would influence the ferromagnetic (FMR) field position significantly, and realize a significant magnetism enhancement in bilayer system. A large voltage induced FMR field shifts of 690 Oe has been achieved in YIG (13 nm)/Pt (3 nm) multilayer heterostructures under a small voltage bias of 4.5 V. The remarkable ME tunability comes from voltage induced extra FM ordering in Pt metal layer near the Pt/YIG interface. The first-principle theoretical simulation reveal that the electrostatic doping induced Pt5+ ions have strong magnetic ordering due to uncompensated d orbit electrons. The large voltage control of FMR change pave a foundation towards novel voltage tunable YIG based spintronics.
Motivated by the connection between 4-manifolds and 2d N=(0,2) theories, we study the dynamics of a fairly large class of 2d N=(0,2) gauge theories. We see that physics of such theories is very rich, much as the physics of 4d N=1 theories. We discover a new type of duality that is very reminiscent of the 4d Seiberg duality. Surprisingly, the new 2d duality is an operation of order three: it is IR equivalence of three different theories and, as such, is actually a triality. We also consider quiver theories and study their triality webs. Given a quiver graph, we find that supersymmetry is dynamically broken unless the ranks of the gauge groups and flavor groups satisfy stringent inequalities. In fact, for most of the graphs these inequalities have no solutions. This supports the folklore theorem that generic 2d N=(0,2) theories break supersymmetry dynamically.
We explore the connection between starspots and plages of three main-sequence stars by studying the chromospheric and photospheric activity over several rotation periods. We present simultaneous photometry and high-resolution ($R\sim 31,500$) spectroscopy of KIC 9652680, a young, superflare-producing G1 star with a rotation period of 1.4 days. Its Kepler light curve shows rotational modulation consistent with a bright hemisphere followed by a relatively dark hemisphere, generating photometric variability with a semi-amplitude of 4%. We find that KIC 9652680 is darkest when its $S$-index of Ca II H & K emission is at its maximum. We interpret this anti-correlation between flux and $S$ to indicate that dark starspots in the photosphere are co-located with the bright plages in the chromosphere, as they are on the Sun. Moving to lower masses and slower rotators, we present K2 observations with simultaneous spectroscopy of EPIC 211928486 (K5V) and EPIC 211966629 (K4V), two active stars in the 650 Myr-old open cluster Praesepe. The K2 photometry reveals that both stars have rotation periods of 11.7 days; while their flux varies by 1 and 2% respectively, their Ca II H & K $S$-indices seem to hold relatively constant as a function of rotational phase. This suggests that extended chromospheric networks of plages are not concentrated into regions of emission centered on the starspots that drive rotational modulation, unlike KIC 9652680. We also note that the Ca II emission of EPIC 211928486 dipped and recovered suddenly over the duration of one rotation, suggesting that the evolution timescale of plages may be of order the rotation period.
We show that in sudden hadronization of QGP a non-equilibrium value of the pion phase space occupancy parameter gamma_q>1 is expected in order to accommodate the entropy excess in QGP and the process of gluon fragmentation. When gamma_q is near to its maximum allowed value, pion overabundance is shown to arise at low $m_\bot$, where the charged pion asymmetry is also amplified. These effects are considered and we show that their magnitude suffices to explain pertinent experimental data obtained in 160-200AGeV Pb- and S- induced reactions.
The dynamical susceptibility of strongly correlated electronic systems can be calculated within the framework of the dynamical mean-field theory (DMFT). The required measurement of the four-point vertex of the auxiliary impurity model is however costly and restricted to a finite grid of Matsubara frequencies, leading to a cutoff error. It is shown that the propagation of this error to the lattice response function can be minimized by virtue of an exact decomposition of the DMFT polarization function into local and nonlocal parts. The former is measured directly by the impurity solver, while the latter is given in terms of a ladder equation for the Hedin vertex that features an unprecedentedly fast decay of frequency summations compared to previous calculation schemes, such as the one of the dual boson approach. At strong coupling the local approximation of the TRILEX approach is viable, but vertex corrections to the polarization should be dropped on equal footing to recover the correct prefactor of the effective exchange. In finite dimensions the DMFT susceptibility exhibits spurious mean-field criticality, therefore, a two-particle self-consistent and frequency-dependent correction term is introduced, similar to the Moriya-$\lambda$ correction of the dynamical vertex approximation. Applications to the two- and three-dimensional Hubbard models on the square and cubic lattices show that the expected critical behavior near an antiferromagnetic instability is recovered.
Pad$\acute{e}$ cosmography has been widely used to probe the cosmic evolution and to investigate the nature of dark energy. In this paper, we find that the Pad$\acute{e}$ approximant can describe the cosmic evolution better than the standard cosmography, and if the luminosity distance $d_L(z)$ described by the Pad$\acute{e}$ approximant is used to reconstruct the dark energy equation of state $w(z)$, then the reconstructed $w(z)$ will approach a constant, i.e. $1/3$ or $0$, when the redshift is very high. This result is general since it is independent of the coefficients in the Pad$\acute{e}$ approximant and the value of the present dimensionless matter density parameter. This intrinsic character will bias the $w(z)$ reconstruction and lead to misconception of the property of dark energy. Therefore, one must exercise caution in investigating the property of dark energy from Pad$\acute{e}$ cosmography when the high redshift data, i.e. $z>2$, are included.
A sum rule has been derived for the static pair correlation function. This rule is the extension of the well-known equation that relates density fluctuation to compressibility. The obtained sum rule is applied to the Bose and Fermi ideal gases as well as BCS and Bogoliubov's models.
Plutonium displays phase transitions with enormous volume differences among its phases and both its Pauli like magnetic susceptibility and resistivity are an order of magnitude larger than those of simple metals. Curium is also highly resistive but its susceptibility is Curie-like at high temperatures and orders antiferromagnetically at low temperatures. The anomalous properties of the late actinides stem from the competition between the itinerancy and localization of its f electrons, which makes the late actinides elemental strongly correlated materials. A central problem in this field is to understand the mechanism by which these materials resolve these conflicting tendencies. In this letter we identify the electronic mechanisms responsible for the anomalous behaviour of late actinides. We revisit the concept of valence using theoretical approach that treats magnetism, Kondo screening, atomic multiplet effects, spin orbit coupling and crystal field splitting on the same footing. Plutonium is found to be in a rare mixed valent state, namely its ground state is a superposition of two distinct valencies. Curium settles in a single valence magnetically ordered state at low temperatures. The f7 atomic configuration of Curium is contrasted with the multiple configuration manifolds present in Plutonium ground state which we characterize by a valence histogram. The balance between the Kondo screening and magnetism is determined by the competition between spin orbit coupling and the strength of atomic multiplets which is in turn regulated by the degree of itinerancy. The approach presented here, highlights the electronic origin of the bonding anomalies in plutonium and can be applied to predict generalized valences and the presence or absence of magnetism in other compounds starting from first principles.
We prove a result on the existence of linear forms of a given Diophantine type.
We systematically investigate open strings in the plane wave background of type IIB string theory. We carefully analyze possible boundary conditions for open strings and find static as well as time-dependent branes. The branes fall into equivalence classes depending on whether they are related by the action of target space isometries. In particular static branes localized at the origin of transverse space and certain time-dependent branes fall into the same equivalence class. We analyze thoroughly the symmetries of all branes we discuss. Apart from symmetries descending from target space isometries, the worldsheet action being free admits a countably infinite number of other global worldsheet symmetries. We find that one can use such worldsheet symmetries to restore seemingly broken target space symmetries. In particular, we show that D-branes localized at arbitrary constant positions which were thought to be 1/4 supersymmetric in fact have sixteen supercharges whilst D-branes which were thought to be non-supersymmetric have eight supercharges. We discuss in detail the quantization in all cases.
We consider vacuum fluctuations of the quantum electromagnetic field in the presence of an infinite and perfectly conducting plate. We evaluate how the change of vacuum fluctuations due to the plate modifies the Casimir-Polder potential between two atoms placed near the plate. We use two different methods to evaluate the Casimir-Polder potential in the presence of the plate. They also give new insights on the role of boundary conditions in the Casimir-Polder interatomic potential, as well as indications for possible generalizations to more complicated boundary conditions.
We investigate pair correlations in trapped fermion and boson gases as a means to probe the quantum states producing the density fluctuations. We point out that "opposite sign correlations" (meaning pair correlations that are positive for fermions and negative for bosons) unambiguously indicate that the quantum many-particle state cannot be "free." In particular, a system of fermions that exhibits positive pair correlations cannot be described by any Slater determinant wavefunction. This insight may help one to interpret results of current experiments on ultracold atomic gases.
For a global function field K of positive characteristic p, we show that Artin conjecture for L-functions of geometric p-adic Galois representations of K is true in a non-trivial p-adic disk but is false in the full p-adic plane. In particular, we prove the non-rationality of the geometric unit root L-functions.