ShantanuT01/DACTYL-Pretraining huggingface dataset:
We theoretically investigate spin-dependent carrier dynamics due to the electron-phonon interaction after ultrafast optical excitation in ferromagnetic metals. We calculate the electron-phonon matrix elements including the spin-orbit interaction in the electronic wave functions and the interaction potential. Using the matrix elements in Boltzmann scattering integrals, the momentum-resolved carrier distributions are obtained by solving their equation of motion numerically. We find that the optical excitation with realistic laser intensities alone leads to a negligible magnetization change, and that the demagnetization due to electron-phonon interaction is mostly due to hole scattering. Importantly, the calculated demagnetization quenching due to this Elliot-Yafet type depolarization mechanism is not large enough to explain the experimentally observed result. We argue that the ultrafast demagnetization of ferromagnets does not occur exclusively via an Elliott-Yafet type process, i.e., scattering in the presence of the spin-orbit interaction, but is influenced to a large degree by a dynamical change of the band structure, i.e., the exchange splitting.
The Jaccard index, also known as Intersection-over-Union (IoU score), is one of the most critical evaluation metrics in medical image segmentation. However, directly optimizing the mean IoU (mIoU) score over multiple objective classes is an open problem. Although some algorithms have been proposed to optimize its surrogates, there is no guarantee provided for their generalization ability. In this paper, we present a novel data-distribution-aware margin calibration method for a better generalization of the mIoU over the whole data-distribution, underpinned by a rigid lower bound. This scheme ensures a better segmentation performance in terms of IoU scores in practice. We evaluate the effectiveness of the proposed margin calibration method on two medical image segmentation datasets, showing substantial improvements of IoU scores over other learning schemes using deep segmentation models.
Active matter is rapidly becoming a key paradigm of out-of-equilibrium soft matter exhibiting complex collective phenomena, yet the thermodynamics of such systems remain poorly understood. In this letter we study the nonequilbrium thermodynamics of large scale active systems capable of mobility-induced phase separation and polar alignment, using a fully under-damped model which exhibits hidden entropy productions not previously reported in the literature. We quantify steady state entropy production at each point in the phase diagram, revealing characteristic dissipation rates associated with the distinct phases and configurational structure. This reveals sharp discontinuities in the entropy production at phase transitions and facilitates identification of the thermodynamics of micro-features, such as defects in the emergent structure. The interpretation of the time reversal symmetry in the dynamics of the particles is found to be crucial.
We study the thermodynamics of maximally supersymmetric U(N) Yang-Mills theory on $\mathds{R}\times S^2$ at large $N$. The model arises as a consistent truncation of ${\cal N}=4$ super Yang-Mills on $\mathds{R}\times S^3$ and as the continuum limit of the plane-wave matrix model expanded around the $N$ spherical membrane vacuum. The theory has an infinite number of classical BPS vacua, labeled by a set of monopole numbers, described by dual supergravity solutions. We first derive the Lagrangian and its supersymmetry transformations as a deformation of the usual dimensional reduction of ${\cal N}=1$ gauge theory in ten dimensions. Then we compute the partition function in the zero 't Hooft coupling limit in different monopole backgrounds and with chemical potentials for the $R$-charges. In the trivial vacuum we observe a first-order Hagedorn transition separating a phase in which the Polyakov loop has vanishing expectation value from a regime in which this order parameter is non-zero, in analogy with the four-dimensional case. The picture changes in the monopole vacua due to the structure of the fermionic effective action. Depending on the regularization procedure used in the path integral, we obtain two completely different behaviors, triggered by the absence or the appearance of a Chern-Simons term. In the first case we still observe a first-order phase transition, with Hagedorn temperature depending on the monopole charges. In the latter the large $N$ behavior is obtained by solving a unitary multi-matrix model with a peculiar logarithmic potential, the system does not present a phase transition and it always appears in a ``deconfined'' phase.
Using light-front holography, we predict simultaneously the pion decay constant and the pion charge radius by taking into account (higher twist) dynamical spin effects whose relative importance is constrained by QCD.
We give a brief review of direct $CP$ violation effects in charmless $B$ decays, both at the inclusive and at the exclusive level. It is emphasized that typical exclusive final states are composed of 2--4 $K$ or $\pi$'s, hence particle identification (in terms of $K/\pi$ separation) is of crucial importance for studying $CP$ violation in these modes. Another kind of ``charmless" final state is also emphasized: $b\to dc\bar c$. The decay rate is tree dominant, while ``$q^2$" is necessarily above $c\bar c$ threshold hence in the domain of perturbative QCD. The $CP$ asymmetry is therefore relatively clean and reliable. Theoretically, a few $\times 10^7$ $B$'s would suffice if one could accumulate modes like $B^+\to D^{+\left(*\right)} \bar D^{0\left(*\right)}$. [To appear in proceedings of ``The Third KEK Topical Conference on   CP Violation --- Its Implications to Particle Physics and Cosmology'',   16--18 November, 1993, KEK, Tsukuba, Japan (Eds. Y. Kuno and Y. Okada).]
We investigate the canonical forms of positive partial transposition (PPT) density matrices in ${\cal C}^2 \otimes {\cal C}^M \otimes {\cal C}^N$ composite quantum systems with rank $N$. A general expression for these PPT states are explicitly obtained. From this canonical form a sufficient separability condition is presented.
We study the problem of dielectric response in the strong coupling regime of a charge transfer insulator. The frequency and wave number dependence of the dielectric function $\epsilon ({\bf q},\omega)$ and its inverse $\epsilon ^{-1}({\bf q},\omega)$ is the main object of consideration. We show that the problem, in general, cannot be reduced to a calculation within the Hubbard model, which takes into account only a restricted number of electronic states near the Fermi energy. The contribution of the rest of the system to the longitudinal response (i.e. to $\epsilon ^{-1}({\bf q},\omega)$) is essential for the whole frequency range. With the use of the spectral representation of the two-particle Green's function we show that the problem may be divided into two parts: into the contributions of the weakly correlated and the Hubbard subsystems. For the latter we propose an approach that starts from the correlated paramagnetic ground state with strong antiferromagnetic fluctuations. We obtain a set of coupled equations of motion for the two-particle Green's function that may be solved by means of the projection technique. The solution is expressed by a two particle basis that includes the excitonic states with electron and hole separated at various distances. We apply our method to the multiband Hubbard (Emery) model that describes layered cuprates. We show that strongly dispersive branches exist in the excitonic spectrum of the 'minimal' Emery model ($1/U_d=U_p=t_{pp}=0$) and consider the dependence of the spectrum on finite oxygen hopping $t_{pp}$ and on-site repulsion $U_p$. The relationship of our calculations to electron energy loss spectroscopy is discussed.
I have performed a search for young low-mass stars and brown dwarfs (BDs) in 2 regions encompassing a total area of 4 deg^2 in the Taurus star-forming region, discovering 15 new members of Taurus. In addition, I present 7 new members outside of these areas from the initial stage of a survey of all of Taurus. These 22 objects exhibit spectral types of M4.5-M9.25 and masses of 0.3-0.015 M_sun according to the theoretical evolutionary models of Baraffe and Chabrier, 7 of which are likely to be BDs. Emission in H(alpha), He I, Ca II, [O I], and [S II] and excess emission in optical and near-IR bands among some of these objects suggest the presence of accretion, outflows, and circumstellar disks. The results from the 4 deg^2 survey have been combined with previous studies of Taurus to arrive at an IMF for a total area of 12.4 deg^2. As in the previous IMFs for Taurus, the updated IMF peaks at a higher mass (0.8 M_sun) than the mass functions in IC 348 and Orion (0.1-0.2 M_sun). Meanwhile, the deficit of BDs in Taurus appears to be less significant (x1.4-1.8) than found in earlier studies (x2) because of a slightly higher BD fraction in the new IMF for Taurus and a lower BD fraction in the new spectroscopic IMF for the Trapezium from Slesnick and coworkers. The spatial distribution of the low-mass stars and BDs discovered in the two new survey areas closely matches that of the more massive members. Thus, on the degree size scales (~3 pc) probed to date, there is no indication that BDs form through ejection.
In strong magnetic fields, massless electrons in graphene populate relativistic Landau levels with the square-root dependence of each level energy on its number and magnetic field. Interaction-induced deviations from this single-particle picture were observed in recent experiments on cyclotron resonance and magneto-Raman scattering. Previous attempts to calculate such deviations theoretically using the unscreened Coulomb interaction resulted in overestimated many-body effects. This work presents many-body calculations of cyclotron and magneto-Raman transitions in single-layer graphene in the presence of Coulomb interaction, which is statically screened in the random-phase approximation. We take into account self-energy and excitonic effects as well as Landau level mixing, and achieve good agreement of our results with the experimental data for graphene on different substrates. Important role of a self-consistent treatment of the screening is found.
Many efforts have been devoted to the studies of the phenomenology in particle physics with extra dimensions. We propose the degenerate fermion star in the five dimensions, and study what effects caused by the geometry of extra dimensions should appear in its structure. We note that Kaluza-Klein excited modes have effects for the larger scale of extra dimensions and examine the conditions on which different layers should be caused in the inside of the stars. We expound how the effects of the extra dimensions appears on physical quantities.
Recently, boron arsenide (BAs) has been measured high thermal conductivity in the experiments, great encouraging for the low-power photoelectric devices. Therefore, in the present work, we have systematically investigated the direct and indirect optical absorptions of BAs and BSb and the doping effect of congeners by using first-principles calculations. We obtain the absorption onset corresponding to the value of indirect bandgap by considering the phonon-assisted second-order optical absorptions. And the redshift of absorption onset, enhancement and smoothness of optical absorptions spectra are also captured in the temperature-dependent calculations. In order to introduce one-order absorptions into the visible range, the doping effect of congeners on optical absorptions is studied without the assists of phonon. It is found that the decrease of local direct bandgap after doping derives from either the small bandgap in the prototypical III-V semiconductors or CBM locating at R$_c$ point. Thus, doping of congeners can improve the direct optical absorptions in visible range.
In this contribution, we briefly analyze the formalism of the unquenched quark model (UQM) and its application to the description of several observables of hadrons. In the UQM, the effects of $q \bar q$ sea pairs are introduced explicitly into the quark model through a QCD-inspired $^{3}P_0$ pair-creation mechanism. We present our description of flavour asymmetry and strangeness in the proton when baryon-meson components are included. In the meson sector, the charmonium and bottomonium spectra with self-energy corrections due to the coupling to the meson-meson components .
Gravitational collapse in (n+2) dimensional quasi-spherical space-time is studied for a fluid with non vanishing radial pressure. An exact analytic solution is obtained (ignoring the arbitrary integration function) for the equation of state $p_{r}=(\gamma-1)\rho.$ The singularity is studied locally by comparing the time of formation of apparent horizon and the central shell focusing singularity while the global nature of the final fate of collapse is characterized by the existence of radial null geodesic. It is revealed that the end state of collapse for D dimension with equation of state $p=-\rho$, for (D$-$1) dimensional dust and (D$-$2)dimension with equation of state $p=\rho$ are identical.
Star-forming galaxies at high redshift show anomalous values of infrared excess, which can be described only by extremizing the existing relations between the shape of their ultraviolet continuum emission and their infrared-to-ultraviolet luminosity ratio, or by constructing \textit{ad-hoc} models of star formation and dust distribution. We present an alternative explanation, based on unveiled AGN activity, to the existence of such galaxies. In fact, the presence of a weak AGN configures as a natural scenario in order to explain the observed spectral properties of such high-$z$ objects in terms of a continuum slope distribution rather than altered infrared excesses, due to the different shape of the AGN continuum emission with respect to quiescent galaxies. To this aim, we directly compare the infrared-to-ultraviolet properties of high-redshift galaxies to those of known categories of AGN (quasars and Seyferts). We also infer the characteristics of their possible X-ray emission. We find a strong similarity between the spectral shapes and luminosity ratios of AGN with the corresponding properties of such galaxies. In addition, we derive expected X-ray fluxes that are compatible with energetics from AGN activity. We conclude that a moderate AGN contribution to the UV emission of such high-$z$ objects is a valid alternative to explain their spectral properties. Even the presence of an active nucleus in each source would not violate the expected quasar statistics. Furthermore, we suggest that the observed similarities between anomalous star-forming galaxies and quasars may provide a benchmark for future theoretical and observational studies on the galaxy population in the early Universe.
$^{17}$C has three states below the $^{16}$C + $n$ threshold with quantum numbers $J^P=3/2^+,1/2^+,5/2^+$. These states have relatively small neutron separation energies compared to the neutron separation and excitation energies of $^{16}$C. This separation of scales motivates our investigation of $^{17}$C in a Halo effective field theory (Halo EFT) with a $^{16}$C core and a valence neutron as degrees of freedom. We discuss various properties of the three states such as electric radii, magnetic moments, electromagnetic transition rates and capture cross sections. In particular, we give predictions for the charge radius and the magnetic moment of the $1/2^+$ state and for neutron capture on $^{16}$C into this state. Furthermore, we discuss the predictive power of the Halo EFT approach for the $3/2^+$ and $5/2^+$ states which are described by a neutron in a $D$-wave relative to the core.
A Galois scaffold, in a Galois extension of local fields with perfect residue fields, is an adaptation of the normal basis to the valuation of the extension field, and thus can be applied to answer questions of Galois module structure. Here we give a sufficient condition for a Galois scaffold to exist in fully ramified Galois extensions of degree $p^2$ of characteristic $p$ local fields. This condition becomes necessary when we restrict to $p=3$. For extensions $L/K$ of degree $p^2$ that satisfy this condition, we determine the Galois module structure of the ring of integers by finding necessary and sufficient conditions for the ring of integers of $L$ to be free over its associated order in $K[Gal(L/K)]$.
Prompted by the recent discovery of pulsed emission from an ultra-luminous X-ray source, M82 X-2 ("ULX-pulsar"), we perform a two-dimensional radiation-hydrodynamic simulation of a super-critical accretion flow onto a neutron star through a narrow accretion column. We set an accretion column with a cone shape filled with tenuous gas with density of $10^{-4} {\rm g}~ {\rm cm}^{-3}$ above a neutron star and solve the two dimensional gas motion and radiative transfer within the column. The side boundaries are set such that radiation can freely escape, while gas cannot. Since the initial gas layer is not in a hydrostatic balance, the column gas falls onto the neutron-star surface, thereby a shock being generated. As a result, the accretion column is composed of two regions: an upper, nearly free-fall region and a lower settling region, as was noted by Basko \& Sunyaev (1976). The average accretion rate is very high; ${\dot M}\sim 10^{2-3} L_{\rm E}/c^2$ (with $L_{\rm E}$ being the Eddington luminosity), and so radiation energy dominates over gas internal energy entirely within the column. Despite the high accretion rate, the radiation flux in the laboratory frame is kept barely below $L_{\rm E}/(4\pi r^2)$ at a distance $r$ in the settling region so that matter can slowly accrete. This adjustment is made possible, since large amount of photons produced via dissipation of kinetic energy of matter can escape through the side boundaries. The total luminosity can greatly exceed $L_{\rm E}$ by several orders of magnitude, whereas the apparent luminosity observed from the top of the column is much less. Due to such highly anisotropic radiation fields, observed flux should exhibit periodic variations with the rotation period, provided that the rotation and magnetic axes are misaligned.
The routing and wavelength assignment problem arises from the investigation of optimal wavelength allocation in an optical network that employs Wavelength Division Multiplexing (WDM). Consider an optical network that is represented by a connected, simple graph $G$. An all-to-all routing $R$ in $G$ is a set of paths connecting all pairs of vertices of $G$. The undirected optical index of $G$ is the minimum integer $k$ to guarantee the existence of a mapping $\phi:R\to\{1,2,\ldots,k\}$, such that $\phi(P)\neq\phi(P')$ if $P$ and $P'$ have common edge(s), over all possible routings $R$. A natural lower bound of the undirected optical index of $G$ is the (undirected) edge-forwarding index, which is defined to be the minimum of the maximum edge-load over all possible all-to-all routings. In this paper, we first derive the exact value of the optical index of the complete $m$-ary trees, and then investigate the gap between undirected optical and edge-forwarding indices.
We have investigated quantum Hall skyrmions at filling factor \nu=1 carrying more than one unit of topological, and hence electric, charge. Using a combination of analytic and numerical methods we find the counterintuitive result that when the Zeeman energy is tuned to values much smaller than the interaction energy (g \mu_B B/(e^2/\epsilon\ell) < 9*10^{-5}),the creation energy of a charge two skyrmion becomes less than twice the creation energy of a charge one skyrmion, i.e. skyrmions bind in pairs. The doubly charged skyrmions are stable to further accretion of charge and exhibit a 10% larger spin per unit charge than charge one skyrmions which would, in principle, signal this pairing.
The gamma-ray burst (GRB) of October 17, 1994 (941017), showed a distinct high energy spectral component extending from $\lesssim$ a few MeV to $\gtrsim$ 200 MeV, in addition to the typical GRB emission which peaked at $\lesssim$ a few hundred keV. The high energy component carried at least $\sim$ 3 times more energy than the lower energy component. It displayed an almost constant flux with a rather hard spectrum ($F_\nu \propto \nu^{-\alpha}$ with $\alpha \sim 0$) from $\lesssim$ 20 s into the burst up to $\sim$ 200 s, while the duration of the GRB, where 90% of the energy in the lower energy component was emitted, was only 77 s. Such a high energy component was seen in only one out of $\sim$ 30 GRBs in which a similar component could have been detected, and thus appears to be quite rare. We examine possible explanations for this high energy spectral component and find that most models fail. The only emission region that provides the right temporal behavior is the reverse shock that goes into the GRB ejecta as it is decelerated by the ambient medium, or possibly the very early forward shock while the reverse shock is still going on. The best candidate for the emission mechanism is synchrotron self-Compton emission from the reverse shock. Even in this model the most natural spectral slope is only marginally consistent with the observed value, and some degree of fine tuning is required in order to improve the agreement. This might suggest that an additional or alternative emission mechanism is at work here. A prediction of this interpretation is that such a high energy component should be accompanied by a bright optical transient, similar to the one observed in GRB 990123.
We present new high resolution spectroscopy of the low mass X-ray binary Cyg X-2 which enables us to refine the orbital solution and rotational broadening of the donor star. In contrast with Elebert et al (2009) we find a good agreement with results reported in Casares et al. (1998). We measure $P=9.84450\pm0.00019$ day, $K_2=86.5\pm1.2$ km s$^{-1}$ and $V \sin i=33.7\pm0.9$ km s$^{-1}$. These values imply $q=M_{2}/M_{1}=0.34 \pm 0.02$ and $M_{1}=1.71\pm 0.21$ M$_{\odot}$ (for $i=62.5 \pm 4^{\circ}$). Therefore, the neutron star in Cyg X-2 can be more massive than canonical. We also find no evidence for irradiation effects in our radial velocity curve which could explain the discrepancy between Elebert et al's and our $K_2$ values.
Both van der Waals corrected density functional theory and classical calculations show that the potential relief of interaction energy between layers of graphite and few-layer graphene can be described by a simple expression containing only the first Fourier components. Thus a set of physical quantities and phenomena associated with in-plane relative vibration, translational motion and rotation of graphene layers are interrelated and are determined by a single parameter characterizing the roughness of the potential energy relief. This relationship is used to estimate the barriers to relative motion and rotation of graphene layers based on experimental measurements of shear mode frequencies.
Quantum oscillations, conventionally thought to be a metallic property, have recently been shown to arise in certain kinds of insulators, with properties very different from those in metals. All departures from the canonical behavior found so far arise only in the amplitude and the phase but not in the frequency. Here I show that such robustness in the behavior of the frequency is only valid for a particle-hole symmetric insulator; in a strongly particle-hole asymmetric insulator, de Haas-van Alphen oscillations (oscillations in magnetization and susceptibility) and Shubnikov-de Haas oscillations (oscillations in the density of states) exhibit different frequencies, with the frequency of the latter changing with temperature. I demonstrate these effects with numerical calculations on a lattice model, and provide a theory to account for the unusual behavior.