ShantanuT01/DACTYL-Pretraining huggingface dataset:
We outline the class of globally regular spherically symmetric solutions to the minimally coupled GR equations asymptotically de Sitter in the origin and asymptotically Schwarzschild at infinity. A source term connects smoothly de Sitter vacuum at the regular center with Minkowski vacuum at infinity and corresponds to anisotropic spherically symmetric vacuum defined macroscopically by the algebraic structure of its stress-energy tensor invariant under boosts in the radial direction. De Sitter-Schwarzschild geometry describes a vacuum nonsingular black hole which evolves, in the course of Hawking evaporation, towards a self-gravitating particle-like structure without horizons, G-lump. Space-time symmetry changes smoothly from the de Sitter group in the center to the Lorentz group at infinity, and the standard formula for the ADM mass relates it to the de Sitter vacuum replacing a singularity at the scale of symmetry restoration. This class of metrics is easily extended to the case of a nonzero background cosmological constant. A source term connects then smoothly two de Sitter vacua with different values of cosmological constant which makes possible to associate anisotropic spherically symmetric vacuum with an r-dependent cosmological term.
We provide strong numerical evidence, using improved variational wave functions, for a ground state with vanishing spin gap in the spin-$1/2$ quantum Heisenberg model on the kagome lattice. Starting from the algebraic $U(1)$ Dirac spin liquid state proposed by Y. Ran $et al.$ [Phys. Rev. Lett. $98$, $117205$ ($2007$)] and iteratively applying a few Lanczos steps, we compute the lowest $S=2$ excitation constructed by exciting spinons close to the Dirac nodes. Our results are compatible with a vanishing spin gap in the thermodynamic limit and in consonance with a power-law decay of long distance spin-spin correlations in real space. The competition with a gapped (topological) spin liquid is discussed.
We investigate the potential role of string and monopole-type junctions in the frustration of domain wall networks using a velocity-dependent one-scale model for the characteristic velocity, $v$, and the characteristic length, $L$, of the network. We show that, except for very special network configurations, $v^2 \lsim (HL)^2 \lsim (\rho_\sigma + \rho_\mu)/\rho_m$ where $H$ is the Hubble parameter and $\rho_\sigma$, $\rho_\mu$ and $\rho_m$ are the average density of domain walls, strings and monopole-type junctions. We further show that if domain walls are to provide a significant contribution to the dark energy without generating exceedingly large CMB temperature fluctuations then, at the present time, the network must have a characteristic length $ L_0 \lsim 10 \Omega_{\sigma 0}^{-2/3} {\rm kpc}$ and a characteristic velocity $v_0 \lsim 10^{-5} \Omega_{\sigma 0}^{-2/3}$ where $\Omega_{\sigma 0}=\rho_{\sigma 0}/\rho_{c 0}$ and $\rho_c$ is the critical density. In order to satisfy these constraints with $\Omega_{\sigma 0} \sim 1$, $\rho_{m 0}$ would have to be at least 10 orders of magnitude larger than $\rho_{\sigma 0}$, which would be in complete disagreement with observations. This result provides very strong additional support for the conjecture that no natural frustration mechanism, which could lead to a significant contribution of domain walls to the dark energy budget, exists.
While quantum field theory could more aptly be called the "quantum field framework" $-$ as it encompasses a vast variety of varying concepts and theories $-$ in comparison, relativity, both special and general, is more commonly portrayed as less of a "general framework". Viewed from this perspective, the paradigm of "analogue space-times" is to promote the specific theory of general relativity (Einstein gravity) to a framework which covers relativistic phenomena at large. Ultimately, this then also gives rise to new proposals for experiments in the laboratory, as it allows one to move general features of the "relativistic framework" from general relativity to entirely new fields. This allows experiments looking into analogies of currently unobservable phenomena of general relativity proper. The only requirement for this to work is the presence of a notion of an upper limit for propagation speeds in this new field. Systems of such a kind abound in physics, as all hyperbolic wave equations fulfil this requirement.   Consequently, models for analogue space-times can be found aplenty. We shall demonstrate this here in two separate analogue space-time models, both taken from electrodynamics in continuous media. First of all, one can distinguish between analytic analogue models (where the analogy is based on some specific hyperbolic differential equation), on the one hand, and algebraic models (where the analogy is fashioned from the more or less explicit appearance of a metric tensor), on the other hand. Yet this distinction is more than just a matter of taste: The analogue space-time model's nature will also determine which physical concepts from general relativity can be taken easily into an experimental context. Examples of this will the main aim of this paper, and the Hawking effect in one of the two models considered the example of most immediate experimental interest.
Extremely peculiar emission lines have been found in the spectra of some active galactic nuclei and quasars. Their origin is totally unknown. We investigate the hypothesis that they are generated from ultra-rapid quasi-periodic oscillations that may occur in jets or black holes, as predicted in a published theoretical paper. We conclude that, although not totally certain, this hypothesis is just as valid as the other highly peculiar hypotheses that have been previously made (e.g. blueshifts due to bulk motions close to the speed of light). We consider ways to further validate our hypothesis.
Action recognition is currently one of the top-challenging research fields in computer vision. Convolutional Neural Networks (CNNs) have significantly boosted its performance but rely on fixed-size spatio-temporal windows of analysis, reducing CNNs temporal receptive fields. Among action recognition datasets, egocentric recorded sequences have become of important relevance while entailing an additional challenge: ego-motion is unavoidably transferred to these sequences. The proposed method aims to cope with it by estimating this ego-motion or camera motion. The estimation is used to temporally partition video sequences into motion-compensated temporal \textit{chunks} showing the action under stable backgrounds and allowing for a content-driven temporal sampling. A CNN trained in an end-to-end fashion is used to extract temporal features from each \textit{chunk}, which are late fused. This process leads to the extraction of features from the whole temporal range of an action, increasing the temporal receptive field of the network.
Using the data observed by the Solar Optical Telescope/Spectro-Polarimeter aboard the Hinode satellite, the horizontal and vertical fields are derived from the wavelength-integrated measures of Zeeman-induced linear and circular polarizations. The quiet intranetwork regions are pervaded by horizontal magnetic elements. We categorize the horizontal intranetwork magnetic elements into two types: one is the non-isolated element which is accompanied by the vertical magnetic elements during its evolution; another is the isolated element which is not accompanied by the vertical magnetic elements. We identify 446 horizontal intranetwork magnetic elements, among them 87 elements are isolated and 359 are non-isolated. Quantitative measurements reveal that the isolated elements have relatively weaker horizontal magnetic fields, almost equal size, and shorter lifetime comparing with the non-isolated elements. Most non-isolated horizontal intranetwork magnetic elements are identified to associate with the emergence of Omega-shaped flux loops. A few non-isolated elements seem to indicate scenarios of submergence of Omega loops or emergence of U-like loops. There is a positive correlation between the lifetime and the size for both the isolated and non-isolated HIFs. It is also found that there is also positive correlation between the lifetime and the magnetic flux density for non-isolated HIFs, but no correlation for isolated HIFs. Even though the horizontal elements show lower magnetic flux density, they could carry the total magnetic flux in the order of magnitude close to 10^25 Mx to the solar surface each day.
We study a complex Ginzburg-Landau equation in the plane, which has the form of a Gross-Pitaevskii equation with some dissipation added. We focus on the regime corresponding to well-prepared unitary vortices and derive their asymptotic motion law.
A study of the semi-analytical approach to four-fermion production in $e^+ e^-$ annihilation is presented. We classify all possible four-fermion final states and present results of new calculations for the `basic' processes with the $WW,ZZ$, and $ZH$ off-shell production together with some examples of `background' processes. The Initial State Radiative corrections are included for the basic processes. Several numerical examples are given in the energy range from LEP2 up to $\sqrt{s}=1$ TeV.
We propose spin transfer torque--magnetoresistive random access memory (STT-MRAM) based on magneto-resistance and spin transfer torque physics of band-pass spin filtering. Utilizing the electronic analogs of optical phenomena such as anti-reflection coating and resonance for spintronic devices, we present the design of an STT-MRAM device with improved features when compared with a traditional trilayer device. The device consists of a superlattice heterostructure terminated with the anti-reflective regions sandwiched between the fixed and free ferromagnetic layers. Employing the Green's function spin transport formalism coupled self-consistently with the stochastic Landau-Lifshitz-Gilbert-Slonczewski equation, we present the design of an STT-MRAM based on the band-pass filtering having an ultra-high TMR (3.5*10e4) and large spin current. We demonstrate that the STT-MRAM design having band-pass spin filtering are nearly 1100% more energy efficient than traditional trilayer magnetic tunnel junction (MTJ) based STT-MRAM. We also present detailed probabilistic switching and energy analysis for a trilayer MTJ and band-pass filtering based STT-MRAM. Our predictions serve as a template to consider the heterostructures for next-generation spintronic device applications.
We report on a study of the Gamow-Teller matrix element contributing to ${}^6$He $\beta$-decay with similarity renormalization group (SRG) versions of momentum- and configuration-space two-nucleon interactions. These interactions are derived from two different formulations of chiral effective field theory ($\chi$EFT) -- without and with the explicit inclusion of $\Delta$-isobars. We consider evolution parameters $\Lambda_{\rm SRG}$ in the range between 1.2 and 2.0 fm$^{-1}$ and, for the $\Delta$-less case, also the unevolved (bare) interaction. The axial current contains one- and two-body terms, consistently derived at tree level (no loops) in the two distinct $\chi$EFT formulations we have adopted here. The ${}^6$He and ${}^6$Li ground-state wave functions are obtained from hyperspherical-harmonics (HH) solutions of the nuclear many-body problem. In $A\,$=$\,6$ systems, the HH method is limited at present to treat only two-body interactions and non-SRG evolved currents. Our results exhibit a significant dependence on $\Lambda_{\text{SRG}}$ of the contributions associated with two-body currents, suggesting that a consistent SRG-evolution of these is needed in order to obtain reliable estimates. We also show that the contributions from one-pion-exchange currents depend strongly on the model (chiral) interactions and on the momentum- or configuration-space cutoffs used to regularize them. These results might prove helpful in clarifying the origin of the sign difference recently found in No-Core-Shell-Model and Quantum Monte Carlo calculations of the ${}^6$He Gamow-Teller matrix element.
The distribution of galaxies on the mass-size plane as a function of redshift or environment is a powerful test for galaxy formation models. Here we use integral-field stellar kinematics to interpret the variation of the mass-size distribution in two galaxy samples spanning extreme environmental densities. The samples are both identically and nearly mass-selected (stellar mass M*>6e9 Msun) and volume-limited. The first consists of nearby field galaxies from the Atlas3D parent sample. The second consists of galaxies in the Coma Cluster (Abell 1656), one of densest environments for which good resolved spectroscopy can be obtained. The mass-size distribution in the dense environment differs from the field one in two ways: (i) spiral galaxies are replaced by bulge-dominated disk-like fast-rotator early-type galaxies (ETGs), which follow the SAME mass-size relation and have the SAME mass distribution as in the field sample; (ii) the slow rotator ETGs are segregated in mass from the fast rotators, with their size increasing proportionally to their mass. A transition between the two processes appears around the stellar mass M_crit=2e11 Msun. We interpret this as evidence for bulge growth (outside-in evolution) and bulge-related environmental quenching dominating at low masses, with little influence from merging, while significant dry mergers (inside-out evolution) and halo-related quenching driving the mass and size growth at the high-mass end. The existence of these two processes naturally explains the diverse size evolution of galaxies of different masses and the separability of mass and environmental quenching.
Charge transport in organic semiconductors is notoriously extremely sensitive to the presence of disorder, both intrinsic and extrinsic, especially for n-type materials. Intrinsic dynamic disorder stems from large thermal fluctuations both in intermolecular transfer integrals and (molecular) site energies in weakly interacting van der Waals solids and sources transient localization of the charge carriers. The molecular vibrations that drive transient localization typically operate at low-frequency (< a-few-hundred cm-1), which renders it difficult to assess them experimentally. Hitherto, this has prevented the identification of clear molecular design rules to control and reduce dynamic disorder. In addition, the disorder can also be extrinsic, being controlled by the gate insulator dielectric properties. Here we report on a comprehensive study of charge transport in two closely related n-type molecular organic semiconductors using a combination of temperature-dependent inelastic neutron scattering and photoelectron spectroscopy corroborated by electrical measurements, theory and simulations. We provide unambiguous evidence that ad hoc molecular design enables to free the electron charge carriers from both intrinsic and extrinsic disorder to ultimately reach band-like electron transport.
We shall construct a 5-dimensional linear system of holomorphic automorphic forms on a 3-dimensional complex ball by applying Borcherds theory of automorphic forms. We shall show that this linear system gives the dual map from the Segre cubic 3-fold to the Igusa quartic 3-fold.
The trace anomaly for free propagation in the context of a conformally invariant scalar field theory defined on a curved manifold of positive constant curvature with boundary is evaluated through use of an asymptotic heat kernel expansion. In addition to their direct physical significance the results are also of relevance to the holographic principle and to Quantum Cosmology.
The simplest variant of gauge gravitation theory in Riemann-Cartan spacetime leading to the solution of the problem of cosmological singularity and dark energy problem is investigated. It is shown that this theory by certain restrictions on indefinite parameters of gravitational Lagrangian in the case of usual gravitating systems leads to Einstein gravitational equations with effective cosmological constant.
We provide lower estimates for the eigenvalues of the laplacian for hypersurfaces of the round sphere.
We estimate the stellar mass for a sample of low surface brightness galaxies (LSBGs) by fitting their multiband spectral energy distributions (SEDs) to the stellar population synthesis (SPS) model. The derived stellar masses (log M*/Msun) span from 7.1 to 11.1, with a mean of log M*/Msun=8.5, which is lower than that for normal galaxies. The stellar mass-to-light ratio (M/L) in each band varies little with absolute magnitude, but increases with higher M*. This trend of M/L with M* is even stronger in bluer bands. In addition, the M/L for our LSBGs slightly declines from the r band to the longer wavelength bands. The log M/L_j (j=g,r,i,and z) have relatively tight relations with optical colors of g-r and g-i. Compared with several representative M/L-color relations (MLCRs) from literature, our MLCRs based on LSBG data are consistently among those literature MLCRs previously defined on diverse galaxy samples, and the existing minor differences between the MLCRs are more caused by the differences in the SED model ingredients including initial mass function, star formation history, and stellar population model, and the line fitting techniques, galaxy samples, and photometric zero-point as well, rather than the galaxy surface brightness itself which distinguishes LSBGs from HSBGs. Our LSBGs would be very likely to follow those representative MLCRs previously defined on diverse galaxy populations, if those main ingredients were taken into account.
We present a quantum Monte Carlo study of a Heisenberg antiferromagnet on a spatially anisotropic square lattice, where the coupling strength in the x-direction ($J_x$) is different from that in the y-direction ($J_y$). By varying the anisotropy $\alpha$ from 0 to 1, we interpolate between the one-dimensional chain and the two-dimensional isotropic square lattice. Both $S=1/2$ and S=1 systems are considered separately in order to facilitate comparison. The temperature dependence of the uniform susceptibility and the spin-spin correlation length are computed down to very low temperatures for various values of $\alpha$. For S=1, the existence of a quantum critical point at $\alpha^{S=1}_c=0.040(5)$ as well as the scaling of the spin gap is confirmed. Universal quantities predicted from the ${\cal O}(3)$ nonlinear $\sigma$ model agree with our results at $\alpha=0.04$ without any adjustable parameters. On the other hand, the $S=1/2$ results are consistent with $\alpha^{S=1/2}_c=0$, as discussed by a number of previous theoretical studies. Experimental implications for $S=1/2$ compounds such as Sr$_2$CuO$_3$ are also discussed.
Three variational vector equations are derived for the extended particle-field object located on the light cone. Point sources are excluded from the pure field equations and all physical magnitudes are free from divergences. Accepting 3D intersections of 4D cone-charges, vector electrogravity explains all observed phenomena under common flat 3D and 1D intervals. External cone-charges contribute to pseudo-Riemannian metrics of proper four-spaces of charged objects, resulting in dilation-compression of their proper time rates. Photon-type gravitational radiation is not associated with metric modulation of flat, laboratory space. The Minkowski-Lorentz equation for free charges corresponds to the equivalence principle for the canonical four-space. The predicted criterion of double unification, particles with fields - gravity with electrodynamics, is confirmed in vector electrogravity.
We derive upper bounds for the potential energy of spherical designs of cardinality close to the Delsarte-Goethals-Seidel bound. These bounds are obtained by linear programming with the use of the Hermite interpolating polynomial of the potential function in suitable nodes. Numerical computations show that the results are quite close to certain lower energy bounds confirming that spherical designs are, in a sense, energy efficient. \end{abstract}
We use solvable two-dimensional gauge theories to illustrate the issues in relating large N gauge theory to string theory. We also give an introduction to recent mathematical work which allows constructing master fields for higher dimensional large N theories. We illustrate this with a new derivation of the Hopf equation governing the evolution of the spectral density in matrix quantum mechanics. Based on lectures given at the 1994 Trieste Spring School on String Theory, Gauge Theory and Quantum Gravity.
We present a detailed spectroscopic investigation of the young eruptive star PV Cep, to improve our understanding of its nature and characterise its circumstellar environment after its last outburst in 2004. The analysis of our medium-resolution spectroscopy in the near-IR (0.9-2.35 um), collected in 2012 at the Large Binocular Telescope with the IR spectrograph LUCIFER, allows us to infer the main stellar parameters (visual extinction, accretion luminosity, mass accretion and ejection rates), and model the inner disc, jet, and wind. The NIR spectrum displays several strong emission lines associated with accretion/ejection activity and circumstellar environment. Our analysis shows that the brightness of PV Cep is fading, as well as the mass accretion rate (2x10^-7 Msun/yr^-1 in 2012 vs ~5x10^-6 Msun/yr^-1 in 2004), which is more than one order of magnitude lower than in the outburst phase. Among the several emission lines, only the [FeII] intensity increased after the outburst. The observed [FeII] emission delineates blue- and red-shifted lobes, both with high- and low-velocity components, which trace an asymmetric jet and wind, respectively. The observed emission in the jet has a dynamical age of ~8 years, indicating that it was produced during the last outburst. The mass ejection rate in both lobes is 1.5x10^-7 Msun/yr^-1, approximately matching the high accretion rate observed during and immediately after the outburst . The observed jet/outflow asymmetries are consistent with an inhomogeneous medium. Our modelling of the CO emission hints at a small-scale gaseous disc ring, extending from ~0.2-0.4 AU to ~3 AU from the source, with an inner temperature of ~3000 K. Our HI lines modelling indicates that most of the observed emission comes from an expanding disc wind at Te=10000 K. The line profiles are strongly affected by scattering, disc screening, and outflow self-absorption.
We consider stochastic semilinear partial differential equations with Lipschitz nonlinear terms. We prove existence and uniqueness of an invariant measure and the existence of a solution for the corresponding Kolmogorov equation in the space $L^2(H;\nu)$, where $\nu$ is the invariant measure. We also prove the closability of the derivative operator and an integration by parts formula. Finally, under boundness conditions on the nonlinear term, we prove a Poincar\'e inequality, a logarithmic Sobolev inequality and the ipercontractivity of the transition semigroup.
We show that the angular spectrum of type-II SPDC contains a continuum of maximally entangled states. For the realization of a bright source of entangled two-photon states, a standard technique is to compensate for the transverse walk-off in the production crystal. We demonstrate that polarization entangled states can be effectively engineered by generalizing this approach. Our method allows to considerably enrich the set of generated entangled states with a controlled tailoring them.