ShantanuT01/DACTYL-Pretraining huggingface dataset:
We report our numerical results for the effect of magnetic anisotropy on a Skyrmion crystal with a high topological number of two, which was recently discovered in an itinerant electron model [R. Ozawa, S. Hayami, and Y. Motome, Phys. Rev. Lett. 118, 147205 (2017)]. By performing numerical simulations based on the kernel polynomial method and the Langevin dynamics for the Kondo lattice model on a triangular lattice, we find that the topological property remains robust against the single-ion anisotropy, while the magnetic texture is deformed continuously. The resultant spin structure is characterized by three wave numbers (triple-$Q$ state), in which the $xy$ component of spins forms a magnetic vortex crystal and the $z$ component of spins behaves a sinusoidal wave. For larger anisotropy, we show that the system exhibits a phase transition from the Skyrmion crystal to topologically trivial phases with vanishing scalar chirality: a single-$Q$ collinear and double-$Q$ noncoplanar states for the easy-axis and easy-plane anisotropy, respectively. We also examine the effect of the single-ion anisotropy in an external magnetic field, and find that the field range of the Skyrmion crystal is rather insensitive to the anisotropy, in contrast to another Skyrmion crystal with the topological number of one whose field range is considerably extended (reduced) by the easy-axis (easy-plane) anisotropy.
We combine the effect of the electron-electron and electron-phonon interactions to study the electronic and optical properties of zb-GaN. We show that only by treating the two effects at the same time it is possible to obtain an unprecedented agreement of the zero and finite-temperature electronic gaps and absorption spectra with the experimental results. Compared to the state-of-the-art results our calculations predict a large effect on the main absorption peak position and width as well as on the overall absorption lineshape. These important modifications are traced back to the combined electron-phonon damping mechanism and non uniform GW level corrections. Our results demonstrate the importance of treating on equal footing the electron and phonon mediated correlation effects to obtain an accurate description of the III-nitrides group physical properties.
Let $G$ be a group acting on a set $X$ of combinatorial objects, with finite orbits, and consider a statistic $\xi : X \to \mathbb{C}$. Propp and Roby defined the triple $(X, G, \xi)$ to be \emph{homomesic} if for any orbits $\mathcal{O}_1, \mathcal{O}_2$, the average value of the statistic $\xi$ is the same, that is \[\frac{1}{{|\mathcal{O}_1|}}\sum_{x \in \mathcal{O}_1} \xi(x) = \frac{1}{|\mathcal{O}_2|}\sum_{y \in \mathcal{O}_2} \xi(y).\]   In 2013 Propp and Roby conjectured the following instance of homomesy. Let $\mathrm{SSYT}_k(m \times n)$ denote the set of semistandard Young tableaux of shape $m \times n$ with entries bounded by $k$. Let $S$ be any set of boxes in the $m \times n$ rectangle fixed under $180^\circ$ rotation. For $T \in \mathrm{SSYT}_k(m \times n)$, define $\sigma_S(T)$ to be the sum of the entries of $T$ in the boxes of $S$. Let $\langle \mathcal{P} \rangle$ be a cyclic group of order $k$ where $\mathcal{P}$ acts on $\mathrm{SSYT}_k(m \times n)$ by promotion. Then $(\mathrm{SSYT}_k(m \times n), \langle \mathcal{P} \rangle, \sigma_S)$ is homomesic.   We prove this conjecture, as well as a generalization to cominuscule posets. We also discuss analogous questions for tableaux with strictly increasing rows and columns under the K-promotion of Thomas and Yong, and prove limited results in that direction.
We present here the results of broadband spectral analysis of low-mass X-ray binary and a black hole candidate 4U 1957+11. The source was observed nine times with the Nuclear Spectroscopic Telescope Array (NuSTAR) between 2018 September and 2019 November. During these observations, the spectral state of 4U 1957+11 evolved marginally. The disc dominant spectra are well described with a hot, multicolour disc blackbody with disc temperature varying in the range $kT_{\rm in} \sim$ 1.35-1.86 keV and a non-thermal component having a steep slope ($\Gamma =$ 2-3). A broad Fe emission line feature (5-8 keV) was observed in the spectra of all the observations. The relativistic disc model was used to study the effect of distance, inclination, and the black hole mass on its spin. Simulations indicate a higher spin for smaller distances and lower black hole mass. At smaller distances and higher mass, spin is maximum and almost independent of the distance. An inverse correlation exists between the spin and the spectral hardening factor for all the cases. The system prefers a moderate spin of about 0.85 for black hole masses between 4-6 M_sun for a 7 kpc distance.
Let $U$ be a point set in the $n$-dimensional affine space ${\rm AG}(n,q)$ over the finite field of $q$ elements and $0\leq k\leq n-2$. In this paper we extend the definition of directions determined by $U$: a $k$-dimensional subspace $S_k$ at infinity is determined by $U$ if there is an affine $(k+1)$-dimensional subspace $T_{k+1}$ through $S_k$ such that $U\cap T_{k+1}$ spans $T_{k+1}$. We examine the extremal case $|U|=q^{n-1}$, and classify point sets NOT determining every $k$-subspace in certain cases.
Dynamic Nuclear Polarization (DNP) presently stands as the preferred strategy to enhance the sensitivity of nuclear magnetic resonance measurements, but its application relies on the use of high-frequency microwave to manipulate electron spins, an increasingly demanding task as the applied magnetic field grows. Here we investigate the dynamics of a system hosting a polarizing agent formed by two distinct paramagnetic centers near a level anti-crossing. We theoretically show that nuclear spins polarize efficiently under a cyclic protocol that combines alternating thermal jumps and radio-frequency pulses connecting hybrid states with opposite nuclear and electronic spin alignment. Central to this process is the difference between the spin-lattice relaxation times of either electron spin species, transiently driving the electronic spin bath out of equilibrium after each thermal jump. Without the need for microwave excitation, this route to enhanced nuclear polarization may prove convenient, particularly if the polarizing agent is designed to feature electronic level anti-crossings at high magnetic fields.
Because of its compatibility with semiconductor-based technologies, hafnia (HfO$_{2}$) is today's most promising ferroelectric material for applications in electronics. Yet, knowledge on the ferroic and electromechanical response properties of this all-important compound is still lacking. Interestingly, HfO$_2$ has recently been predicted to display a negative longitudinal piezoelectric effect, which sets it apart form classic ferroelectrics (e.g., perovskite oxides like PbTiO$_3$) and is reminiscent of the behavior of some organic compounds. The present work corroborates this behavior, by first-principles calculations and an experimental investigation of HfO$_2$ thin films using piezoresponse force microscopy. Further,the simulations show how the chemical coordination of the active oxygen atoms is responsible for the negative longitudinal piezoelectric effect. Building on these insights, it is predicted that, by controlling the environment of such active oxygens (e.g., by means of an epitaxial strain), it is possible to change the sign of the piezoelectric response of the material.
We analyze the spectrum of harmonic flow, $v_n(p_T)$ for $n=0\text{--}5$, in event-by-event hydrodynamic simulations of Pb+Pb collisions at the CERN Large Hadron Collider ($\sqrt{s_{NN}}=2.76\,{\text{TeV}}$) with principal component analysis (PCA). The PCA procedure finds two dominant contributions to the two-particle correlation function. The leading component is identified with the event plane $v_n(p_T)$, while the subleading component is responsible for factorization breaking in hydrodynamics. For $v_0$, $v_1$, and $v_3$ the subleading flow is a response to the radial excitation of the corresponding eccentricity. By contrast, for $v_2$ the subleading flow in \emph{peripheral collisions} is dominated by the nonlinear mixing between the leading elliptic flow and radial flow fluctuations. In the $v_2$ case, the sub-sub-leading mode more closely reflects the response to the radial excitation of $\varepsilon_2$. A consequence of this picture is that the elliptic flow fluctuations and factorization breaking change rapidly with centrality, and in central collisions (where the leading $v_2$ is small and nonlinear effects can be neglected) the subsub-leading mode becomes important. Radial flow fluctuations and nonlinear mixing also play a significant role in the factorization breaking of $v_4$ and $v_5$. We construct good geometric predictors for the orientation and magnitudes of the leading and subleading flows based on a linear response to the geometry, and a quadratic mixing between the leading principal components. Finally, we suggest a set of measurements involving three point correlations which can experimentally corroborate the nonlinear mixing of radial and elliptic flow and its important contribution to factorization breaking as a function of centrality.
We probe the high-ionization circumgalactic medium by examining absorber kinematics, absorber-galaxy kinematics, and average absorption profiles of 31 OVI absorbers from the "Multiphase Galaxy Halos" Survey as a function of halo mass, redshift, inclination, and azimuthal angle. The galaxies are isolated at $0.12<z_{\rm gal}<0.66$ and are probed by a background quasar within $D\approx 200$ kpc. Each absorber-galaxy pair has Hubble Space Telescope images and COS quasar spectra, and most galaxy redshifts have been accurately measured from Keck/ESI spectra. Using the pixel-velocity two-point correlation function (TPCF) method, we find that OVI absorber kinematics have a strong halo mass dependence. Absorbers hosted by $\sim L^{\ast}$ galaxies have the largest velocity dispersions, which we interpret to be that the halo virial temperature closely matches the temperature at which the collisionally ionized OVI fraction peaks. Lower mass galaxies and group environments have smaller velocity dispersions. Total column densities follow the same behavior, consistent with theoretical findings. After normalizing out the observed mass dependence, we studied absorber-galaxy kinematics with a modified TPCF and found non-virialized motions due to outflowing gas. Edge-on minor axis gas has large optical depths concentrated near the galaxy systemic velocity as expected for bipolar outflows, while face-on minor axis gas has a smoothly decreasing optical depth distribution out to large normalized absorber-galaxy velocities, suggestive of decelerating outflowing gas. Accreting gas signatures are not observed due to "kinematic blurring" in which multiple line-of-sight structures are observed. These results indicate that galaxy mass dominates OVI properties over baryon cycle processes.
What is the lowest temperature to which one can trace the growth of the dephasing time in low-dimensional conductors? I consider the fundamental limitation, the crossover from weak to strong localization, as well as several experimental reasons for frequently observed saturation of the dephasing time (hot-electron effects, dephasing by external noise). Recent progress in our understanding of the electron-phonon interaction in disordered conductors is also briefly discussed.
Calculating the Wigner distribution function in the reaction plane, we are able to probe the phase-space behavior in time-dependent Hartree-Fock during a heavy-ion collision. We compare the Wigner distribution function with the smoothed Husimi distribution function. Observables are defined to give a quantitative measure for local and global equilibration. We present different reaction scenarios by analyzing central and non-central $^{16}O+$$^{16}O$ and $^{96}Zr+$$^{132}Zn$ collisions. It is shown that the initial phase-space volumes of the fragments barely merge. The mean values of the observables are conserved in fusion reactions and indicate a "memory effect" in time-dependent Hartree-Fock. We observe strong dissipation but no evidence for complete equilibration.
We consider a class of tautological top intersection products on the moduli space of stable pairs consisting of semistable vector bundles together with N sections on a smooth complex projective curve C. We show that when N is large, these intersection numbers can equally be computed on the Grothendieck Quot scheme of coherent sheaf quotients of the rank N trivial sheaf on C. The result has applications to the calculation of the intersection theory of the moduli space of semistable bundles on C.
We show the existence of geometric quotients for the spaces of certain classes of morphisms of sheaves on projective space, modulo the canonical action of the group of automorphisms.
We present an overview and description of the eMERLIN Galaxy Evolution survey (eMERGE) Data Release 1 (DR1), a large program of high-resolution 1.5 GHz radio observations of the GOODS-N field comprising $\sim140$ hours of observations with eMERLIN and $\sim40$ hours with the Very Large Array (VLA). We combine the long baselines of eMERLIN (providing high angular resolution) with the relatively closely-packed antennas of the VLA (providing excellent surface brightness sensitivity) to produce a deep 1.5 GHz radio survey with the sensitivity ($\sim 1.5\mu$Jy beam$^{-1}$), angular resolution ($0.2"$--$0.7"$) and field-of-view ($\sim15' \times 15'$) to detect and spatially resolve star-forming galaxies and AGN at $z\gtrsim 1$. The goal of eMERGE is to provide new constraints on the deep, sub-arcsecond radio sky which will be surveyed by SKA1-mid. In this initial publication, we discuss our data analysis techniques, including steps taken to model in-beam source variability over a $\sim20$ year baseline and the development of new point spread function/primary beam models to seamlessly merge eMERLIN and VLA data in the $uv$ plane. We present early science results, including measurements of the luminosities and/or linear sizes of $\sim500$ galaxes selected at 1.5 GHz. In combination with deep Hubble Space Telescope observations, we measure a mean radio-to-optical size ratio of $r_{\rm eMERGE}/r_{\rm HST}\sim1.02\pm0.03$, suggesting that in most high-redshift galaxies, the $\sim$GHz continuum emission traces the stellar light seen in optical imaging. This is the first in a series of papers which will explore the $\sim$kpc-scale radio properties of star-forming galaxies and AGN in the GOODS-N field observed by eMERGE DR1.
In a recent paper with Sprang and Zudilin, the following result was proved: if $a$ is large enough in terms of $\varepsilon>0$, then at least $2^{(1-\varepsilon)\frac{\log a}{\log \log a}}$ values of the Riemann zeta function at odd integers between $3$ and $a$ are irrational. This improves on the Ball-Rivoal theorem, that provides only $\frac{1-\varepsilon}{1+\log 2} \log a$ such irrational values -- but with a stronger property: they are linearly independent over the rationals.In the present paper we generalize this recent result to both $L$-functions of Dirichlet characters and Hurwitz zeta function. The strategy is different and less elementary: the construction is related to a Pad\'e approximation problem, and a generalization of Shidlovsky's lemma is used to apply Siegel's linear independence criterion. We also improve the analogue of the Ball-Rivoal theorem in this setting: we obtain $\frac{1-\varepsilon}{1+\log 2} \log a$ linearly independent values $L(f,s)$ with $s\leq a$ of a fixed parity, when $f$ is a Dirichlet character. The new point here is that the constant $1+\log 2$ does not depend on $f$.
A $d$-dimensional branching diffusion, $Z$, is investigated, where the linear attraction or repulsion between particles is competing with an Ornstein-Uhlenbeck drift, with parameter $b$ (we take $b>0$ for inward O-U and $b<0$ for outward O-U). This work has been motivated by [4], where a similar model was studied, but without the drift component.   We show that the large time behavior of the system depends on the interaction and the drift in a nontrivial way. Our method provides, inter alia, the SLLN for the non-interactive branching (inward) O-U process.   First, regardless of attraction ($\gamma >0$) or repulsion ($\gamma <0$), a.s., as time tends to infinity, the center of mass of $Z$   (i) converges to the origin, when $b>0$;   (ii) escapes to infinity exponentially fast (rate $|b|$), when $b<0$.   We then analyze $Z$ as viewed from the center of mass, and finally, for the system as a whole, we show a number of results/conjectures regarding the long term behavior of the system; some of these are scaling limits, while some others concern local extinction.
The results of a CO line survey in central cluster galaxies with cooling flows are presented. Cold molecular gas is detected with the IRAM 30m telescope, through CO(1-0) and CO(2-1) emission lines in 6-10 among 32 galaxies. The corresponding gas masses are between 3.10^8 and 4.10^10 Msol. These results are in agreement with recent CO detections by Edge (2001). A strong correlation between the CO emission and the Halpha luminosity is also confirmed. Cold gas exists in the center of cooling flow clusters and these detections may be interpreted as an evidence of the long searched very cold residual of the hot cooling gas.
The possible source of the production of neutrino with large masses is considered. For this purpose the reaction nu+n to e+p+gamma, in which the electron in neW+ vertex is produced off-mass-shell, is studied.
Tseliakhovich & Hirata recently discovered that higher-order corrections to the cosmological linear-perturbation theory lead to supersonic coherent baryonic flows just after recombination (i.e. z~1020), with rms velocities of ~30 km/s relative to the underlying dark-matter distribution, on comoving scales of ~<3 Mpc/h. To study the impact of these coherent flows we performed high-resolution N-body plus SPH simulations in boxes of 5.0 and 0.7 Mpc/h, for bulk-flow velocities of 0 (as reference), 30 and 60 km/s. The simulations follow the evolution of cosmic structures by taking into account detailed, primordial, non-equilibrium gas chemistry (i.e. H, He, H2, HD, HeH, etc.), cooling, star formation, and feedback effects from stellar evolution. We find that these bulk flows suppress star formation in low-mass haloes (i.e. Mvir<~10^8Msun until z~13, lower the abundance of the first objects by ~1%-20%, and, as consequence, delay cosmic star formation history by ~2e7yr. The gas fractions in individual objects can change up to a factor of two at very early times. Coherent bulk flow, therefore, has implications for (i) the star-formation in the lowest-mass haloes (e.g. dSphs), (ii) the start of reionization by suppressing it in some patches of the Universe, and (iii) the heating (i.e. spin temperature) of neutral hydrogen. We speculate that the patchy nature of reionization and heating on several Mpc scales could lead to enhanced differences in the HI spin-temperature, giving rise to stronger variations in the HI brightness temperatures during the late dark ages.
The March 5th, 1979 gamma-ray transient has long been thought to be fundamentally different from the classic gamma-ray bursts (GRBs). It had recurrences, pulsations, and a soft spectral component unlike classic GRBs. With the exception of the soft component reported from the Konus experiment, the unusual characteristics of March 5th were detectable main peak differs markedly from the published Konus spectrum. Rather than being dominated by a soft component similar to that observed in the soft gamma repeaters (SGRs), the ICE-PVO spectrum appears to be consistent with a classic GRB spectrum, especially above 100 keV. We believe that, given the ICE-PVO spectral observations, the March 5th transient would have been classified as a classic GRB when it was discovered.   The SGRs and GRBs could be consanguineous: high-velocity neutron stars initially produce SGR events (and, occasionally a GRB like March 5th) and when they are older and in the galactic corona, they go through a GRB phase. The March 5th event demonstrates that high-velocity neutron stars at distances of tens kpc are capable of producing events like classic GRBs.
We use the Quench Action approach to study the non-equilibrium dynamics after a quantum quench in the Hubbard model in the limit of infinite interaction. We identify a variety of low-entangled initial states for which we can directly compute the overlaps with the Hamiltonian's eigenstates. For these initial states, we analytically find the rapidity distributions of the stationary state characterising the expectation values of all local observables. Some of the initial states considered are not reflection symmetric and lead to non-symmetric rapidity distributions. To study such cases, we have to introduce a generalised form for the reduced entropy which measures the entropy restricted to states with non-zero overlap. The initial states considered are of direct experimental realisability and also represent ideal candidates for studying non-equilibrium dynamics in the Hubbard model for finite interactions.
In this paper we consider multi-loop integrals appearing in MHV scattering amplitudes of planar N=4 SYM. Through particular differential operators which reduce the loop order by one, we present explicit equations for the two-loop eight-point finite diagrams which relate them to massive hexagons. After the reduction to two-dimensional kinematics, we solve them using symbol technology. The terms invisible to the symbols are found through boundary conditions coming from double soft limits. These equations are valid at all-loop order for double pentaladders and allow to solve iteratively loop integrals given lower-loop information. Comments are made about multi-leg and multi-loop integrals which can appear in this special kinematics. The main motivation of this investigation is to get a deeper understanding of these tools in this configuration, as well as for their application in general four-dimensional kinematics and to less supersymmetric theories.
We present CO luminosity evolution of both elliptical and spiral galaxies based on a galactic wind model and a bulge-disk model, respectively. We have found that the CO luminosity peaks around the epoch of galactic wind caused by collective supernovae $\sim$ 0.85 Gyr after the birth of the elliptical with $M = 2 \cdot 10^{12} M_\odot$ while $\sim$ 0.36 Gyr after the birth of the bulge with $M = 2 \cdot 10^{11} M_\odot$. After these epochs, the CO luminosity decreases abruptly because the majority of molecular gas was expelled from the galaxy system as the wind. Taking account of typical masses of elliptical galaxies and bulges of spiral galaxies, we suggest that CO emission can be hardly detected from galaxies with redshift $z \sim 1 - 4$ unless some amplification either by galaxy mergers and/or by gravitational lensing is working. Therefore, our study explains reasonably why CO emission was detected from the high-redshift quasar BR 1202$-$0725 at $z =4.7$ while not detected from the powerful radio galaxies with $1 < z < 4$.
We have carried out a two loop computation of the low-energy effective action for the four-dimensional N=2 supersymmetric Yang-Mills system coupled to hypermultiplets, with the chiral superfields of the vector multiplet lying in an abelian subalgebra. We have found a complete cancellation at the level of the integrands of Feynman amplitudes, and therefore the two loop contribution to the action, effective or Wilson, is identically zero.