ShantanuT01/DACTYL-Pretraining huggingface dataset:
Chiral phonons were initially proposed and further verified experimentally in two-dimensional (2D) hexagonal crystal lattices. Many intriguing features brought about by chiral phonons are attributed to the pseudo-angular momenta which are associated with the threefold rotational symmetry of hexagonal lattices. Here, we go beyond the hexagonal crystals and investigate the chiral phonons in systems with fourfold rotational symmetry. We clarify the symmetry requirements for the emergence of chiral phonons in both 2D square lattices and 3D tetragonal lattices. For 2D, the realization of $C_4$ chiral phonons requires the breaking of time-reversal symmetry; while for 3D, they can exist on the $C_4$-invariant path in a chiral tetragonal lattice. These phonons have the advantage that they can be more readily coupled with optical transitions, which facilitates their experimental detection. We demonstrate our idea via model analysis and first-principles calculations of concrete materials, including the MnAs monolayer and the $\alpha$-cristobalite. Our work reveals chiral phonons beyond the hexagonal lattices and paves the way for further exploration of chiral phonon physics in square/tetragonal materials and metamaterials.
We demonstrate a possibility of computation of inelastic scattering cross-section in a multi-peripheral model by application of the Laplace method to multidimensional integral over the domain of physical process. The constrained maximum point of scattering cross-section integral under condition of the energy-momentum conservation has been found. In the vicinity of this point the integrand is substituted for an expression of Gaussian type, which made possible to compute this integral numerically. The paper has two parts. The hunting procedure of the constrained maximum point is considered and the properties of this maximum point are discussed in the given part of the paper. It is shown that virtuality of all internal lines of the "comb" diagram reduced at the constrained maximum point with energy growth. In the second part of the paper we give some arguments in favor of consideration of the mechanism of virtuality reduction as the mechanism of the total hadron scattering cross-section growth, which is not taken into account within the framework of Regge theory.
We show that Multiple Weyl and double Weyl points arise in a chiral elastic system through stacking many two-dimensional honeycomb mechanical structures. On the distinct kz plane, the band structures calculated from tight-binding model exhibit the presence of Weyl points at Brillouin vertices and double Weyl Points at Brillouin centre. Based on the tight-binding model, we design a practical chiral mechanical structure which can be fabricated by current 3D printing technology. The numerical calculation illustrates several Weyl and double-Weyl points as expected in our analysis of tight-binding model. To verify the topological feature, topological charges of every degeneracy are calculated. Within these Weyl points, we theoretically prove that the existence of topologically protected surface modes, and their robustness against defects are also demonstrated.
We establish a Riesz potential criterion for Lebesgue continuity points of functions of bounded $\mathbb{A}$-variation, where $\mathbb{A}$ is a $\mathbb{C}$-elliptic differential operator of arbitrary order. This result might even be of interest for classical functions of bounded variation.
Lattice birth-and-death Markov dynamics of particle systems with spins from the set of non-negative integers are constructed as unique solutions to certain stochastic equations. Pathwise uniqueness, strong existence, Markov property and joint uniqueness in law are proven, and a martingale characterization of the process is given. Sufficient conditions for the existence of an invariant distribution are formulated in terms of Lyapunov functions. We apply obtained results to discrete analogs of the Bolker--Pacala--Dieckmann--Law model and an aggregation model.
Polarization properties of turbulent stochastically inhomogeneous ultrarelativistic QED plasma are studied. It is shown that the sign of nonlinear turbulent Landau damping corresponds to an instability of the spacelike modes and, for sufficiently large turbulent fields, to an actual instability of a system.
In this paper, the weak convergence of impulsive recurrent process with semi-Markov switching in the scheme of Levy approximation is proved. Singular perturbation problem for the compensating operator of the extended Markov renewal process is used to prove the relative compactness.
In this article, we study an inverse problem for the following convective Brinkman-Forchheimer (CBF) equations:   \begin{align*}   \boldsymbol{u}_t-\mu \Delta\boldsymbol{u}+(\boldsymbol{u}\cdot\nabla)\boldsymbol{u}+\alpha\boldsymbol{u}+\beta|\boldsymbol{u}|^{r-1}\boldsymbol{u}+\nabla p=\boldsymbol{F}:=f \boldsymbol{g}, \ \ \ \nabla\cdot\boldsymbol{u}=0,   \end{align*}   in a bounded domain $\Omega\subset\mathbb{R}^2$ with smooth boundary $\partial\Omega$, where $\alpha,\beta,\mu>0$ and $r\in[1,3]$. The investigated inverse problem consists of reconstructing the vector-valued velocity function $\boldsymbol{u}$, the pressure field $p$ and the scalar function $f$. For the divergence free initial data $\boldsymbol{u}_0 \in \mathbb{L}^2(\Omega)$, we prove the existence of a solution to the inverse problem for two-dimensional CBF equations with the integral overdetermination condition, by showing the existence of a unique fixed point for an equivalent operator equation (using an extension of the contraction mapping theorem). Moreover, we establish the uniqueness and Lipschitz stability results of the solution to the inverse problem for 2D CBF equations with $r \in[1,3]$.
We have presented a model in which the new generalized Chaplygin gas interacts with matter. We find that there exists a stable scaling solution at late times in the evolution of the universe. Moreover, the phantom crossing scenario is observed in this model.
An enviromental-random effect over a deterministic population mo\-del, a resource ({\it e.g.}, a fish stock) is introduced. It is assumed that the harvest activity is concentrated at a non predetermined sequence of instants, at which the abundance reaches a certain predetermined level, for then to fall abruptly a constant capture quota (pulse harvesting). So that, the abundance is modeled by a stochastic impulsive type differential equation, incorporating an standard Brownian motion in the per capita rate of growth. With this random effect, the pulse times are images of a random variable, more precisely, they are "stopping-times" of the stochastic process. The proof of the finite expectation of the next access time, {\it i.e.}, the feasibility of the regulation, is the main result.
We present constraints on the physical properties (including stellar mass, age, and star formation rate) of 207 $6\lesssim z \lesssim8$ galaxy candidates from the Reionization Lensing Cluster Survey (RELICS) and companion Spitzer-RELICS surveys. We measure photometry using T-PHOT and perform spectral energy distribution fitting using EA$z$Y and BAGPIPES. Of the 207 candidates for which we could successfully measure Spitzer fluxes, 23 were demoted to likely low redshift ($z<4$). Among the remaining high redshift candidates, we find intrinsic stellar masses between $1\times10^6\rm{M_{\odot}}$ and $4\times10^9\rm{M_\odot}$, and rest-frame UV absolute magnitudes between $-22.6$ and $-14.5$ mag. While our sample is mostly comprised of $L_{UV}/L^*_{UV}<1$ galaxies, there are a number of brighter objects in the sample, extending to $L_{UV}/L^*_{UV}\sim2$. The galaxies in our sample span approximately four orders of magnitude in stellar mass and star-formation rates, and exhibit ages ranging from maximally young to maximally old. We highlight 11 galaxies which have detections in Spitzer/IRAC imaging and redshift estimates $z\geq6.5$, several of which show evidence for some combination of evolved stellar populations, large contributions of nebular emission lines, and/or dust. Among these is PLCKG287+32-2013, one of the brightest $z\sim7$ candidates known (AB mag 24.9) with a Spitzer 3.6$\mu$m flux excess suggesting strong [OIII] + H-$\beta$ emission ($\sim$1000\AA\ rest-frame equivalent width). We discuss the possible uses and limits of our sample and present a public catalog of Hubble 0.4--1.6$\mu$m + Spitzer 3.6$\mu$m and 4.5$\mu$m photometry along with physical property estimates for all 207 objects in the sample. Because of their apparent brightnesses, high redshifts, and variety of stellar populations, these objects are excellent targets for follow-up with James Webb Space Telescope.
We present a detection of a broad Ly-alpha absorber (BLA) with a matching O VI line in the nearby universe. The BLA is detected at z = 0.01028 in the high S/N spectrum of Mrk 290 obtained using the Cosmic Origins Spectrograph. The Ly-alpha absorption has two components, with b(HI) = 55 +/- 1 km/s and b(HI) = 33 +/- 1 km/s, separated in velocity by v ~ 115 km/s. The O VI, detected by FUSE at z = 0.01027, has a b(OVI) = 29 +/- 3 km/s and is kinematically well aligned with the broader HI component. The different line widths of the BLA and OVI suggest a temperature of T = 1.4 x 10^5 K in the absorber. The observed line strength ratios and line widths favor an ionization scenario in which both ion-electron collisions and UV photons contribute to the ionization in the gas. Such a model requires a low-metallicity of -1.7 dex, ionization parameter of log U ~ -1.4, a large total hydrogen column density of N(H) ~ 4 x 10^19 cm^-2, and a path length of 400 kpc. The line of sight to Mrk 290 intercepts at the redshift of the absorber, a megaparsec scale filamentary structure extending over 20 deg in the sky, with several luminous galaxies distributed within 1.5 Mpc projected distance from the absorber. The collisionally ionized gas in this absorber is likely tracing a shock-heated gaseous structure, consistent with a few different scenarios for the origin, including an over-dense region of the WHIM in the galaxy filament or highly ionized gas in the extended halo of one of the galaxies in the filament. In general, BLAs with metals provide an efficient means to study T ~ 10^5 - 10^6 K gas in galaxy halos and in the intergalactic medium. A substantial fraction of the baryons "missing" from the present universe is predicted to be in such environments in the form of highly ionized plasma.
It is shown that monotone Boolean functions on the Boolean cube capture the expected number of primes, under he usual identification by binary expansion. This answers a question posed by G.Kalai.
We consider a Neumann problem for strictly convex variational functionals of linear growth. We establish the existence of minimisers among $\operatorname{W}^{1,1}$-functions provided that the domain under consideration is simply connected. Hence, in this situation, the relaxation of the functional to the space of functions of bounded variation, which has better compactness properties, is not necessary. Similar $\operatorname{W}^{1,1}$-regularity results for the corresponding Dirichlet problem are only known under rather restrictive convexity assumptions limiting its non-uniformity up to the borderline case of the minimal surface functional, whereas for the Neumann problem no such quantified version of strong convexity is required.
We use asymptotic analysis and numerical simulations to study peak-type singular solutions of the supercritical biharmonic NLS. These solutions have a quartic-root blowup rate, and collapse with a quasi self-similar universal profile, which is a zero-Hamiltonian solution of a fourth-order nonlinear eigenvalue problem.
Preparation and transfer of quantum states is a fundamental task in quantum information. We propose a protocol to prepare a state in the left and center quantum dots of a triple dot array and transfer it directly to the center and right dots. Initially the state in the left and center dots is prepared combining the exchange interaction and magnetic field gradients. Once in the desired state, ac gate voltages in the outer dots are switched on, allowing to select a given photoassisted long-range path and to transfer the prepared state directly from one edge to the other with high fidelity. We investigate the effect of charge noise on the protocol and propose a configuration in which the transfer can be performed with high fidelity. Our proposal can be experimentally implemented and is a promising avenue for transferring quantum states between two spatially separated two-level systems.
The confining geometries of fermions in 2D structures exhibits interesting results that have highest symmetry. Delusion can be considered as the topological effect which is topological invariant. Topologically, genus zero surfaces needs excess of pentagons while in surfaces g>2 surfaces needs excess of heptagons. The curvature effect and the rise of effective gauge field can be interpreted from delusion effects in hexagonal lattice. This idea is novel in its scope as it can state theoretical description of structures and their stability.
We compare simulations, including the Illustris simulations, to observations of CIV and CII absorption at z=2-4. These are the CIV column density distribution function in the column density range $10^{12} - 10^{15}$ cm$^{-2}$, the CIV equivalent width distribution at 0.1 - 2 \AA, and the covering fractions and equivalent widths of CIV 1548 and CII 1337 around DLAs. In the context of the feedback models we investigate, all CIV observations favour the use of more energetic wind models, which are better able to enrich the gas surrounding halos. We propose two ways to achieve this; an increased wind velocity and an increase in wind thermal energy. However, even our most energetic wind models do not produce enough absorbers with CIV equivalent width > 0.6 \AA, which in our simulations are associated with the most massive haloes. All simulations are in reasonable agreement with the CII covering fraction and equivalent widths around Damped Lyman-$\alpha$ absorbers, although there is a moderate deficit in one bin 10 - 100 kpc from the DLA. Finally, we show that the CIV in our simulations is predominantly photoionized.
Non-local boxes are hypothetical ``machines'' that give rise to superstrong non-local correlations, leading to a stronger violation of Bell/CHSH inequalities than is possible within the framework of quantum mechanics. We show how non-local boxes can be used to perform any two-party secure computation. We first construct a protocol for bit commitment and then show how to achieve oblivious transfer using non-local boxes. Both have been shown to be impossible using quantum mechanics alone.
Asinowski, Bacher, Banderier and Gittenberger (A. Asinowski, A. Bacher, C. Banderier and B. Gittenberger. Analytic combinatorics of lattice paths with forbidden patterns, the vectorial kernel method, and generating functions for pushdown automata. Algorithmica, pp. 1-43, 2019.) recently developed the vectorial kernel method - a powerful extension of the classical kernel method that can be used for paths that obey constraints that can be described by finite automata, e.g. avoid a fixed pattern, avoid several patterns at once, stay in a horizontal strip and many others more. However, they only considered walks with steps of length one. In this paper we will generalize their results to walks with longer steps. We will also give some applications of this extension and prove a conjecture about the asymptotic behavior of the expected number of ascents in Schroeder paths.
Asteroseismology of solar-like oscillators often relies on the comparisons between stellar models and stellar observations in order to determine the properties of stars. The values of the global seismic parameters, $\nu_\mathrm{max}$ (the frequency where the smoothed amplitude of the oscillations peak) and $\Delta \nu$ (the large frequency separation), are frequently used in grid-based modeling searches. However, the methods by which $\Delta \nu$ is calculated from observed data and how $\Delta \nu$ is calculated from stellar models are not the same. Typically for observed stars, especially for those with low signal-to-noise data, $\Delta \nu$ is calculated by taking the power spectrum of a power spectrum, or with autocorrelation techniques. However, for stellar models, the actual individual mode frequencies are calculated and the average spacing between them directly determined. In this work we try to determine the best way to combine model frequencies in order to obtain $\Delta \nu$ that can be compared with observations. For this we use stars with high signal-to-noise observations from Kepler as well as simulated TESS data of Ball et al. (2018). We find that when determining $\Delta \nu$ from individual mode frequencies the best method is to use the $\ell=0$ modes with either no weighting or with a Gaussian weighting around $\nu_\mathrm{max}$.
{The Galactic centre (GC) is a unique astrophysical laboratory to study the stellar population of galactic nuclei because it is the only galactic nucleus whose stars can be resolved down to milliparsec scales. However, the extreme and spatially highly variable interstellar extinction towards the GC poses a serious obstacle to photometric stellar classification.} {Our goal is to identify hot, massive stars in the nuclear stellar disc (NSD) region through combining near-infrared (NIR) and mid-infrared (MIR) photometry, and thus to demonstrate the feasibility of this technique, which may gain great importance with the arrival of the James Webb Space Telescope (JWST).} {We combined the GALACTICNUCLEUS NIR survey with the IRAC/Spitzer MIR survey of the GC. We applied the so-called Rayleigh-Jeans colour excess (RJCE) de-reddening method to our combined NIR-MIR data to identify potential hot stars in colour-magnitude diagrams (CMDs).} {Despite the very low angular resolution of IRAC we find 12 clear candidates for young massive stars among the $1\,065$ sources that meet our selection criteria. Seven out of these 12 stars are previously known hot, massive stars belonging to the Arches and Quintuplet clusters, as well as sources detected by the Hubble Space Telescope/NICMOS Paschen-$\alpha$ survey. Five of our massive star candidates have not been previously reported in the literature.} {We show that the RJCE method is a valuable tool to identify hot stars in the GC using photometry alone. Upcoming instruments with high angular resolution MIR imaging capabilities such as the JWST could surely make more substantial use of this de-reddening method and help establish a far more complete census of hot, young stars in the GC area than what is possible at the moment.}
We present an investigation of the rotation and non-radial motion of a coronal mass ejection (CME) from AR 12468 on 2015 December 16 using observations from SDO, SOHO, STEREO A and Wind. The EUV and HMI observations of the source region show that the associated magnetic flux rope (MFR) axis pointed to the east before the eruption. We use a nonlinear fore-free field (NLFFF) extrapolation to determine the configuration of the coronal magnetic field and calculate the magnetic energy density distributions at different heights. The distribution of the magnetic energy density shows a strong gradient toward the northeast. The propagation direction of the CME from a Graduated Cylindrical Shell (GCS) modeling deviates from the radial direction of the source region by about 45 degr in longitude and about 30 degr in latitude, which is consistent with the gradient of the magnetic energy distribution around the AR.The MFR axis determined by the GCS modeling points southward, which has rotated counterclockwise by about 95 degr compared with the orientation of the MFR in the low corona.The MFR reconstructed by a Grad-Shafranov (GS) method at 1 AU has almost the same orientation as the MFR from the GCS modeling, which indicates that the MFR rotation occurred in the low corona. It is the rotation of the MFR that caused the intense geomagnetic storm with the minimum Dst of -155 nT. These results suggest that the coronal magnetic field surrounding the MFR plays a crucial role in the MFR rotation and propagation direction.
I investigate the consistency of the VIMOS Public Extragalactic Redshift Survey v7 galaxy sample with the expansion history and linear growth rate predicted by General Relativity (GR) and a Planck (2015) cosmology. To do so, I measure the redshift-space power spectrum, which is anisotropic due to both redshift-space distortions (RSD) and the Alcock-Paczynski (AP) effect. In Chapter 6, I place constraints of $f \sigma_8(0.76) = 0.44 \pm 0.04$ and $f \sigma_8(1.05) = 0.28 \pm 0.08$, which remain consistent with GR at 95% confidence. Marginalising over the anisotropic AP effect degrades the constraints by a factor of three but allows $F_{AP} \equiv (1+z) D_A H/c$ to be simultaneously constrained. The VIPERS v7 joint-posterior on $(f \sigma_8, F_{AP})$ shows no compelling deviation from GR.   Chapter 7 investigates the inclusion of a simple density transform: `clipping' prior to the RSD analysis. This tackles the root-cause of non-linearity and may extend the validity of perturbation theory. Moreover, this marked statistic would amplify signatures of shielded modified gravity models and includes information not available to the power spectrum. I show that a linear real-space power spectrum with a Kaiser factor and a Lorentzian damping yields a significant bias without clipping, but that this may be removed with a strict threshold; similar behaviour is observed for the data. Estimates of $f \sigma_8$ for different thresholds are highly correlated, but this may be obtained using mocks. A maximum likelihood estimate from a combination of thresholds is shown to achieve a 16% decrease in statistical error relative to a single-threshold estimate. The results are encouraging to date but represent a work in progress; the final analysis will be submitted to Astronomy & Astrophysics as Wilson et al. (2016).
The bosonic topological transition (BTT) is a quantum critical point between the bosonic symmetry protected topological phase and the trivial phase. In this work, we derive a description of this transition in terms of compact quantum electrodynamics (QED) with four fermion flavors ($N_f=4$). This allows us to describe the transition in a lattice model with the maximal microscopic symmetry: an internal SO(4) symmetry. Within a systematic renormalization group analysis, we identify the critical point with the desired O(4) emergent symmetry and all expected deformations. By lowering the microscopic symmetry we recover the previous $N_f=2$ non-compact QED description of the BTT. Finally, by merging two BTTs we recover a previously discussed theory of symmetric mass generation, as an SU(2) quantum chromodynamics-Higgs theory with $N_f=4$ flavors of SU(2) fundamental fermions and one SU(2) fundamental Higgs boson. This provides a consistency check on both theories.
We present numerical results within the one-dimensional disordered Hubbard model for several characteristic indicators of the many-body localization (MBL). Considering traditionally studied charge disorder (i.e., the same disorder strength for both spin orientations) we find that even at strong disorder all signatures consistently show that while charge degree of freedom is non-ergodic, the spin is delocalized and ergodic. This indicates the absence of the full MBL in the model that has been simulated in recent cold-atom experiments. Full localization can be restored if spin-dependent disorder is used instead.
The crystal structure and the magnetic properties of the W1-xNbxO3-d, (x<0.03) system have been investigated. In contrast to the orthorhombic diamagnetic WO3, the material with x=0.01 is paramagnetic down to 5 K. Introducing of 2.5 at. % of Nb into WO3 leads to a tetragonal structure and to a weak itinerant ferromagnetic ordering below TC= 225 K. The saturation magnetic moment at 5 K is 1.07*10-3 mB, whereas the paramagnetic effective moment is 0.06 mB per mole. This high ratio indicates itinerant ferromagnetism in W0.975Nb0.025O3-d.