arXiv subjects

Bin Chen

Publications and source records attributed to Bin Chen.

At least 649 records · Page 36Linked to original sources

arXiv2016

Short interval expansion of Rényi entropy on torus

We investigate the short interval expansion of the Rényi entropy for two-dimensional conformal field theory (CFT) on a torus. We require the length of the interval $\ell$ to be small with respect to the spatial and temporal sizes of the torus. The operator product expansion of the twist operators allows us to compute the short interval expansion of the Rényi entropy at any temperature. In particular, we pay special attention to the large $c$ CFTs dual to the AdS$_3$ gravity and its cousins. At both low and high temperature limits, we read the Rényi entropies to order $\ell^6$, and find good agreements with holographic results. Moreover, the expansion allows us to read $1/c$ contribution, which is hard to get by expanding the thermal density matrix. We generalize the study to the case with the chemical potential as well.

hep-th↗

arXiv2016

Variance-based uncertainty relations for incompatible observables

We formulate uncertainty relations for arbitrary finite number of incompatible observables. Based on the sum of variances of the observables, both Heisenberg-type and Schrödinger-type uncertainty relations are provided. These new lower bounds are stronger in most of the cases than the ones derived from some existing inequalities. Detailed examples are presented.

quant-ph↗

arXiv2016

New investigations on the transverse spin of structured optical fields

Guided waves and surface waves can be taken as two typical examples of structured optical fields with the transverse spin. Analytical derivations are developed to demonstrate that (i) guided waves also carry the transverse spin that depends on the mean direction of propagation, which may have important applications in spin-dependent unidirectional optical interfaces; (ii) the quantization form of the transverse spin is for the first time revealed, which is not obvious and related to an ellipticity; (iii) from a unified point of view, the transverse spin can be attributed to the presence of an effective rest mass of structured optical fields; (iv) the transverse spin can also be described by the spin matrix of the photon field; (v) unlike a free optical field whose spin projection on the propagation direction is the only observable, owing to the effective rest mass, the spin projection of structured optical fields on other directions is also an observable, such that one can develop an optical analogy of spintronics. A preliminary idea about the potential applications of the transverse spin is presented, but an in-depth and complete study will be presented in our next work.

quant-ph↗

arXiv2016

Higher spin entanglement entropy at finite temperature with chemical potential

It is generally believed that the semiclassical AdS$_3$ higher spin gravity could be described by a two dimensional conformal field theory with ${\cal{W}}$-algebra symmetry in the large central charge limit. In this paper, we study the single interval entanglement entropy on the torus in the CFT with a ${\cW}_3$ deformation. More generally we develop the monodromy analysis to compute the two-point function of the light operators under a thermal density matrix with a ${\cW}_3$ chemical potential to the leading order. Holographically we compute the probe action of the Wilson line in the background of the spin-3 black hole with a chemical potential. We find exact agreement.

hep-th↗

arXiv2016

Global Structure of Exact Scalar Hairy Dynamical Black Holes

We study the global structure of some exact scalar hairy dynamical black holes which were constructed in Einstein gravity either minimally or non-minimally coupled to a scalar field. We find that both the apparent horizon and the local event horizon (measured in luminosity coordinate) monotonically increase with the advanced time as well as the Vaidya mass. At late advanced times, the apparent horizon approaches the event horizon and gradually becomes future outer. Correspondingly, the space-time arrives at stationary black hole states with the relaxation time inversely proportional to the $1/(n-1)$ power of the final black hole mass, where $n$ is the space-time dimension. These results strongly support the solutions describing the formation of black holes with scalar hair. We also obtain new charged dynamical solutions in the non-minimal theory by introducing an Maxwell field which is non-minimally coupled to the scalar. The presence of the electric charge strongly modifies the dynamical evolution of the space-time.

hep-th↗

arXiv2016

Sum uncertainty relations based on Wigner-Yanase skew information

We study sum uncertainty relations for arbitrary finite $N$ quantum mechanical observables. Some uncertainty inequalities are presented by using skew information introduced by Wigner and Yanase. These uncertainty inequalities are nontrivial as long as the observables are mutually noncommutative. The relations among these new and existing uncertainty inequalities have been investigated. Detailed examples are presented.

quant-ph↗

arXiv2016

Synthesis, characterization and physical properties of layered bismuthide PtBi$_2$

We report details of single crystal growth of stoichiometric bismuthide PtBi$_2$ whose structure consists of alternate stacking of Pt layer sandwiched by Bi bilayer along the $c$-axis. The compound crystallizes in space group P-3 with a hexagonal unit cell of $a$=$b$=6.553$Å$, $c$=6.165$Å$. The magnetization data show opposite sign for fields parallel and perpendicular to the Pt layers, respectively. The $T$-dependent resistivity is typical of a metal and the magnetic response shows clear two types of charge carriers and the validity of the semi-classical Kohler's rule. Its physical properties was discussed in comparison with recently proposed topological superconductor $β$-PdBi$_2$.

cond-mat.str-el↗

arXiv2016

The First Focused Hard X-ray Images of the Sun with NuSTAR

We present results from the the first campaign of dedicated solar observations undertaken by the \textit{Nuclear Spectroscopic Telescope ARray} ({\em NuSTAR}) hard X-ray telescope. Designed as an astrophysics mission, {\em NuSTAR} nonetheless has the capability of directly imaging the Sun at hard X-ray energies ($>$3~keV) with an increase in sensitivity of at least two magnitude compared to current non-focusing telescopes. In this paper we describe the scientific areas where \textit{NuSTAR} will make major improvements on existing solar measurements. We report on the techniques used to observe the Sun with \textit{NuSTAR}, their limitations and complications, and the procedures developed to optimize solar data quality derived from our experience with the initial solar observations. These first observations are briefly described, including the measurement of the Fe K-shell lines in a decaying X-class flare, hard X-ray emission from high in the solar corona, and full-disk hard X-ray images of the Sun.

astro-ph.SR↗

arXiv2016

Global sausage oscillation of solar flare loops detected by the Interface Region Imaging Spectrograph

An observation from the Interface Region Imaging Spectrograph reveals coherent oscillations in the loops of an M1.6 flare on 2015 March 12. Both the intensity and Doppler shift of Fe~{\sc{xxi}}~1354.08Å~show clear oscillations with a period of $\sim$25 seconds. Remarkably similar oscillations were also detected in the soft X-ray flux recorded by the Geostationary Operational Environmental Satellites (GOES). With an estimated phase speed of $\sim$2420~km~s$^{-1}$ and a derived electron density of at least 5.4$\times$10$^{10}$ cm$^{-3}$, the observed short-period oscillation is most likely the global fast sausage mode of a hot flare loop. We find a phase shift of $\sim$$π$/2 (1/4 period) between the Doppler shift oscillation and the intensity/GOES oscillations, which is consistent with a recent forward modeling study of the sausage mode. The observed oscillation requires a density contrast between the flare loop and coronal background of a factor $\geqslant$42. The estimated phase speed of the global mode provides an lower limit of the Alfvén speed outside the flare loop. We also find an increase of the oscillation period, which might be caused by the separation of the loop footpoints with time.

astro-ph.SR↗

arXiv2016

Exact formation of hairy planar black holes

We consider Einstein gravity minimally coupled to a scalar field with a given potential in general dimensions. We obtain large classes of static hairy planar black holes which are asymptotic to AdS space-times. In particular, for a special case $μ=(n-2)/2$, we obtain new classes of exact dynamical solutions describing black holes formation. We find there are two classes of collapse solutions. The first class solutions describe the evolution start from AdS space-time with a naked singularity at the origin. The space-time is linearly unstable and evolves into stationary black hole states even under small perturbation. The second class solutions describe the space-time spontaneously evolves from AdS vacua into stationary black hole states undergoing non-linear instability. We also discuss the global properties of all these dynamical solutions.

hep-th↗

arXiv2016

Experimental Determination of the Fermi Surface of Sr3Ir4Sn13

The stannide family of materials A3T4Sn13 (A = La,Sr,Ca, T = Ir,Rh) is interesting due to the interplay between a tunable lattice instability and phonon-mediated superconductivity with Tc ~ 5-7 K. In Sr3Ir4Sn13 a structural transition temperature T* ~ 147 K associated with this instability has been reported, which is believed to result from a superlattice distortion of the high temperature phase on cooling. Here we report the first experimental study of the electronic structure of a member of this material family - Sr3Ir4Sn13 through measurements of quantum oscillations and comparison with density functional theory calculations. Our measurements reveal good agreement with theory using the lattice parameters consistent with a body-centred cubic lattice of symmetry I-43d of the low temperature phase. The study of the fermiology of Sr3Ir4Sn13 we present here should help inform models of multiband superconductivity in the superconducting stannides.

cond-mat.supr-con↗

arXiv2016

Resolving the Fan-Spine Reconnection Geometry of a Small-Scale Chromospheric Jet Event with the New Solar Telescope

Jets present ubiquitously in both quiet and active regions on the Sun. They are widely believed to be driven by magnetic reconnection. A fan-spine structure has been frequently reported in some coronal jets and flares, regarded as a signature of ongoing magnetic reconnection in a topology consisting of a magnetic null connected by a fan-like separatrix surface and a spine. However, for small-scale chromospheric jets, clear evidence of such structures is rather rare, although they are implied in earlier works that show an inverted-Y-shaped feature. Here we report high-resolution (0$"$.16) observations of a small-scale chromospheric jet obtained by the New Solar Telescope (NST) using 10830~Å filtergrams. Bi-directional flows were observed across the separatrix regions in the 10830~Å images, suggesting that the jet was produced due to magnetic reconnection. At the base of the jet, a fan-spine structure was clearly resolved by the NST, including the spine and the fan-like surface, as well as the loops before and after the reconnection. A major part of this fan-spine structure, with the exception of its bright footpoints and part of the base arc, was invisible in the extreme ultraviolet and soft X-ray images (observed by the Atmosphere Imaging Assembly and the X-Ray Telescope, respectively), indicating that the reconnection occurred in the upper chromosphere. Our observations suggest that the evolution of this chromospheric jet is consistent with a two-step reconnection scenario proposed by \citet{Torok2009}

astro-ph.SR↗

arXiv2015

Non-vanishing and sign changes of Hecke eigenvalues for half-integral weight cusp forms

In this paper, we consider three problems about signs of the Fourier coefficients of a cusp form $\mathfrak{f}$ with half-integral weight:\begin{itemize}\item[--]The first negative coefficient of the sequence $\{\mathfrak{a}\_{\mathfrak{f}}(tn^2)\}\_{n\in \N}$,\item[--]The number of coefficients $\mathfrak{a}\_{\mathfrak{f}}(tn^2)$ of same signs,\item[--]Non-vanishing of coefficients $\mathfrak{a}\_{\mathfrak{f}}(tn^2)$ in short intervals and in arithmetic progressions,\end{itemize}where $\mathfrak{a}\_{\mathfrak{f}}(n)$ is the $n$-th Fourier coefficient of $\mathfrak{f}$ and $t$ is a square-free integersuch that $\mathfrak{a}\_{\mathfrak{f}}(t)\not=0$.

math.NT↗

arXiv2015

Monotonicity of eigenvalues of geometric operaters along the Ricci-Bourguignon flow

In this paper, we study monotonicity of eigenvalues of Laplacian-type operator $-Δ+cR$, where $c$ is a constant, along the Ricci-Bourguignon flow. For $c\neq0$, We derive monotonicity of the lowest eigenvalue of Laplacian-type operator $-Δ+cR$ which generalizes some results of Cao \cite{Cao2007}. For $c=0$, We derive monotonicity of the first eigenvalue of Laplacian which generalizes some results of Ma \cite{Ma2006}. Moreover, we prove that when $(M_{3}, g_{0})$ is a closed three manifold with positive Ricci curvature, the eigenvalue of the Laplacian diverges as $t \rightarrow T$ on a limited maximal time in terval $[0, T)$, which generalizes some results of Cerbo and Fabrizio \cite{Fabrizio2007}.

math.DG↗

arXiv2015

Lower bound of local quantum uncertainty for high-dimensional bipartite quantum systems

Quantum correlations are of fundamental importance in quantum phenomena and quantum information processing studies. The measure of quantum correlations is one central issue. The recently proposed measure of quantum correlations, the local quantum uncertainty (LQU), satisfies the full physical requirements of a measure of quantum correlations. In this work, by using operator relaxation, a closed form lower bound of the LQU for arbitrary-dimensional bipartite quantum states is derived. We have compared the lower bound and the optimized LQU for several typical quantum states.

quant-ph↗

arXiv2015

Quasinormal modes of Gauss-Bonnet black holes at large D

Einstein's General Relativity theory simplifies dramatically in the limit that the spacetime dimension D is very large. This could still be true in the gravity theory with higher derivative terms. In this paper, as the first step to study the gravity with a Gauss-Bonnet(GB) term, we compute the quasi-normal modes of the spherically symmetric GB black hole in the large D limit. When the GB parameter is small, we find that the non-decoupling modes are the same as the Schwarzschild case and the decoupled modes are slightly modified by the GB term. However, when the GB parameter is large, we find some novel features. We notice that there are another set of non-decoupling modes due to the appearance of a new plateau in the effective radial potential. Moreover, the effective radial potential for the decoupled vector-type and scalar-type modes becomes more complicated. Nevertheless we manage to compute the frequencies of the these decoupled modes analytically. When the GB parameter is neither very large nor very small, though analytic computation is not possible, the problem is much simplified in the large D expansion and could be numerically treated. We study numerically the vector-type quasinormal modes in this case.

hep-th↗

arXiv2015

Particle Acceleration by a Solar Flare Termination Shock

Solar flares - the most powerful explosions in the solar system - are also efficient particle accelerators, capable of energizing a large number of charged particles to relativistic speeds. A termination shock is often invoked in the standard model of solar flares as a possible driver for particle acceleration, yet its existence and role have remained controversial. We present observations of a solar flare termination shock and trace its morphology and dynamics using high-cadence radio imaging spectroscopy. We show that a disruption of the shock coincides with an abrupt reduction of the energetic electron population. The observed properties of the shock are well-reproduced by simulations. These results strongly suggest that a termination shock is responsible, at least in part, for accelerating energetic electrons in solar flares.

astro-ph.SR↗

arXiv2015

Probing the gravitational Faraday rotation using quasar X-ray microlensing

The effect of gravitational Faraday rotation was predicted in the 1950s, but there is currently no practical method for measuring this effect. Measuring this effect is important because it will provide new evidence for correctness of general relativity, in particular, in the strong field limit. We predict that the observed degree and angle of the X-ray polarization of a cosmologically distant quasar microlensed by the random star field in a foreground galaxy or cluster lens vary rapidly and concurrently with flux during caustic-crossing events using the first simulation of quasar X-ray microlensing polarization light curves. Therefore, it is possible to detect gravitational Faraday rotation by monitoring the X-ray polarization of gravitationally microlensed quasars. Detecting this effect will also confirm the strong gravity nature of quasar X-ray emission.

astro-ph.HE↗