arXiv subjects

Bin Wang

Publications and source records attributed to Bin Wang.

At least 937 records · Page 52Linked to original sources

arXiv2014

Entanglement Entropy as a Probe of the Proximity Effect in Holographic Superconductors

We study the entanglement entropy as a probe of the proximity effect of a superconducting system by using the gauge/gravity duality in a fully back-reacted gravity system. While the entanglement entropy in the superconducting phase is less than the entanglement entropy in the normal phase, we find that near the contact interface of the superconducting to normal phase the entanglement entropy has a different behavior due to the leakage of Cooper pairs to the normal phase. We verify this behavior by calculating the conductivity near the boundary interface.

hep-th↗

arXiv2014

A model study of the chiral phase diagram of QCD

In this paper we study the chiral phase transition of QCD at finite temperature and density by using the rank-2 confining separable gluon propagator model in the framework of Dyson-Schwinger Equations. The critical end point is located at (T_CEP, μ_CEP) = (69 MeV, 270.3 MeV). It is also found that the first order phase transition might not end at one point, but experiences a two-phase coexisting meta-stable state. A comparison with the results in the previous literature is given.

hep-ph↗

arXiv2014

Compound Effect of Alfvén Waves and Ion-cyclotron Waves on Heating/Acceleration of Minor Ions via the Pickup Process

A scenario is proposed to explain the preferential heating of minor ions and differential streaming velocity between minor ions and protons observed in the solar corona and in the solar wind. It is demonstrated by test particle simulations that minor ions can be nearly fully picked up by intrinsic Alfvén-cyclotron waves observed in the solar wind based on the observed wave energy density. Both high frequency ion-cyclotron waves and low frequency Alfvén waves play crucial roles in the pickup process. A minor ion can first gain a high magnetic moment through the resonant wave-particle interaction with ion-cyclotron waves, and then this ion with a large magnetic moment can be trapped by magnetic mirror-like field structures in the presence of the lower-frequency Alfvén waves. As a result, the ion is picked up by these Alfvén-cyclotron waves. However, minor ions can only be partially picked up in the corona due to low wave energy density and low plasma beta. During the pickup process, minor ions are stochastically heated and accelerated by Alfvén-cyclotron waves so that they are hotter and flow faster than protons. The compound effect of Alfvén waves and ion-cyclotron waves is important on the heating and acceleration of minor ions. The kinetic properties of minor ions from simulation results are generally consistent with in situ and remote features observed in the solar wind and solar corona.

astro-ph.SR↗

arXiv2014

Probing excitonic states in ultraclean suspended two-dimensional semiconductors by photocurrent spectroscopy

The optical response of semiconducting monolayer transition-metal dichalcogenides (TMDCs) is dominated by strongly bound excitons that are stable even at room temperature. However, substrate-related effects such as screening and disorder in currently available specimens mask many anticipated physical phenomena and limit device applications of TMDCs. Here, we demonstrate that that these undesirable effects are strongly suppressed in suspended devices. Extremely robust (photogain >1,000) and fast (response time <1ms) photoresponse combined with the high quality of our devices allow us to study, for the first time, the formation, binding energies, and dissociation mechanisms of excitons in TMDCs through photocurrent spectroscopy. By analyzing the spectral positions of peaks in the photocurrent and by comparing them with first-principles calculations, we obtain binding energies, band gaps and spin-orbit splitting in monolayer TMDCs. For monolayer MoS2, in particular, we estimate an extremely large binding energy for band-edge excitons, Ebind > 570meV. Along with band-edge excitons, we observe excitons associated with a van Hove singularity of rather unique nature. The analysis of the source-drain voltage dependence of photocurrent spectra reveals exciton dissociation and photoconversion mechanisms in TMDCs.

cond-mat.mes-hall↗

arXiv2014

On Zeilberger Conjecture

We prove a conjecture by D. Zeilberger on the determinant of a certain matrix and relate it to a problem of non-existence of 1-cycles in this note.

math.CO↗

arXiv2014

Critical behavior of Born-Infeld AdS black holes in the extended phase space thermodynamics

We study the thermodynamics of $D$-dimensional Born-Infeld AdS black holes in the extended phase space. We find that the usual small-large black hole phase transition, which exhibits analogy with the Van de Waals liquid-gas system holds in all dimensions greater than three. However, different from the four-dimensional case, in the system of higher dimensional Born-Infeld AdS black holes there is no reentrant phase transition. For the three-dimensional Born-Infeld AS black hole, there does not exist critical phenomena.

hep-th↗

arXiv2014

Holographic parity violating charged fluid dual to Chern-Simons modified gravity

We discuss the $(2+1)$-dimensional parity violating charged fluid on a finite cutoff surface $Σ_c$, dual to the nondynamical and dynamical Chern-Simons (CS) modified gravities. Using nonrelativistic long-wavelength expansion method, the field equations are solved up to $\mathcal{O}(ε^2)$ in the nondynamical model. It is shown that there exists nonvortical dual fluid with shear viscosity $η$ and Hall viscosity $η_A$ on the cutoff surface $Σ_c$. The ratio of shear viscosity over entropy density $η/s$ of the fluid takes the universal value $1/{4π}$, while the ratio of Hall viscosity over entropy density $η_A/s$ depends on the $Σ_c$ and black brane charge $q$. Moreover the nonvortical dual fluid obeys the magnetohydrodynamic (MHD) equation. However, these kinematic viscosities $ν$ and $ν_A$ related to $η$ and $η_A$ do not appear in this MHD equation, due to the constraint condition $\tilde{\partial}^2β_j=0$ for the $(2+1)$-dimensional dual fluid. Then, we extend our discussion to the dynamical CS modified gravity and show that the dual vortical fluid possesses another so-called Curl viscosity $ζ_A$, whose ratio to entropy density $ζ_A/s$ also depends on the $Σ_c$ and $q$. Moreover, the value of $η/s$ still equals to $1/4π$ and the result of $η_A/s$ agrees to the previous result under the probe limit of the pseudo scalar field at the infinite boundary in the charged black brane background for the dynamical CS modified gravity. This vortical dual fluid corresponds to the magnetohydrodynamic (MHD) turbulence equation in plasma physics.

hep-th↗

arXiv2013

Combination of Diverse Ranking Models for Personalized Expedia Hotel Searches

The ICDM Challenge 2013 is to apply machine learning to the problem of hotel ranking, aiming to maximize purchases according to given hotel characteristics, location attractiveness of hotels, user's aggregated purchase history and competitive online travel agency information for each potential hotel choice. This paper describes the solution of team "binghsu & MLRush & BrickMover". We conduct simple feature engineering work and train different models by each individual team member. Afterwards, we use listwise ensemble method to combine each model's output. Besides describing effective model and features, we will discuss about the lessons we learned while using deep learning in this competition.

cs.LG↗

arXiv2013

The effect of Dark Matter and Dark Energy interactions on the peculiar velocity field and the kinetic Sunyaev-Zel'dovich effect

The interaction between Dark Matter and Dark Energy has been proposed as a mechanism to alleviate the coincidence problem. We analyze the effect of the interaction on the evolution of the gravitational field and propose two new observables based on its effect on the matter peculiar velocity field. We find that for different model parameters the matter peculiar velocity could be factor 2 times larger or 5 times smaller than the amplitude of velocity perturbations in the concordance LCDM cosmological model at the same scales. We compare the effect on the peculiar velocities with those on the Integrated Sachs-Wolfe effect and we show that velocities can potentially provide constraints on the strength of the interaction stronger than those currently available. We show that the current upper limits on the amplitude of the kinetic Sunyaev-Zel'dovich power spectrum provide constraints on the coupling within the dark sectors that are consistent with those obtained previously from the CMB and galaxy clusters. In particular, we show that current upper limits from the Atacama Cosmology Telescope and the South Pole Telescope favor Dark Energy decaying into Dark Matter, as required to solve the coincidence problem.

astro-ph.CO↗

arXiv2013

Building a Holographic Superconductor with Higher-derivative Couplings

We discuss the gravitational dual of a holographic superconductor consisting of a U(1) gauge field, a complex scalar field coupled to a charged AdS black hole and a higher-derivative coupling between the U(1) gauge field and the scalar with coupling constant η. In the presence of a magnetic field, the system possesses localized spatially dependent droplet solutions which, in the low temperature limit, have smaller critical temperature for η>0 than the droplet solutions without the interaction term (η=0). In the weak magnetic field limit, the opposite behavior is observed: the critical temperature increases as we increase η. We also calculate the energy gap in the probe limit and find that it is larger for η<0 than the energy gap in the conventional case (η=0).

hep-th↗

arXiv2013

Bandgap Engineering of Strained Monolayer and Bilayer MoS2

We report the influence of uniaxial tensile mechanical strain in the range 0-2.2% on the phonon spectra and bandstructures of monolayer and bilayer molybdenum disulfide (MoS2) two-dimensional crystals. First, we employ Raman spectroscopy to observe phonon softening with increased strain, breaking the degeneracy in the E' Raman mode of MoS2, and extract a Grüneisen parameter of ~1.06. Second, using photoluminescence spectroscopy we measure a decrease in the optical band gap of MoS2 that is roughly linear with strain, ~45 meV% strain for monolayer MoS2 and ~120 meV% strain for bilayer MoS2. Third, we observe a pronounced strain-induced decrease in the photoluminescence intensity of monolayer MoS2 that is indicative of the direct-to-indirect transition of the character of the optical band gap of this material at applied strain of ~1.5%, a value supported by first-principles calculations that include excitonic effects. These observations constitute the first demonstration of strain engineering the band structure in the emergent class of two-dimensional crystals, transition-metal dichalcogenides.

cond-mat.mes-hall↗

arXiv2013

Horizon instability of massless scalar perturbations of an extreme Reissner-Nordström-AdS black hole

We study the stability of extreme Reissner-Nordström-AdS black hole under massless scalar perturbations. We show that the perturbation on the horizon of the extreme Reissner-Nordström-AdS black hole experiences a power-law decay, instead of an exponential decay as observed in the nonextreme AdS black hole. On the horizon of the extreme Reissner-Nordström-AdS black hole, the blow up happens at lower order derivative of the scalar field compared with that of the extreme Reissner-Nordström black hole, which shows that extreme AdS black holes tend to instability in comparison to black holes in asymptotic flat space-times.

hep-th↗

arXiv2013

A Model for Dark Energy decay

We discuss a model of non perturbative decay of dark energy into hot and cold dark matter. This model provides a mechanism from the field theory to realize the energy transfer from dark energy into dark matter, which is the requirement to alleviate the coincidence problem. The advantage of the model is the fact that we accommodate a mean life compatible with the age of the universe. We also argue that supersymmetry is a natural set up, though not essential.

gr-qc↗

arXiv2013

Observing the inhomogeneity in the holographic models of superconductors

We study the gravity duals of striped holographic superconductors in the AdS black hole and AdS soliton backgrounds. We show the dependences of the condensation and the critical temperature/critical chemical potential on the inhomogeneity in these two different spacetimes. By exploring the dynamics of the normal phase through the scalar field perturbation, we argue that the pair susceptibility and the conductivity can be possible phenomenological indications to disclose the property of inhomogeneity.

hep-th↗

arXiv2013

Superradiant instability of extremal brane-world Reissner-Nordström black holes to charged scalar perturbations

We examine the stability of extremal braneworld Reissner-Nordström black holes under massive charged scalar perturbations. We show that similar to the four-dimensional case, the superradiant amplification can occur in braneworld charged holes. More interestingly we find that when the spacetime dimension is higher than four, a trapping potential well can emerge outside the braneworld black hole. This potential well is the extra dimensional effect and does not exist in four dimensions. It triggers the superradiant instability of the extremal braneworld charged holes.

gr-qc↗

arXiv2013

Dynamical gap from holography in the charged dilaton black hole

We study the holographic non-relativistic fermions in the presence of bulk dipole coupling in charged dilatonic black hole background. We explore the nontrivial effects of the bulk dipole coupling, the fermion charge as well as the dilaton field on the flat band, the Fermi surface and the emergence of the gap by investigating the spectral function of the non-relativistic fermion system. In particular, we find that the presence of the flat band in the non-relativistic case will suppress the Fermi momentum. Besides, we observe that the effect of the dipole coupling in the dilaton gravity is more explicit. Finally, we consider the non-relativistic fermions at nonzero temperature. A phase transition from insulator to a conducting state is observed as the fermion system becomes hotter.

hep-th↗

arXiv2013

Holographic charged fluid dual to third order Lovelock gravity

We study the dual fluid on a finite cutoff surface outside the black brane horizon in the third order Lovelock gravity. Using nonrelativistic long-wavelength expansion, we obtain the incompressible Navier-Stokes equations of dual fluid with external force density on the finite cutoff surface. The viscosity to entropy density ratio $η/s$ is independent of cutoff surface and does not get modification from the third order Lovelock gravity influence. The obtained ratio agrees with the results obtained by using other methods, such as the Kubo formula at the AdS boundary and the membrane paradigm at the horizon in the third order Lovelock gravity. These results can be related by Wilson renormalization group flow. However the kinematic viscosity receives correction from the third order Lovelock term. We show that the equivalence between the isentropic flow of the fluid and the radial component of the gravitational equation observed in the Einstein and Gauss-Bonnet gravities also holds in the third order Lovelock gravity. This generalization brings more understandings of relating the gravity theory to the dual fluid.

hep-th↗

arXiv2013

Testing lepton flavor universality in terms of data of BES III and charm-tau factory

The recent measurements on $R_K$ and $R_π$ imply that there exists a possible violation of the leptonic flavor universality which is one of the cornerstones of the standard model. It is suggested that a mixing between sterile and active neutrinos might induce such a violation. In this work we consider the scenarios with one or two sterile neutrinos to explicitly realize the data while the constraints from the available experiments have been taken into account. Moreover, as indicated in literature, the deviation of the real PMNS matrix from the symmetric patterns may be due to a $μ-τ$ asymmetry, therefore the measurements on $R_{D(D_s)eμ} = Γ(D(D_s)\rightarrow e^+ν_e)/Γ(D(D_s)\rightarrow μ^+ν_μ)$ and $R_{D(D_s)μτ} = Γ(D(D_s)\rightarrow μ^+ν_μ)/Γ(D(D_s)\rightarrow μ^+τ_τ)$ (and for some other heavy mesons $B^{\pm}$ and $B_c$ etc.) may shed more light on physics responsible for the violation of the leptonic flavor universality. The data of BES III are available to test the universality and that of the future charm-tau factory will provide more accurate information towards the aspect, in this work, we will discuss $R_{D(D_s)eμ}$ and $R_{D(D_s)μτ}$ in all details and also briefly consider the cases for $B^{\pm}$ and $B_c$.

hep-ph↗