Holographic Schwinger effect in spinning black hole backgrounds

We perform a potential analysis for the holographic Schwinger effect in spinning Myers-Perry black holes.We compute the potential between the produced pair by evaluating the classical action of a string attached on a probe D3-brane at an intermediate position in the AdS bulk.We find that increasing the angular momentum reduces the potential barrier,thus enhancing the Schwinger effect,consistent with previous findings obtained via the local Lorentz transformation.In particular,these effects are more visible for the particle pair lying in the transversal plane compared with that along the longitudinal orientation.In addition,we discuss how the Schwinger effect changes with the shear viscosity to entropy density ratio at strong coupling under the influence of angular momentum.

New holographic Weyl superconductors in Lifshitz gravity

We build holographic p-wave conductor(insulator)/superconductor models via the numerical method with a new form of Weyl coupling in five-dimensional Lifshitz gravity,and then investigate how the Weyl coupling parameterγand the Lifshitz scaling parameter z affect the superconductor models.In the conductor/superconductor model,an increase in the Weyl correction(Lifshitz scaling)enhances(inhibits)the superconductor phase transition.Meanwhile,both the Weyl correction(when the Lifshitz parameter is large enough and fixed)and the Lifshitz scaling suppress the growth of the real part of the conductivity.The Weyl correction used here(CB^(2))shows weaker effects on the critical value than the previous Weyl correction(CF^(2)).In the insulator/superconductor model,larger vaules of the Weyl parameter hinder the formation of condensate.However,in increase in the Lifshitz scaling enhances the appearance of condensate.In addition,the calculation suggests that a competitive relation may exist between the Weyl correction and the Lifshitz scaling.

Excited states of holographic superconductors from massive gravity

In this paper,we generalize the study of the model of holographic superconductors in excited states to the framework of massive gravity at the probe limit.By taking into account the effect of a massive graviton,we numerically present a family of solutions for holographic superconductors in excited states and find that the critical temperatures can be higher due to the effect of the massive graviton,in comparison with the superconductor in Einstein gravity.We also investigate the condensates and conductivities in the ground state and the excited states by studying various parameters that determine the framework of gravity background.

<i>n</i>+ 1 Dimensional Gravity Duals to Quantum Criticalities with Spontaneous Symmetry Breaking

We reexamine the charged AdS domain wall solution to the Einstein-Abelian-Higgs model proposed by Gubser et al. as holographic superconductors at quantum critical points and comment on their statement about the uniqueness of gravity solutions. We generalize their explorations from 3 + 1 dimensions to arbitrary n + 1 Ds and find that the n + 1 ≥ 5D charged AdS domain walls are unstable against electric perturbations.

Holographic superconductor on a novel insulator

We construct a holographic superconductor model, based on a gravity theory, which exhibits novel metal-insulator transitions. We investigate the condition for the condensation of the scalar field over the parameter space, and then focus on the superconductivity over the insulating phase with a hard gap, which is supposed to be Mott-like. It turns out that the formation of the hard gap in the insulating phase benefits the superconductivity.This phenomenon is analogous to the fact that the pseudogap phase can promote the pre-pairing of electrons in high Tccuprates. We expect that this work can shed light on understanding the mechanism of high Tcsuperconductivity from the holographic side.

Introduction to holographic superconductor models

In the last years it has been shown that some properties of strongly coupled superconductors can be potentially described by classical general relativity living in one higher dimension,which is known as holographic superconductors.This paper gives a quick and introductory overview of some holographic superconductor models with s-wave,p-wave and d-wave orders in the literature from point of view of bottom-up,and summarizes some basic properties of these holographic models in various regimes.The competition and coexistence of these superconductivity orders are also studied in these superconductor models.

Holographic axion model: A simple gravitational tool for quantum matter

This is a complete and exhaustive review on the so-called holographic axion model—a bottom-up holographic system characterized by the presence of a set of shift symmetric scalar bulk fields whose profiles are taken to be linear in the spatial coordinates.This simple model implements the breaking of translational invariance of the dual field theory by retaining the homogeneity of the background geometry and therefore allowing for controllable and fast computations. The usages of this model are very vast and they are a proof of the spectacular versatility of the framework. In this review, we touch upon all the up-to-date aspects of this model from its connection with massive gravity and effective field theories, to its role in modeling momentum dissipation and elastic properties ending with all the phenomenological features and its hydrodynamic description. In summary, this is a complete guide to one of the most used models in Applied Holography and a must-read for any researcher entering this field.

The dynamical holographic QCD method for hadron physics and QCD matter

In this paper we present a short overview on the dynamical holographic QCD(DhQCD)method for hadron physics and QCD matter.The five-dimensional DhQCD model is constructed in the graviton-dilaton-scalar framework with the dilaton background fieldΦand the scalar field X dual to the gluon condensate and the chiral condensate operator thus can represent the gluodynamics(linear confinement)and chiral dynamics(chiral symmetry breaking),respectively.The dilaton background field and the scalar field are a function of the 5th dimension,which plays the role of the energy scale,in this way,the DhQCD model can resemble the renormalization group from ultraviolet(UV)to infrared(IR).By solving the Einstein equation,the metric structure at IR is automatically deformed by the nonperturbative gluon condensation and chiral condensation in the vacuum.We review the results on the hadron spectra including the glueball spectra,the light/heavy meson spectra,as well as on QCD phase transitions,and thermodynamical as well as transport properties in the framework of the DhQCD model.

A holographic description of theta-dependent Yang-Mills theory at finite temperature

Theta-dependent gauge theories can be studied using holographic duality through string theory in certain spacetimes.By this correspondence we consider a stack of N_0 dynamical DO-branes as D-instantons in the background sourced by N_c coincident non-extreme black D4-branes.According to the gauge-gravity duality,this D0-D4 brane system corresponds to Yang-Mills theory with a theta angle at finite temperature.We solve the IIA supergravity action by taking account into a sufficiently small backreaction of the Dinstantons and obtain an analytical solution for our D0-D4-brane configuration.Subsequently,the dual theory in the large N_c limit can be holographically investigated with the gravity solution.In the dual field theory,we find that the coupling constant exhibits asymptotic freedom,as is expected in QCD.The contribution of the theta-dependence to the free energy gets suppressed at high temperatures,which is basically consistent with the calculation using the Yang-Mills instanton.The topological susceptibility in the large N_c limit vanishes,and this behavior remarkably agrees with the implications from the simulation results at finite temperature.Moreover,we finally find a geometrical interpretation of the theta-dependence in this holographic system.

Lifshitz引力中的全息p波超导体

在探子极限下,通过数值方法研究了Lifshitz参数z对超导体相变的影响。具体来说,把带质量的麦克斯韦复矢量场耦合到4维Lifshitz黑洞中构造了p波超导体。发现时空各向异性程度的增加抑制导体/超导体相变和电导率。在临界温度附近,系统经历二阶相变,与平均场论结果一致。在一定程度上,此复矢量场模型是SU(2)Yang-Mills模型带一般质量的推广。

Horava-Lifshitz引力中的全息绝缘体/超导体相变

在探子极限下,通过数值方法研究了Horava-Lifshitz参数α对绝缘体/超导体相变的影响。具体来说,把带质量的麦克斯韦复标量场耦合到4维Horava-Lifshitz黑洞中,构造了s波绝缘体/超导体相变模型。发现在临界温度附近,系统经历二阶相变,与平均场论结果一致。高阶修正强度增加时,临界化学势变大,即绝缘体/超导体相变被抑制。同时,电导率虚部的第二个极点沿着频率轴向右移动,即准粒子激发态能量增加。

Horava-Lifshitz引力中超导体的临界行为

在探子极限下,通过解析方法和边缘稳定模式研究了Horava-Lifshitz中s波绝缘体/超导体相变的临界行为,尤其得到了修正引力参数α对临界化学势的影响。具体来说:对于α>0,标量场满足的SturmLiouville方程总存在一个最小本征值,即超导体相变的临界化学势。同时,对于任意修正引力参数,标量场在径向方向分布总存在一个边缘稳定模,即n=0模。并且,随着修正参数α的增加,临界化学势增加,即相变变得困难。此外,本文结果与通过数值方法所得结果一致。

黑洞的经典与量子性质

黑洞是基础物理中最为神秘的研究客体之一.本文综述了我们过去围绕黑洞这一议题所取得的研究进展:黑洞的观测图像与其中的光环与阴影,黑洞热力学与第一定律,黑洞的全息性质及其在超流动力学中的应用,弱与强宇宙监督猜想以及借用黑洞对它们的检验,圈量子引力对黑洞熵微观起源的量子几何解释.

在类比系统中研究引力和黑洞的性质

引力和量子力学的融合是理解时空起源和引力本质的重要问题,也是一个长期悬而未决的基础物理学根本问题。理论物理学家们对此提出了诸多理论猜想,也做出了许多预言。然而一些相关的预言涉及的效应极其微弱,因此难以通过实验观测加以证实。通过类比引力系统,人们可以将这些引力效应转化为实验室可测可控系统的一些效应。对这些类比系统的研究一方面可以帮助人们更深入地理解引力的性质本身,另一方面也可以为其他相关领域的研究提供启发和新的思路。文章将以几个具体的类比系统为例简要介绍类比引力研究的历史和最近的一些研究进展。

A pedagogical review on solvable irrelevant deformations of 2D quantum field theory

This is a pedagogical review on TT^(-)deformation of two dimensional quantum field theories.It is based on three lectures which the author gave at ITP-CAS in December 2018.This review consists of four parts.The first part is a general introduction to TT^(-)deformation.Special emphasises are put on the deformed classical Lagrangian and the exact solvability of the spectrum.The second part focuses on the torus partition sum of the TT^(-)/JT^(-)deformed conformal field theories and modular invariance/covariance.In the third part,different perspectives of TT^(-)deformation are presented,including its relation to random geometry,2D topological gravity and holography.We summarize more recent developments until January 2021 in the last part.

Instability of AdS black holes with lattices

Anti-de Sitter(AdS)black holes with lattices are essential for optical conductivity studies in the holographic approach.We investigate the instability of these black holes that can result in the holographic description of charge density waves.In the presence of homogeneous axion fields,we show that the instability of AdS-Reissner-Nordström(AdS-RN)black holes is always suppressed.However,in the presence of Q-lattices,we find that the unstable region becomes the smallest in the vicinity of the critical region for the metal/insulator phase transition.This novel phenomenon is reminiscent of the behavior of the holographic entanglement entropy during quantum phase transitions.

AdS/Deep-Learning made easy:simple examples

Deep learning has been widely and actively used in various research areas.Recently,in gauge/gravity duality,a new deep learning technique called AdS/DL(Deep Learning)has been proposed.The goal of this paper is to explain the essence of AdS/DL in the simplest possible setups,without resorting to knowledge of gauge/gravity duality.This perspective will be useful for various physics problems:from the emergent spacetime as a neural network to classical mechanics problems.For prototypical examples,we choose simple classical mechanics problems.This method is slightly different from standard deep learning techniques in the sense that we not only have the right final answers but also obtain physical understanding of learning parameters.