Browsing by Author "Wu, Shang-Yu"

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Black hole remnant in asymptotic anti-de Sitter space
(2015-12-21)
Wen, Wen-Yu
;
Wu, Shang-Yu
;
電子物理學系
;
Department of Electrophysics
The solution of a remnant was suggested for the black hole ground state after surface gravity is corrected for the loop quantum effect. On the other hand, a Schwarzschild black hole in asymptotic anti-de Sitter space would tunnel into the thermal soliton solution known as the Hawking-Page phase transition. In this letter, we investigate the low temperature phase of a three-dimensional Banados-Teitelboim-Zanelli (BTZ) black hole and four-dimensional AdS Schwarzschild black hole. We find that the thermal soliton is energetically favored rather than the remnant solution at low temperature in three dimensions, while a Planck-size remnant is still possible in four dimensions. Though the BTZ remnant seems energetically disfavored, we argue that it is still possible to find in the overcooled phase if strings were present, and its implication is discussed.
Charged BTZ-like black hole solutions and the diffusivity-butterfly velocity relation
(2018-01-15)
Ge, Xian-Hui
;
Sin, Sang-Jin
;
Tian, Yu
;
Wu, Shao-Feng
;
Wu, Shang-Yu
We show that there exists a class of charged BTZ-like black hole solutions in Lifshitz spacetime with a hyperscaling violating factor. The charged BTZ black hole is characterized by a charge-dependent logarithmic term in the metric function. As concrete examples, we give five such charged BTZ-like black hole solutions and the standard charged BTZ metric can be regarded as a special instance of them. In order to check the recent proposed universal relations between diffusivity and the butterfly velocity, we first compute the diffusion constants of the standard charged BTZ black holes and then extend our calculation to arbitrary dimension d, exponents z and theta. Remarkably, the case d = theta and z = 2 is a very special in that the charge diffusion D-c is a constant and the energy diffusion D-e might be ill-defined, but v(B)(2)tau diverges. We also compute the di ff usion constants for the case that the DC conductivity is fi nite but in the absence of momentum relaxation.
Chiral Hall effect and chiral electric waves
(2015-01-14)
Pu, Shi
;
Wu, Shang-Yu
;
Yang, Di-Lun
;
物理研究所
;
丘成桐中心
We investigate the vector and axial currents induced by external electromagnetic fields and chemical potentials in chiral systems at finite temperature. Similar to the normal Hall effect, we find that an axial Hall current is generated in the presence of the electromagnetic fields along with an axial chemical potential, which may be dubbed as the "chiral Hall effect" (CHE). The CHE is related to the interactions of chiral fermions and exists with a nonzero axial chemical potential. We argue that the CHE could lead to nontrivial charge distributions at different rapidity in asymmetric heavy ion collisions. Moreover, we study the chiral electric waves led by the fluctuations of the vector and axial chemical potentials along with the chiral electric separation effect, where a density wave propagates along the applied electric field. Combining with the normal/chiral Hall effects, the fluctuations of chemical potentials thus result in Hall density waves. The Hall density waves may survive even at zero chemical potentials and become nondissipative. We further study the transport coefficients including the Hall conductivities, damping times, wave velocities, and diffusion constants of chiral electric waves in a strongly coupled plasma via the AdS/CFT correspondence.
Dipole coupling effect of holographic fermion in charged dilatonic gravity
(2012-06-06)
Wen, Wen-Yu
;
Wu, Shang-Yu
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物理研究所
;
Institute of Physics
In this Letter, we study the dipole coupling effect of holographic fermion in a charged dilatonic black hole proposed by Gubser and Rocha (2010) [1]. It is found that the property of Fermi liquid is rigid under perturbation of dipole coupling, and the Fermi momentum is linearly shifted. A gap is dynamically generated as the coupling becomes large enough and the Fermi surface ceases to exist as the bulk dipole coupling further increases. (C) 2012 Elsevier B.V. All rights reserved.
Drag force of Anisotropic plasma at finite U(1) chemical potential
(2016-05-05)
Cheng, Long
;
Ge, Xian-Hui
;
Wu, Shang-Yu
;
電子物理學系
;
Department of Electrophysics
We perform the calculation of the drag force acting on amassive quark moving through an anisotropic N = 4 SU(N) Super Yang-Mills plasma in the presence of a U(1) chemical potential. We present the numerical results for any value of the anisotropy and arbitrary direction of the quark velocity with respect to the direction of the anisotropy. We find the effect of the chemical potential or charge density will enhance the drag force for our charged solution.
Elliptic flow from thermal photons with magnetic field in holography
(2014-01-28)
Mueller, Berndt
;
Wu, Shang-Yu
;
Yang, Di-Lun
;
物理研究所
;
丘成桐中心
We compute the elliptic flow v(2) of thermal photons in a strongly coupled plasma with constant magnetic field via gauge/gravity duality. The D3/D7 embedding is applied to generate the contributions from massive quarks. By considering the cases in 2 + 1 flavor super Yang-Mills analogous to the photon production in quark gluon plasma, we obtain the thermal photon v(2), which is qualitatively consistent with the direct photon v(2) measured at the relativistic heavy ion collider at intermediate energy. However, due to the simplified setup, the thermal photon v(2) in our model should be regarded as the upper bound for the v(2) generated by solely a magnetic field in the strongly coupled scenario.
Holographic chiral electric separation effect
(2014-04-10)
Pu, Shi
;
Wu, Shang-Yu
;
Yang, Di-Lun
;
物理研究所
;
丘成桐中心
We investigate the chiral electric separation effect, where an axial current is induced by an electric field in the presence of both vector and axial chemical potentials, in a strongly coupled plasma via the Sakai-Sugimoto model with a U(1)(R) x U(1)(L) symmetry. By introducing different chemical potentials in U(1)(R) and U(1)(L) sectors, we compute the axial direct current (DC) conductivity stemming from the chiral current and the normal DC conductivity. We find that the axial conductivity is approximately proportional to the product of the axial and vector chemical potentials for arbitrary magnitudes of the chemical potentials. We also evaluate the axial alternating current (AC) conductivity induced by a frequency-dependent electric field, where the oscillatory behavior with respect to the frequency is observed.
Holographic model of a two-band superconductor
(2014-03-11)
Wen, Wen-Yu
;
Wu, Mu-Sheng
;
Wu, Shang-Yu
;
物理研究所
;
丘成桐中心
We construct a holographic two-band superconductor model with interband Josephson coupling. We investigate the effects the Josephson coupling has on the superconducting condensates and the critical temperature for their formation numerically, as well as analytically where possible. We calculate the ac conductivity and find it qualitatively similar to the single band superconductor. We investigate the nodal structure of our holographic two-band superconductor from the low temperature behavior of the thermal conductivity and find it nodeless.
Holographic Models Without Translational Invariance
(2017-01)
Wu, Shang-Yu
;
電子物理學系
;
Department of Electrophysics
In this proceeding paper, we briefly discuss some holographic models without translational invariance. We construct holographic models which possess the linear temperature resistivity and various anomalous transports consistent with the cuprate strange metal. We also compute the fermion spectral function in the context of holographic massive gravity which is argued to correspond to the system without translational invariance. Our fermion spectral function calculations provide supporting evidences on the interpretation of holographic massive gravity as a disordered system.
Holographic photon production with magnetic field in anisotropic plasmas
(2013-08-01)
Wu, Shang-Yu
;
Yang, Di-Lun
;
物理研究所
;
Institute of Physics
We investigate the thermal photon production from constant magnetic field in a strongly coupled and anisotropic plasma via the gauge/gravity duality. The dual geometry with pressure anisotropy is generated from the axion-dilaton gravity action introduced by Mateos and Trancancelli and the magnetic field is coupled to fundamental matters(quarks) through the D3/D7 embeddings. We find that the photon spectra with different quark mass are enhanced at large frequency when the photons are emitted parallel to the anisotropic direction with larger pressure or perpendicular to the magnetic field. However, in the opposite conditions for the emitted directions, the spectra approximately saturate isotropic results in the absence of magnetic field. On the other hand, a resonance emerges at moderate frequency for the photon spectrum with heavy quarks when the photons move perpendicular to the magnetic field. The resonance is more robust when the photons are polarized along the magnetic field. On the contrary, in the presence of pressure anisotropy, the resonance will be suppressed. There exist competing effects of magnetic field and pressure anisotropy on meson melting in the strongly coupled super Yang-Mills plasma, while we argue that the suppression led by anisotropy may not be applied to the quark gluon plasma.
Holographic study of the jet quenching parameter in anisotropic systems
(2016-10-28)
Wang, Luying
;
Wu, Shang-Yu
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電子物理學系
;
Department of Electrophysics
We first calculate the jet quenching parameter of an anisotropic plasma with a U(1) chemical potential via AdS/CFT duality. The effects of charge, anisotropy parameter, and quark motion direction on the jet quenching parameter are investigated. We then discuss the situation of an anisotropic black brane in the IR region. We study both the jet quenching parameters along the longitudinal direction and the transverse plane.
Hyperscaling violating black hole solutions and magneto-thermoelectric DC conductivities in holography
(2017-08-28)
Ge, Xian-Hui
;
Tian, Yu
;
Wu, Shang-Yu
;
Wu, Shao-Feng
;
電子物理學系
We derive new black hole solutions in Einstein-Maxwell-axion-dilaton theory with a hyperscaling violation exponent. We then examine the corresponding anomalous transport exhibited by cuprate strange metals in the normal phase of high-temperature superconductors via gauge-gravity duality. Linear-temperature-dependence resistivity and quadratic-temperature-dependence inverse Hall angle can be achieved. In the high-temperature regime, the heat conductivity and Hall Lorenz ratio are proportional to the temperature. The Nernst signal first increases as temperature goes up, but it then decreases with increasing temperature in the high-temperature regime.
Linear and quadratic in temperature resistivity from holography
(2016-11-22)
Ge, Xian-Hui
;
Tian, Yu
;
Wu, Shang-Yu
;
Wu, Shao-Feng
;
電子物理學系
We present a new black hole solution in the asymptotic Lifshitz spacetime with a hyperscaling violating factor. A novel computational method is introduced to compute the DC thermoelectric conductivities analytically. We find that both the linear-T and quadratic-T contributions to the resistivity can be realized, indicating that a more detailed comparison with experimental phenomenology can be performed in this scenario.
Magnetothermoelectric DC conductivities from holography models with hyperscaling factor in Lifshitz spacetime
(2017-11-01)
Chen, Ze-Nan
;
Ge, Xian-Hui
;
Wu, Shang-Yu
;
Yang, Guo-Hong
;
Zhang, Hong-Sheng
We investigate an Einstein-Maxwell-Dilaton-Axion holographic model and obtain two branches of a charged black hole solution with a dynamic exponent and a hyperscaling violation factor when a magnetic field presents. The magnetothermoelectric DC conductivities are then calculated in terms of horizon data by means of holographic principle. We find that linear temperature dependence resistivity and quadratic temperature dependence inverse Hall angle can be achieved in our model. The well-known anomalous temperature scaling of the Nernst signal and the Seebeck coefficient of cuprate strange metals are also discussed. (C) 2017 The Author(s). Published by Elsevier B.V.
Mimic the optical conductivity in disordered solids via gauge/gravity duality
(2014-02-05)
Sun, Jia-Rui
;
Wu, Shang-Yu
;
Zhang, Hai-Qing
;
物理研究所
;
Institute of Physics
We study the optical conductivity in a (2 + 1)-dimensional non-relativistic field theory holographically dual to a (3 + 1)-dimensional charged Lifshitz black brane within the Einstein-Maxwell-dilaton theory. Surprisingly, we find that the optical AC conductivity satisfies the nontrivial (non-)power law scaling in the high frequency regime rather than approaching to a constant when the dynamical critical exponent z > 1, which is qualitatively similar to those in various disordered solids in condensed matter systems. Besides, this (non-)power law scaling behavior shows some universality, which is robust against the temperatures. We argue that the peculiar scaling behavior of AC conductivity may stem from the couplings of the dilaton field with the gauge fields and also the logarithmic behavior near the boundary in the Lifshitz spacetime. (C) 2014 The Authors. Published by Elsevier B.V. All rights reserved.
Novel features of the transport coefficients in Lifshitz black branes
(2013-04-23)
Sun, Jia-Rui
;
Wu, Shang-Yu
;
Zhang, Hai-Qing
;
物理研究所
;
Institute of Physics
We study the transport coefficients, including the conductivities and shear viscosity of the non-relativistic field theory dual to the Lifshitz black brane with multiple U(1) gauge fields by virtue of the gauge/gravity duality. Focusing on the case of double U(1) gauge fields, we systematically investigate the electric, thermal, and thermoelectric conductivities for the dual nonrelativistic field theory. In the large frequency regime, we find a nontrivial power law behavior in the electric alternating current conductivity when the dynamical critical exponent z > 1 in (2 + 1)-dimensional field theory. The relations between this novel feature and the "symmetric hopping model" in condensed matter physics are discussed. In addition, we also show that the Kovtun-Starinets-Son bound for the shear viscosity to the entropy density is not violated by the additional U(1) gauge fields and dilaton in the Lifshitz black brane. DOI: 10.1103/PhysRevD.87.086005
On the possibility of blue tensor spectrum within single field inflation
(2015-11-01)
Cai, Yi-Fu
;
Gong, Jinn-Ouk
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Pi, Shi
;
Saridakis, Emmanuel N.
;
Wu, Shang-Yu
We present a series of theoretical constraints on the potentially viable inflation models that might yield a blue spectrum for primordial tensor perturbations. By performing a detailed dynamical analysis we show that, while there exists such possibility, the corresponding phase space is strongly bounded. Our result implies that, in order to achieve a blue tilt for inflationary tensor perturbations, one may either construct a non-canonical inflation model delicately, or study the generation of primordial tensor modes beyond the standard scenario of single slow-roll field. (C) 2015 The Authors. Published by Elsevier B.V.
Phase structure in a dynamical soft-wall holographic QCD model
(2013-04-01)
He, Song
;
Wu, Shang-Yu
;
Yang, Yi
;
Yuan, Pei-Hung
;
物理研究所
We consider the Einstein-Maxwell-dilaton system with an arbitrary kinetic gauge function and a dilaton potential. A family of analytic solutions is obtained by the potential reconstruction method. We then study its holographic dual QCD model. The kinetic gauge function can be fixed by requesting the linear Regge spectrum of mesons. We calculate the free energy to obtain the phase diagram of the holographic QCD model and interpret our result as the heavy quarks system by comparing the recent lattice QCD simulation. We finally obtain the equations of state in our model.
Vortex in Holographic Two-band Superconductor
(2016-03)
Wu, Shang-Yu
;
電機學院
;
College of Electrical and Computer Engineering
A single static vortex in a holographic two-band superconductor is constructed. We investigate the effect of the interband coupling to the condensate profile. We estimate the first critical magnetic field, and compute characteristic lengths like penetration and coherence lengths and conclude both bands in our superconductor behave type II.