Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

We construct novel black strings that are neither time-translation invariant, nor axisymmetric, nor translationally invariant in the string direction, but nevertheless have a helical Killing vector field. These solutions branch from the superradiant instability of D = 6 Myers-Perry black strings with equal angular momenta. We coin these solutions as black resonator strings and we find that they have more entropy than Myers-Perry black strings for the energies and angular momenta where both solutions coexist. We also construct Kaluza-Klein geons, which share the symmetries of black resonator strings, but are horizonless. Unlike in other superradiant systems, Kaluza-Klein geons are not the horizonless limit of black resonator strings and are instead entirely separate solutions.

DOI： 10.1007/jhep02(2023)069

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

We investigate the effect of superradiant scattering of gravitational perturbations on the stability of rotating black strings, focusing on the six dimensional equal-spinning Myers-Perry black string. We find that rapidly rotating black strings are unstable to gravitational superradiant modes within a bounded range of string lengths. The instability occurs because momentum along the string direction creates a potential barrier that allows for the confinement of superradiant modes. Yet, five dimensional Myers-Perry black holes do not have stable particle orbits so, unlike other known superradiant systems, these black strings remain stable to perturbations with sufficiently high azimuthal mode number — this is a ‘finite-m’ superradiant instability. For some parameters, this instability competes with the Gregory-Laflamme instability, but otherwise exists independently. The onset of this instability is degenerate and branches to multiple steady-state solutions. This paper is the first of a trilogy: in the next two, we construct two distinct families of rotating strings emerging from the superradiant onset (the ‘black resonator strings’ and ‘helical black strings’). We argue that similar physics is present in 5-dimensional Kerr black strings, but not in D > 6 equal-spinning Myers-Perry black strings.

DOI： 10.1007/jhep01(2023)147

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Superradiance is known as a wave amplification process caused by rotating or charged black holes. We argue that the superradiance of stationary black holes in asymptotically AdS spacetimes can be characterized by the ability of energy extraction. Specifically, we demonstrate that energy can be extracted from Reissner-Nordström-AdS₄ and Kerr-AdS₄ under appropriate time-dependent boundary conditions at conformal boundaries. This indicates that energy can be extracted from thermal states dual to these black holes by applying appropriate time-dependent sources. We also show that the energy extraction can be realized as a reversible process.

DOI： 10.1007/jhep10(2022)024

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Other Link： https://link.springer.com/article/10.1007/JHEP10(2022)024/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Recently, Arutyunov, Bassi and Lacroix have shown that 2D non-linear sigma model with a deformed T^1,1 background is classically integrable [arXiv:2010.05573 [hep-th]]. This background includes a Kalb-Ramond two-form with a critical value. Then the sigma model has been conjectured to be non-integrable when the two-form is off critical. We confirm this conjecure by explicitly presenting classical chaos. With a winding string ansatz, the system is reduced to a dynamical system described by a set of ordinary differential equations. Then we find classical chaos, which indicates non-integrability, by numerically computing Poincaré sections and Lyapunov spectra for some initial conditions.

DOI： 10.1007/jhep05(2021)158

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Other Link： https://link.springer.com/article/10.1007/JHEP05(2021)158/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

We study rotating global AdS solutions in five-dimensional Einstein gravity coupled to a multiplet complex scalar within a cohomogeneity-1 ansatz. The onset of the gravitational and scalar field superradiant instabilities of the Myers-Perry-AdS black hole mark bifurcation points to black resonators and hairy Myers-Perry-AdS black holes, respectively. These solutions are subject to the other (gravitational or scalar) instability, and result in hairy black resonators which contain both gravitational and scalar hair. The hairy black resonators have smooth zero-horizon limits that we call graviboson stars. In the hairy black resonator and graviboson solutions, multiple scalar components with different frequencies are excited, and hence these are multioscillating solutions. The phase structure of the solutions are examined in the microcanonical ensemble, i.e. at fixed energy and angular momenta. It is found that the entropy of the hairy black resonator is never the largest among them. We also find that hairy black holes with higher scalar wavenumbers are entropically dominant and occupy more of phase space than those of lower wavenumbers.

DOI： 10.1007/jhep05(2021)011

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

The AdS soliton is a nonsingular spacetime that has a flat conformal boundary with a compact S¹ direction. We find a horizonless cohomogeneity-1 metric that describes nonlinear gravitational oscillations of the AdS soliton in five dimensions. We call this spacetime the resonating AdS soliton. This solution is obtained as the nonlinear extension of normal modes of the AdS soliton dual to spin-2 glueball excitations. The boundary energy momentum tensor of the resonating AdS soliton has time periodic components, and it is interpreted as a coherently excited state in the dual field theory. Physical quantities of the resonating AdS soliton are multivalued at a fixed energy, suggesting a transition between different frequency solutions. The energy of the resonating AdS soliton is higher than that of the undeformed AdS soliton, in accordance with the positive energy conjecture proposed by Horowitz and Myers.

DOI： 10.1007/jhep08(2020)136

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Black resonators and geons in global AdS are rapidly rotating, low-energy solutions with a helical Killing field. We study the linear mode stability of equal angular momenta, five-dimensional black resonators and geons under scalar, electromagnetic, and gravitational perturbations. We find that black resonators are unstable to the superradiant instability, in agreement with previously known results. Perhaps surprisingly, many geons appear linearly stable, despite having an ergoregion. This apparent stability implies that geons are important long-lived, low-energy states in the dual gauge theory. However, we do find that geons are unstable within a certain range of parameter space. We comment on the nature of this instability and to its possible endpoints. We also report on new non-spinning oscillating geons, which we construct within a cohomogeneity two ansatz. Given the existing arguments that suggest our linear stability results may be extended nonlinearly, our findings indicate that most geons are generic and long-lived solutions.

DOI： 10.1007/jhep07(2020)206

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/jhep04(2020)127

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Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

DOI： 10.1088/1361-6382/ab7418

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Other Link： https://iopscience.iop.org/article/10.1088/1361-6382/ab7418/pdf

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.nuclphysb.2019.114901

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

We establish a holographic bottom-up model which covers both the baryonic and quark matter phases in cold and dense QCD. This is obtained by including the baryons using simple approximation schemes in the V-QCD model, which also includes the backreaction of the quark matter to the dynamics of pure Yang-Mills. We examine two approaches for homogeneous baryon matter: baryons as a thin layer of noninteracting matter in the holographic bulk, and baryons with a homogeneous bulk gauge field. We find that the second approach exhibits phenomenologically reasonable features. At zero temperature, the vacuum, baryon, and quark matter phases are separated by strongly first order transitions as the chemical potential varies. The equation of state in the baryonic phase is found to be stiff, i.e., the speed of sound clearly exceeds the value c_s² = 1/3 of conformal plasmas at high baryon densities.

DOI： 10.1007/jhep07(2019)003

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Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

DOI： 10.1088/1361-6382/ab1d76

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Other Link： https://iopscience.iop.org/article/10.1088/1361-6382/ab1d76/pdf

Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevd.98.126005

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.98.126005/fulltext

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.physletb.2018.08.038

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Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevd.95.066019

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Other Link： http://link.aps.org/article/10.1103/PhysRevD.95.066019

Publishing type：Research paper (scientific journal)   Publisher：EDP Sciences  

DOI： 10.1051/epjconf/201612602018

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/jhep08(2016)048

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Other Link： http://link.springer.com/content/pdf/10.1007/JHEP08(2016)048.pdf

We discuss the ringdown behavior of the nonequilibrium Green's function in a
strongly coupled theory with the holographic dual with a focus on
quasinormal-mode equilibration. We study the time resolved spectral function
for a probe scalar in Vaidya-AdS spacetime in detail as a complement to the
preceding work arXiv:1603.06935 using further numerical results in very
nonadiabatic temperature changes. It is shown that the relaxation of the
nonequilibrium spectral function obtained through the Wigner transform is
governed by the lowest quasinormal mode frequency. The timescale of the
background temperature change is also observed in the frequency analysis. We
then consider a toy model motivated by the quasinormal mode behavior and
discuss these main features in numerical results are simply realized.

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Other Link： http://arxiv.org/pdf/1605.08387v2

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/jhep03(2016)035

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Time dependent perturbations of states in the holographic dual of a 3+1 dimensional confining theory are considered. The perturbations are induced by varying the coupling to the theory’s most relevant operator. The dual gravitational theory belongs to a class of Einstein-dilaton theories which exhibit a mass gap at zero temperature and a first order deconfining phase transition at finite temperature. The perturbation is realized in various thermal bulk solutions by specifying time dependent boundary conditions on the scalar, and we solve the fully backreacted Einstein-dilaton equations of motion subject to these boundary conditions. We compute the characteristic time scale of many thermalization processes, noting that in every case we examine, this time scale is determined by the imaginary part of the lowest lying quasi-normal mode of the final state black brane. We quantify the dependence of this final state on parameters of the quench, and construct a dynamical phase diagram. Further support for a universal scaling regime in the abrupt quench limit is provided.

DOI： 10.1007/jhep08(2015)008

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/jhep06(2015)086

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Other Link： http://link.springer.com/content/pdf/10.1007/JHEP06(2015)086.pdf

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/jhep10(2014)151

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Other Link： http://link.springer.com/content/pdf/10.1007/JHEP10(2014)151.pdf

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/jhep04(2014)099

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/jhep04(2013)128

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Other Link： http://link.springer.com/article/10.1007/JHEP04(2013)128/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevd.86.045011

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Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevd.85.114038

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Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevd.84.125007

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Other Link： http://link.aps.org/article/10.1103/PhysRevD.84.125007

We show a novel charge structure of baryons in electromagnetic field due to
the chiral anomaly. A key connection is to treat baryons as solitons of mesons.
We use Skyrmions to calculate the charge distributions in a single nucleon and
find an additional charge. We also perform calculations of charge distribution
for classical multi-baryons with B=2, 3,...,8 and 17; they show amusing charge
distributions.

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Other Link： http://arxiv.org/pdf/1103.5443v2

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.physletb.2010.11.043

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.physletb.2010.06.008

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Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevd.78.106001

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Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevd.77.126015

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Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1143/ptp.119.863

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1088/1126-6708/2007/05/014

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