Editorial: New Frontiers in Holographic Duality -- From quantum complexity and black holes to hydrodynamics and neutron stars

Over the last twenty five years, holographic duality has revolutionised our understanding of gauge theories, quantum many-body systems and also quantum black holes. This topical issue is a collection of review articles on recent advances in fundamentals of holographic duality and its applications with special focus on a few areas where it is inter-disciplinary to a large measure. The aim is to provide a sufficient background on relevant phenomenology and other theoretical areas such as quantum information theory to researchers whose primary expertise is in quantum fields, strings and gravity, and also the necessary concepts and methods of holography to researchers in other fields, so that these recent developments could be grasped and hopefully further developed by a wider community. The topics relating to fundamental aspects include understanding of bulk spacetime reconstruction in holography in the framework of quantum error correction along with the spectacular advances in resolution of the information paradoxes of quantum black holes; quantum complexity and its fundamental role in connecting holography with quantum information theory; theoretical and experimental advances in quantum simulators for information mirroring and scrambling in quantum black holes, and teleportation via wormholes; and a pedagogical review on wormholes also. The topics related to applied holography include applications to hydrodynamic attractor and its phenomenological implications, modelling of equation of state of QCD matter in neutron stars, and finally estimating hadronic contribution to light-by-light scattering for theoretical computation of the muon's $g-2$.Comment: 4 pages; Editorial for the special topical issue "New Frontiers in Hologrpahic Duality" of EPJ

Floating Black Hole in the Karch-Randall Model and its Holographic Dual

To investigate the holography in the Karch-Randall (KR) braneworld model, we construct time-symmetric initial data of black holes floating in the bulk, and compare it with its holographic dual, which is described by four-dimensional self-gravitating quantum field theory in asymptotically AdS_4 spacetime. We also give a definition and an explicit formula of mass in the KR model extending the definition by Abbott and Deser for asymptotically AdS spacetime. We obtain supporting evidence for the holography in the KR model such as good agreements of phase structures and characteristic values between the two theories, and find clues that the Hawking-Page transition of the four-dimensional quantum theory in a microcanonical ensemble is holographically dual to a transition in the bulk black hole configuration.Comment: 24 pages, 11 figure

Holography, Entropy and Extra Dimensions

We show that higher dimensional models (brane worlds) in which the scale of quantum gravity $M_*$ is much smaller than the apparent scale $M_P \sim 10^{19}$ GeV are in conflict with bounds arising from holography and black hole entropy. The thermodynamic entropy of astrophysical black holes and sub-horizon volumes during big bang nucleosynthesis exceed the relevant bounds unless $M_* > 10^{(4-6)}$ TeV, so a hierarchy relative to the weak scale is unavoidable. We discuss the implications for extra dimensions as well as holography.Comment: 9 pages, LaTeX; Clarified use of covariant bound and corrected geometry of ADD black holes. Main conclusions unchanged. To appear in PL

Testing Holographic Principle from Logarithmic and Higher Order Corrections to Black Hole Entropy

The holographic principle is tested by examining the logarithmic and higher order corrections to the Bekenstein-Hawking entropy of black holes. For the BTZ black hole, I find some disagreement in the principle for a holography screen at spatial infinity beyond the leading order, but a holography with the screen at the horizon does not, with an appropriate choice of a period parameter, which has been undetermined at the leading order, in Carlip's horizon-CFT approach for black hole entropy in any dimension. Its higher dimensional generalization is considered to see a universality of the parameter choice. The horizon holography from Carlip's is compared with several other realizations of a horizon holography, including induced Wess-Zumino-Witten model approaches and quantum geometry approach, but none of the these agrees with Carlip's, after clarifications of some confusions. Some challenging open questions are listed finally.Comment: To appear in JHEP. The corrections in Sec.2 with those that follow are more clearly explained. Careful distingtion between the implications of my results to AdS/CFT and to the holograhic principl

Higher-Dimensional Origin of Extended Black Hole Thermodynamics

Holographic braneworlds are used to present a higher-dimensional origin of extended black hole thermodynamics. In this framework, classical, asymptotically anti-de Sitter black holes map to quantum black holes in one dimension less, with a conformal matter sector that backreacts on the brane geometry. Varying the brane tension alone leads to a dynamical cosmological constant on the brane, and, correspondingly, a variable pressure attributed to the brane black hole. Thus, standard thermodynamics in the bulk, including a work term coming from the brane, induces extended thermodynamics on the brane, exactly, to all orders in the backreaction. A microsopic interpretation of the extended thermodynamics of specific quantum black holes is given via double holography

Localization & Exact Holography

We consider the AdS_2/CFT_1 holographic correspondence near the horizon of big four-dimensional black holes preserving four supersymmetries in toroidally compactified Type-II string theory. The boundary partition function of CFT_1 is given by the known quantum degeneracies of these black holes. The bulk partition function is given by a functional integral over string fields in AdS_2. Using recent results on localization we reduce the infinite-dimensional functional integral to a finite number of ordinary integrals over a space of localizing instantons. Under reasonable assumptions about the relevant terms in the effective action, these integrals can be evaluated exactly to obtain a bulk partition function. It precisely reproduces all terms in the exact Rademacher expansion of the boundary partition function as nontrivial functions of charges except for the Kloosterman sum which can in principle follow from an analysis of phases in the background of orbifolded instantons. Our results can be regarded as a step towards proving `exact holography' in that the bulk and boundary partition functions computed independently agree for finite charges. Since the bulk partition function defines the quantum entropy of the black hole, our results enable the evaluation of perturbative as well as nonperturbative quantum corrections to the Bekenstein-Hawking-Wald entropy of these black holes