arXiv subjects

Jun Nian

Publications and source records attributed to Jun Nian.

At least 19 recordsLinked to original sources

arXiv2026

Schwarzian Theory and Cosmological Constant Problem

Observational data in cosmology indicate a small, positive, and nonvanishing cosmological constant that dominates the energy budget of the present universe. The origin of the cosmological constant from a quantum perspective remains unresolved, with a discrepancy of approximately 120 orders of magnitude between its observed value and theoretical estimates. Motivated by earlier work of Gibbons, we analyze the cosmological constant problem within a quantum-gravitational framework based on Schwarzian theory and its ensemble averaging. We then derive the phenomenological value of the dark energy density and obtain the corresponding equation of state. In this model, the cosmological constant arises from the ensemble average of time-reparametrization modes.

hep-th↗

arXiv2026

Replica Phase Transition with Quantum Gravity Corrections

Motivated by bulk replica wormholes, we study the boundary effective theory that describes the near-horizon fluctuations of a near-extremal Reissner-Nordstr\"om black hole. This theory consists of a Schwarzian mode and a $U(1)$ phase mode. We compute the partition function of this boundary theory on connected geometries, from which the entropy is derived. Our analysis reveals a rich phase structure, in which the dominance of connected or disconnected configurations leads to a phase transition controlled by the temperature and the coupling constants $C$, $K$, and $\mathcal{E}$ of the 1d effective theory.

hep-th↗

arXiv2025

Quantum Corrections to Randall-Sundrum Model from JT Gravity

We investigate quantum corrections to the Randall-Sundrum (RS) model in the near-extremal black brane background with quantum corrections in the near-horizon. The near-horizon geometry is described by Jackiw-Teitelboim gravity, and the quantum fluctuations are governed by the Schwarzian action. We introduce the Schwarzian modes into the RS metric, derive the quantum-corrected equation for the Kaluza-Klein (KK) modes via the Schwinger-Dyson equation, calculate the correction to the KK mass spectrum, and discuss the impact of quantum corrections on the Goldberger-Wise mechanism. Our work introduces both quantum corrections and temperature into the RS model, providing insights into cosmology and phase transitions within it.

hep-th↗

arXiv2025

Quantum Corrections to $\eta/s$ from JT Gravity

We revisit the computation of the shear viscosity to entropy ratio $\eta/s$ at finite chemical potential in a holographic model that takes into account the quantum fluctuations in the IR region of near-extremal black branes. Such quantum corrections can be computed from JT gravity and generate non-trivial temperature dependence for $\eta/s$, which deviates from the universal $1/4\pi$ result. In the semi-classical regime, $\eta/s$ attains a minimum which is below the KSS bound, generated by the presence of the quantum effects. In the quantum regime at lower temperatures, $\eta/s$ increases and is well above the KSS bound. We also compare the shear viscosity to the quantum-corrected absorption cross-section of near-extremal black holes, and find agreement.

hep-th↗

arXiv2025

Quantum Corrections in the Low-Temperature Fluid/Gravity Correspondence

Attempts to construct a low-temperature version of the fluid/gravity correspondence have faced obstacles manifested in the form of logarithmic terms in the frequency, $\log(\omega)$, leading to non-local in time constitutive relations for the stress tensor and the charge current. These difficulties can be broadly presented as a breakdown of the hydrodynamic description due to additional infrared modes. We employ new quantum insights into the physics of near-extremal black holes, brought about in the context of Jackiw-Teitelboim gravity, as an effective description of quantum fluctuations in the throat, to revisit the fluid/gravity correspondence at very low temperatures. The quantum corrections naturally include a new length scale, $C$, and an effective action that parametrizes the breaking of near-horizon symmetries. We show that with an appropriate choice of order of limits in the derivative expansion within the low-temperature regime, the $\log(\omega)$ infrared divergence can be resolved. By quantum averaging the infrared Schwarzian modes as an effective extra contribution to the long-wavelength fluid modes, the resulting low-temperature effective fluid description is consistent. We present the dispersion relations for all the relevant hydrodynamic modes. We also revisit the shear viscosity to entropy density ratio and find that at very low temperatures the universal $\frac{1}{4\pi}$ bound is violated due to quantum correction.

hep-th↗

arXiv2025

Explorations of Universality in the Entropy and Hawking Radiation of Non-Extremal Kerr AdS$_4$ Black Holes

We comprehensively discuss various microscopic approaches to the Bekenstein-Hawking entropy for rotating, electrically charged, asymptotically AdS$_4$ non-extremal black holes in gauged supergravity. We apply the covariant phase space formalism to the near-horizon region to obtain a Cardy-formula-based microscopic explanation for the entropy, consistent with the Kerr/CFT correspondence. From the dual boundary CFT point of view, we estimate the free partition function in the matrix model approximation in the high-temperature regime and find qualitative agreement with the supergravity answer. All these different approaches match in the appropriate limits and support the universality of AdS black hole entropy even at high temperatures, far away from extremality. Prompted by the consistency of the results of statistical explanations for the AdS$_4$ black hole entropy, we discuss aspects of the rate of Hawking radiation at high temperatures from the CFT$_2$ perspective and found it to be universally proportional to the horizon area.

hep-th↗

arXiv2025

Quantum Gravity Corrections to the Scalar Quasi-Normal Modes in Near-Extremal Reissener-Nordstr\"{o}m Black Holes

We investigate quantum corrections to scalar quasi-normal modes (QNMs) in the near-extremal Reissner-Nordstr\"om black hole background with quantum correction in the near-horizon AdS$_2\times \mathrm{S}^2$ region. By performing a dimensional reduction, we obtain an effective Jackiw-Teitelboim (JT) gravity theory, whose quantum fluctuations are captured by the Schwarzian action. Using path integral techniques, we derive the quantum-corrected scalar field equation, which modifies the effective potential governing the QNMs. These corrections are extended from the near-horizon region to the full spacetime via a matching procedure. We compute the corrected QNMs using both the third-order WKB method and the Prony method and find consistent results. Our analysis reveals that quantum corrections can lead to substantial shifts in the real parts of QNM frequencies, particularly for small-mass or near-extremal black holes, while the imaginary parts remain relatively stable. This suggests that quantum gravity effects may leave observable imprints on black hole perturbation spectra, which could be potentially relevant for primordial or microscopic black holes.

hep-th↗

arXiv2024

Quantum-Corrected Holographic Wilson Loop Expectation Values and Super-Yang-Mills Confinement

Confinement is a well-known phenomenon in the infrared regime of (supersymmetric) Yang-Mills theory. While both experimental observations and numerical simulations have robustly confirmed its existence, the underlying physical mechanism remains elusive. Unraveling the theoretical origin of confinement continues to be a profound and longstanding challenge in both physics and mathematics. Motivated by recent advances in quantum Jackiw-Teitelboim gravity, we investigate the Wilson loop expectation values in the large-$N$ limit of $\mathscr{N}=4$ super-Yang-Mills theory at finite chemical potential, employing a holographic approach within the background of an extremal AdS$_5$ Reissner-Nordstr\"om black brane. Our results reveal that quantum gravitational fluctuations in the near-horizon region significantly modify the holographic Wilson loop expectation values. These values exhibit an area-law behavior, indicative of a confining quark-antiquark potential. Within this framework, our findings suggest that confinement in the super-Yang-Mills theory arises as a consequence of near-horizon quantum gravity fluctuations in the bulk extremal AdS$_5$ black brane geometry.

hep-th↗

arXiv2024

Quantum Corrections to Holographic Strange Metal at Low Temperature

The holographic approach to the strange metal phase relies on near-extremal asymptotically AdS$_4$ electrically charged black branes with important input from their AdS$_2$ near-horizon throat geometry. Motivated by the current understanding of the role of quantum fluctuations in the throat of near-extremal black holes, we revisit some transport properties. We model quantum gravitational and gauge fluctuations in the throat region by adopting results in Jackiw-Teitelboim gravity, effectively leading to quantum corrections for the dual CFT$_1$ Green's function in the near-horizon infrared region. We use the quantum-corrected Green's function to compute the conductivity for (2+1)-dimensional holographic strange metals and obtain corrections for the DC resistivity and the optical conductivity. We also compare the quantum-corrected holographic approach with results from the complex Sachdev-Ye-Kitaev model and point out qualitative differences. Although experimental detection for the quantum-corrected holographic approach to the DC resistivity requires higher precision than current experimental accuracy, future experiments with improved technologies could detect these quantum corrections. Interestingly, including quantum corrections to the optical conductivity does provide a plausible explanation for the experimental anomalous power-law behavior detected in various strange metals.

hep-th↗

arXiv2023

Hawking Radiation, Entanglement Entropy, and Information Paradox of Kerr Black Holes

The black hole information paradox is a long-standing problem in theoretical physics. Despite some recent progress, many issues remain open and should be clarified. In this paper, we study the information paradox of Kerr black holes and propose a new resolution with precise physical meanings. We compute the time-dependent Hawking radiation rate during the Kerr black hole evaporation using both the gravity and the conformal field theory approaches. Based on the consistent result from both approaches, we formulate the information paradox on top of the time evolution of the entanglement entropy between a Kerr black hole and its Hawking radiation quanta. To resolve the information paradox, we carefully keep track of the ingoing Hawking quanta through the Kerr black hole as a quantum wormhole and microscopically derive the Page curve as a time-delay effect. The result matches the previously obtained semi-classical Page curve and has a natural interpretation in quantum information theory.

hep-th↗

arXiv2023

Arm-Locking Frequency Noise Suppression for Astronomical Middle-Frequency Interferometric Gravitational Wave Observatory

For space gravitational wave (GW) detection, arm locking is a proposal useful in decreasing the frequency noise of the laser sources for current developing space missions LISA and Taiji/TianQin. In this paper, we study the application of arm locking to the Astrodynamical Middle-frequency Interferometric Gravitational wave Observatory (AMIGO) to decrease the frequency noise of laser sources. For AMIGO, the arm-locking technique can suppress the laser frequency noise by three orders of magnitude. The advantage of this is to make the auxiliary noise assignment for AMIGO easier and more relaxed. For the first-generation time-delay interferometry (TDI) configuration, the laser frequency noise contribution is already below the core noise contribution. For the simple Michelson TDI configuration (X0), the arm locking makes the acceleration-thrust scheme, the delay-line scheme, or the combined scheme easier to implement. Within a relatively short period of less than a day (compared to less than twenty days for LISA/Taiji), the Doppler frequency pulling can be efficiently reduced to within $\pm$ 0.001 Hz and does not affect the mission duty cycle much.

astro-ph.IM↗

arXiv2023

Gravitational waves of nonextremal Kerr black holes from conformal symmetry

In the low-energy limit, the near region of a generic Kerr black hole has been conjectured to be holographically dual to a two-dimensional conformal field theory. In this paper, we consider a test object orbiting in the near region of a nonextremal Kerr black hole. We first couple it to a massless scalar field. The resulting scalar radiation at the horizon is computed from the perspectives of gravity and dual conformal field theory. Considering the influence of nonzero temperature, the agreement of both computations is found. Then, we generalize the analysis to the gravitational radiation and find agreement again. The agreement supports the conjectured holography and provides a potential theoretical tool for gravitational wave computations.

hep-th↗

arXiv2023

Universal Cardy-Like Behavior of 3D Partition Functions from Supersymmetric Localization

We investigate 3d $\mathscr{N}=2$ supersymmetric gauge theories on $S^1 \times S^2$ and the corresponding 2d effective field theories arising in the limit of small ratio of radii, $\beta=R_{S^1}/R_{S^2}\to 0$. We evaluate the exact partition function of these theories in the framework of supersymmetric localization on curved backgrounds. As a result, we establish a finite-$N$ map between a particular, superconformal-index-inspired partition function and the topologically twisted index. Taking the large-$N$ limit of the partition functions, we reproduce the entropy functions of either spherically symmetric, magnetically charged, or rotating, electrically charged asymptotically AdS$_4$ black holes. We then recast the problem of evaluating the 3d partition functions directly in the framework of rigid supersymmetry. By carefully tracking the background fields, we find that in the small-$\beta$ limit, the partition functions of these 3d large-$N$ superconformal field theories have a universal behavior related to the coefficients of the R-symmetry or flavor symmetry 2-point current correlation functions, thus obtaining a universal Cardy-like formula for 3d $\mathscr{N}=2$ superconformal field theories.

hep-th↗

arXiv2022

A Non-Unitary Conformal Field Theory Approach to Two-Dimensional Turbulence

Fluid turbulence is a far-from-equilibrium phenomenon and remains one of the most challenging problems in physics. Two-dimensional, fully developed turbulence may possess the largest possible symmetry, the conformal symmetry. We focus on the steady-state solution of two-dimensional bounded turbulent flow and propose a $c=0$ boundary logarithmic conformal field theory for the inverse energy cascade and another bulk conformal field theory in the classical limit $c\rightarrow -\infty$ for the direct enstrophy cascade. We show that these theories give rise to the Kraichnan-Batchelor scaling $k^{-3}$ and the Kolmogorov-Kraichnan scaling $k^{-5/3}$ for the enstrophy and the energy cascades, respectively, with the expected cascade directions, fluxes, and fractal dimensions. We also made some new predictions for future numerical simulations and experiments to test.

hep-th↗

arXiv2022

Logarithmic Corrections to the Entropy of Rotating Black Holes and Black Strings in AdS$_5$

We investigate logarithmic corrections to the entropy of supersymmetric, rotating, asymptotically AdS$_5$ black holes and black strings. Within the framework of the AdS/CFT correspondence, the entropy of these black objects is determined, on the field theory side, by the superconformal index and the refined topologically twisted index of $\mathcal{N}=4$ supersymmetric Yang-Mills theory, respectively. We read off the logarithmic correction from those field-theoretic partition functions. On the gravity side, we take the near-horizon limit and apply the Kerr/CFT correspondence whose associated charged Cardy formula describes the degeneracy of states at subleading order and determines the logarithmic correction to the entropy. We find perfect agreement between these two approaches. Our results provide a window into precision microstate counting and demonstrate the efficacy of low-energy, symmetry-based approaches such as the Kerr/CFT correspondence for asymptotically AdS black objects under certain conditions.

hep-th↗

arXiv2021

Retarded Green's Function from Rotating AdS Black Holes: Emergent CFT$_2$ and Viscosity

Using the AdS/CFT correspondence we consider the retarded Green's function in the background of rotating near-extremal AdS$_4$ black holes. Following the canonical AdS/CFT dictionary into the asymptotic boundary we get a CFT$_3$ result. We also take a new route and zoom in on the near-horizon region, blow up this region and show that it yields a CFT$_2$ result. We argue that the decoupling of the near-horizon region is akin to the decoupling of the near-throat region of a D3-brane, which led to the original formulation of the AdS/CFT correspondence, thus implying that the Kerr/CFT correspondence follows as a decoupling of the standard AdS/CFT correspondence applied to rotating black holes. As a byproduct, we compute the shear viscosity to entropy density ratio for the strongly coupled boundary CFT$_3$, and find that it violates the $1 / (4 π)$ bound.

hep-th↗

arXiv2021

Exact Multi-Instanton Solutions to Selfdual Yang-Mills Equation on Curved Spaces

We find exact multi-instanton solutions to the selfdual Yang-Mills equation on a large class of curved spaces with $SO(3)$ isometry, generalizing the results previously found on $\mathbb{R}^4$. The solutions are featured with explicit multi-centered expressions and topological properties. As examples, we demonstrate the approach on several different curved spaces, including the Einstein static universe and $\mathbb{R} \times$ dS$_3^E$, and show that the exact multi-instanton solutions exist on these curved backgrounds.

hep-th↗

arXiv2021

Toward an Effective CFT$_2$ from $\mathcal{N}=4$ Super Yang-Mills and Aspects of Hawking Radiation

Using $\mathcal{N}=4$ supersymmetric Yang-Mills theory we recover important aspects of the near-extremal thermodynamics of AdS$_5$ black holes including both the outer and the inner horizons with their corresponding entropy and energy. This $\mathcal{N}=4$ supersymmetric Yang-Mills theory approach to black hole thermodynamics leads to an effective CFT$_2$ interpretation similar to the work by Callan and Maldacena. We corroborate this effective CFT$_2$ by implementing a particular near-horizon limit that geometrizes the Virasoro algebras as asymptotic symmetries. Using the effective CFT$_2$ picture, we discuss aspects of the Hawking radiation rate for a region of the near-extremal AdS$_5$ black hole quantum evolution.

hep-th↗