We study the quantum Ising model on (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>2</mn><mo>+</mo><mn>1</mn></mrow></math>)-dimensional anti-de Sitter space using matrix product states (MPS) and matrix product operators (MPOs). We explore the bulk phase diagram of the theory on regular tessellations of hyperbolic space with coordination number seven and find disordered and ordered phases separated by a phase transition. We find that the boundary-boundary spin correlation function exhibits power law scaling deep in the disordered phase of the Ising model consistent with holography. At the critical point, we find the boundary entanglement entropy scales logarithmically with subsystem size but away from this, we see a linear scaling. In comparison, the full system exhibits a volume law scaling, which is expected in chaotic and/or highly connected systems. We also measure out of time ordered correlators (OTOCs) to explore the scrambling behavior of the theory.

United States

Abhishek Samlodia

Simon Catterall

Alexander F. Kemper

Yannick Meurice

Goksu Can Toga

Quantum Ising model on (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>2</mn><mo>+</mo><mn>1</mn></mrow></math>)-dimensional anti–de Sitter space using tensor networks

We study the double cone geometry proposed by Saad-Shenker-Stanford in de Sitter space. We show that with the inclusion of static patch observers, the double cone leads to a linear ramp consistent with random matrix behavior, where the ramp comes from the relative timeshift between two clocks sitting at opposite static patches.

China

Zhenbin Yang

Yuzhen Zhang

Wenwen Zheng

Remarks on the de Sitter double cone

Recently, Ref. [1] proved the energy conservation formula for particle decay in Kerr spacetime: <math altimg='si10.svg'><mrow><msub><mi>m</mi><mn>0</mn></msub><mo linebreak='goodbreak'>=</mo><msub><mi>m</mi><mn>1</mn></msub><mspace width='0.16em' /><msub><mi>&#947;</mi><mn>01</mn></msub><mo linebreak='goodbreak'>+</mo><msub><mi>m</mi><mn>2</mn></msub><mspace width='0.16em' /><msub><mi>&#947;</mi><mn>02</mn></msub></mrow></math>, where <italic>m</italic> <inf>0</inf> is the initial particle, <italic>m</italic> <inf>1</inf> and <italic>m</italic> <inf>2</inf> are the decay products, and <italic>&#947;</italic> <inf>01</inf>, <italic>&#947;</italic> <inf>02</inf> are the relative Lorentz factors between particle 0 and particle 1, and between particle 0 and particle 2, respectively. This conclusion shows that the particle splitting process exhibits a mass defect, which is converted into kinetic energy in the center-of-mass frame. In this paper, we extend it to Kerr&#8211;de Sitter spacetime. Through derivation, we obtain the same energy conservation result as in Kerr spacetime. In addition, we find that, for a fixed cosmological constant, a larger decay radius leads to a larger specific angular momentum of particle 0, larger masses of particles 1 and 2, a smaller absolute value of their specific energy, smaller relative Lorentz factors among the three particles, and smaller four-velocities of the three particles. For a fixed decay radius, a larger cosmological constant leads to larger specific angular momenta of particle 0 and particle 2, smaller masses of particles 1 and 2, a larger absolute value of their specific energy, larger relative Lorentz factors among the three particles, and larger four-velocities of the three particles.

Ke Wang

Xiao-Xiong Zeng

Particle decay and energy conservation in Kerr-de Sitter spacetime

The observable Universe has undergone periods of expansion that are well approximated by de Sitter (dS) space. Still lacking is a quantum-mechanical description of dS spacetime, both globally and when restricted to the static patch. We develop a novel prescription, to the best of our knowledge, for computing holographic complexity in the dS static patch to determine its microscopic features. Specifically, we propose that the natural candidate for dS complexity is the volume of extremal “timelike” surfaces restricted to the static patch, anchored to the cosmological horizon or an observer worldline. Our anchoring prescription provides a clear definition of a reference state, overcoming a common ambiguity in prior definitions of de Sitter holographic complexity. The late-time growth of our complexity functional is linear and proportional to the number of degrees of freedom associated with the cosmological horizon and, therefore, does not exhibit hyperfast growth. Our results imply the dS static patch is characterized by a quantum-mechanical system, with a finite-dimensional Hilbert space whose evolution is governed by a chaotic Hamiltonian.

Iceland

Vyshnav Mohan

Sweden

Watse Sybesma

de Sitter complexity grows linearly in the static patch

We investigate a static, asymptotically flat black hole whose central region approaches a de Sitter vacuum. The geometry is controlled by the ADM mass <italic>M</italic> <inf>0</inf> and a core scale <italic>R</italic>, and is generated by an exponentially decaying anisotropic source. After clarifying the stress tensor and the horizon structure, we study scalar-field perturbations, greybody transmission, Hawking emission and the optical image produced by an optically thin infalling flow. The horizon analysis shows that two horizons exist below the critical value <italic>R</italic>/ <italic>M</italic> <inf>0</inf>&#8239;&#8771;&#8239;0.7768, where they merge into an extremal configuration. Increasing the core scale lowers the peak of the scalar effective potential and shifts the quasinormal spectrum away from the Schwarzschild value, with the largest fractional deviations occurring for low multipoles and higher overtones within the WKB domain of validity. The greybody bound indicates stronger filtering as the core becomes more extended, while the QNM&#8211;greybody correspondence gives a complementary estimate of the transmission probability in the eikonal regime. The Hawking temperature decreases as the extremal configuration is approached, suppressing the emission rate and shifting its maximum to lower frequencies. For a simple optically thin infalling flow, ray tracing shows a small decrease in the apparent shadow scale and in the peak intensity as the core scale is increased.

Azerbaijan

Iran

Brazil

N. Heidari

A.A. Araújo Filho

Russia

V. Vertogradov

Türkiye

A. Övgün

Signatures of a de Sitter-core black hole in ringing, transmission and optical appearance

We study the stability of $\textit{d}$-dimensional ($\textit{d}$ = 3, 4, 5) de Sitter and Minkowski spacetimes within the framework of semiclassical gravity sourced by a strongly coupled quantum field with a gravity dual. Our stability results are derived from a careful analysis of the $\textit{d}$-dimensional Lichnerowicz equation with mass-squared $\textit{m}$ and of semiclassical equations involving the dimensionless parameter $\textit{γ}$ . For $\textit{d}$ = 3, we find that Minkowski spacetime is always unstable against perturbations, whereas de Sitter spacetime becomes stable when a dimensionless parameter $\textit{γ}$ exceeds a critical value. In $\textit{d}$ = 4, both de Sitter and Minkowski spacetimes become unstable when the parameter $\textit{γ}$ exceeds its critical value. In contrast, in $\textit{d}$ = 5, de Sitter and Minkowski spacetimes remain stable for almost all values of the parameter $\textit{γ}$ , except for a regime in which higher-curvature corrections become comparable to the Einstein tensor.

Japan

Akihiro Ishibashi

Kengo Maeda

Takashi Okamura

Instability thresholds for de Sitter and Minkowski spacetimes in holographic semiclassical gravity

In this paper, we would like to investigate whether a generalized Einsteinian cubic gravity, in which three possible cubic interactions $$\mathcal{P}$$ , $$\mathcal{C}$$ , and $$\mathcal{C}'$$ are treated on an equal footing, admits a de Sitter solution as its stable cosmological solution. As a result, we are able to confirm the existence of the corresponding de Sitter solution for this gravity by solving analytically its field equations. Remarkably, only the cubic interaction $$\mathcal{P}$$ gives rise to the existence of the de Sitter solution. Then, we convert the field equations into the corresponding dynamical system for a stability analysis purpose. A fixed point of this dynamical system is found and shown to be equivalent to the obtained de Sitter solution. However, the perturbed dynamical system turns out to be incomplete, leaving undetermined information of the stability of the fixed point (or equivalently the de Sitter solution). Fortunately, we show that this loophole can be cured once the well-known Starobinsky term $$R^2$$ is introduced into the action of the generalized Einsteinian cubic gravity, despite the fact that it contributes nothing to the value of the de Sitter solution.

Vietnam

Tuan Do

Effect of $$R^2$$ on the stability of de Sitter solution of the generalized Einsteinian cubic gravity

We construct a manifestly covariant and coordinate-free plane-wave representation of scalar two-point functions in $\textit{d}$-dimensional anti-de Sitter spacetime. The construction is based on a new class of holomorphic plane waves defined globally on the universal covering of the AdS via chiral cones in the complex null cone. Imposing AdS invariance, locality, positive definiteness and a spectral condition, we obtain integral representations as superpositions over relative homology cycles, reproducing the standard maximally analytic solutions in terms of Legendre functions of the second kind. In Poincaré coordinates, the two-point functions diagonalize into a Källén-Lehmann superposition of ($\textit{d}$ – 1)-dimensional Minkowski correlators where the weight is a product of Bessel functions. This diagonalization clarifies the relation between Euclidean and Lorentzian AdS quantum field theory and allows Wick rotation of Euclidean Feynman diagrams to Lorentzian integrals supported on a single Poincaré patch while preserving full AdS covariance.

Italy

Ugo Moschella

Two point functions and quantum fields in the anti-de Sitter universe

Recently, energy extraction from rotating black holes via the magnetic reconnection has attracted significant attention. In this study, we employ the magnetic reconnection mechanism to investigate energy extraction from a novel Kerr-de Sitter black hole and properly compare the results with those from a conventional Kerr-de Sitter black hole in both circular orbits and the plunging region. Our research demonstrates that, under the condition of smaller X-point location or a larger cosmological constant, the new Kerr-de Sitter black hole exhibits superior energy extraction performance compared to the conventional one when employing the magnetic reconnection. Notably, at lower values of the spin parameter <italic>a</italic>/ <italic>M</italic>, the new black hole shows a distinct advantage over the conventional Kerr-de Sitter black hole.

Jing-Yang Liu

Bo Zhao

Chao-Hui Wang

Energy extraction from a novel Kerr-de Sitter black hole via magnetic reconnection

In this article, we test the validity of the weak cosmic censorship conjecture (wCCC) in the background of a quantum Kerr–de Sitter (qKdS) black hole, incorporating exact backreaction from quantum matter fields. Using a test particle approach, we analyze whether an extremal qKdS black hole can be over-extremized to expose a naked singularity. Our results indicate that the black hole remains stable against horizon-destroying processes induced by infalling matter. Quantum corrections enhance the horizon’s robustness rather than destabilize it, offering further evidence that wCCC remains preserved in the presence of quantum effects.

India

Ankit Anand

Ankur Dey

Kerr–de Sitter black holes: quantum aspects and cosmic censorship conjecture