<p>We study nonequilibrium initial states of quantum fields in curved spacetime and develop a framework for describing global quenches as unitary perturbations of the initial density matrix. Using the Keldysh-Schwinger functional integral, we derive expressions for postquench correlators in arbitrary geometries and apply the method to both Minkowski and de Sitter backgrounds. In flat space, the approach reproduces the known relaxation behavior for massive fields and reveals qualitatively distinct dynamics in the massless case. In de Sitter space, we find that the late-time decay of quench-induced corrections depends sensitively on the mass and may influence the behavior of cosmological observables such as the power spectrum. The framework also extends straightforwardly to non-Gaussian initial states, providing a basis for future studies of loop effects and primordial non-Gaussianities.</p>

Russia

Ivan A. Belkovich

Damir Sadekov

Gleb S. Zverev

Global quenches and correlator dynamics in de Sitter space

We generalize the de Sitter static patch holographic proposal and the bilayer holographic entanglement entropy prescription to de Sitter geometries containing a bubble of smaller positive or vanishing cosmological constant. When the causal patch of an observer at the center of the bubble overlaps with the “parent” de Sitter region, we propose that the full spacetime can be holographically encoded on two holographic screens. The leading geometrical entanglement entropy between the two screens, which can be constant or time-dependent in some cases, never exceeds the Gibbons-Hawking entropy associated with the “parent” de Sitter space. When the causal patch of the observer at the center of the bubble is causally disconnected from the “parent” de Sitter region, the holographic proposal no longer applies, and more than two holographic screens are required to encode the whole spacetime.

Cyprus

Anastasios Irakleous

France

François Rondeau

Nicolaos Toumbas

Holography for de Sitter bubble geometries

<p>This work aims to develop a global formulation for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">N</mi><mo>=</mo><mn>2</mn></math> harmonic/projective anti–de Sitter (AdS) superspace <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>AdS</mi><mrow><mn>4</mn><mo stretchy="false">|</mo><mn>8</mn></mrow></msup><mo>×</mo><msup><mi>S</mi><mn>2</mn></msup><mo>≃</mo><msup><mi>AdS</mi><mrow><mn>4</mn><mo stretchy="false">|</mo><mn>8</mn></mrow></msup><mo>×</mo><mi mathvariant="double-struck">C</mi><msup><mi>P</mi><mn>1</mn></msup></math> that allows for a simple action of superconformal (and hence AdS isometry) transformations. First of all, we provide an alternative supertwistor description of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">N</mi></math>-extended AdS superspace in four dimensions, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>AdS</mi><mrow><mn>4</mn><mo stretchy="false">|</mo><mn>4</mn><mi mathvariant="script">N</mi></mrow></msup></math>, which corresponds to a realization of the connected component <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi mathvariant="sans-serif">O</mi><mi mathvariant="sans-serif">S</mi><mi mathvariant="sans-serif">p</mi></mrow><mrow><mn>0</mn></mrow></msub><mo stretchy="false">(</mo><mi mathvariant="script">N</mi><mo stretchy="false">|</mo><mn>4</mn><mo>;</mo><mi mathvariant="double-struck">R</mi><mo stretchy="false">)</mo></mrow></math> of the AdS isometry supergroup as <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mrow><mi mathvariant="sans-serif">S</mi><mi mathvariant="sans-serif">U</mi></mrow><mo stretchy="false">(</mo><mn>2</mn><mo>,</mo><mn>2</mn><mo stretchy="false">|</mo><mi mathvariant="script">N</mi><mo stretchy="false">)</mo><mo>∩</mo><mrow><mi mathvariant="sans-serif">O</mi><mi mathvariant="sans-serif">S</mi><mi mathvariant="sans-serif">p</mi></mrow><mo stretchy="false">(</mo><mi mathvariant="script">N</mi><mo stretchy="false">|</mo><mn>4</mn><mo>;</mo><mi mathvariant="double-struck">C</mi><mo stretchy="false">)</mo></mrow></math>. The proposed realization yields the following properties: (i) <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>AdS</mi><mrow><mn>4</mn><mo stretchy="false">|</mo><mn>4</mn><mi mathvariant="script">N</mi></mrow></msup></math> is an open domain of the compactified <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">N</mi></math>-extended Minkowski superspace, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mover accent="true"><mi mathvariant="double-struck">M</mi><mo stretchy="false">¯</mo></mover><mrow><mn>4</mn><mo stretchy="false">|</mo><mn>4</mn><mi mathvariant="script">N</mi></mrow></msup></math>; (ii) the infinitesimal <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">N</mi></math>-extended superconformal transformations naturally act on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>AdS</mi><mrow><mn>4</mn><mo stretchy="false">|</mo><mn>4</mn><mi mathvariant="script">N</mi></mrow></msup></math>; and (iii) the isometry transformations of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>AdS</mi><mrow><mn>4</mn><mo stretchy="false">|</mo><mn>4</mn><mi mathvariant="script">N</mi></mrow></msup></math> are described by those superconformal transformations which obey a certain constraint. The obtained results for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>AdS</mi><mrow><mn>4</mn><mo stretchy="false">|</mo><mn>4</mn><mi mathvariant="script">N</mi></mrow></msup></math> are then applied to develop a supertwistor formulation for an AdS flag superspace <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>AdS</mi><mrow><mn>4</mn><mo stretchy="false">|</mo><mn>8</mn></mrow></msup><mo>×</mo><msub><mi mathvariant="double-struck">F</mi><mn>1</mn></msub><mo stretchy="false">(</mo><mn>2</mn><mo stretchy="false">)</mo></math> that we identify with the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">N</mi><mo>=</mo><mn>2</mn></math> harmonic/projective AdS superspace. This construction makes it possible to read off the superconformal and AdS isometry transformations acting on the analytic subspace of the harmonic superspace.</p>

Australia

Nowar E. Koning

Sergei M. Kuzenko

Anti–de Sitter flag superspace

We construct static, spherically symmetric wormhole solutions with a nontrivial redshift function, inspired by noncommutative geometry, in which point sources are replaced by Gaussian smearing of minimal length, yielding a regular shape function. Within this framework, we derive model-independent relations that isolate the role of the redshift function in controlling the stress-energy components and the violation of the null energy condition (NEC). Negative or suitably tuned redshifts confine the exotic matter to a thin neighbourhood of the throat. We then reformulate this redshift engineering in matter terms through a quasi-de Sitter equation of state (EOS) with localised Gaussian or Lorentzian perturbations, obtaining minimally exotic wormholes that are regular, horizon-free, and asymptotically flat. Finally, we extend the analysis to a Chaplygin-like EOS, introducing a nonlinear coupling between pressure and density that yields redshift wells with possible local blueshift regions and tunable anisotropies governed by a certain nonlinearity parameter. Together, these results provide a unified and physically transparent framework for constructing traversable noncommutative-geometry-inspired wormholes with controlled, spatially localised exotic matter content.

United Arab Emirates

Davide Batic

Denys Dutykh

Mark Essa Sukaiti

Noncommutative geometry-inspired wormholes supported by quasi-de Sitter and Chaplygin-like equations of state

We discuss and extend some aspects pertaining to the canonical quantisation of JT gravity in de Sitter space, including the problem of time and the construction of a Hilbert space. We then extend this discussion to other two dimensional models obtained by changing the dilaton potential and show that the canonical quantisation procedure can be carried out for a large class of such models. Some discussion leading towards a path integral understanding for states, other than the Hartle Hawking state, is also included here, along with comments pertaining to Holography and the entropy of de Sitter space.

India

Indranil Dey

Kanhu Nanda

Akashdeep Roy

Japan

Sunil Sake

Sandip Trivedi

JT gravity in de Sitter space and its extensions

The Hilbert-Schmidt measure is a useful geometric tool used to investigate the properties on the manifold of mixed Gaussian states in multimode continuous variable quantum systems. In this work, we study the relationship between the scalar curvature and quantum entanglement across causally disconnected regions (open charts) in de Sitter spacetime. We first consider a two-mode squeezed state shared between Alice and Bob, where the Gaussian channel models the effects of spacetime curvature. We employ logarithmic negativity as a witness for quantum entanglement. We study the impact of the mass, parameter <italic>p</italic> and squeezing parameter on the scalar curvature and entanglement. We find an interesting interplay between scalar curvature and entanglement for certain values of the mass and parameter <italic>p</italic>. By varying <italic>p</italic>, we thus explore how information geometry and entanglement are influenced by both ultraviolet and infrared modes. Moreover, the relationship between scalar curvature and entanglement is discussed under the influence of various parameters characterizing the geometric system under consideration.

Morocco

Mohamed Amazioug

Mohammed Daoud

Scalar curvature and entanglement of the Gaussian state manifold in de Sitter spacetime

Based on the Comisso–Asenjo mechanism, we investigate the kinematic images of plasma before and after magnetic reconnection in Kerr–Anti-de Sitter(Kerr–AdS) black holes. Following a brief review of the Comisso–Asenjo process in Kerr–AdS black holes, we introduce the hotspot model and the imaging method. Building upon these foundational theories, we obtain the trajectory of the plasma and the temporal evolution of the hotspot images. It is found that there are three flares within the observing time, which is driven by the Comisso–Asenjo mechanism. We also discuss the influence of the cosmological parameter on the hotspot imaging. The results indicate that the hotspot image enlarges as the absolute value of $$\Lambda $$ increases, demonstrating that the cosmological constant significantly affects the hotspot.

China

Xiao-Xiong Zeng

Ke Wang

Hotspot image driven by magnetic reconnection in Kerr–anti de Sitter black holes

In this study, we analyze $\textit{f}$($\textit{R}$) gravity employing the $$ f(R) = R+ \alpha _1 R^p - \alpha _2 R^{-q} $$ model within the Friedmann–Lemaître–Robertson–Walker (FLRW) background. We derive the Friedmann equations via modified gravity action and subsequently reexpress them in terms of the standard Friedmann equations. Our investigation explores the behavior of a bouncing cosmological model within this modified gravity context, offering a potential solution to the singularity problem encountered in the standard Big Bang cosmology. We represent cosmological parameters as functions of cosmic time and scrutinize the conditions for a cosmic bounce. Additionally, we reconstruct the $\textit{f}$($\textit{R}$) gravity model using the redshift parameter and graphically present cosmological parameters as functions of redshift. These plots reveal an accelerated nature of Universe expansion. Furthermore, we reconstruct $\textit{f}$($\textit{R}$) gravity models for scale factors, $$a(t) = e^{e^{\lambda t}}$$ which exhibits the bouncing behavior. Finally, we investigated the stability scenario by examining the sound speed. The resulting graph of sound speed plotted against redshift confirms late-time stability.

Pakistan

M. Ilyas

Saudi Arabia

Khalid Masood

South Korea

Nehad Shah

Dynamical analysis of bouncing cosmology in the Capozziello–De Laurentis model of $\textit{f}$($\textit{R}$) gravity

We study perturbative unitarity bounds on the field-space curvature in de Sitter spacetime, using the momentum-space entanglement approach recently proposed by Duaso Pueyo, Goodhew, McCulloch, and Pajer. As an illustration, we perform a perturbative computation of the purity in two-scalar models and compare the resulting unitarity bounds with those obtained via a flat space approximation. In particular, we find that perturbative unitarity imposes an upper bound on the field-space curvature of the Hubble scale order, in addition to a bound analogous to the flat space result. This reflects the thermal nature of de Sitter spacetime. We also discuss generalizations to higher-dimensional field spaces.

Qianhang Cai

Tomoya Inada

Masataka Ishikawa

Kanji Nishii

Toshifumi Noumi

Perturbative unitarity bounds on field-space curvature in de Sitter spacetime: purity vs scattering amplitude

In this study, we investigate a scenario based on the effects of the Loop Quantum Gravity (LQG) on the electromagnetic sector of the Standard Model of Fundamental Interactions and Particle Physics (SM). Starting from a post-Maxwellian version of electromagnetism that includes LQG effects, we derive and discuss the influence of LQG parameters on classical quantities such as the components of the stress-tensor. Furthermore, we inspect the propagation of electromagnetic waves and examine the optical properties of the QED vacuum in this scenario. Among these, we contemplate the combined effect of the LQG parameters and a homogeneous background magnetic field on the propagation of electromagnetic waves by considering issues such as group velocities and refractive indices of the QED vacuum, in detail. Finally, with the aid of the previously analyzed LQG-extended photonic dispersion relations, we re-discuss the kinematics of the Compton effect and conclude that an interesting nonlinear profile emerges in the wavelengths of the incoming and deflected photons.

Brazil

P.A.L. Mourão

G.L.L.W. Levy

J.A. Helayël-Neto

Reassessing aspects of LQG-modified dispersion relations of photons * P. A. L. Mourão is support by CAPES. G. L. L. W. L. Levy is support by the Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), Grant No. E-26/202.437/2024.