Russia

United Kingdom

Spiros Cotsakis

Erratum to: Friedmann–Lemaître universes and their metamorphoses

We show that the Yang–Baxter (YB) deformed backgrounds of the Wess–Zumino–Witten (WZW) model based on the $$H_{{4}}$$ Lie group can be considered as solutions of the generalized supergravity equations (GSEs). Then, by applying the Poisson–Lie T-duality in the presence of spectator fields, we obtain the non-Abelian target space duals of those models. It is shown that all dual models (except for one model) are integrable and most interestingly, they satisfy the GSEs. As a final remark, we show that all solutions of the GSEs for the original models are trivial.

Iran

Ali Eghbali

Simin Ghasemi-Sorkhabi

Adel Rezaei-Aghdam

Integrable deformed $$H_{{4}}$$ WZW models and their non-Abelian duals as solutions of generalized supergravity equations

This work explores the impact of gravitational cracking on energy exchange within a self-gravitating sphere. For such a purpose, we use the isotropic extension of Einstein’s universe solution, modified through gravitational decoupling using extended minimal geometric deformation, which previously exhibited notable energy exchange behavior between its fluid components. This study bridges two critical concepts in the analysis of static self-gravitating spheres within the framework of General Relativity, traditionally examined independently. Our findings indicate that the onset of fractures markedly influences the energy exchange that sustains the sphere. Compared to a system in hydrostatic equilibrium, gravitational cracking significantly accelerates this exchange, occurring inwardly in the inner regions and outwardly in the outer regions of the disturbed system. Notably, the energy exchange intensifies in the outer regions, becoming more pronounced as the relativistic fluids gain energy density.

Ecuador

S. Medina

J. Andrade

D. Santana

Pakistan

Azerbaijan

Tayyab Naseer

Effect of gravitational cracking on energy exchange in relativistic fluids: a first approach

The hybrid metric-Palatini gravity with Lagrangian density $$L =R+f(\mathcal {R},\mathcal {R}_{\mu \nu }\mathcal {R}^{\mu \nu })$$ is considered, where $\textit{R}$ is the metric Ricci scalar and $$\mathcal {R}_{\mu \nu }$$ is the Palatini Ricci tensor. Contrary to the standard hybrid metric-Palatini theory, because of the term $$\mathcal {R}_{\mu \nu }\mathcal {R}^{\mu \nu }$$ in the action, the model can not be analytically transformed to a scalar-tensor theory. However, on top of a maximally symmetric space-times like the FRW universe, there is a way to solve for a metric compatible connection which we will follow in this paper. The cosmological implications of the resulting model will then be fully considered. The best fit values of the model and cosmological parameters will be obtained by confronting the model with the recent observational data on the Hubble parameter. We will see that the observational data can be explained very good in this model, but, significant deviations from the standard $$\Lambda $$ CDM model could be seen in derivatives of the Hubble parameter $\textit{q}$, $\textit{j}$ and $\textit{s}$. We will perform a statefinder analysis for the model and show that its behavior differs from that of the $$\Lambda $$ CDM model. Also, we will consider the recently proposed $\textit{Om}$ diagnostics to categorize the dark energy type of the model and obtain the $$\omega $$ -varying alternative of the model that mimics the Hubble flow.

Shahab Shahidi

Shiva Kayedi

Cosmological implications of hybrid metric-Palatini $$f(\mathcal {R},\mathcal {R}_{\mu \nu }\mathcal {R}^{\mu \nu })$$ gravity

The greybody factor of quantum Oppenheimer–Snyder-de Sitter spacetime is examined in this study. We determined the effective potential and examined its role under several physical factors, such as mass, rotational momentum, and quantum parameters, by transforming the Klein–Gordon equation into a Schrödinger-like wave equation through tortoise coordinates. Our results show that the absorption and scattering of massless scalar fields are strongly affected by the decrease in the effective potential caused by an increase in the quantum parameter. It is observed that the appearance of the quantum factor significantly increases the Schwarzschild–de Sitter black hole’s effective potential. We discovered that waves behave differently at the event horizon, with lower-frequency waves bouncing off possible impediments and higher-frequency waves more readily penetrating them. Our investigation of the greybody component further demonstrates the significance of effective potential in wave transmission and reflection, demonstrating a substantial link between wave frequency and emission rates. In order to understand particle behavior at black hole horizons, it is shown that higher-frequency waves are more likely to pass through potential barriers, whereas lower-frequency waves prefer to reflect. This study advances our understanding of quantum field theory in curved spacetime and black hole thermodynamics, particularly in relation to scalar field interactions with black holes.

China

Zhiwei Lv

Sulaman Shaukat

Kuwait

Orhan Donmez

Faisal Javed

Arfa Waseem

Quantum effects on greybody factor via quantum Oppenheimer–Snyder-dS spacetime

Within the framework of the phenomenological type-I seesaw mechanism, heavy singlet Majorana neutrinos are introduced to explain the origin of neutrino masses. We propose a novel search strategy for these heavy Majorana neutrinos through the lepton-number-violating process $$e^{-}p \rightarrow jN\rightarrow j(\mu ^{+}W^{-})$$ at the Future Circular electron-hadron Collider (FCC-eh), which would utilize a 60 GeV electron beam colliding with a 50 TeV proton beam. Focusing on the decay mode $$N\rightarrow \mu ^{+}W^{-}\rightarrow \mu ^{+}J$$ , where $\textit{J}$ denotes a fat-jet from the hadronic decays of a highly boosted $\textit{W}$ boson, we investigate the discovery potential of this signature. By performing a detailed signal-to-background analysis and detector simulations, we present $$2\sigma $$ exclusion limits and $$5\sigma $$ discovery reaches in terms of parameter space regions.

Jie-Fen Shen

Yan-Ju Zhang

Lin Han

Searching for heavy majorana neutrinos at the FCC-eh via lepton-number-violating and fat-jet final states

We investigate the classical and quantum dynamics of $\textit{f}$($\textit{R}$) gravity’s rainbow in the presence of a perfect fluid, employing Schutz’s formalism to establish a well-defined notion of time. In the classical regime, we derive and solve the equations of motion, obtaining both analytical and numerical solutions. Through canonical quantisation, we formulate the Schrödinger–Wheeler–DeWitt (SWD) equation for the quantum model. By solving its eigenfunctions, we construct the wave function of the Universe and obtain analytical solutions in scenarios dominated by stiff matter. Our results highlight the impact of rainbow gravity on quantum evolution, particularly in modifying the structure of the wave function and shaping the transition from the quantum to the classical regime.

Chile

Andrés Burton-Villalobos

Giovanni Otalora

Manuel Gonzalez-Espinoza

Yoelsy Leyva

Classical and quantum cosmology of $\textit{f}$($\textit{R}$) gravity’s rainbow in Schutz’s formalism

Utilizing the Tomita–Takesaki modular theory, we derive a closed-form analytic expression for the Araki–Uhlmann relative entropy between a single-mode squeezed state and the vacuum state in a free relativistic massive scalar Quantum Field Theory within wedge regions of Minkowski spacetime. Similarly to the case of coherent states, this relative entropy is proportional to the smeared Pauli–Jordan distribution. Consequently, the Araki–Uhlmann entropy between a single-mode squeezed state and the vacuum satisfies all expected properties: it remains positive, increases with the size of the Minkowski region under consideration, and decreases as the mass parameter grows.

Brazil

Marcelo Guimaraes

Itzhak Roditi

Silvio Sorella

Arthur Vieira

Relative entropy of single-mode squeezed states in Quantum Field Theory

In the phase space perspective, scalar field slow roll inflation is described by a heteroclinic orbit from a saddle type fixed point to a final attractive point. In many models the saddle point resides in the scalar field asymptotics, and thus for a comprehensive view of the dynamics a global phase portrait is necessary. For this task, in the literature one mostly encounters dynamical variables that either render the initial or the final state singular, thus obscuring the full picture. In this work we construct a hybrid set of variables which allow the depiction of both the initial and final states distinctly in nonsingular manner. To illustrate the method, we apply these variables to portray various interesting types of scalar field inflationary models like metric Higgs inflation, metric Starobinsky inflation, pole inflation, and a nonminimal Palatini model.

Estonia

Laur Järv

Dmitri Kraiko

Global portraits of inflation in nonsingular variables

In this work, we constrain the bounce energy scale $$\rho _{s\downarrow }^{1/4}$$ in a generic bouncing-cosmology framework using the probable nanohertz stochastic gravitational-wave signal from NANOGrav 15-year, EPTA DR2, PPTA DR3, and IPTA DR2. A full Bayesian fit to the analytic stochastic-GW spectrum, for the first time, reveals two distinct posterior branches in $$\bigl (\rho _{s\downarrow }^{1/4},\,w_{1}\bigr )$$ : one near $$w_{1}\approx 0.3$$ and another at $$w_{1}\gg 1$$ , where $$w_{1}$$ is the contraction-phase equation of state. We find that current PTA data strongly favor the bounce hypothesis over six conventional SGWB sources, while yielding smaller Bayes factors than its parent dual inflation–bounce scenario as the bounce scale is explicit. Both branches imply $$\rho _{s\downarrow }^{1/4}>M_\textrm{pl}$$ , indicating a trans-Planckian probe. In particular, the $$w_{1}\gg 1$$ branch violates the dominant energy condition, motivating novel early-Universe physics. These results, confirmed by an accelerated machine learning approach, offer a rare observational window into UV completions of cosmology.

Junrong Lai

Changhong Li

Probing the bounce energy scale in bouncing cosmologies with pulsar timing arrays