The processes of $ K^-p \to \pi^0 \pi^0 \Sigma^0 $ and $ K^- p \to \pi^0 \Lambda(1405) $ are studied within the effective Lagrangian approach. In addition to the “background” contribution from the $\textit{u}$-channel nucleon pole term, the contribution from the $ \Sigma(1660) $ resonance with spin-parity $ J^P=1/2^+ $ is also considered. For the $ K^-p \to \pi^0 \pi^0 \Sigma^0 $ reaction, we perform a calculation for the total and differential cross sections by considering the contribution from the $ \Sigma(1660) $ intermediate resonance decaying into $ \pi^0 \Lambda(1405) $ with $ \Lambda(1405) $ decaying into $ \pi^0 \Sigma^0 $ . With our model parameters, the available experimental data on both the $ K^-p \to \pi^0 \pi^0 \Sigma^0 $ and $ K^- p \to \pi^0 \Lambda(1405) $ reactions can be fairly well reproduced. It is shown that the contribution from the $ \Sigma(1660) $ resonance is necessary, and that these experimental measurements could be used to determine some properties of the $ \Sigma(1660) $ resonance.

China

Xing-Yi Ji

Si-Wei Liu

Wen-Tao Lyu

De-Min Li

En Wang

Ju-Jun Xie

Role of Σ(1660) in the $\textit{K}$ $^{−}$ $\textit{p}$ → $\textit{π}$ $^{0}$ $\textit{π}$ $^{0}$Σ$^{0}$ reaction * Supported by the National Key R&D Program of China (2023YFA1606703, 2024YFE0105200), the National Natural Science Foundation of China (12435007, 12475086, 12192263, 12361141819, 1252200936), the Natural Science Foundation of Henan (232300421140, 252300423951) and the Zhengzhou University Young Student Basic Research Projects (PhD students) (ZDBJ202522)

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

A modified gravitational model whose action is given by an arbitrary function of the Ricci scalar, the matter Lagrangian density, a scalar field, and its kinetic term is investigated as an extension of the gravitational sector including an additional dynamical degree of freedom. Within this framework, the causal structure of rotating cosmological solutions is analyzed by considering Gödel and Gödel-type spacetimes as background geometries used as theoretical probes of the model consistency. Different matter sources are examined, including a perfect fluid and scalar-field configurations. It is found that the standard Gödel metric is not compatible with the scalar sector of the theory unless the model reduces to the General Relativity limit. In contrast, Gödel-type geometries admit a wider class of solutions whose causal properties depend on the model parameters and on the matter content. In particular, perfect-fluid sources may lead to either causal or noncausal configurations, whereas scalar-field configurations constrain the geometry to the causal limit, preventing the formation of closed timelike curves, highlighting that the scalar field plays a nontrivial dynamical role distinct from that of a cosmological constant.

Brazil

L. Evangelista

M. Silva

J. Moretti

A. Santos

Causality and its violation in $$f(R,\mathcal {L}_m,\phi ,g^{\mu \nu }\nabla _\mu \phi \nabla _\nu \phi )$$ gravity

In this paper we consider the localization of the gravitino field on a codimension-one thick brane within the framework of $\textit{f}$($\textit{R}$, $\textit{Q}$, $\textit{P}$) gravity. First, setting $$F(\phi ) = \phi $$ , we derive the potential functions for various parameters. Under appropriate coupling parameters, we can find the localized zero mode and some resonance states. Furthermore, we use these resonance states as initial data to investigate the evolution of the gravitino resonances. It can be observed that various parameters on the brane affect the evolution duration. We focus on comparing the localization behavior of the gravitino field on the brane for the cases with $$k=0$$ and $$k\ne 0$$ .

Xiang-Nan Zhou

Miao Wang

Zhi-Chao Duan

Localization of gravitino field on $\textit{f}$($\textit{R}$, $\textit{Q}$, $\textit{P}$) brane

One of the most popular competitors to the CDM paradigm as an explanation for the late-time acceleration of the universe is the modification of general relativity (GR), with models such as <italic>f</italic>( <italic>R</italic>) gravity among the main motivations. In this study, we consider an exponential <italic>f</italic>( <italic>R</italic>) gravity model as a possible extensions of the GR. The extra scalar degrees of freedom and their effects on the cosmic expansion and structure formation are continuously considered in this scenario. By combining the PPS, BBN, CC, DESI-DR2, and CMB datasets, we imposed limitations on this model. We performed a detailed statistical analysis of the free model parameter <italic>b</italic> together with the standard cosmological parameters. Our analysis yields values of <italic>H</italic> <inf>0</inf> that are slightly lower than those obtained in &#923;CDM, indicating no significant relaxation of the <italic>H</italic> <inf>0</inf> tension. In contrast, the model predicts systematically higher values of <italic>S</italic> <inf>8</inf>, leading to a moderate alleviation of the <italic>S</italic> <inf>8</inf> tension by up to &#8239;&#8764;&#8239;1.2 <italic>&#963;</italic> when late-time datasets are included. Overall, these results demonstrate that although the considered <italic>f</italic>( <italic>R</italic>) gravity model does not resolve all cosmological tensions simultaneously, it provides a consistent improvement in the description of large-scale structure formation.

India

Saurabh Verma

Archana Dixit

Anirudh Pradhan

M.S. Barak

Testing exponential <italic>f</italic>( <italic>R</italic>) gravity with CMB, DESI-DR2, and supernova data

In this work, we investigate the internal structure and physical features of compact stars in the background of modified gravity, specifically within <italic>f</italic>( <italic>R, G</italic>) gravity, where <italic>R</italic> represents the Ricci scalar and <italic>G</italic> denotes the Gauss&#8211;Bonnet invariant. The interior spacetime of the stellar configuration is described by the Kohler&#8211;Chao metric, which provides a suitable geometric representation for dense compact objects. Our analysis considers ten well-known compact star candidates, namely Her X-1, SAX J1808.4-3658, SMC X-1, LMC X-4, Cen X-3, 4U 1820-30, PSR J1903+327, 4U 1608-52, Vela X-1, and PSR J1614-2230. To incorporate higher-curvature effects, the functional form of <italic>f</italic>( <italic>R, G</italic>) is decomposed into two independent contributions, <italic>f</italic> <inf>1</inf>( <italic>R</italic>) and <italic>f</italic> <inf>2</inf>( <italic>G</italic>), representing the Ricci scalar and Gauss&#8211;Bonnet sectors, respectively. For the <italic>R</italic>-dependent part, we adopt the Hu&#8211;Sawicki type model, while three different models, namely logarithmic and power-law models, are considered for the Gauss&#8211;Bonnet contribution. This reconstruction gives three distinct modified gravity models used to study the different features of compact stellar configurations. Using these models, we study the physical viability of the stellar structures by examining anisotropic pressure content, equilibrium scenario through the Tolman&#8211;Oppenheimer&#8211;Volkoff equation, energy conditions, and stability conditions. The obtained results demonstrate that the energy density, radial pressure, tangential pressure, and anisotropy remain well-behaved throughout the stellar interior for all considered stars. The analysis indicates that the proposed <italic>f</italic>( <italic>R, G</italic>) models together with the Kohler&#8211;Chao interior solution provide physically consistent and stable configurations for compact stars within the modified gravity framework.

Saudi Arabia

Ahdab K. Althukair

Azerbaijan

Pakistan

M. Ilyas

Greece

Russia

Euaggelos E. Zotos

Kohler-Chao interior solutions for compact stellar objects in <italic>f</italic>( <italic>R, G</italic>) gravity

We study the holographic realization of the SO(6) R-symmetry of $$ \mathcal{N} $$ = 4 super Yang-Mills with unitary gauge group. Focusing on 1/2 BPS states in the [0, $\textit{J}$, 0] representation of SO(6) , it is known that depending on the scaling of $\textit{J}$ with $\textit{N}$, these are best described holographically in terms of gravitational waves ($\textit{J}$ ≪ $\textit{N}$) or D3 brane giant gravitons ($\textit{J}$ ~ $\textit{N}$). These two descriptions are bridged by the dielectric effect, as the D3 giant can be regarded as a puffed-up configuration of gravitational waves. The natural non-BPS branes for symmetry operators are either 4-branes or non-BPS Kaluza-Klein monopoles. We show that the former can be regarded as a dielectric expansion of the latter, in parallel to the charged operators. We also propose symTh and symTFT candidates for the SO(6) symmetry, whose operators at the boundary must correspond to the non-BPS branes.

Spain

Francesco Mignosa

Diego Rodriguez-Gomez

Non-Abelian R-symmetry and dielectric branes

We assess the impact of measuring deeply virtual Compton scattering (DVCS) off protons using the planned detector at the Electron-Ion Collider in China (EicC), which is proposed as an upgrade to the High Intensity Heavy-Ion Accelerator Facility (HIAF). We develop a neural-network architecture to flexibly parameterize Compton form factors (CFFs), reliably extrapolate into unmeasured kinematic regions, and provide robust uncertainty estimates using the replica method. The framework is fitted to available worldwide DVCS data using the $ {\mathrm{Gepard}}$ software. We find a significant reduction in the uncertainties of all CFFs after incorporating pseudo-data from single and double polarization asymmetries at the EicC, with particularly strong improvements in the sea-quark region.

Yuan-Yuan Huang

Xu Cao

Taifu Feng

Croatia

Krešimir Kumerički

Yu Lu

Assessing the impact of the Electron-Ion Collider in China on deeply virtual Compton scattering * Supported by the National Key R&D Program of China (2023YFA1606703), the National Natural Science Foundation of China (12547111, 12235008, 12405105) and (PK.1.1.10.0004) co-financed by the European Union and through the European Regional Development Fund - Competitiveness and Cohesion Programme 2021-2027. TF also thanks the Hebei Natural Science Foundation (A2022201017, A2023201041) and Natural Science Foundation of Guangxi Autonomous Region (2022GXNSFDA035068)

<p>We make use of the improved K-matrix algorithm to obtain unitarized amplitudes in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>R</mi><mo>+</mo><mi>α</mi><msup><mi>R</mi><mn>2</mn></msup></math> gravity (the so-called Starobinsky model, of cosmological relevance). The procedure is of some complexity because infrared divergences are present and need to be properly regulated. We focus on the behavior of a bona fide scalar resonance, known to exist in this model, and compare it to an apparent resonance detected in previous studies, thus confirming that the latter seems to be an artifact due to the introduction of the infrared regulator. We analyze the existence of other dynamical resonances and dwell on the amplitudes made unitary by this procedure.</p>

Iñigo Asiáin

Antonio Dobado

Domènec Espriu

Unitarization of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>R</mi><mo>+</mo><mi>α</mi><msup><mi>R</mi><mn>2</mn></msup></math> gravity

The non-conservation of the energy-momentum tensor in $\textit{f}$($\textit{R}$, $\textit{T}$) gravity can be interpreted as an effective manifestation of dissipation. Motivated by this, we propose a new formulation of $\textit{f}$($\textit{R}$, $\textit{T}$) gravity based on the Herglotz variational principle, which extends the usual Hamilton variational principle to dissipative systems by allowing the Lagrangian to depend explicitly on the action. The resulting gravitational field equations extend those of $\textit{f}$($\textit{R}$, $\textit{T}$) gravity by including Herglotz contributions. In the Newtonian limit, these contributions modify the gravitational potential, allowing us to constrain the Herglotz vector through Mercury’s perihelion precession and the relativistic light deflection. The Herglotz corrections lead to a scaling law consistent with observations from the Cassini spacecraft. Examining two representative cosmological models, the Herglotz vector effectively reduces to a single function that, under suitable conditions, can play the role of a cosmological constant, providing an alternative mechanism for the Universe’s accelerated expansion. Within the Herglotz variational approach, the linear $$f(R,T)=R+\alpha T$$ model, previously ruled out in the standard formulation due to its fixed deceleration parameter, becomes consistent with observations for a certain choice of the Herglotz vector.

Romania

Marek Wazny

Lehel Csillag

Portugal

Miguel Pinto

Tiberiu Harko

Herglotz-type $\textit{f}$($\textit{R}$, $\textit{T}$) gravity