This research paper explores the structure of hypothetical compact stars, known as strange stars, within the framework of a novel modified theory of gravity called $$f(R,\Sigma ,T)$$ gravity. This theory extends General Relativity by making gravity dependent not only on the Ricci curvature scalar $\textit{R}$ but also on a torsion scalar $$\Sigma $$ and the trace of the matter energy–momentum tensor $\textit{T}$. This introduces a richer coupling between geometry and matter. The study presents a highly exotic, multi-layered stellar model composed of five distinct regions, each with a unique equation of state and geometric properties. The model features a dark-energy-like core with powerful repulsive gravity (anti-gravity), surrounded by successive layers of dust, exotic radiation, and a stiff matter crust, all enveloped by a standard Schwarzschild vacuum exterior. A key finding is the prevalence of negative energy densities and pressures in several layers, a hallmark of exotic matter. These configurations, enabled by the $$f(R,\Sigma ,T)$$ framework, lead to repulsive gravitational effects that radically alter the star’s internal equilibrium. The analysis demonstrates how additional geometry-driven forces within this theory can support such exotic structures, potentially preventing gravitational collapse and resulting in a stable, non-singular object. This work demonstrates that $$f(R,\Sigma ,T)$$ gravity allows for new and complex classes of compact objects with stratified, exotic matter distributions, whose properties and observational signatures would differ significantly from those predicted by standard General Relativity.

Egypt

M. Bakry

Saudi Arabia

A. Eid

Tahia Dabash

The impact of $$f(R,\Sigma ,T)$$ gravity on strange star structure

We study spacetime four-point functions of chiral primary operators for superstrings propagating in AdS $\textit{× S}$ $\textit{× T}$ from the worldsheet perspective, allowing for external states with arbitrary spectral flow charges. We work at small boundary cross-ratio and consider both extremal (supersymmetry-protected) and non-extremal configurations. The string correlators involve a non-trivial integration over the worldsheet moduli, and we demonstrate how the exchange of short and long strings is encoded in distinct integration regions. We interpret our results in terms of the operator product expansion in the boundary theory, and make explicit the precise matching with the available data for the relevant holographic correlators.

Argentina

Emiliano Barone

Sergio Iguri

Nicolas Kovensky

Julián Toro

Superstring four-point functions in AdS3 $\textit{× S}$ 3 $\textit{× T}$ 4

The energy-momentum tensor form factor <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><mo stretchy="false">(</mo><mi>t</mi><mo stretchy="false">)</mo></math> is finite and negative in hadronic models and lattice QCD when only strong forces are included. However, when electromagnetic forces are considered, the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><mo stretchy="false">(</mo><mi>t</mi><mo stretchy="false">)</mo></math> of charged hadrons undergoes a dramatic change: at small <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>t</mi></math>, it changes sign and diverges like <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>1</mn><mo>/</mo><msqrt><mrow><mo>−</mo><mi>t</mi></mrow></msqrt></math> as shown for the proton in the classical model by Białynicki-Birula based on residual nuclear forces which can be understood as a mean field approach. We construct an analogous neutron model and show that this framework accurately explains the electromagnetic proton-neutron mass difference. We demonstrate that, after appropriately rescaling the residual nuclear forces, the model can reproduce lattice data on the nucleon <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><mo stretchy="false">(</mo><mi>t</mi><mo stretchy="false">)</mo></math> up to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><mo>−</mo><mi>t</mi><mo stretchy="false">)</mo><mo>≲</mo><mn>1</mn><mtext> </mtext><mtext> </mtext><msup><mi>GeV</mi><mn>2</mn></msup></mrow></math> as well as QED effects. Based on this realistic model description, we show that the proton and neutron <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><mo stretchy="false">(</mo><mi>t</mi><mo stretchy="false">)</mo></math> form factors are practically indistinguishable down to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><mo>−</mo><mi>t</mi><mo stretchy="false">)</mo><mo>≈</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>4</mn></mrow></msup><mtext> </mtext><mtext> </mtext><msup><mi>GeV</mi><mn>2</mn></msup></mrow></math>, far below what can currently be accessed experimentally. We conclude that in the foreseeable future the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><mo stretchy="false">(</mo><mi>t</mi><mo stretchy="false">)</mo></math> form factors of the proton and neutron will practically look the same in experiments and phenomenology.

United States

Andrea Mejia

Peter Schweitzer

Energy-momentum tensor form factor <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>D</mi><mo stretchy="false">(</mo><mi>t</mi><mo stretchy="false">)</mo></mrow></math> of the proton and neutron

We propose boundary terms for the action of the NS sector of supergravity on $\textit{M}$ × $\textit{S}$ × $\textit{T}$ spacetimes — where $\textit{M}$ is an AdS or a linear dilaton background — that render the Brown-York stress tensor and the on-shell action finite. For AdS backgrounds, we show that the on-shell action yields a free energy with chemical potentials determined by the $\textit{B}$-field. TsT (T-duality + shift + T-duality) transformations of these backgrounds generate classes of linear dilaton backgrounds distinguished by their boundary conditions. Among them, there is one class of backgrounds that reproduces features of the single-trace $$ T\overline{T} $$ deformation. These backgrounds have additional chemical potentials that can be turned off by large gauge transformations of the $\textit{B}$-field. We show that the Brown-York stress tensor of these backgrounds reproduces the energies and the trace flow equation of $$ T\overline{T} $$ -deformed CFTs. We also show that the on-shell action matches the $$ T\overline{T} $$ partition function and discuss the interpretation of these results.

China

Luis Apolo

The on-shell action of supergravity & the $\textit{B}$-side of TsT and single-trace $$ T\overline{T} $$

The decay <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>A</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>H</mi></math> is a characteristic signal of two-Higgs-doublet models (2HDMs), where <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>A</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi></math> lie primarily within the same <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi><mi>U</mi><mo stretchy="false">(</mo><mn>2</mn><msub><mo stretchy="false">)</mo><mi>L</mi></msub></math> multiplet, leading to a coupling of order <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>g</mi><mn>2</mn></msub></math> to the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math> boson. The subsequent decay <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mo stretchy="false">→</mo><mi>t</mi><msup><mi>t</mi><mrow><mo stretchy="false">(</mo><mo>*</mo><mo stretchy="false">)</mo></mrow></msup></math> is particularly promising, as it gives rise to distinct final states involving multiple leptons and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>b</mi></math>-jets. The required splitting between <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>A</mi></msub></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>H</mi></msub></math> can naturally occur near the electroweak scale while being consistent with perturbative unitarity. Whereas dedicated ATLAS and CMS searches focused on the region with both top-quarks on-shell, we cover lower masses where one top quark is off-shell by recasting Standard Model <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover><mi>Z</mi></math> measurements of ATLAS and CMS. The obtained limits on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>σ</mi><mo stretchy="false">(</mo><mi>A</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>H</mi><mo stretchy="false">)</mo><mo>×</mo><mi>Br</mi><mo stretchy="false">(</mo><mi>H</mi><mo stretchy="false">→</mo><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover><mo stretchy="false">)</mo></math> are between 0.12 pb and 0.62 pb. Interestingly, we observe these stringent limits despite a preference (up to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>2.5</mn><mi>σ</mi></math>) for a nonzero new physics signal, most pronounced around for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>m</mi></mrow><mrow><mi>A</mi></mrow></msub><mo>≈</mo><mn>450</mn><mi>–</mi><mn>460</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>H</mi></msub><mo>≈</mo><mn>290</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>, with a best-fit value of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>σ</mi><mo stretchy="false">(</mo><mi>A</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>H</mi><mo stretchy="false">)</mo><mo>×</mo><mi>Br</mi><mo stretchy="false">(</mo><mi>H</mi><mo stretchy="false">→</mo><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover><mo stretchy="false">)</mo><mo>≈</mo><mn>0.3</mn><mtext> </mtext><mtext> </mtext><mi>pb</mi></math>. This cross section can be accommodated within a top-philic 2HDM for a top-Yukawa coupling of the second Higgs doublet of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0.16</mn><mo>≲</mo><msub><mi>μ</mi><mi>t</mi></msub><mo>≲</mo><mn>0.33</mn></math>.

Germany

Saiyad Ashanujjaman

Switzerland

Guglielmo Coloretti

Andreas Crivellin

South Africa

India

Siddharth P. Maharathy

Bruce Mellado

Constraining <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>A</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>H</mi></math> with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mo stretchy="false">→</mo><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover></math> in the low-mass region

We explore the cosmological consequences of a modified cosmology inspired by string T-duality. We incorporate the zero-point length correction, <italic>l</italic> <inf>0</inf>, into the gravitational potential and derive the modified Friedmann equations via thermodynamic approach at the apparent horizon of a Friedmann-Robertson-Walker (FRW) universe. The resulting framework introduces a dimensionless coupling parameter <math altimg='si63.svg'><mrow><mi>&#946;</mi><mo>&#8764;</mo><msubsup><mi>l</mi><mn>0</mn><mn>2</mn></msubsup><msubsup><mi>H</mi><mn>0</mn><mn>2</mn></msubsup></mrow></math> quantifying deviations from the standard &#923;CDM model. Using Bayesian inference with <small-caps>Cobaya</small-caps> and MCMC sampling, we constrain the model parameter against late-time observations, including PantheonPlus and Union3 Type Ia supernovae, cosmic chronometers, DESI DR2 BAO measurements, and Amati-calibrated GRBs. The joint analysis yields an upper bound <math altimg='si64.svg'><mrow><mi>&#946;</mi><mo>&#8818;</mo><mi mathvariant='script'>O</mi><mo>(</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>3</mn></mrow></msup><mo>)</mo></mrow></math> (68% C.L.), implying that any deviation from the standard &#923;CDM scenario ( <math altimg='si65.svg'><mrow><mi>&#946;</mi><mo linebreak='goodbreak'>=</mo><mn>0</mn></mrow></math>) is extremely small within the current observational precision. Model comparison through the Akaike Information Criterion shows that the &#923;CDM and T-duality models provide statistically equivalent fits to the data, exhibiting only a marginal preference for &#923;CDM. These results provide the first quantitative observational constraints on the cosmological imprint of string T-duality-inspired modifications and underscore the potential of future high-precision surveys to test possible residual effects of such corrections in the late-time Universe.

Spain

G.G. Luciano

Chile

A. Paliathanasis

Iran

A. Sheykhi

Observational constraints on the modified cosmology inspired by string T-duality

Photon flux benchmark models together with recent experimental estimations for pomeron energy fluxes and structure functions are implemented within Monte Carlo simulation, to determine their impact on physical observables and on the signal strength uncertainty of the yet-to-be observed semi-exclusive $$t\bar{t}$$ production in proton–proton ($\textit{pp}$) collisions at Large Hadron Collider (LHC) and Future Circular Collider (FCC) energies. Expected cross-section rises by a factor of $$\sim 50$$ and $$\sim 22$$ for pomeron-induced and photon-induced processes respectively from LHC to FCC energy regime. TensorFlow deep neural networks were implemented to discriminate semi-exclusive processes against non-peripheral $$t\bar{t}X$$ background, achieving an Area Under the Curve (AUC) test performance of $$0.9917 \pm 0.0002$$ for the photon-induced signal. At detector level, following the geometry of the CMS detector at CERN, the minimum Hadronic Forward energy observable was identified as the most effective discriminator against non-peripheral $$t\bar{t}X$$ background. In the context of low pileup $\textit{pp}$ data and based on the Asimov dataset, by considering the statistical effects and the systematic contribution from pomeron/photon schemes to the total uncertainty a 5- $$\sigma $$ significance is expected for pomeron-induced and photon-induced $$t\bar{t}$$ production modes with 1 fb $$^{-1}$$ and 4.7 fb $$^{-1}$$ integrated luminosity datasets respectively. The systematic contribution to the total uncertainty is 25.1% and 7.6% respectively, highlighting the potential for experimental observation using Run 2 and Run 3 LHC data, allowing further studies within the LHC forward physics program.

Mexico

A. Cota Rodríguez

Jesús V. Corral

J. Murillo Quijada

Impact of neutral fluxes and signal significance optimization on semi-exclusive $$pp \rightarrow t\bar{t}$$ production via deep learning training

If axions simultaneously have the scalar couplings to the nucleons and pseudoscalar couplings to the electrons, it may mediate a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">P</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">T</mi></math>-violating interaction between the electronic shell and nuclei in the molecules. The polyatomic molecule RaOH, which is considered a promising platform for the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">P</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">T</mi></math>-violation searches, is studied for its sensitivity to such interactions. Because of the long-range nature (on molecular scales) of the axion-mediated interaction, it is important whether the molecular parameter is sensitive to the vibration of the molecule. Our results imply that the impact of the vibrations on the axion-mediated electron-nucleon interaction in the molecule is similar to the impact on the short-range electron-nucleon scalar-pseudoscalar interaction studied earlier.

Russia

Anna Zakharova

<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="script">P</mi></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="script">T</mi></mrow></math>-violating axion-mediated interactions in the RaOH molecule

In this work, we investigate the relativistic structure of white dwarfs (WDs) within the framework of modified gravity theory <math altimg='si3.svg'><mrow><mi>f</mi><mrow><mo>(</mo><mi>R</mi><mo>,</mo><mi>T</mi><mo>,</mo><msub><mi>L</mi><mi>m</mi></msub><mo>)</mo></mrow><mo linebreak='goodbreak'>=</mo><mi>R</mi><mo linebreak='goodbreak'>+</mo><mi>&#945;</mi><mi>T</mi><msub><mi>L</mi><mi>m</mi></msub></mrow></math>, which introduces a non-minimal coupling between matter and curvature. Using a realistic equation of state (EoS) that includes contributions from a relativistic degenerate electron gas and ionic lattice effects, we solve the modified Tolman-Oppenheimer-Volkoff (TOV) equations for two standard choices of the matter Lagrangian density: <math altimg='si9.svg'><mrow><msub><mi>L</mi><mi>m</mi></msub><mo linebreak='goodbreak'>=</mo><mi>p</mi></mrow></math> and <math altimg='si6.svg'><mrow><msub><mi>L</mi><mi>m</mi></msub><mo linebreak='goodbreak'>=</mo><mo>&#8722;</mo><mi>&#961;</mi></mrow></math>. We show that the extra <italic>&#945;TL<inf>m</inf></italic> term significantly alters the mass-radius relation of WDs, especially at high central densities <math altimg='si11.svg'><mrow><mo>(</mo><msub><mi>&#961;</mi><mi>c</mi></msub><mo>&#8819;</mo><msup><mn>10</mn><mn>8</mn></msup><mo linebreak='goodbreak'>&#8722;</mo><msup><mn>10</mn><mn>9</mn></msup><mspace width='0.16em' /><mrow><mi mathvariant='normal'>g</mi></mrow><mo linebreak='goodbreak'>/</mo><mi>c</mi><msup><mi>m</mi><mn>3</mn></msup><mo>)</mo></mrow></math>, allowing for stable super-Chandrasekhar configurations. In particular, depending on the sign and magnitude of the parameter <italic>&#945;</italic>, the maximum mass can increase or decrease, and in some regimes, the usual critical point indicating the transition from stability to instability disappears. Our findings suggest that <italic>f</italic>( <italic>R, T, L<inf>m</inf></italic>) gravity provides a viable framework to explain the existence of massive WDs beyond the classical Chandrasekhar limit. Using Bayesian inference with WD observational data, we further constrain the coupling parameter <italic>&#945;</italic> for the two choices of the Lagrangian density <italic>L<inf>m</inf></italic>.

Brazil

Edson Otoniel

Juan M.Z. Pretel

Clésio E. Mota

César O.V. Flores

Victor B.T. Alves

Franciele M. da Silva

White dwarf structure in <italic>f</italic>( <italic>R, T, L<inf>m</inf></italic>) gravity: Beyond the Chandrasekhar mass limit

In this work, we examine the influence of nonlinear electrodynamics (NED) and <italic>f</italic>( <italic>R, T</italic>) gravity on quasi-periodic oscillations (QPOs) around a magnetically charged black hole. By analyzing the effective potential, specific energy, and angular momentum of circular orbits, we study how the NED parameter <italic>&#945;</italic> and the gravitational coupling parameter <italic>&#946;</italic> affect orbital dynamics. Increasing <italic>&#945;</italic> leads to systematic deviations from the Reissner-Nordstr&#246;m behavior, reflected in shifts in the ISCO radius and orbital frequencies. We further explore QPO-generating radii using the Relativistic Precession (RP), Warped Disk (WD), and Epicyclic Resonance (ER2-ER4) models. We further extend our analysis by performing an MCMC-based parameter estimation using QPO data from black holes spanning a wide range of mass scales. This approach yields consistent observational constraints on the model parameters.

Bidyut Hazarika

Abhishek Baruah

Prabwal Phukon

Observational constraints on <italic>f</italic>( <italic>R, T</italic>) gravity coupled with NED from black hole quasi periodic oscillations