This study explores the structure of compact stars using an extended theory of gravity known as <math altimg='si1.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi mathvariant='script'>R</mi><mo>,</mo><mi mathvariant='script'>G</mi><mo>,</mo><mi mathvariant='script'>T</mi><mo stretchy='false'>)</mo></math> gravity, where <math altimg='si3.svg'><mi mathvariant='script'>R</mi></math>, is the Ricci scalar, <math altimg='si4.svg'><mi mathvariant='script'>G</mi></math>, the Gauss-Bonnet invariant, and <math altimg='si5.svg'><mi mathvariant='script'>T</mi></math> the trace of the energy-momentum tensor. Focusing on massive radio pulsars, specifically neutron stars with masses greater than 1.8 solar masses, utilize these extreme astrophysical environments to test gravity in regimes unreachable by Earth-based experiments. We adopt a linear form of the theory, <math altimg='si18.svg'><mi>f</mi><mo stretchy='false'>(</mo><mrow><mi mathvariant='script'>R</mi><mo>,</mo><mi mathvariant='script'>G</mi><mo>,</mo><mi mathvariant='script'>T</mi></mrow><mo stretchy='false'>)</mo><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mi mathvariant='script'>R</mi><mo linebreak='goodbreak' linebreakstyle='after'>+</mo><mi>&#945;</mi><mi mathvariant='script'>G</mi><mo linebreak='goodbreak' linebreakstyle='after'>+</mo><mi>&#946;</mi><mi mathvariant='script'>T</mi></math>, with <italic>&#945;</italic>, <cross-ref refid='fn0010' id='crf0390'>1</cross-ref> and <italic>&#946;</italic> are dimensional constants, and derive an exact analytical solution for anisotropic perfect fluid spheres in hydrostatic equilibrium. This model incorporates the compactness factor <math altimg='si7.svg'><mi>C</mi><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mfrac><mrow><mn>2</mn><mi>G</mi><mi>M</mi></mrow><mrow><mi>R</mi><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></mfrac></math>, to describe all physical properties within the stellar interior. To constrain the model, we employ observational data from the pulsar <italic>U</italic>1724, using its mass and radius to fix the parameters at their upper bounds: <math altimg='si8.svg'><msub><mrow><mi>&#945;</mi></mrow><mrow><mn>1</mn></mrow></msub><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mfrac><mrow><mi>&#945;</mi></mrow><mrow><msup><mrow><mi>R</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></mfrac><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mo>&#177;</mo><mn>0.023</mn></math> and <math altimg='si9.svg'><msub><mrow><mi>&#946;</mi></mrow><mrow><mn>1</mn></mrow></msub><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mfrac><mrow><mi>&#946;</mi></mrow><mrow><msup><mrow><mi>&#954;</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></mfrac><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mo>&#177;</mo><mn>0.001</mn></math>. The resulting model is consistent with physical viability and observational constraints. Notably, the squared sound speed in this framework remains below the theoretical limit ( <math altimg='si10.svg'><mmultiscripts><mrow><mtext mathvariant='normal'>c</mtext></mrow><mrow><mi>s</mi></mrow><none /><none /><mrow><mn>2</mn></mrow></mmultiscripts><mo linebreak='goodbreak' linebreakstyle='after'>&lt;</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup><mo stretchy='false'>/</mo><mn>3</mn></math>), contrasting with general relativity results. Without assuming a specific equation of state, the model exhibits linear behavior and predicts a core density several times higher than nuclear saturation density ( <math altimg='si11.svg'><msub><mrow><mi>&#961;</mi></mrow><mrow><mtext>nuc</mtext></mrow></msub><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mn>2.6</mn><mo>&#215;</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>14</mn></mrow></msup></math> g/cm 3), with surface density <math altimg='si12.svg'><msub><mrow><mi>&#961;</mi></mrow><mrow><mi>s</mi></mrow></msub></math>, also exceeding this threshold. Additionally, the derived mass-radius relation agrees well with existing astrophysical observations.

Egypt

South Africa

G.G.L. Nashed

Constraining linear form of <math altimg='si1.svg'><mi>f</mi><mo stretchy='false'>(</mo><mrow><mi mathvariant='script'>R</mi><mo>,</mo><mi mathvariant='script'>G</mi><mo>,</mo><mi mathvariant='script'>T</mi></mrow><mo stretchy='false'>)</mo></math> gravity from astrophysical observations of the Pulsar U1724

In this paper, we investigate Friedmann Robertson Walker (FRW) space time filled with a perfect fluid in <math altimg='si1.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>R</mi><mo>,</mo><msub><mrow><mi>L</mi></mrow><mrow><mi>m</mi></mrow></msub><mo stretchy='false'>)</mo></math> modified theory framework formulated by Harko and Lobo (2010), where <italic>R</italic> is the Ricci scalar curvature, <math altimg='si2.svg'><msub><mrow><mi>L</mi></mrow><mrow><mi>m</mi></mrow></msub></math> is the ideal fluid's Lagrangian. Two specific non-linear <math altimg='si1.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>R</mi><mo>,</mo><msub><mrow><mi>L</mi></mrow><mrow><mi>m</mi></mrow></msub><mo stretchy='false'>)</mo></math> functional forms are assumed: <math altimg='si3.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>R</mi><mo>,</mo><msub><mrow><mi>L</mi></mrow><mrow><mi>m</mi></mrow></msub><mo stretchy='false'>)</mo><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mfrac><mrow><mi>R</mi></mrow><mrow><mn>2</mn></mrow></mfrac><mo linebreak='goodbreak' linebreakstyle='after'>+</mo><mo stretchy='false'>(</mo><mn>1</mn><mo linebreak='badbreak' linebreakstyle='after'>+</mo><mi>&#945;</mi><mi>R</mi><mo stretchy='false'>)</mo><msub><mrow><mi>L</mi></mrow><mrow><mi>m</mi></mrow></msub></math> representing a non-minimal coupling case and <math altimg='si4.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>R</mi><mo>,</mo><msub><mrow><mi>L</mi></mrow><mrow><mi>m</mi></mrow></msub><mo stretchy='false'>)</mo><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mfrac><mrow><mi>R</mi></mrow><mrow><mn>2</mn></mrow></mfrac><mo linebreak='goodbreak' linebreakstyle='after'>+</mo><msubsup><mrow><mi>L</mi></mrow><mrow><mi>m</mi></mrow><mrow><mi>n</mi></mrow></msubsup><mo linebreak='goodbreak' linebreakstyle='after'>+</mo><mi>&#946;</mi></math> representing a minimal coupling case. Here, we use a cubic parametrization of the deceleration parameter that produces an accelerating universe to obtain the exact solution for the field equations. We investigate the evolution of cosmological parameters including pressure and energy density. Using <math altimg='si5.svg'><msub><mrow><mi>L</mi></mrow><mrow><mi>m</mi></mrow></msub><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mi>&#961;</mi></math> and a cubic parametrization of the deceleration parameter to account for late-time cosmic acceleration. We analyze the evolution of cosmological parameters in terms of both cosmic time and redshift and constrain model parameters using observational datasets from <math altimg='si6.svg'><mi>H</mi><mo stretchy='false'>(</mo><mi>z</mi><mo stretchy='false'>)</mo></math>, Pantheon, BAO, H(z)+Pantheon, H(z)+BAO+Pantheon. The results show a transition of the deceleration parameter from deceleration to acceleration and indicate a possible quintessence-like behavior at the present epoch. The findings suggest that the proposed models can effectively describe the universe's expansion history in agreement with observations.

India

Kangujam Priyokumar Singh

Syed Sabanam

Anil Kumar Yadav

Asem Jotin Meitei

Modeling through the cubic parametrization of the deceleration parameter in <italic>f</italic>( <italic>R</italic>, <italic>Lm</italic>) gravity with observational constraints

This study examines the structure and stability of dark energy stars within the context of $$R^2$$ gravity, with the gravity model defined by $$f(R) = R + a R^2$$ (the Starobinsky model). Specifically, dark energy is a mysterious force that can prevent the gravitational collapse of compact objects to singularities. To characterize dark energy, we consider modified Chaplygin fluid as an equation of state (EoS) of matter and study its mass-radius relation for different model parameters. By numerically solving the modified Tolman–Oppenheimer–Volkoff (TOV) equations, our primary objective is to examine the influence of variations in the $$R^2$$ gravity parameter $\textit{a}$ on the energy density, pressure, mass-radius and mass-central density relationships of dark energy stars. Our findings reveal that the variation of $\textit{a}$ does not significantly impact on the $$(M-R)$$ relations but comfortably exceeds the 2 $$M_{\odot }$$ limit. Additionally, we examine the dynamical stability of these stars by evaluating the static stability criterion, adiabatic index, and sound speed. Finally, we compare our results with various astrophysical observational data and discuss future observations that could validate the predictions of our model.

Ayan Banerjee

Saudi Arabia

Safiqul Islam

Uzbekistan

Javlon Rayimbaev

Inomjon Ibragimov

Sokhibjan Muminov

Ikram Davletov

Comprehensive analysis of dark energy stars in $\textit{R}$-squared gravity

In this paper, we investigate regular black hole solutions in the (2+1)-dimensional versions of general relativity and $\textit{f}$($\textit{R}$, $\textit{T}$) gravity, both coupled to nonlinear electrodynamics. By admitting that the matter content that generates such geometries satisfies the Maxwell limit condition, we obtain a class of regular black holes that give rise to new solutions and successfully reproduce particular cases found in earlier studies of (2+1)-dimensional general relativity. Moreover, we discover the first regular black hole solutions in (2+1)-dimensional $\textit{f}$($\textit{R}$, $\textit{T}$) gravity and explore both qualitatively and quantitatively the non-conservation of the energy–momentum tensor present in those solutions.

Portugal

Miguel Pinto

Brazil

Roberto Maluf

Spain

Gonzalo Olmo

Regular black hole solutions in $$(2 + 1)$$ -dimensional $\textit{f}$($\textit{R}$, $\textit{T}$) gravity coupled to nonlinear electrodynamics

We focus on the inflationary predictions of <italic>&#946;</italic>-exponential potential models, in which the inflaton is associated with a field that determines the size of extra dimensions. This provides a well-motivated starting point for exploring physics at very high energy scales. Consequently, we incorporate an <math altimg='si1.svg'><msup><mrow><mi>R</mi></mrow><mrow><mn>2</mn></mrow></msup></math> term within the Palatini formulation of gravity. Additionally, we extend our analysis by examining the effects of reheating on inflationary observables, considering various scenarios for the reheat temperature. We present the inflationary predictions for spectral index <math altimg='si2.svg'><msub><mrow><mi>n</mi></mrow><mrow><mi>s</mi></mrow></msub></math>, tensor-to-scalar ratio <italic>r</italic>, and the running of the spectral index <math altimg='si3.svg'><mi mathvariant='normal'>d</mi><msub><mrow><mi>n</mi></mrow><mrow><mi>s</mi></mrow></msub><mo stretchy='false'>/</mo><mi mathvariant='normal'>d</mi><mi mathvariant='normal'>ln</mi><mo>&#8289;</mo><mi>k</mi></math> in the context of a <italic>&#946;</italic>-exponential potential minimally coupled in Palatini <math altimg='si1.svg'><msup><mrow><mi>R</mi></mrow><mrow><mn>2</mn></mrow></msup></math> gravity. Furthermore, we confront our results with observational constraints from BICEP/Keck, Planck 2018, and the most recent Planck+ACT DR6 data released by the ACT collaboration. We also consider the projected sensitivities of upcoming CMB experiments, including CMB-S4, LiteBIRD, and SPIDER. Our findings demonstrate the viability of the model, even in light of the tighter constraints expected from future data.

Türkiye

United States

Nilay Bostan

Rafid H. Dejrah

Inflationary dynamics and observables: <italic>&#946;</italic>-exponential models in Palatini <italic>R</italic> 2 gravity

We explore dark matter phenomenology in Myrzakulov <math altimg='si1.svg'><mi>F</mi><mo stretchy='false'>(</mo><mi>R</mi><mo>,</mo><mi>T</mi><mo stretchy='false'>)</mo></math> gravity, formulated via the vielbein approach in Weitzenb&#246;ck spacetime. In this torsion-based extension of gravity, dark matter emerges as a geometric effect rather than a particle species, with curvature and torsion contributing dynamically to the field equations.

Davood Momeni

Kazakhstan

Ratbay Myrzakulov

Dark matter constraints in Myrzakulov <italic>F</italic>( <italic>R</italic>, <italic>T</italic>) gravity: A vielbein approach in Weitzenb&#246;ck spacetime with observational data

Jets with different radius parameters $\textit{R}$ are an important tool for probing quantum chromodynamics processes at different angular scales. Jets with small $$R=0.2$$ are instrumental in measurements of the substructure of large-$\textit{R}$ jets resulting from collimated hadronic decays of energetic $\textit{W}$, $\textit{Z}$, and Higgs bosons, top quarks, and of potential new resonances. This paper presents measurements of the energy scale, resolution, and associated uncertainties of jets with radius parameters $$R=0.2$$ and 0.6, obtained using the ATLAS detector. The results are based on $$37~\text {fb}^{-1}$$ of proton–proton collision data from the Large Hadron Collider at a centre-of-mass energy of $$\sqrt{s}=13$$ TeV. A new $\textit{in situ}$ method for measuring jet energy scale differences between data and Monte Carlo simulations is presented. The systematic uncertainties in the jet energy scale for central jets $$(|\eta | < 1.2)$$ typically vary from 1% to about 5% as a function of $$|\eta |$$ at very low transverse momentum, $$p_{\text {T}},$$ of around 20 GeV for both $$R=0.2$$ and 0.6 jets. The relative energy resolution ranges from $$(35 \pm 6)\%$$ at $$p_{\text {T}} = 20$$ GeV to $$(6 \pm 0.5)\%$$ at $$p_{\text {T}} = 300$$ GeV for central $$R=0.2$$ jets, and is found to be slightly worse for $$R=0.6$$ jets. Finally, the effect of close-by hadronic activity on the jet energy scale is investigated and is found to be well modelled by the ATLAS Monte Carlo simulations.

France

G. Aad

Norway

E. Aakvaag

B. Abbott

United Arab Emirates

S. Abdelhameed

Germany

K. Abeling

N. Abicht

S. Abidi

M. Aboelela

Morocco

A. Aboulhorma

Israel

H. Abramowicz

Y. Abulaiti

Italy

United Kingdom

B. Acharya

A. Ackermann

C. Adam Bourdarios

Poland

L. Adamczyk

S. Addepalli

M. Addison

J. Adelman

A. Adiguzel

T. Adye

A. Affolder

Y. Afik

M. Agaras

A. Aggarwal

Romania

C. Agheorghiesei

Azerbaijan

F. Ahmadov

S. Ahuja

China

X. Ai

G. Aielli

A. Aikot

M. Ait Tamlihat

B. Aitbenchikh

M. Akbiyik

Sweden

T. Åkesson

A. Akimov

Japan

D. Akiyama

N. Akolkar

S. Aktas

G. Alberghi

Canada

J. Albert

P. Albicocco

G. Albouy

S. Alderweireldt

Z. Alegria

Switzerland

M. Aleksa

I. Aleksandrov

C. Alexa

Greece

T. Alexopoulos

F. Alfonsi

M. Algren

M. Alhroob

Czechia

B. Ali

H. Ali

S. Ali

S. Alibocus

M. Aliev

G. Alimonti

W. Alkakhi

C. Allaire

B. Allbrooke

J. Allen

P. Allport

A. Aloisio

Argentina

F. Alonso

C. Alpigiani

Z. Alsolami

A. Alvarez Fernandez

M. Alves Cardoso

M. Alviggi

M. Aly

Y. Amaral Coutinho

A. Ambler

C. Amelung

M. Amerl

C. Ames

D. Amidei

B. Amini

K. Amirie

A. Amirkhanov

S. Amor Dos Santos

K. Amos

D. Amperiadou

S. An

V. Ananiev

C. Anastopoulos

T. Andeen

J. Anders

A. Anderson

A. Andreazza

S. Angelidakis

A. Angerami

A. Anisenkov

A. Annovi

C. Antel

E. Antipov

M. Antonelli

F. Anulli

M. Aoki

T. Aoki

Energy scale and resolution for anti- $$k_t$$ jets with radius parameters $$R=0.2$$ and 0.6 measured in proton-proton collisions at $$\sqrt{s} = 13$$ TeV with the ATLAS detector

In this article, we probe the trilinear <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>R</mi></math>-parity violating (RPV) supersymmetric (SUSY) scenarios with specific nonzero interactions in the light of neutrino oscillation, Higgs, and flavor observables. We attempt to fit the set of observables using a state-of-the-art Markov Chain Monte Carlo (MCMC) setup and study its impact on the model parameter space. Our main objective is to constrain the trilinear couplings individually, along with some other SUSY parameters relevant to the observables. We present the constrained parameter regions in the form of marginalized posterior distributions on different two-dimensional parameter planes. We perform our analyses with two different scenarios characterized by our choices for the lightest SUSY particle (LSP), bino, and stop. Our results indicate that the lepton number violating trilinear couplings <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>λ</mi><mrow><mi>i</mi><mn>33</mn></mrow></msub></math> (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>i</mi><mo>=</mo><mn>1</mn></math>, 2) and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>λ</mi><mrow><mi>j</mi><mn>33</mn></mrow><mo>′</mo></msubsup></math> (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>j</mi><mo>=</mo><mn>1</mn></math>, 2, 3) can be at most of the order of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>10</mn><mrow><mo>−</mo><mn>4</mn></mrow></msup></math> or even smaller while <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>tan</mi><mi>β</mi></math> is restricted to below 15 even when <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>3</mn><mi>σ</mi></math> allowed regions are considered. We further comment on the possible LHC signatures of these LSPs focusing on and around the best-fit regions.

Arghya Choudhury

Sourav Mitra

Arpita Mondal

Subhadeep Mondal

Markov chain Monte Carlo analysis to probe trilinear <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>R</mi></math>-parity violating SUSY scenarios and possible LHC signatures

A test of lepton universality between muons and electrons is performed using $\textit{B}$ → $\textit{K}$ $\textit{ℓ}$ $\textit{ℓ}$ decays (where $\textit{ℓ}$ = $\textit{e}$, $\textit{μ}$), in the dilepton invariant-mass-squared region above 14.3 GeV $\textit{/c}$ . The data used for the measurement consists of beauty meson decays produced in proton-proton collisions, corresponding to an integrated luminosity of 9 fb , collected by the LHCb experiment between 2011 and 2018. The ratio of branching fractions for $\textit{B}$ $\textit{→ K}$ $\textit{μ}$ $\textit{μ}$ and $\textit{B}$ $\textit{→ K}$ $\textit{e}$ $\textit{e}$ decays is measured to be $$ {R}_K=1.0{8}_{-0.09}^{+0.11}{\left(\textrm{stat}\right)}_{-0.04}^{+0.04}\left(\textrm{syst}\right) $$ , which is consistent with the Standard Model prediction of unity. This constitutes the most precise test of lepton flavour universality using $\textit{B}$ → $\textit{K}$ $\textit{ℓ}$ $\textit{ℓ}$ decays with dilepton invariant-mass-squared above the $\textit{ψ}$(2$\textit{S}$) mass, whilst being the first of its kind at a hadron collider.

Netherlands

R. Aaij

A. Abdelmotteleb

C. Abellan Beteta

F. Abudinén

T. Ackernley

A. Adefisoye

B. Adeva

M. Adinolfi

P. Adlarson

C. Agapopoulou

C. Aidala

Z. Ajaltouni

S. Akar

K. Akiba

J. Albrecht

F. Alessio

Z. Aliouche

P. Alvarez Cartelle

R. Amalric

S. Amato

J. Amey

Y. Amhis

L. An

L. Anderlini

M. Andersson

A. Andreianov

P. Andreola

M. Andreotti

D. Andreou

A. Anelli

D. Ao

F. Archilli

Measurement of the branching fraction ratio $\textit{R}$