In this work, we explore the feasibility of realizing the Dark Dimension Scenario through T-fold compactifications on $\textit{T}$ × $\textit{S}$ , where the base of the internal space $\textit{S}$ naturally acts as the requisite mesoscopic extra dimension. Utilizing Scherk-Schwarz reduction from 5D to 4D, and applying duality twists from both elliptic and parabolic conjugacy classes of subgroups of the T-duality group associated with $\textit{T}$ , we stabilize the volume of $\textit{T}$ and several other moduli. This approach generates a potential characterized by two runaway directions, one aligned with the Scherk-Schwarz radion. Further stabilization efforts yield a decreasing potential trajectory demanded by the Dark Dimension Scenario.

Netherlands

Guo-En Nian

Stefan Vandoren

Towards a string realization of the Dark Dimension via T-folds

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

The arrival time of electromagnetic signals traveling in chiral cosmic media is investigated in the context of Maxwell-Carroll-Field-Jackiw electrodynamics. Considering the interstellar medium (ISM) as a cold, ionized, chiral plasma, we derive the time delay between two traveling signals, expressed in terms of a modified dispersion measure (DM) which receives additional contribution from the chiral parameters. Faraday rotation angle is also addressed in this chiral plasma scenario, yielding modified rotation measures (RM). Using DMs data from five pulsars, we establish constraints on the chiral parameter magnitude at the order of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>23</mn></mrow></msup><mi>–</mi><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>22</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math>. On the other hand, the Faraday rotation retrieved from RM measurements implied upper constraints as tight as <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>10</mn><mrow><mo>−</mo><mn>36</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>.

Brazil

Filipe S. Ribeiro

Pedro D.S. Silva

Manoel M. Ferreira

Constraining <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>C</mi><mi>P</mi><mi>T</mi></mrow></math>-odd electromagnetic chiral parameters with pulsar timing

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

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 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.

United States

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

The self-dual condition, which ensures invariance under electromagnetic duality, manifests as a partial differential equation in nonlinear electromagnetism theories. The general solution to this equation is expressed in terms of an auxiliary field, $\textit{τ}$, and Courant-Hilbert functions, $\textit{ℓ}$($\textit{τ}$), which depend on $\textit{τ}$. Recent studies have shown that duality-invariant nonlinear electromagnetic theories fulfill the principle of causality under the conditions $$ \frac{\partial \ell }{\partial \tau}\ge 1 $$ and $$ \frac{\partial^2\ell }{\partial {\tau}^2}\ge 0 $$ .

China

H. Babaei-Aghbolagh

Iran

Komeil Babaei Velni

Germany

Song He

Zahra Pezhman

Root- $$ T\overline{T} $$ deformations on causal self-dual electrodynamic theories

Big Bang nucleosynthes describes a significant process in the early universe, responsible for the formation of light nuclei a while after the Big Bang explosion. Its sensitivity to the expansion rate makes BBN an effective probe for testing deviations from standard cosmology, particularly within the framework of modified theories of gravity. In this article, we investigate the evolution of the Universe through Big Bang nucleosynthesis within the framework of <math altimg='si2.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>T</mi><mo>,</mo><mspace width='0.25em' /><mi>B</mi><mo>,</mo><mspace width='0.25em' /><msub><mrow><mi>T</mi></mrow><mrow><mi mathvariant='script'>G</mi></mrow></msub><mo>,</mo><mspace width='0.25em' /><msub><mrow><mi>B</mi></mrow><mrow><mi mathvariant='script'>G</mi></mrow></msub><mo stretchy='false'>)</mo></math> gravity. Here, <math altimg='si3.svg'><mi>T</mi><mo>,</mo><mspace width='0.25em' /><mi>B</mi><mo>,</mo><mspace width='0.25em' /><msub><mrow><mi>T</mi></mrow><mrow><mi mathvariant='script'>G</mi></mrow></msub></math> and <math altimg='si4.svg'><msub><mrow><mi>B</mi></mrow><mrow><mi mathvariant='script'>G</mi></mrow></msub></math> correspond to the torsion, boundary term, teleparallel Gauss-Bonnet term, and Gauss-Bonnet boundary term, respectively. To explore the deviation from the teleparallel equivalent of general relativity, we apply the transformation <math altimg='si2.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>T</mi><mo>,</mo><mspace width='0.25em' /><mi>B</mi><mo>,</mo><mspace width='0.25em' /><msub><mrow><mi>T</mi></mrow><mrow><mi mathvariant='script'>G</mi></mrow></msub><mo>,</mo><mspace width='0.25em' /><msub><mrow><mi>B</mi></mrow><mrow><mi mathvariant='script'>G</mi></mrow></msub><mo stretchy='false'>)</mo></math> = <math altimg='si5.svg'><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mi>T</mi><mo linebreak='goodbreak' linebreakstyle='after'>+</mo><mi mathvariant='script'>F</mi><mo stretchy='false'>(</mo><mi>T</mi><mo>,</mo><mspace width='0.25em' /><mi>B</mi><mo>,</mo><mspace width='0.25em' /><msub><mrow><mi>T</mi></mrow><mrow><mi mathvariant='script'>G</mi></mrow></msub><mo>,</mo><mspace width='0.25em' /><msub><mrow><mi>B</mi></mrow><mrow><mi mathvariant='script'>G</mi></mrow></msub><mo stretchy='false'>)</mo></math>. For an in-depth analysis of the Big Bang nucleosynthesis, we choose five distinct models from gravity and compared the results with the observational limits on <math altimg='si6.svg'><mo stretchy='true'>|</mo><mfrac><mrow><mi mathvariant='normal'>&#916;</mi><msub><mrow><mi mathvariant='script'>T</mi></mrow><mrow><mi>f</mi></mrow></msub></mrow><mrow><msub><mrow><mi mathvariant='script'>T</mi></mrow><mrow><mi>f</mi></mrow></msub></mrow></mfrac><mo stretchy='true'>|</mo></math> to examine restrictions on the free parameters associated with these models. Our outcomes indicate that <math altimg='si2.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>T</mi><mo>,</mo><mspace width='0.25em' /><mi>B</mi><mo>,</mo><mspace width='0.25em' /><msub><mrow><mi>T</mi></mrow><mrow><mi mathvariant='script'>G</mi></mrow></msub><mo>,</mo><mspace width='0.25em' /><msub><mrow><mi>B</mi></mrow><mrow><mi mathvariant='script'>G</mi></mrow></msub><mo stretchy='false'>)</mo></math> gravity can agree with the constraint of big bang nucleosynthesis, and hence build a valid view of the universe. Moreover, we take the limiting cases of the assumed theory, that is, <math altimg='si7.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>T</mi><mo>,</mo><mi>B</mi><mo stretchy='false'>)</mo></math> and <math altimg='si8.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>T</mi><mo stretchy='false'>)</mo></math> theories, which also ensure consistency with BBN data.

Pakistan

Abdul Malik Sultan

Manahil Ali

Shamaila Rani

Azerbaijan

Nadeem Azhar

N. Myrzakulov

Uzbekistan

Sanjar Shaymatov

Constraining Big Bang nucleosynthesis in <math altimg='si1.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>T</mi><mo>,</mo><mi>B</mi><mo>,</mo><msub><mrow><mi>T</mi></mrow><mrow><mi mathvariant='script'>G</mi></mrow></msub><mo>,</mo><msub><mrow><mi>B</mi></mrow><mrow><mi mathvariant='script'>G</mi></mrow></msub><mo stretchy='false'>)</mo></math> gravity

We present a unified treatment of cosmic inflation within the framework of Myrzakulov Gravity, exploring its realization in three different formalisms: metric (curvature-based), teleparallel (torsion-based), and symmetric teleparallel (non-metricity-based). For each case, we derive the corresponding field equations in a flat FLRW background, study inflationary solutions driven by a scalar field, and compute observable quantities such as the scalar spectral index <math altimg='si1.svg'><msub><mrow><mi>n</mi></mrow><mrow><mi>s</mi></mrow></msub></math> and the tensor-to-scalar ratio <italic>r</italic>.

Inflation in Myrzakulov <italic>F</italic>( <italic>R</italic>, <italic>T</italic>) gravity: A comparative study in metric, symmetric teleparallel, and Weitzenb&#246;ck formalisms

This article explores how modifications to gravity influence the structure of the brane, with the goal of identifying the gravitational model that most closely reflects the one governing our physical universe. To achieve this, we consider a generalization of standard General Relativity. The stability of the model is evaluated through probabilistic measurements, revealing minimum points that represent the most probable and stable configurations of the brane for different values of the gravitational terms. Furthermore, the location of fermions on the brane is affected by gravitational variations, with the presence of resonance modes and the possibility of leakage of massive fermions into the bulk. Numerical analyses are presented, showing that the increase in the influence of gravitational terms increases the certainty of the location of massless fermions on the brane. All these results provide important insights for understanding the dynamics of the braneworld universe.

A.R.P. Moreira

Mexico

Shi-Hai Dong

Braneworld- <italic>f</italic>( <italic>R</italic>, <italic>T</italic>, <italic>G</italic>)

We present an analytic reconstruction of one-loop amplitudes for the process $$ 0\to \overline{q} qt\overline{t}H $$ . Our calculation is a novel use of analytic reconstruction, retaining explicit covariance in the massive spin states through the massive spinor-helicity formalism. The analytic reconstruction relies on embedding the massive five-point kinematics in a fully massless eight-point phase space while still building a minimal ansatz directly in the five-point phase space. In order to obtain compact analytic expressions it is necessary to identify suitable partial fraction decompositions and extract common numerator factors, which we achieve through careful inspection of limits in which pairs of denominators vanish. We find that the resulting amplitudes are more numerically efficient than ones computed using automatic methods but that the gains are not as significant as in the massless case, at least at present. The method opens the door to applications at two-loop order, where numerical efficiency and improvements in the reconstruction methodology are more crucial, especially with regards to the number of free parameters in the ansatz.

John Campbell

United Kingdom

Giuseppe Laurentis

R. Ellis

Analytic reconstruction with massive particles: one-loop amplitudes for $$ 0\to \overline{q} qt\overline{t}H $$