We study the viability of light thermal dark matter (DM) in the sub-GeV mass range in view of the stringent new DAMIC-M limits on DM-electron scattering. Considering a Dirac fermion singlet DM charged under a new Abelian gauge symmetry <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo></math>, we outline two possibilities: (i) family nonuniversal <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo></math> gauge coupling with resonantly enhanced DM annihilation into Standard Model (SM) fermions, and (ii) family universal dark <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo></math> gauge symmetry where relic density is set by DM annihilation into light gauge bosons. As an illustrative example of the first class of models, we consider a gauged <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>L</mi><mi>μ</mi></msub><mo>−</mo><msub><mi>L</mi><mi>τ</mi></msub></math> extension of the SM having interesting detection prospects at several experiments. While both of these classes of models lead to the observed DM relic and consistency with DAMIC-M together with other experimental limits, the second class of models also lead to strong DM self-interactions, potentially solving the small-scale structure issues of cold dark matter. While a vast part of the parameter space in both the models is already ruled out, the current allowed region of parameter space can be further probed at ongoing or future experiments, keeping the models testable.

India

Debasish Borah

Satyabrata Mahapatra

Narendra Sahu

Vicky Singh Thounaojam

Light thermal dark matter models in the light of DAMIC-M 2025 constraints

Flavor hierarchies emerge from a single hierarchical parameter <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi></math> in a one-flavon Froggatt–Nielsen scheme. Fixing <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi><mo>=</mo><mn>5.357</mn></math> from charged-lepton ratios (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>m</mi></mrow><mrow><mi>e</mi></mrow></msub><mo>:</mo><mtext> </mtext><mtext> </mtext><msub><mrow><mi>m</mi></mrow><mrow><mi>μ</mi></mrow></msub><mo>:</mo><msub><mrow><mi>m</mi></mrow><mrow><mi>τ</mi></mrow></msub><mo>∝</mo><msup><mrow><mi>ε</mi></mrow><mrow><mn>5</mn></mrow></msup><mo>:</mo><msup><mrow><mi>ε</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>:</mo><mn>1</mn></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ε</mi><mo>=</mo><mn>1</mn><mo>/</mo><mi>B</mi></math>), we reproduce quark masses and Cabibbo-Kobayashi-Maskawa targets at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>M</mi><mi>Z</mi></msub></math> with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo></math> coefficients. The same <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ε</mi></math> gives viable lepton textures and benchmarks for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>U</mi><mrow><mi>PMNS</mi></mrow></msub></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>∑</mo><msub><mi>m</mi><mi>ν</mi></msub></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mrow><mi>β</mi><mi>β</mi></mrow></msub></math>. Compact correlations (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">|</mo><msub><mrow><mi>V</mi></mrow><mrow><mi>u</mi><mi>s</mi></mrow></msub><mo stretchy="false">|</mo><mo>,</mo><mo stretchy="false">|</mo><msub><mrow><mi>V</mi></mrow><mrow><mi>c</mi><mi>b</mi></mrow></msub><mo stretchy="false">|</mo><mo>,</mo><mo stretchy="false">|</mo><msub><mrow><mi>V</mi></mrow><mrow><mi>u</mi><mi>b</mi></mrow></msub><mo stretchy="false">|</mo><mo>,</mo><msubsup><mrow><mi>θ</mi></mrow><mrow><mn>13</mn></mrow><mrow><mi>PMNS</mi></mrow></msubsup></mrow></math>) follow from powers of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ε</mi></math>.

United States

Vernon Barger

One-flavon flavor: A single hierarchical parameter <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi></math> organizes quarks and leptons at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>M</mi><mi>Z</mi></msub></math>

In this work, we derive a new class of analytic black hole solutions within the framework of <math altimg='si8.svg'><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><msub><mi mathvariant='script'>L</mi><mi>m</mi></msub><mo>,</mo><mi>T</mi><mo>)</mo></mrow></math> gravity, where the black hole is surrounded by an anisotropic fluid acting as the matter source. We consider both linear and nonlinear forms of the function <math altimg='si8.svg'><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><msub><mi mathvariant='script'>L</mi><mi>m</mi></msub><mo>,</mo><mi>T</mi><mo>)</mo></mrow></math>, enabling a detailed exploration of how anisotropic pressures and different <math altimg='si8.svg'><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><msub><mi mathvariant='script'>L</mi><mi>m</mi></msub><mo>,</mo><mi>T</mi><mo>)</mo></mrow></math> influence the spacetime structure. Furthermore, we derive the conditions on the coupling parameters ( <italic>&#946;</italic> <inf>1</inf>, <italic>&#946;</italic> <inf>2</inf>, <italic>&#946;</italic> <inf>3</inf>) under which the energy condition is satisfied. Utilising these constraints, we then investigate the thermodynamic behaviour of the resulting black hole solutions in the presence of various matter fields. An important outcome of this study is that the results obtained deviate from those predicted by standard General Relativity. It is also observed that these deviations depend explicitly on the interaction between the matter Lagrangian <math altimg='si9.svg'><msub><mi mathvariant='script'>L</mi><mi>m</mi></msub></math> and the trace <italic>T</italic> of the energy-momentum tensor.

Aniruddha Ghosh

Ujjal Debnath

The new black hole solution with anisotropic fluid in <math altimg='si8.svg'><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><msub><mi mathvariant='script'>L</mi><mi>m</mi></msub><mo>,</mo><mi>T</mi><mo>)</mo></mrow></math> gravity: Thermodynamics

The observed matter–antimatter asymmetry of the Universe remains a fundamental challenge in modern physics. In this work, we explore gravitational baryogenesis within the framework of <italic>f</italic>( <italic>T, L<inf>m</inf></italic>) gravity, where the gravitational Lagrangian depends on both the torsion scalar <italic>T</italic> and the matter Lagrangian <italic>L<inf>m</inf></italic>. We consider three representative models and examine their ability to generate the observed baryon-to-entropy ratio. Our analysis shows that couplings involving both torsion and the matter Lagrangian, <math altimg='si35.svg'><mrow><msub><mi>&#8706;</mi><mi>&#956;</mi></msub><mrow><mo>(</mo><mo>&#8722;</mo><mi>T</mi><mo linebreak='badbreak'>&#8722;</mo><mfrac><msub><mi>L</mi><mi>m</mi></msub><msub><mi>L</mi><mn>0</mn></msub></mfrac><mo>)</mo></mrow></mrow></math>, can successfully account for the baryon asymmetry for decoupling temperatures in the range 10 12&#8211;10 14&#8201;GeV, while remaining consistent with small deviations from General Relativity. These results highlight the capacity of <italic>f</italic>( <italic>T, L<inf>m</inf></italic>) gravity to provide novel mechanisms for baryogenesis, demonstrating that the interplay between torsion and matter-sector contributions can naturally generate the observed asymmetry. The framework also remains compatible with late-time cosmological evolution, offering a unified setting for early- and late-time dynamics.

Portugal

Daniel F P Cruz

David S. Pereira

Francisco S N Lobo

Gravitational baryogenesis in <italic>f</italic>( <italic>T, L<inf>m</inf></italic>) gravity

In the context of the left-right symmetric model, we study the interplay of neutrinoless double beta (0 <italic>&#957;&#946;&#946;</italic>) decay, parity-violating M&#248;ller scattering, and high-energy colliders, resulting from the Yukawa interaction of the right-handed doubly-charged scalar to electrons, which could evade the severe constraints from charged lepton flavor violation. The 0 <italic>&#957;&#946;&#946;</italic> decay amplitude receives additional contributions from right-handed sterile neutrinos. The half-life, calculated in the effective field theory framework, allows for an improved description of the contributions involving non-zero mixing between left- and right-handed <italic>W</italic> bosons and those arising from exchanging a light right-handed neutrino. We find that the relative sensitivities between the low-energy (or high-precision) and high-energy experiments are affected by the left-right mixing. On the other hand, our results show how the interplay of collider and low-energy searches provides a manner to explore regions that are inaccessible to 0 <italic>&#957;&#946;&#946;</italic> decay experiments.

China

Gang Li

Michael J. Ramsey-Musolf

Sebastián Urrutia Quiroga

Italy

Juan Carlos Vasquez

Dissecting lepton number violating interactions in the left-right symmetric model: 0 <italic>&#957;&#946;&#946;</italic> decay, M&#248;ller scattering, and collider searches

This study rigorously examines the influence of dark matter within the framework of <math altimg='si10.svg'><mrow><mi>f</mi><mo>(</mo><mi mathvariant='script'>R</mi><mo>,</mo><msub><mi mathvariant='script'>L</mi><mi>m</mi></msub><mo>)</mo></mrow></math> gravity, with a particular emphasis on its critical role in facilitating traversable wormhole solutions. By employing anisotropic matter sources modeled through Bose-Einstein condensates and Einasto density profiles, we derive a novel class of wormhole solutions. The construction of the shape function relies on the density profile equation in conjunction with modified field equations, thereby establishing a theoretical foundation for these solutions. Careful selection of parameters ensures that the proposed solutions satisfy all requisite conditions for traversability. Moreover, we conduct a systematic evaluation of energy conditions across two distinct scenarios, further validating the physical viability of the models. The investigation also extends to analyzing anisotropic effects, exoticity parameters, and active gravitational mass. This work presents a comprehensive exploration of the physical feasibility and stability of wormhole structures within the context of <math altimg='si10.svg'><mrow><mi>f</mi><mo>(</mo><mi mathvariant='script'>R</mi><mo>,</mo><msub><mi mathvariant='script'>L</mi><mi>m</mi></msub><mo>)</mo></mrow></math> modified gravity theories, offering significant contributions to our understanding of the interplay between dark matter and advanced gravitational phenomena.

H Aruna Kumara

Chaitra Chooda Chalavadi

V. Venkatesha

Investigating wormhole structures in <math altimg='si10.svg'><mrow><mi>f</mi><mo>(</mo><mi mathvariant='script'>R</mi><mo>,</mo><msub><mi mathvariant='script'>L</mi><mi>m</mi></msub><mo>)</mo></mrow></math> gravity: Implications for dark matter

We present, to our knowledge, the first systematic study of early-late cosmic evolution and acceleration in the framework of <math altimg='si15.svg'><mrow><mi>f</mi><mo>(</mo><mi>T</mi><mo>,</mo><msub><mi mathvariant='script'>L</mi><mi>m</mi></msub><mo>)</mo></mrow></math> gravity, an extension of teleparallel theories coupling torsion with the matter Lagrangian. By incorporating the Big-Bang Nucleosynthesis (BBN) bound on the freeze-out temperature, we obtain a tight constraint on the inverse-torsion parameter, ensuring consistency with early-time physics. Employing Markov Chain Monte Carlo analyses with progressively richer observational datasets, CC, Union3, and SN22 supernovae, we constrain a well-motivated model and reconstruct key cosmological functions. The reconstructed Hubble and distance modulus functions show excellent agreement with the observations, confirming the observational viability of the model. The model successfully reproduces the observed late-time expansion history, yielding a transition from deceleration to acceleration through the deceleration parameter. The effective equation of state is found to remain negative throughout, with present values <math altimg='si16.svg'><mrow><msub><mi>w</mi><mn>0</mn></msub><mo linebreak='goodbreak'>&gt;</mo><mo>&#8722;</mo><mn>1</mn></mrow></math>, indicating a quintessence-like behavior rather than a cosmological constant or phantom regime. These results highlight the ability of <math altimg='si15.svg'><mrow><mi>f</mi><mo>(</mo><mi>T</mi><mo>,</mo><msub><mi mathvariant='script'>L</mi><mi>m</mi></msub><mo>)</mo></mrow></math> gravity to mimic the concordance scenario while allowing controlled deviations in the expansion history.

Sai Swagat Mishra

Suchita Patel

P.K. Sahoo

BBN to late-time acceleration in <math altimg='si15.svg'><mrow><mi>f</mi><mo>(</mo><mi>T</mi><mo>,</mo><msub><mi mathvariant='script'>L</mi><mi>m</mi></msub><mo>)</mo></mrow></math> gravity

The dimensional reduction of M-theory couplings at order <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mo>ℓ</mo><mi>p</mi><mn>6</mn></msubsup></math> is known to produce one-loop <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mrow><mi>α</mi></mrow><mrow><mo>′</mo><mn>3</mn></mrow></msup></math> corrections in type IIA string theory. In this paper, we perform the Kaluza-Klein reduction of the M-theory Chern-Simons coupling <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>t</mi><mn>8</mn></msub><msub><mi>ε</mi><mn>11</mn></msub><mi>A</mi><msup><mi>R</mi><mn>4</mn></msup></math> at this order. By meticulously accounting for nongauge-invariant total derivative terms, we derive the complete set of corresponding one-loop, gauge-invariant couplings in the type IIA effective action. Our results not only reproduce the standard Chern-Simons term <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>t</mi><mn>8</mn></msub><msub><mi>ε</mi><mn>10</mn></msub><mi>B</mi><msup><mi>R</mi><mn>4</mn></msup></math>—which is gauge invariant up to total derivatives—but also unveil a new set of gauge-invariant couplings involving Ramond-Ramond and Neveu-Schwarz–Neveu-Schwarz field strengths. To validate our findings, we test their consistency under string dualities. We dimensionally reduce the derived type IIA couplings on a K3 manifold and show that the resulting one-loop <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>α</mi><mo>′</mo></msup></math> corrections in six dimensions transform under S-duality into the dimensional reduction of the tree-level heterotic string Chern-Simons coupling <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>H</mi><mrow><mi>μ</mi><mi>ν</mi><mi>α</mi></mrow></msub><msup><mi mathvariant="normal">Ω</mi><mrow><mi>μ</mi><mi>ν</mi><mi>α</mi></mrow></msup></math> on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>T</mi><mn>4</mn></msup></math>. This nontrivial agreement provides strong evidence for the correctness of both the M-theory Chern-Simons term and its reduction to type IIA.

Iran

Mohammad R. Garousi

Dimensional reduction of the M-theory Chern-Simons term at order <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mo>ℓ</mo><mi>p</mi><mn>6</mn></msubsup></math>

We discuss that the string/M-theory partition function requires a choice of ensembles, depending on which background fields are held fixed. The background fields correspond to worldvolume couplings in the effective action approach to the superstring, which we extrapolate to the M2-brane. One natural ensemble in this context, which we call the M2-ensemble, corresponds to fixing the value of the M-theory three-form potential. In holographic setups the choice of ensemble is important when comparing to observables in the dual field theory. Indeed, in AdS holography the M2-ensemble does not map gravitational observables directly to field theory observables at a fixed rank $\textit{N}$, but rather to observables in the grand canonical ensemble. We remark that many M2-brane partition functions take a simple form in this ensemble hinting at one-loop exactness. We also discuss how in AdS holography, the M2-ensemble does correspond to the canonical ensemble in the field theory, i.e. the (2,0) theory at fixed rank $\textit{N}$.

United Kingdom

Friðrik Gautason

Jesse Muiden

Ensembles in M-theory and holography

Within the framework of the next-to-minimal supersymmetric (SUSY) extension of the Standard Model (SM) with a local B-L gauge symmetry (N-B-LSSM), we study lepton flavor violating (LFV) $ \tau\rightarrow e M^+ M^- $ decays: $ \tau \rightarrow e \pi^+\pi^- $ , $ \tau \rightarrow e \pi^+K^- $ , and $ \tau \rightarrow e K^+K^- $ . Based on the latest experimental data, the influence of different sensitive parameters on the branching ratios is considered. It can be seen from the numerical analysis that the main sensitive parameters and LFV sources are non-diagonal elements corresponding to the initial and final leptons. This work can provide a basis for discovering the existence of new physics (NP).

Rong-Zhi Sun

Shu-Min Zhao

Shuang Di

Xing-Xing Dong

Study of ${\boldsymbol\tau\rightarrow {\boldsymbol e M^+ M^-}}$ decays in N-B-LSSM * Supported by National Natural Science Foundation of China (NNSFC) (12075074), Natural Science Foundation of Hebei Province (A2023201040, A2022201022, A2022201017, A2023201041), Natural Science Foundation of Hebei Education Department (QN2022173), Post-graduate's Innovation Fund Project of Hebei University (HBU2024SS042), the Project of the China Scholarship Council (CSC) (202408130113). X. Dong acknowledges support from Fundação para a Ciência e a Tecnologia (FCT, Portugal) through the projects CFTP FCT Unit (UIDB/00777/2020, UIDP/00777/2020)