Based on a sample of $2.7\times10^{9}$ $\psi(3686)$ events collected by the BESIII detector operating at the BEPCII collider, the decay $\psi(3686)\to\gamma\chi_{cJ}, \chi_{cJ}\to\eta\eta\eta^{\prime}$ is analyzed. The decay modes $\chi_{c1}$ and $\chi_{c2}\to\eta\eta\eta^{\prime}$ are observed for the first time, and their corresponding branching fractions are determined to be ${\cal{B}}(\chi_{c1}\to\eta\eta\eta^{\prime}) = $ $ (1.40\, \pm 0.13\, (\text{stat.}) \pm 0.09\, (\text{sys.})) \times 10^{-4}$ and ${\cal{B}}(\chi_{c2}\to\eta\eta\eta^{\prime}) = (4.18\, \pm 0.84\, (\text{stat.}) \pm 0.48\, (\text{sys.})) \times 10^{-5}$ . An upper limit on the branching fraction of $\chi_{c0}\to\eta\eta\eta^{\prime}$ is set as $2.59 \times 10^{-5}$ at a 90% confidence level (CL). A partial wave analysis (PWA) of the decay $\chi_{c1}\to\eta\eta\eta^{\prime}$ is performed to search for the $1^{-+}$ exotic state $\eta_1(1855)$ . The PWA result indicates that the structure in the $\eta\eta^{\prime}$ mass spectrum is attributed to $f_0(1500)$ , while in the $\eta\eta$ mass spectrum, it is attributed to the $0^{++}$ phase space. The upper limit of ${\cal{B}}(\chi_{c1}\to\eta_{1}(1855)\eta) \cdot {\cal{B}}(\eta_{1}(1855)\to\eta\eta^{\prime}) \lt $ $ 9.79 \times 10^{-5}$ is set based on the PWA at 90% CL.

China

M. Ablikim

Russia

M.N. Achasov

Sweden

P. Adlarson

X.C. Ai

Germany

R. Aliberti

Italy

A. Amoroso

Q. An

Y. Bai

O. Bakina

Y. Ban

H.R. Bao

Poland

V. Batozskaya

Mongolia

K. Begzsuren

N. Berger

M. Berlowski

M. Bertani

D. Bettoni

F. Bianchi

E. Bianco

A. Bortone

I. Boyko

United States

R.A. Briere

A. Brueggemann

H. Cai

M.H. Cai

X. Cai

A. Calcaterra

G.F. Cao

N. Cao

Türkiye

S.A. Cetin

X.Y. Chai

J.F. Chang

G.R. Che

Y.Z. Che

C.H. Chen

Chao Chen

G. Chen

H.S. Chen

H.Y. Chen

M.L. Chen

S.J. Chen

S.L. Chen

S.M. Chen

T. Chen

X.R. Chen

X.T. Chen

X.Y. Chen

Y.B. Chen

Y.Q. Chen

Z. Chen

Z.J. Chen

Z.K. Chen

S.K. Choi

X. Chu

G. Cibinetto

F. Cossio

United Kingdom

J. Cottee-Meldrum

J.J. Cui

H.L. Dai

J.P. Dai

A. Dbeyssi

R.E. de Boer

D. Dedovich

C.Q. Deng

Z.Y. Deng

A. Denig

I. Denysenko

M. Destefanis

F. De Mori

B. Ding

X.X. Ding

Y. Ding

Y.X. Ding

J. Dong

L.Y. Dong

M.Y. Dong

X. Dong

M.C. Du

S.X. Du

Y.Y. Duan

P. Egorov

G.F. Fan

J.J. Fan

Y.H. Fan

J. Fang

S.S. Fang

W.X. Fang

Y.Q. Fang

R. Farinelli

L. Fava

F. Feldbauer

G. Felici

C.Q. Feng

J.H. Feng

L. Feng

Q.X. Feng

Search for $\textit{η}$ $_{1}$(1855) in $\textit{χ}$ $\textit{cJ}$ → $\textit{ηηη}$′ decays * Supported in part by National Key R&D Program of China (2023YFA1606000, 2023YFA1606704); National Natural Science Foundation of China (NSFC) (11635010, 11935015, 11935016, 11935018, 12025502, 12035009, 12035013, 12061131003, 12192260, 12192261, 12192262, 12192263, 12192264, 12192265, 12221005, 12225509, 12235017, 12361141819); the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program; CAS (YSBR-101); 100 Talents Program of CAS; The Institute of Nuclear and Particle Physics (INPAC) and Shanghai Key Laboratory for Particle Physics and Cosmology; Agencia Nacional de Investigación y Desarrollo de Chile (ANID), Chile (ANID PIA/APOYO AFB230003); German Research Foundation DFG (FOR5327); Istituto Nazionale di Fisica Nucleare, Italy; Knut and Alice Wallenberg Foundation (2021.0174, 2021.0299); Ministry of Development of Turkey (DPT2006K-120470); National Research Foundation of Korea ( NRF-2022R1A2C1092335); National Science and Technology fund of Mongolia; National Science Research and Innovation Fund (NSRF) via the Program Management Unit for Human Resources Institutional Development, Research and Innovation of Thailand ( B50G670107); Polish National Science Centre (2024/53/B/ST2/00975); Swedish Research Council (2019.04595); U. S. Department of Energy (DE-FG02-05ER41374)

We investigate the cosmological dynamics of Parameterized Absolute Parallelism (PAP) geometry within the framework of modified $$f(R,\Sigma ,T)$$ gravity. By generalizing the Gauss–Bonnet invariant $${\mathcal {G}}_b$$ using the PAP curvature tensor $$B^{\alpha }{}_{\mu \nu \sigma },$$ we incorporate both Riemannian curvature and torsion effects into a unified framework. The modified field equations are derived for a spatially flat FLRW background, and exact analytical solutions for the Hubble parameter, scale factor, energy density, and pressure are obtained under a constant equation-of-state parameter $$\omega .$$ Our analysis shows that the PAP deformation parameter $\textit{b}$ and matter–torsion coupling $$\eta $$ significantly modify cosmic expansion, the effective equation of state, and curvature diagnostics. Furthermore, we explore the role of $${\mathcal {G}}_b$$ in torsion-driven Gauss–Bonnet inflation and demonstrate how PAP corrections alter the slow-roll dynamics, enabling sustained inflation even for flat potentials. A detailed stability analysis reveals the critical regions in the $$(b,\eta )$$ parameter space separating stable and unstable cosmological phases. This unified approach recovers General Relativity, teleparallel gravity, and minimally coupled PAP models as limiting cases, offering new insights into early- and late-time acceleration driven by torsion and higher-curvature effects.

Egypt

Tahia Dabash

Saudi Arabia

A. Eid

M. Bakry

Gauss–Bonnet effects in $$f(R,\Sigma ,T)$$ gravity

We have studied an <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi><mi>O</mi><mo stretchy="false">(</mo><mn>4</mn><mo stretchy="false">)</mo></math> gauged <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>O</mi><mo stretchy="false">(</mo><mn>5</mn><mo stretchy="false">)</mo></math> Skyrmion on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi mathvariant="normal">I</mi><mspace depth="0.0ex" height="0.0ex" width="-0.2em"></mspace><mi mathvariant="normal">R</mi></mrow><mrow><mn>4</mn></mrow></msup></mrow></math>, which can be seen as a static soliton in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>4</mn><mo>+</mo><mn>1</mn></math> dimensions. This is a sequel of the known <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi><mi>O</mi><mo stretchy="false">(</mo><mi>D</mi><mo stretchy="false">)</mo></math> gauged <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>O</mi><mo stretchy="false">(</mo><mi>D</mi><mo>+</mo><mn>1</mn><mo stretchy="false">)</mo></math> Skyrmions on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi mathvariant="normal">I</mi><mspace depth="0.0ex" height="0.0ex" width="-0.2em"></mspace><mi mathvariant="normal">R</mi></mrow><mrow><mi>D</mi></mrow></msup></mrow></math> in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><mo>=</mo><mn>2</mn></math> and in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><mo>=</mo><mn>3</mn></math>, which are likewise localized to an absolute scale and topologically stable, their energies being bounded below by the winding number. In the absence of an analytic proof of existence, some such solutions are constructed numerically. Two families of solutions are found, of which only one possesses a gauge decoupling limit. The curvatures of both of these solutions decay as <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>r</mi><mrow><mo>−</mo><mn>3</mn></mrow></msup></math>, a property they share with the Yang-Mills instantons on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi mathvariant="normal">I</mi><mspace depth="0.0ex" height="0.0ex" width="-0.2em"></mspace><mi mathvariant="normal">R</mi></mrow><mrow><mn>4</mn></mrow></msup></mrow></math>.

Spain

Francisco Navarro-Lérida

Ireland

D.H. Tchrakian

SO(4) gauged O(5) Skyrmion on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi mathvariant="normal">R</mi><mn>4</mn></msup></math>

The <italic>r</italic>-process abundance peaks, particularly near mass number <italic>A</italic>&#8239;&#8764;&#8239;130, reflect underlying nuclear structure effects such as closed neutron shells, yet modeling the nucleosynthesis in this region remains hindered by uncertain neutron-capture rates. These rates are especially sensitive to nuclear level densities (NLDs) and <italic>&#947;</italic>-ray strength functions of neutron-rich nuclei, where experimental data are scarce. We present the first experimental constraint on the NLD of 141Cs using the <italic>&#946;</italic>-Oslo method, extending sensitivity to the neutron-rich regime near the <math altimg='si9.svg'><mrow><mi>N</mi><mo linebreak='goodbreak'>=</mo><mn>82</mn></mrow></math> closed shell. Our data allow for critical calibration of microscopic NLD models and reveal that 141Cs lies near the limit of statistical model applicability. Using this experimental input, we evaluate radiative neutron-capture rates across neighboring isotones using both Hauser&#8211;Feshbach (HF) and High Fidelity Resonance (HFR) models. Our results show order-of-magnitude rate increases for nuclei along the <math altimg='si2.svg'><mrow><mi>N</mi><mo linebreak='goodbreak'>=</mo><mn>86</mn></mrow></math> line, signaling a transition to resonance-dominated capture in this region. These findings underscore the importance of constraining NLDs to improve <italic>r</italic>-process reaction network predictions, particularly in environments where the validity of statistical models breaks down.

Canada

B. Greaves

D. Mücher

A. Spyrou

Belgium

S. Goriely

Switzerland

D. Rochman

H.C. Berg

D.L. Bleuel

J.A. Clark

C. Dembski

P.A. Deyoung

E. Good

C.M. Harris

Austria

A.J. Koning

Norway

A.C. Larsen

S.N. Liddick

S.M. Lyons

M. Markova

M.J. Mogannam

G. Owens-Fryar

A. Palmisano-Kyle

A.L. Richard

E.K. Ronning

D. Santiago-Gonzalez

G. Savard

M.K. Smith

A. Sweet

A. Tsantiri

Probing the limits of statistical neutron capture for the <italic>r</italic> process: Experimental constraints on 141Cs nuclear level densities

We introduce a novel level crossing phenomenon in the mass mixing between QCD axions: one canonical QCD axion and one $ Z_{{\cal{N}}} $ axion. The level crossing can occur at or slightly before the QCD phase transition critical temperature, depending on the ratio of the axion decay constants, $ \sim 1.69 $ . The cosmological evolution of the mass eigenvalues in these two scenarios is similar; however, the transition of axion energy density differs significantly. Finally, we estimate the relic density of the QCD axion dark matter in this context. Additionally, this level crossing may have some interesting cosmological implications.

Hai-Jun Li

Yu-Feng Zhou

Mass mixing between QCD axions * Supported by the CAS Project for Young Scientists in Basic Research YSBR-006, the National Key R&D Program of China (2017YFA0402204), and the National Natural Science Foundation of China (11821505, 11825506, 12047503)

We use a modified relativistic quark model to study the properties of excited charmed and charmed strange mesons. We calculate the masses and wave functions of conventional charmed and charmed strange mesons incorporating both spin and $\textit{S}$-$\textit{D}$ mixing effects and fit parameters of the potential model with known experimental states using differential evolution techniques. Using leading Born-Oppenheimer expansion, we compute the spectrum and wave functions of the first gluonic excited state of charmed and charmed strange mesons. We examine the effects of gluonic excitation on the spectrum of the resulting hybrid mesons. Using our calculated spectrum and wave functions, we determine the radiative transitions of the conventional and hybrid open charm mesons. We compare our calculations with experimental data and other works. We expect our results will be beneficial in the detection of charmed and charmed strange conventional and hybrid mesons.

Pakistan

Saba Noor

Faisal Akram

Bilal Masud

Study of excited $\textit{D}$ and D$_{s}$ mesons in a relativized quark model * F. A. acknowledges HEC grant 20-15728/NRPU/R&D/HEC/2021, Pakistan

This study investigates the intrinsic electric dipole moment (EDM) of the $\textit{τ}$ lepton, which is an important quantity in the search for physics beyond the Standard Model (BSM). In preparation for future measurements at the Super Tau-Charm Facility (STCF), we employ Monte Carlo simulations of the $ e^+e^- \rightarrow \tau^+\tau^- $ process and optimize the analysis methodology for EDM extraction. Machine learning techniques are implemented to efficiently identify signal events ( $ \tau^\pm\rightarrow \pi^\pm\pi^0\nu_\tau $ ), which result in a significant improvement in signal-to-noise ratio. Our optimized event selection algorithm achieves 80.0% signal purity with 6.3% efficiency. We develop an analytical approach for $\textit{τ}$ lepton momentum reconstruction and derive the squared spin density matrix along with optimal observables, which maximize the sensitivity to $ d_\tau $ . The relationship between these observables and the EDM is established with the estimated sensitivity of $ |d_\tau| \lt 3.89\times 10^{-18}\,e\cdot\mathrm{cm} $ at a 68% confidence level. These results provide a foundation for future experimental measurements of the $\textit{τ}$ lepton EDM in STCF experiments.

Xulei Sun

Yongcheng Wu

Xiaorong Zhou

Sensitivity study of the tau lepton electric dipole moment at the Super Tau-Charm Facility * Supported by the National Key R&D Program of China (2022YFA1602200, 2023YFA1607200); the National Natural Science Foundation of China (NSFC) (12341501, 12341503, 12341504); the international partnership program of the Chinese Academy of Sciences (211134KYSB20200057). Xulei Sun is supported by the Undergraduate Research Program of the University of Science and Technology of China and the Xinhe Scholar Program of the School of the Gifted Young

This paper investigates the spectral form factor (SFF) of the quadratic $\textit{R}$-para-particle Sachdev-Ye-Kitaev ($\textit{R}$-PSYK ) model with various random matrix ensemble couplings. We generalize previous work on Gaussian Unitary Ensemble (GUE) couplings to all three Gaussian ensembles (GUE, GOE, GSE) and three circular ensembles (CUE, COE, CSE). Through analytical and numerical methods, we establish precise correspondences between GUE and CUE results, demonstrating their SFFs satisfy $$ {\mathcal{K}}_{\textrm{GUE}}(2t) $$ ≈ $$ {\mathcal{K}}_{\textrm{CUE}}(t) $$ in the time regime 1 ≪ $\textit{t}$ ≪ $\textit{N}$. For the symplectic ensembles, we observe similar behavior with appropriate time rescaling, while we only provide the calculation method for the orthogonal ensembles.

Tingfei Li

Spectral form factor of quadratic $\textit{R}$-para-particle SYK model with random matrix coupling

We investigate the thermodynamic phase structure of four-dimensional <italic>R</italic>-charged black holes&#8211;characterized by four independent <math altimg='si11.svg'><mrow><mi>U</mi><mo>(</mo><mn>1</mn><mo>)</mo></mrow></math> charges&#8211;through the lens of Lyapunov exponents associated with unstable circular orbits of both massless and massive particles. Considering three distinct charge configurations (equal, partially unequal, and fully unequal), we show that the thermal profile of the Lyapunov exponent can effectively probe the black hole phase transitions. Furthermore, we demonstrate that the discontinuous jump in the Lyapunov exponent acts as an order parameter, with the associated critical exponent <math altimg='si12.svg'><mrow><mi>&#948;</mi><mo linebreak='goodbreak'>=</mo><mn>1</mn><mo linebreak='goodbreak'>/</mo><mn>2</mn></mrow></math> near the critical point&#8211;consistent across all charge configurations studied. This supports the proposed universality of the exponent and the broader connection between dynamical chaos and thermodynamic phase transitions.

India

Mozib Bin Awal

Prabwal Phukon

Probing thermodynamic phase transitions of 4D <italic>R</italic>-charged black holes via lyapunov exponent

In this work we introduce the rescaled <math altimg='si1.svg'><msup><mi mathvariant='script'>R</mi><mn>2</mn></msup></math>-corrected minimally coupled scalar field theory, a theory that contains minimal quantum corrections of the single scalar field Lagrangian. We develop the theoretical framework in the Jordan frame where the baryons geodesics are free fall geodesics and we do not treat the theory as a two scalar field theory in the Einstein frame. The theoretical framework can be reduced to a single scalar field theory framework by using a perturbative expansion at the level of the field equations, making the resulting theory easy to tackle analytically. The first two quantum corrections contain two terms, a linear <math altimg='si20.svg'><mrow><mo>&#8764;</mo><mi mathvariant='script'>R</mi></mrow></math> and a quadratic term <math altimg='si21.svg'><mrow><mo>&#8764;</mo><msup><mi mathvariant='script'>R</mi><mn>2</mn></msup></mrow></math>. The effect of the linear term alters the Einstein-Hilbert term, making the resulting theory a rescaled version of Einstein-Hilbert gravity. Due to the presence of the rescaled Einstein-Hilbert term <math altimg='si22.svg'><mrow><mo>&#8764;</mo><mi>&#955;</mi><mfrac><mi mathvariant='script'>R</mi><mrow><mn>16</mn><mi>&#960;</mi><mi>G</mi></mrow></mfrac></mrow></math>, the gravitational constant will no longer be that of Newton&#8217;s, but a rescaled one <math altimg='si23.svg'><mfrac><mi>G</mi><mi>&#955;</mi></mfrac></math> and hence gravity can be stronger primordially, or even weaker. The perspective of having stronger gravity primordially, is compatible with intuition, since one expects a stronger gravity primordially, but having a weaker gravity for some reason is not prohibited theoretically. The attribute of our theoretical framework is that it allows a stronger gravity primordially, which returns to ordinary gravity as the curvature of the Universe decreases. We examine the effects of the quantum terms on several mainstream scalar field inflationary potentials, such as hybrid inflation, monomial inflation and power-law inflation, and we demonstrate that the hybrid inflation and power-law inflation, which are 3-parameter models, are compatible with the Atacama Cosmology Telescope data in the strong gravity limit, while the monomial inflation, which is a 4-parameter model, can be compatible with the Atacama Cosmology Telescope data in the weak gravity limit, however the model suffers from perturbative expansion break down during inflation.

Greece

Kazakhstan

V.K. Oikonomou

Strong gravity effects on <math altimg='si1.svg'><msup><mi mathvariant='script'>R</mi><mn>2</mn></msup></math>-corrected single scalar field inflation and compatibility with the ACT data