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)

Axions and axion-like particles can be generated in the early universe through mechanisms such as misalignment production, thermal processes, and the decay of topological defects. In this study, we show that scalar perturbations in the early universe can produce a significant amount of these particles primarily through mass parametric resonance effects. Scalar perturbations induce temperature fluctuations during the particle mass transition era, e.g., during the QCD phase transition. These temperature fluctuations modulate the particle mass, transferring energy into the field through parametric mass resonance, a nonlinear process. This mechanism exhibits substantially unstable regions that could lead to explosive particle production. Notably, it does not generate additional isocurvature perturbations.

Ruifeng Zheng

Puxian Wei

Qiaoli Yang

Generation of axions and axion-like particles through mass parametric resonance induced by scalar perturbations in the early universe

The study of extra charged gauge bosons beyond the Standard Model has always been of great interest. Future muon colliders will have a significant advantage in discovering exotic particles. In this paper, by studying the $ \mu^+ \mu^- \to W^{\prime +} W^{\prime -} \to e^+ e^- n_e \bar{n}_e $ process, we explore the properties of $ W^\prime $ in the alternative left-right model. The cross section and angular distribution of the final electron are investigated in a scenario of different $ W^\prime $ masses and right-handed coupling constants. The forward-backward asymmetry is also an important observable to reflect the properties of $ W^\prime $ . We provide a method to effectively suppress the background processes by imposing constraints on the transverse momentum $ P_T $ and azimuthal angle of the final-state electrons $\textit{α}$. With cuts of $ 600 \lt P_T \lt 3500 $ GeV and $ 0.5 \lt \alpha \lt 3 $ , the significance exceeds 5$\textit{σ}$ for 4.8 TeV $ W^\prime $ at a collision energy of 10 TeV.

Liuxin Zhao

Honglei Li

Zhi-Long Han

Fei Huang

Xinyi Yan

Extra charged gauge boson $\textit{W}$′ in Alternative Left-Right Model at future muon collider * This work is supported by the Natural Science Foundation of Shandong Province (ZR2022MA065, ZR2024QA138), and University of Jinan Disciplinary Cross-Convergence Construction Project 2024 (XKJC-202404)

High-precision regression of physical parameters from black hole images generated by General Relativistic Ray Tracing (GRRT) is essential for investigating spacetime curvature and advancing black hole astrophysics. However, owing to limitations in observational resolution, high observational costs, and imbalanced distributions of positive and negative samples, black hole images often suffer from data scarcity, sparse parameter spaces, and complex structural characteristics. These factors pose significant challenges to conventional regression methods based on simplified physical models. To overcome these challenges, this study introduces the Multiscale Adaptive Network (MANet), a novel regression framework grounded in deep learning. MANet integrates an Adaptive Channel Attention (ACA) module to selectively enhance features in physically informative regions. Meanwhile, a Multiscale Enhancement Feature Pyramid (MEFP) is employed to capture fine-grained spatial structures, such as photon rings and accretion disks, while alleviating information loss due to downsampling. Experimental evaluations on GRRT-simulated datasets demonstrate that MANet substantially improves parameter estimation accuracy and generalization capability in high-dimensional parameter spaces, outperforming existing baseline approaches. This framework presents a promising avenue for high-precision parameter regression in Event Horizon Telescope (EHT) data analysis and broader astrophysical imaging applications characterized by sparse and noisy data.

Jialei Wei

Ao Liu

Dejiang Li

Cuihong Wen

Physical parameter regression from black hole images using a multiscale adaptive neural network * Supported by the Natural Science Foundation of Hunan Province under grant No. 2023JJ30384; the National Natural Science Foundation of China under Grants No. 12374408; the University Students' Innovation and Entrepreneurship Training Program Project

We perform the first computation of phase-transition parameters to cubic order in $ \lambda\sim m^2/T^2 $ , where $\textit{m}$ is the scalar mass and $\textit{T}$ is the temperature, in a simple model resembling the Higgs sector of the SMEFT. We use dimensional reduction, including 1-loop matching corrections for terms of dimension 6 (in 4-dimensional units), 2-loop contributions for dimension-4 ones and 3-loops for the squared mass. We precisely quantify the size of the different corrections, including renormalization-group running as well as quantum effects from light fields in the effective theory provided by the Coleman-Weinberg potential, and discuss briefly the implications for gravitational waves. Our results suggest that, for strong phase transitions, 1-loop corrections from dimension-6 operators can compete with 2-loop ones from quartic couplings and largely surpass those from 3-loop thermal masses.

Spain

Mikael Chala

Luis Gil

Zhe Ren

Phase transitions in dimensional reduction up to three loops * Supported by MCIN/AEI (10.13039/501100011033) and ERDF (grants PID2021-128396NB-I00 and PID2022-139466NB-C22), from the Junta de Andalucía grants FQM 101 and P21-00199 and from Consejería de Universidad, Investigación e Innovación, Gobierno de España and Unión Europea – NextGenerationEU under grants AST22 6.5 and CNS2022-136024. MC and LG are further supported by the RyC and FPU programs under contract numbers RYC2019-027155-I and FPU23/02026, respectively.

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 discuss the appearance of superconducting strings in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>E</mi><mn>6</mn></msub></math> grand unification, keeping track of the magnetic monopole flux that precedes the formation of the string flux tube. This flux matching ensures compatibility with the quantum tunneling of a monopole-antimonopole pair on a metastable string. We identify two realistic <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>E</mi><mn>6</mn></msub></math> models with superconducting (metastable) strings that also carry zero modes of the right-handed Majorana neutrinos and dark matter particles. Depending on the symmetry breaking scale associated with the strings, the latter could be a source of observable gravitational waves, intermediate scale dark matter, and the observed baryon asymmetry via leptogenesis. Topologically stable superconducting strings also appear if the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>E</mi><mn>6</mn></msub></math> symmetry breaking leaves unbroken the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mn>2</mn></msub></math> subgroup of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mn>4</mn></msub></math>, the center of SO(10). The zero modes of the Standard Model fermions are the charge carriers in this case. Finally, the flux matching condition ensures that the Aharonov-Bohm phase change in going around the metastable strings is an integer multiple of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>2</mn><mi>π</mi></math> for all fields. The fields in the spinorial representation of SO(10) acquire a phase change of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>exp</mi><mo stretchy="false">(</mo><mo>±</mo><mi>i</mi><mi>π</mi><mo stretchy="false">)</mo></math> if taken around the topologically stable <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mn>2</mn></msub></math> string.

South Korea

Rinku Maji

Qaisar Shafi

Superconducting strings in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>E</mi><mn>6</mn></msub></math>

We discover a surprising relationship between exceptional effective field theories (EFTs) in de Sitter space and a notion of generalized energy conservation (GEC) of an <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>S</mi></mrow></math> matrix defined in an extended Poincaré patch of four-dimensional de Sitter. By demanding that such an <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>S</mi></mrow></math> matrix has support only when the total energies of in and out states are equal, we constrain the coupling constants in theories of self-interacting scalars living in the exceptional series of de Sitter representations. We rediscover the theories of Dirac-Born-Infeld (DBI) and special Galileon, and when increasing the conformal dimension, we find evidence for new exceptional theories where the four-point scalar self-interactions are uniquely fixed in terms of a single coupling constant. We conjecture that for each integer conformal dimension <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Δ</mi><mo>≥</mo><mn>4</mn></math>, there is at least one exceptional EFT that can be entirely fixed by GEC.

Zong-Zhe Du

David Stefanyszyn

New Exceptional Effective Field Theories in de Sitter Space from Generalized Energy Conservation

We analyze the complexity factor in spherically symmetric stars undergoing dissipative collapse in the presence of shear. The interior spacetime is described by a general spherically symmetric metric, and the corresponding Einstein field equations are derived. Matching the interior spacetime to the exterior Vaidya geometry yields the boundary condition governing the temporal evolution of the collapsing body. The interior matter distribution obeys the Euclidean condition, i.e. the areal radius is identical to the proper radius as the star collapses. We present a complete model of a Euclidean star and investigate its physical viability. We further investigate the notion of complexity as defined by Herrera in terms of the pressure anisotropy, density inhomogeneity and heat flux. The novelty of our work is the demonstration of the interplay of these factors to the complexity in a shearing model which is absent in earlier treatments.

South Africa

Wesley Govender

Lindani Majozi

Megandhren Govender

Sunil Maharaj

Exploring complexity in the presence of shear and heat dissipation

We simulate the heavy quarkonium equilibration through transport in a static and homogeneous quark-gluon plasma (QGP) box within the semiclassical Boltzmann approach, incorporating both the leading-order and next-to-leading-order dissociation and regeneration reactions. The scattering amplitudes involved are taken from perturbative computations based on effective color-electric dipole coupling of the heavy quarkonium with thermal gluons. By coupling the Langevin simulation of single heavy quark diffusion and the Boltzmann transport of the heavy quarkonium in a real-time fashion, we demonstrate how the kinetic and chemical equilibrium of heavy quarkonium with single heavy quarks in the medium is achieved in terms of both the bound state’s yields and momentum distributions. The pertinent equilibration time turns out to be comparable to the lifetime of the QGP created in the most central heavy-ion collisions at the LHC energies. The role of the intricate interplay between the open and hidden heavy sector in the process of equilibration is highlighted. This work provides a dynamical way of understanding the phenomenological success of the statistical hadronization model for charmonium production in relativistic heavy-ion collisions and also paves the way for realistic phenomenological applications to heavy quarkonium transport.

Shouxing Zhao

Min He

Simulation of heavy quarkonium equilibration in the quark-gluon plasma