Spontaneous breaking of discrete symmetries like <italic>Z</italic> <inf>2</inf> leads to the formation of stable topological defects such as domain walls which, if allowed to dominate, can potentially be in conflict with cosmological observations. Incorporating explicit <italic>Z</italic> <inf>2</inf>-breaking bias terms can lead to annihilation of such walls while also emitting stochastic gravitational waves (GW). We study the role of heavy right-handed neutrinos present in the type-I seesaw framework to generate such a bias term via quantum corrections. This offers interesting correlations among the seesaw scale, GW peak amplitude and peak frequency which can be probed at present and future experiments related to GW as well as precision measurements of the cosmic microwave background (CMB). In flavor symmetric UV complete scenarios with degenerate RHNs at leading order, such tiny coupling of RHNs to a <italic>Z</italic> <inf>2</inf>-odd scalar can also lead to small mass splittings suitable for explaining the observed baryon asymmetry of the universe via resonant leptogenesis.

India

Debasish Borah

Indrajit Saha

Gravitational waves from seesaw assisted collapsing domain walls

We present an exact four-dimensional black string solution immersed in perfect fluid dark matter within an anti-de Sitter background. By solving the Einstein field equations for an anisotropic fluid, we obtain a metric function that modifies the standard black string geometry through a logarithmic term governed by the dark matter parameter <italic>&#945;</italic>. The event horizon radii are analytically determined using the Lambert <italic>W</italic> function, and the Kretschmann scalar confirms a genuine curvature singularity at the origin alongside the expected asymptotic behavior. Furthermore, we evaluate the thermodynamic properties of the solution. The heat capacity diverges at a critical horizon radius for <italic>&#945;</italic>&#8239;&gt;&#8239;0, a behavior commonly associated with a thermodynamic phase transition in a regime where the weak energy condition is violated.

Brazil

L.G. Barbosa

L.C.N. Santos

Black string immersed in perfect fluid dark matter

Recently, Ref. [1] proved the energy conservation formula for particle decay in Kerr spacetime: <math altimg='si10.svg'><mrow><msub><mi>m</mi><mn>0</mn></msub><mo linebreak='goodbreak'>=</mo><msub><mi>m</mi><mn>1</mn></msub><mspace width='0.16em' /><msub><mi>&#947;</mi><mn>01</mn></msub><mo linebreak='goodbreak'>+</mo><msub><mi>m</mi><mn>2</mn></msub><mspace width='0.16em' /><msub><mi>&#947;</mi><mn>02</mn></msub></mrow></math>, where <italic>m</italic> <inf>0</inf> is the initial particle, <italic>m</italic> <inf>1</inf> and <italic>m</italic> <inf>2</inf> are the decay products, and <italic>&#947;</italic> <inf>01</inf>, <italic>&#947;</italic> <inf>02</inf> are the relative Lorentz factors between particle 0 and particle 1, and between particle 0 and particle 2, respectively. This conclusion shows that the particle splitting process exhibits a mass defect, which is converted into kinetic energy in the center-of-mass frame. In this paper, we extend it to Kerr&#8211;de Sitter spacetime. Through derivation, we obtain the same energy conservation result as in Kerr spacetime. In addition, we find that, for a fixed cosmological constant, a larger decay radius leads to a larger specific angular momentum of particle 0, larger masses of particles 1 and 2, a smaller absolute value of their specific energy, smaller relative Lorentz factors among the three particles, and smaller four-velocities of the three particles. For a fixed decay radius, a larger cosmological constant leads to larger specific angular momenta of particle 0 and particle 2, smaller masses of particles 1 and 2, a larger absolute value of their specific energy, larger relative Lorentz factors among the three particles, and larger four-velocities of the three particles.

China

Ke Wang

Xiao-Xiong Zeng

Particle decay and energy conservation in Kerr-de Sitter spacetime

We present a measurement of the ortho-positronium decay rate using a novel method in which the time-dependent pick-off contribution is determined directly from the simultaneous time-resolved registration of both 2 <italic>&#947;</italic> and 3 <italic>&#947;</italic> annihilation channels recorded with the J-PET detector. This approach eliminates the model-dependent systematic uncertainty associated with Monte Carlo-based pick-off subtraction that limited previous experiments, and introduces no material-dependent systematic floor. From a fit to the 2 <italic>&#947;</italic> lifetime spectrum we obtain <math altimg='si8.svg'><mrow><mstyle mathvariant='normal'><mi>&#915;</mi></mstyle><mo linebreak='goodbreak'>=</mo><mn>7.040</mn><mrow><mo>(</mo><mn>6</mn><mo>)</mo></mrow><mo linebreak='goodbreak'>&#215;</mo><msup><mn>10</mn><mn>6</mn></msup><mspace width='0.16em' /><msup><mrow><mi mathvariant='normal'>s</mi></mrow><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup></mrow></math>, consistent with the QED bound-state prediction evaluated to <math altimg='si9.svg'><mrow><mi mathvariant='script'>O</mi><mo>(</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>3</mn></mrow></msup><mo>)</mo></mrow></math> level. Since the time-dependent pick-off contributes only a small fraction to the total decay rate, its uncertainty is strongly suppressed in the extraction of the vacuum decay rate, and the precision scales directly with the available statistics. A precision roadmap shows that the next generation of the J-PET detector can surpass existing measurements and reach sensitivity to the <math altimg='si2.svg'><mrow><mi mathvariant='script'>O</mi><mo>(</mo><msup><mi>&#945;</mi><mn>2</mn></msup><mo>)</mo></mrow></math> radiative corrections. Such tests are of particular relevance given the reported discrepancies between positronium spectroscopy data and non-relativistic QED (NRQED) predictions, which motivate independent precision measurements of bound-state QED observables.

Poland

S. Sharma

K. Dulski

E.Y. Beyene

N. Chug

Italy

C. Curceanu

E. Czerwiński

M. Das

K.V. Eliyan

M. Gorgol

J. Hajduga

B. Jasińska

K. Kacprzak

T. Kaplanoglu

Ł. Kapłon

K. Kasperska

A. Khreptak

T. Kozik

K. Kubat

D. Kumar

S.K. Kundu

A.K. Venadan

E. Lisowski

F. Lisowski

J. Mędrala-Sowa

W. Mryka

S. Moyo

S. Niedźwiecki

S. Parzych

A. Pandey

P. Pandey

Chile

A. Porcelli

B. Rachwał

M. Rädler

M. Skurzok

E.Ł. Stępień

T. Szumlak

P. Tanty

K. Tayefi Ardebili

S. Tiwari

P. Moskal

First direct determination of the pick-off contribution to the ortho-positronium decay rate

We explore novel generation of genuine multipartite entanglement within gravitational particle production processes during inflationary stages. To this end, we focus on perturbative production mechanisms, considering a non-minimally coupled scalar inflaton field with quartic self-coupling potential and computing probability amplitudes arising from its gravitational interaction with background perturbations. The corresponding entanglement amount is quantified using the recently proposed Entanglement Distance, that provides a <italic>geometric interpretation of particle entanglement, in terms of the Fubini-Study metric</italic>. We observe that, in the limit of negligible squeezing, the total amount of entanglement is dominated by the infrared cutoff scale, in agreement with previous studies analyzing the von Neumann entropy within bipartite scenarios. We then show that <italic>non-negligible multipartite entanglement signatures may emerge across inflation, even during the latest stages of slow-roll</italic>, highlighting their dependence on inflationary momentum scales. Generalizations to regimes with non-negligible squeezing, cubic non-Gaussianities, additional spectator fields and possible observational signatures are also discussed.

Alessio Belfiglio

Roberto Franzosi

Kazakhstan

United States

Orlando Luongo

Geometric multipartite entanglement from gravitational particle production

We study the impact of imposing an infinite-future condition on Gaussian-process (GP) reconstructions of <italic>H</italic>( <italic>z</italic>) from 37 cosmic-chronometer measurements. Implementing the asymptotic limit <math altimg='si4.svg'><mrow><mi>H</mi><mo>(</mo><mo>&#8722;</mo><mn>1</mn><mo>)</mo><mo>=</mo><mn>0</mn></mrow></math> expected in constant- <italic>w</italic>CDM with <math altimg='si1.svg'><mrow><mi>w</mi><mo linebreak='goodbreak'>&gt;</mo><mo>&#8722;</mo><mn>1</mn></mrow></math> as a pseudo-point at <math altimg='si5.svg'><mrow><mi>z</mi><mo linebreak='goodbreak'>=</mo><mo>&#8722;</mo><mn>1</mn></mrow></math> with tunable uncertainty <math altimg='si6.svg'><msub><mi>&#963;</mi><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msub></math> lowers the GP-inferred Hubble constant from <math altimg='si26.svg'><mrow><msub><mi>H</mi><mn>0</mn></msub><mo linebreak='goodbreak'>=</mo><mn>68.71</mn><mo>&#177;</mo><mn>6.08</mn></mrow></math> to <italic>H</italic> <inf>0</inf>&#8239;&#8771;&#8239;(64.67&#8211;65.86)&#8239;&#177;&#8239;(4.45&#8211; <math altimg='si27.svg'><mrow><mrow><mn>4.85</mn><mo>)</mo><mspace width='0.33em' /></mrow><mrow><mrow><mi mathvariant='normal'>k</mi></mrow><mi>m</mi><mspace width='0.16em' /><msup><mi>s</mi><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup><mspace width='0.16em' /><mi>M</mi><mi>p</mi><msup><mi>c</mi><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup></mrow></mrow></math>. The resulting <italic>H</italic> <inf>0</inf> remains within &#8239;&#8764;&#8239;0.32&#8211;0.61&#8201; <italic>&#963;</italic> of the <italic>Planck</italic> &#923;CDM value, while the separation from representative local distance-ladder measurements increases to &#8239;&#8764;&#8239;1.45&#8211;1.83&#8201; <italic>&#963;</italic>. A scan over <math altimg='si6.svg'><msub><mi>&#963;</mi><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msub></math> shows that the shift is governed by the effective pseudo-point weight, interpolating between the hard-condition and data-dominated limits. Finally, constant- <italic>w</italic>CDM Markov Chain Monte Carlo (MCMC) fits to the same <italic>H</italic>( <italic>z</italic>) data with <italic>H</italic> <inf>0</inf> fixed to the GP-inferred values show that &#937; <inf><italic>m</italic></inf> is only weakly affected, whereas lower <italic>H</italic> <inf>0</inf> shifts <italic>w</italic> toward less negative values; allowing curvature broadens constraints and remains consistent with <math altimg='si9.svg'><mrow><msub><mstyle mathvariant='normal'><mi>&#937;</mi></mstyle><mi>k</mi></msub><mo linebreak='goodbreak'>=</mo><mn>0</mn></mrow></math>.

Yuan-Bo Xie

Cheqiu Lyu

Zhiyuan Mo

Wei Hong

Tong-Jie Zhang

Probing the hubble tension with an infinite-future condition on the hubble parameter

In this work, we study a cosmological model driven by Generalized ModMax nonlinear electrodynamics. We find that, with an appropriate choice of the theory’s parameters, the universe’s initial singularity can be avoided. Moreover, we also find that this model has an inflationary epoch that is consistent with the current values for <italic>N, n<inf>s</inf></italic> and <italic>r</italic>. Therefore, using Generalized ModMax, we can construct a non singular Universe with an inflationary epoch.

Mexico

Spain

M. Sabido

V. Sierra

Generalized ModMax and the early universe

Neutron-rich nuclei near the <math altimg='si6.svg'><mrow><mi>N</mi><mo linebreak='goodbreak'>=</mo><mn>126</mn></mrow></math> shell closure are vital for <italic>r</italic>-process nucleosynthesis but remain challenging to produce. Multinucleon transfer reactions offer a promising route. We investigate the role of shell effects in such processes by extending the CLIM-H model with a deformation-dependent mass formula and a scaling factor <italic>a</italic> that linearly adjusts the shell-correction strength. Calculations for 136Xe on 208Pb, 204Hg, and 208Hg targets reveal a dual role: shell effects enhance few-nucleon transfers near the entrance channel but strongly suppress fragments requiring the transfer of many nucleons, most severely for the doubly magic 208Pb. This suppression stems from the cumulative transfer probabilities and is aggravated by lower survival after deexcitation. Thus, optimal production of exotic <math altimg='si6.svg'><mrow><mi>N</mi><mo linebreak='goodbreak'>=</mo><mn>126</mn></mrow></math> nuclei requires avoiding strongly shell-closed collision partners at <math altimg='si6.svg'><mrow><mi>N</mi><mo linebreak='goodbreak'>=</mo><mn>126</mn></mrow></math>, as exemplified by doubly magic 208Pb. We propose 238U + 204Hg at <italic>E</italic> <inf>c.m.</inf>&#8239;&#8771;&#8239;1.45 <italic>V<inf>B</inf></italic> as a superior system, predicting significantly enhanced yields.

F.C. Dai

P.W. Wen

C.J. Lin

J.J. Liu

X.X. Xu

K.L. Wang

Y.D. Chen

H.L. Yang

Role of shell effects on producing neutron-rich nuclei in the <math altimg='si6.svg'><mrow><mi>N</mi><mo linebreak='goodbreak'>=</mo><mn>126</mn></mrow></math> region via multinucleon transfer reactions

Testing Lorentz symmetry in strong gravitational fields provides a unique probe of extensions to standard model. The orbital motions of the S-stars around the supermassive black hole Sgr A* provide a natural laboratory for such tests. In this paper, we analyze the S2 orbital data focusing on a static and spherically symmetric black hole within Kalb–Ramond gravity, where the deviations from general relativity are encoded in a single Lorentz-violating parameter ℓ introduced by the Kalb–Ramond tensor field. Using a full 14-dimensional Markov Chain Monte Carlo analysis under uniform and Gaussian priors, we obtain <math altimg='si41.svg'><mrow><mi>&#8467;</mi><mo linebreak='goodbreak'>=</mo><msubsup><mrow><mn>1.60</mn><mo>&#215;</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>5</mn></mrow></msup></mrow><mrow><mo>&#8722;</mo><mn>1.76</mn><mo>&#215;</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>4</mn></mrow></msup></mrow><mrow><mo>+</mo><mn>1.38</mn><mo>&#215;</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>4</mn></mrow></msup></mrow></msubsup></mrow></math> and <math altimg='si42.svg'><mrow><mi>&#8467;</mi><mo linebreak='goodbreak'>=</mo><msubsup><mrow><mo>&#8722;</mo><mn>1.02</mn><mo>&#215;</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>5</mn></mrow></msup></mrow><mrow><mo>&#8722;</mo><mn>1.19</mn><mo>&#215;</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>4</mn></mrow></msup></mrow><mrow><mo>+</mo><mn>1.26</mn><mo>&#215;</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>4</mn></mrow></msup></mrow></msubsup></mrow></math> at 1 <italic>&#963;</italic> confidence level, respectively. These constraints are about three orders of magnitude tighter than those from Event Horizon Telescope imaging of Sgr A*. We also perform MCMC simulation by fitting data of S38 and S55 stars, as well as their joint analysis. Our results show that the best fit values of &#8467; in all simulations are always of <math altimg='si43.svg'><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>5</mn></mrow></msup></math> order, but S2 star provides the most stringent constraints on the parameters because S2 star has higher precision observational data comparing to the fewer public data for other two stars.

Qi Qi

Yu Sang

Xiao-Mei Kuang

Detecting Lorentz-violation induced by a tensor field with S-star’s motion around Sgr A*

Deep learning is emerging as a powerful research paradigm across diverse scientific fields. In nuclear physics, it serves primarily to refine theoretical models. This study systematically evaluates multiple deep learning approaches for predicting the <italic>&#945;</italic> decay half life, using only fundamental physical inputs proton number <italic>Z</italic>, mass number <italic>A</italic>, decay energy <italic>Q<inf>&#945;</inf></italic>, and angular momentum <italic>l</italic>-without incorporating any pre-existing physical model. And it has good generalization ability. We demonstrate that the Tabular Prior-data Fitted Network (TabPFN) achieves the highest predictive accuracy. In parallel, the Kolmogorov-Arnold Network (KAN) yields an explicit analytical expression with accuracy rivaling that of established phenomenological formulas. This dual capability offers a high-precision, interpretable framework for simplifying complex nuclear models and can provide intuitive physical insights.

Tian Liang Zhao

Xiao Jun Bao

Explore the high precision and interpretability of deep learning in the calculation of <italic>&#945;</italic> decay half life