Compact formulas (2.1), (3.14) presented in this paper permit to formulate the Kallen-Lehmann harmonic decompositions of the products of two spinor and of spinor and scalar harmonic functions on AdS and Wightman functions on dS spaces; the correct flat space limit of the corresponding Kallen-Lehmann densities is demonstrated, the connection between poles of the Kallen-Lehmann density and the late-time divergence of the spinor-scalar loop is traced in the Yukawa model with light scalar field. Also in section 4 the relatively simple, suitable for calculations Kallen-Lehmann representations of the real parts of spinor and scalar one-loop self-energies on dS space-time are proposed, and corresponding spectral equations for conformal dimensions in the chain approximation are written down.

Russia

Boris Altshuler

Kallen-Lehmann representation for Spinor-Scalar Loops in de Sitter Space-time. Spectral equations

It is commonly believed that a unitary supersymmetric quantum field theory (QFT) involving graviton and gravitino fields on fixed 4-dimensional de Sitter spacetime ($\textit{dS}$ ) cannot exist due to known challenges associated with supersymmetry (SUSY) in $\textit{dS}$ . In this paper, we contradict this expectation by presenting a new unitary supersymmetric QFT on $\textit{dS}$ : the free supersymmetric theory of the chiral graviton and chiral gravitino fields. By chiral we mean that the corresponding field strengths are anti-self-dual, and the gauge potentials are complex, each carrying a single complex propagating degree of freedom. The global SUSY transformations are generated by the standard Dirac Killing spinors of $\textit{dS}$ . The theory overcomes the known obstacles to unitary global SUSY on $\textit{dS}$ by closing the commutator between two SUSY transformations on $\textit{so}$(4, 2) ⊕ $\textit{u}$(1) rather than the de Sitter algebra $\textit{so}$(4, 1). Crucially, the $\textit{so}$(4, 2) symmetry is realised through unconventional conformal-like transformations. This free theory cannot become interacting while preserving SUSY in a way that makes the spin-2 sector the true graviton sector of General Relativity, as the three-graviton coupling cannot be $\textit{u}$(1)-invariant.

United Kingdom

Atsushi Higuchi

Belgium

Vasileios Letsios

Unitary rigid supersymmetry for the chiral graviton and chiral gravitino in de Sitter spacetime

We interpret the Euclidean solution of JT de Sitter gravity as the Coleman-de Luccia instanton for the decay of the low-entropy horizon of its static patch solution into either a Big Crunch or an infinite-entropy Lorentzian de Sitter cosmology. As in previous work by one of the authors, the Big Crunch is interpreted as bounding the entropy of the static state. The principle of detailed balance then guarantees it will transition back to a higher entropy causal diamond in the expanding cosmology. We then construct a family of explicit quantum mechanical models and appropriate metastable states, with transition probabilities well approximated by the semi-classical calculations in JT de Sitter gravity.

United States

Tom Banks

Sidan A

JT de Sitter gravity as a model of Coleman-de Luccia tunneling

We present a formulation of the three- and four-point amplitudes on the Coulomb branch of $$ \mathcal{N} $$ = 4 SYM as integrals over the symplectic Grassmannian. We demonstrate that their kinematic spaces are equivalent to symplectic Grassmannians SpGr($\textit{n}$, 2$\textit{n}$). For the three-point case, we express the amplitude as an integral over the symplectic Grassmannian in a specific little group frame. In the four-point case, we show that the integral yields the amplitude up to a known kinematic factor. Building on the four-dimensional analysis, we also express the six-dimensional $$ \mathcal{N} $$ = (1, 1) SYM amplitude in terms of four-dimensional variables in a form that makes its symplectic Grassmannian structure manifest.

Germany

Veronica Cortes

Yassine Maazouz

Subramanya Hegde

India

Amit Suthar

Symplectic Grassmannian description of the Coulomb branch three and four point amplitudes

Cross sections for neutron and proton transfer channels were measured in the proton-rich system 92Mo+ 54Fe using the PRISMA magnetic spectrometer. The energy dependence of the absolute transfer cross sections was investigated over a beam energy range spanning from slightly above to below the Coulomb barrier. A significant enhancement was observed in the 2 <italic>p</italic> and <math altimg='si1.svg'><mrow><mn>2</mn><mi>p</mi><mo linebreak='goodbreak'>+</mo><mn>2</mn><mi>n</mi></mrow></math> pickup and stripping channels compared to expectations based on independent single-nucleon transfer, suggesting strong correlations in the multinucleon transfer mechanism.

Croatia

T. Mijatović

S. Szilner

Italy

L. Corradi

F. Galtarossa

G. Pollarolo

Poland

G. Colucci

E. Fioretto

A. Goasduff

A. Gottardo

D. Jelavić Malenica

M. Milin

G. Montagnoli

D. Montanari

N. Soić

A.M. Stefanini

Spain

J.J. Valiente Dobón

Revealing nucleon-nucleon correlation effects through sub-Coulomb transfer reactions in 92Mo+ 54Fe

An attempt is made to explain the experimentally observed binary decay of some fission fragments of 252Cf(sf) while traversing the degrader foil. Assuming these fragments are born in metastable shape-isomer/cluster states formed during the initial binary fission, an influence of the Coulomb field of the foil nuclei on decay barriers and half-lives of these states is investigated.

F.O. Otakhonov

Sh. A. Kalandarov

G.G. Adamian

N.V. Antonenko

Yu. V. Pyatkov

D.V. Kamanin

Influence of the Coulomb field of foil nuclei on half-lives of cluster states in fission fragments

In this study, we investigate the inflationary dynamics of Rainbow <italic>f</italic>( <italic>R</italic>) gravity characterized by <italic>f</italic>( <italic>R</italic>)&#8239;&#8771;&#8239; <italic>&#945;Rn</italic>, with the rainbow deformation <math altimg='si8.svg'><mrow><mover accent='true'><mi>f</mi><mo>&#732;</mo></mover><mrow><mo>(</mo><mi>H</mi><mo>)</mo></mrow><mo>&#8764;</mo><msup><mi>H</mi><mi>&#955;</mi></msup></mrow></math> and <math altimg='si9.svg'><mrow><mover accent='true'><mi>g</mi><mo>&#732;</mo></mover><mo linebreak='goodbreak'>=</mo><mn>1</mn></mrow></math>. The effects of the rainbow parameter <italic>&#955;</italic> and the curvature exponent <italic>n</italic> on inflationary observables are analyzed under the Atacama Cosmology Telescope (ACT) constraint 0.9709&#8239;&lt;&#8239; <italic>n<inf>s</inf></italic>&#8239;&lt;&#8239;0.9777. Numerical results reveal a clear correlation among <italic>n, &#955;</italic>, and the tensor-to-scalar ratio <italic>r</italic>, such that decreasing <italic>n</italic> corresponds to increasing <italic>&#955;</italic>, accompanied by a growth in <italic>r</italic> within observational limits. Negative values of <italic>&#955;</italic> (typically for <italic>n</italic>&#8239;&#8776;&#8239;3) yield a quasi&#8211;de Sitter inflationary phase with a nearly constant Hubble parameter and suppressed tensor modes, while positive <italic>&#955;</italic> (for <italic>n</italic>&#8239;&#8818;&#8239;2.2) drive a quintessence&#8211;like inflationary regime with enhanced expansion and a time-dependent curvature. Using power&#8211;law solutions <italic>a</italic>( <italic>t</italic>)&#8733; <italic>tp</italic>, we relate the expansion exponent to the number of <italic>e</italic>-folds <italic>N</italic>&#8239;&#8771;&#8239;50&#8211;60. Small deviations between the matter and effective equations of state indicate a mild breaking of <math altimg='si10.svg'><mrow><msub><mi>w</mi><mi>e</mi></msub><mo linebreak='goodbreak'>=</mo><mi>w</mi></mrow></math>, suggesting the emergence of matter&#8211;like behavior within the quintessence&#8211;like inflationary field. At low curvature, we further show that a logarithmic Nojiri&#8211;Odintsov correction <italic>f</italic>( <italic>R</italic>)&#8239;&#8771;&#8239; <italic>&#945;</italic>&#8242;ln&#8201;( <italic>R</italic>/ <italic>&#956;</italic> 2) naturally dominates the dynamics, giving rise to a late&#8211;time quintessence phase ( <math altimg='si11.svg'><mrow><mo>&#8722;</mo><mn>1</mn><mo linebreak='goodbreak'>&lt;</mo><msub><mi>w</mi><mi>e</mi></msub><mo linebreak='goodbreak'>&lt;</mo><mo>&#8722;</mo><mn>1</mn><mo linebreak='goodbreak'>/</mo><mn>3</mn></mrow></math> for <math altimg='si12.svg'><mrow><mi>&#955;</mi><mo linebreak='goodbreak'>&gt;</mo><mo>&#8722;</mo><mn>1</mn></mrow></math>) that asymptotically approaches a de Sitter attractor ( <math altimg='si13.svg'><mrow><msub><mi>w</mi><mi>e</mi></msub><mo>&#8594;</mo><mo>&#8722;</mo><mn>1</mn></mrow></math> as &#1013; <inf>1</inf>&#8239;&#8594;&#8239;0 or <math altimg='si14.svg'><mrow><mi>&#955;</mi><mo linebreak='goodbreak'>=</mo><mo>&#8722;</mo><mn>1</mn></mrow></math>). Thus, the combined <italic>Rn</italic> and logarithmic contributions provide a unified geometric framework in which early&#8211;time inflation and late&#8211;time cosmic acceleration naturally arise from different curvature regimes of Rainbow <italic>f</italic>( <italic>R</italic>) gravity, consistent with ACT observational data.

Türkiye

A.I. Keskin

Rainbow <italic>f</italic>( <italic>R</italic>) Inflation: de Sitter-Quintessence Phases

We investigate the relationship between thermodynamic phase transitions and the Lyapunov exponent of charged regular anti-de Sitter black holes in quasi-topological gravity. Our results show that the Lyapunov exponent displays multivalued behavior during phase transitions. Moreover, along the coexistence curve the Lyapunov exponent changes discontinously and continuously at the critical point. Near the critical point, the Lyapunov exponent follows a power-law behavior with a critical exponent of 1/2, suggesting its role as an order parameter and encodes information on black hole phase transitions.

China

Hao Xie

Si-Jiang Yang

Probing phase transitions of regular black holes in anti-de Sitter space with Lyapunov exponent

We consider soft graviton scattering for a theory where Einstein’s gravity is minimally coupled to a scalar field in the presence of a cosmological constant, i.e. in a background de Sitter space. Employing a perturbative expansion in a small cosmological constant, we compute leading, subleading and sub-subleading corrections to Weinberg’s soft graviton amplitude for the tree-level scatterings in the static patch of de Sitter space. We observe similar universal features of the soft graviton amplitude as found in (2023) 055 for the soft photons.

Divyesh Solanki

Pratik Chattopadhyay

Srijit Bhattacharjee

Perturbative soft graviton theorems in de Sitter spacetime

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.

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.