The aim of this study is to examine a non-local short pulse equation and understand how its dynamics differ from those of its classical local counterpart. To achieve this, we introduce a Lax pair and develop a $\textit{k}$-fold Darboux transformation, which forms the analytical foundation for constructing exact solutions. Using this method, we derive various solutions, including breathers and stable and unstable solitons over zero and non-zero backgrounds. The exact solutions are then used to train a neural network-based framework using Levenberg–Marquardt artificial neural networks (LM-ANN), which aims to approximate the solitonic structures. Model performance is evaluated using the relative error norm based on the Euclidean distance between the predicted and exact solutions. Surface plots, contour maps, and error visualizations are presented to illustrate approximation quality. To investigate model sensitivity and robustness, we explore multiple activation functions and network architectures, and introduce Gaussian noise at 1%, 2%, and 3% levels to both training and testing datasets. Monte Carlo simulations with multiple noise realizations are conducted, and statistical performance is summarized using the mean and standard deviation of the relative error. Results are reported through comparative tables and graphical analyses. By integrating analytical soliton construction with LM-ANN-based regression and systematic robustness testing, this study presents a hybrid framework for solving the non-local short pulse equation, offering accurate and stable solutions even under noise, a valuable contribution to the analysis of nonlinear systems affected by uncertainty.

China

H. Riaz

Aamir Farooq

Hybrid analytical and neural-network approaches to the non-local short pulse equation

This paper investigates the dynamical effects of particles moving in the Kerr spacetime and its nine single-parameter modified spacetimes, including Bardeen, Ayon-Beato and Garcia (ABG), Hayward, Kerr–Newman (KN), Kerr–Taub–NUT (KTN), Braneworld Kerr (BK), Kerr-MOG, Kerr–Sen, and Perfect Fluid Dark Matter (PFDM) black holes. Using quasi-periodic oscillation (QPO) observational data, we constrain the free parameters of the ten spacetimes through $$\chi ^2$$ analysis under the relativistic precession model of QPO. We constrain the modification parameters for the nine single-parameter modified spacetimes and provide the spin and mass ranges of three microquasars within the ten spacetime models (including Kerr) at the $$68\%$$ confidence level (CL). The results demonstrate that, at the $$68 \%$$ CL, the QPO data impose stringent constraints on the free parameters, as evidenced by the narrow confidence intervals. Among them, only the KN spacetime yields a modification parameter constraint spanning both negative and positive values (encompassing the Kerr case at zero). In contrast, all other tested geometries mandate positive-definite parameters at $$68 \%$$ CL, demonstrating statistical deviation of the Kerr solution. This highlights the significance of exploring modifications to the Kerr spacetime. Finally, we evaluate the spacetime models using the Bayes factor and the Akaike Information Criterion (AIC). Based on the current QPO observational data, the Bayesian factor analysis indicates that the ABG, Hayward, KN, BK, and Kerr-MOG spacetime have a slight advantage over the Kerr solution, while the Bardeen, KTN, Kerr–Sen, and PFDM spacetime are somewhat inferior to the Kerr model. In contrast, the AIC analysis shows that the Kerr spacetime remains the optimal model under the current QPO data.

Shining Yang

Jianbo Lu

Wenmei Li

Mou Xu

Jingyang Xu

Observational constraints on the Kerr and its several single-parameter modified spacetimes using quasi-periodic oscillation data

We present the results of a search for the charged-lepton-flavor violating decays $\textit{B}$ → $\textit{K}$ $\textit{τ}$ $\textit{ℓ}$ , where $\textit{ℓ}$ is either an electron or a muon. The results are based on 365 fb and 711 fb datasets collected with the Belle II and Belle detectors, respectively. We use an exclusive hadronic $\textit{B}$-tagging technique, and search for a signal decay in the system recoiling against a fully reconstructed $\textit{B}$ meson. We find no evidence for $\textit{B}$ → $\textit{K}$ $\textit{τ}$ $\textit{ℓ}$ decays and set upper limits on the branching fractions in the range of (2.9–6.4)×10 at 90% confidence level.

I. Adachi

Y. Ahn

H. Aihara

N. Akopov

S. Alghamdi

M. Alhakami

A. Aloisio

K. Amos

M. Angelsmark

N. Anh Ky

C. Antonioli

D. Asner

H. Atmacan

V. Aushev

M. Aversano

R. Ayad

V. Babu

H. Bae

N. Baghel

S. Bahinipati

P. Bambade

Sw. Banerjee

S. Bansal

M. Barrett

J. Baudot

A. Baur

A. Beaubien

F. Becherer

J. Becker

J. Bennett

F. Bernlochner

V. Bertacchi

M. Bertemes

E. Bertholet

M. Bessner

S. Bettarini

B. Bhuyan

F. Bianchi

T. Bilka

D. Biswas

A. Bobrov

D. Bodrov

J. Borah

A. Boschetti

A. Bozek

M. Bračko

P. Branchini

R. Briere

T. Browder

A. Budano

S. Bussino

M. Campajola

L. Cao

G. Casarosa

C. Cecchi

M.C. Chang

P. Cheema

B. Cheon

K. Chilikin

J. Chin

H.E. Cho

K. Cho

S.J. Cho

S.K. Choi

S. Choudhury

I. Consigny

L. Corona

J. Cui

E. De La Cruz-Burelo

S. De La Motte

G. Marino

G. Pietro

R. Sangro

M. Destefanis

A. Canto

J. Dingfelder

Z. Doležal

I. Domínguez Jiménez

T. Dong

X. Dong

M. Dorigo

G. Dujany

P. Ecker

D. Epifanov

R. Farkas

P. Feichtinger

T. Ferber

T. Fillinger

C. Finck

G. Finocchiaro

F. Forti

A. Frey

B. Fulsom

A. Gale

E. Ganiev

M. Garcia-Hernandez

R. Garg

G. Gaudino

V. Gaur

V. Gautam

Search for lepton flavor-violating decay modes $\textit{B}$

The path integral over massless quantum fields in Minkowski space with scattering boundary conditions defines a Carrollian partition function on the null boundary. We develop this framework for non-Abelian gauge theory, both from a general perspective and through explicit examples that highlight subtle aspects of soft modes and asymptotic symmetries. These include falloff conditions, Goldstone modes and their antipodal matching, and factors of two associated with conditionally convergent integrals arising in the derivation of soft theorems. We employ path integral (rather than canonical) methods throughout.

United States

Per Kraus

Richard Myers

Carrollian partition function for bulk Yang-Mills theory

It is known that the double-scaled SYK model (DSSYK) reduces to JT gravity with a negative cosmological constant by zooming in on the lower edge $\textit{E}$ = – $\textit{E}$ of the spectrum. We find that the de Sitter JT gravity (i.e. JT gravity with a positive cosmological constant) is reproduced from DSSYK by taking a scaling limit around the upper edge $\textit{E}$ = $\textit{E}$ of the spectrum. We also argue that the appearance of de Sitter JT gravity is consistent with the behavior of the classical solution of the sine dilaton gravity.

Japan

Kazumi Okuyama

de Sitter JT gravity from double-scaled SYK

We relate the counting of refined BPS numbers on compact elliptically fibred Calabi-Yau threefolds $\textit{X}$ to Wilson loop expectations values in the gauge theories that emerge in various rigid local limits of the 5d supergravity theory defined by M-theory compactification on $\textit{X}$. In these local limits $\textit{X}$ the volumes of curves in certain classes go to infinity, the corresponding very massive M2-brane states can be treated as Wilson loop particles and the refined topological string partition function on $\textit{X}$ becomes a sum of terms proportional to associated refined Wilson loop expectation values. The resulting ansatz for the complete refined topological partition function on $\textit{X}$ is written in terms of the proportionality coefficients which depend only on the $\textit{ϵ}$ deformations and the Wilson loop expectations values which satisfy holomorphic anomaly equations. Since the ansatz is quite restrictive and can be further constrained by the one-form symmetries and E-string type limits for large base curves, we can efficiently evaluate the refined BPS numbers on $\textit{X}$, which we do explicitly for local gauge groups up to rank three and $\textit{h}$ ($\textit{X}$) = 5. These refined BPS numbers pass an impressive number of consistency checks imposed by the direct counting of these numbers using the moduli space of one dimensional stable sheaves on $\textit{X}$ and give us numerical predictions for the complex structure dependency of the refined BPS numbers.

Min-xin Huang

Sheldon Katz

Germany

United Kingdom

Albrecht Klemm

Xin Wang

Refined BPS numbers on compact Calabi-Yau threefolds from Wilson loops

We study the minimal requirements to obtain axion strings for axions with exponentially good quality. These ingredients appear in theories where an axion coming from a higher-form gauge field mixes with the phase of a complex scalar field. The resulting axion is perturbatively massless and inherits a high-quality shift symmetry from the global higher-form symmetry while being compatible with a post-inflationary axion scenario. Axions produced in this manner share features of both extra-dimensional and ordinary axions but are ultimately distinct from either. We refer to such axions as $\textit{higher axions}$, as the mechanism responsible for the mixing is that of higher-groups. We present a simple toy model on a 5-dimensional manifold with boundary. The boundary hosts the complex scalar that provides axion strings through standard mechanisms. In addition, we study how these scenarios may arise in heterotic and type II string theory compactifications.

Vazha Loladze

Arthur Platschorre

Mario Reig

Higher axion strings

The operator product expansion (OPE) of twist operators in the replica trick framework enables a long-distance expansion of the mutual information (MI) in conformal field theories (CFTs). In this expansion, the terms are labeled by primary operators, as contributions from descendant operators can be resummed into conformal blocks. However, for the MI, the expansion involves primaries from the multi-replica theory, which includes far more operators than those in the original theory. In this work, we develop a method to resum this series, yielding an expansion in terms of the primaries of the original theory, specifically restricted to the two-copy sector. This is achieved by expressing the twist operators in a non-local manner across different replicas and using a modular flow representation to obtain the $\textit{n}$ → 1 limit of the Rényi index. We explicitly compute the resulting “enhanced conformal blocks,” which, surprisingly, provide excellent approximations to the MI of generalized free fields across the full range of cross ratios. Remarkably, this approximation appears to be exact in the limit of large spacetime dimensions.

Netherlands

Cesar Agón

Argentina

Horacio Casini

Umut Gürsoy

Guim Planas

Mutual information from modular flow in CFTs

We explore the non-perturbative aspects of $\textit{c}$ = 1 string with compactified Euclidean time, its 0 + 0 dimensional matrix model duals (at self-dual radius), and 0 + 1 dimensional Matrix Quantum Mechanics (free fermion) description. We calculate the instanton normalizations, disk two-point function, and annulus one-point function in worldsheet formalism using string field theory insights. We further match them with the corresponding predictions from the matrix model descriptions. We also have some results and remarks regarding the multi ZZ instanton normalizations and the general (1, $\textit{n}$) ZZ instanton normalization for $\textit{c}$ = 1 string at both self-dual and generic radius.

India

Rishabh Kaushik

$\textit{c}$ = 1, $\textit{R}$ = 1 and $\textit{N}$ ≫ 1: ZZ instantons in 2D string theory and matrix integrals

We study the non-modal stability of black hole spacetimes under linear perturbations. We show that large-amplitude growth can occur at finite time, despite asymptotic decay of linear perturbations. In the example presented, the physical mechanism is a transient form of superradiance, and is qualitatively similar to the transition to turbulence in Navier-Stokes shear flows. As part of the construction we provide a theorem for the positivity of QNM energies, and introduce a truncated-Hamiltonian approach to black hole pseudospectra which does not suffer from convergence issues.