We study classical background electric fields and the Schwinger effect in de Sitter space. We show that a constant electric field in de Sitter requires the photon to have a tachyonic mass proportional to the Hubble scale. This has physical implications for the induced Schwinger current that affect its IR behaviour. To study this, we recompute the Schwinger current in de Sitter space for charged fermions and minimally coupled scalars, imposing a physically consistent renormalization condition. We find a $\textit{finite and positive}$ Schwinger current even in the massless limit. This is in contrast to previous calculations in the literature, which found a negative IR divergence. We also obtain the first result for the Schwinger current of a non-minimally coupled scalar, including the conformally coupled case, which we find exhibits behaviour very similar to that of the fermion current. Our results may have physical implications for both magnetogenesis and inflationary dark matter production.

Spain

Mar Bastero-Gil

Portugal

Paulo B. Ferraz

António Torres Manso

Slovenia

Italy

Lorenzo Ubaldi

Roberto Vega-Morales

Schwinger current in de Sitter space * This work has been partially supported by Junta de Andalucía Projects P21-00199 and A-FQM-472-UGR20 (FEDER funds); SRA (10.13039/501100011033) and ERDF (PID2022-139466NB-C21) (R.V.M.); PID2022-140831NB-I00, funded by MICIU/AEI/10.13039/501100011033 and FEDER, UE (M.B.G., A.T.M.); by FCT CERN (10.54499/2024.00252.CERN) (M.B.G., A.T.M., P.F.); FCT Grant No. SFRH/BD/151475/2021 and 10.54499/SFRH/BD/151475/2021 (P.F.). LU is supported by the Slovenian Research Agency under research core funding No. P1-0035 and by research grants J1-60026 and J1-4389. This article is based upon work from COST Action COSMIC WISPers CA21106, supported by COST (European Cooperation in Science and Technology). R.V.M. thanks the Mainz Institute for Theoretical Physics (MITP) of the Cluster of Excellence PRISMA$^{+}$ (Project ID 390831469) for its hospitality and partial support during the completion of this work

We investigate the direct $\rm CP $ violation in the decay $ D^\pm \to \pi^\pm \pi^+ \pi^- $ incorporating the $ a_0^0(980) $ - $ f_0(980) $ mixing mechanism. The integrated mixing intensities $ \overline \xi_{fa} $ and $ \overline \xi_{af} $ are calculated using meson masses and coupling constants extracted from various theoretical models and experimental data, yielding values of appreciable magnitude. We find that when the invariant mass of the $ \pi^+\pi^- $ pair lies near the $ f_0(980) $ resonance, this isospin-breaking mechanism can enhance the $\rm CP $ asymmetry. The enhancement is particularly pronounced when the $ f_0(980) $ carries a significant $ n\bar{n} $ quark component and the $ f_0(980) $ and $ \sigma(600) $ mixing angle is approximately $ 26^\circ $ . After accounting for non-factorizable effects, we find these corrections tend to partially cancel the leading-order contributions, resulting in a suppression of the $\rm CP $ violations relative to the naive factorization predictions. It is emphasized that the $ a_0^0(980) $ - $ f_0(980) $ mixing mechanism should be taken into account in both theoretical and experimental studies of $\rm CP $ violation in $\textit{B}$ or $\textit{D}$ meson decays.

China

Shi-Ji Cao

Jing-Juan Qi

Yi-Fan Zhao

Chao Wang

Zhen-Yang Wang

Xin-Heng Guo

Direct CP violation in ${ {\boldsymbol D}^{\bf\pm }\to {\boldsymbol\pi}^{\bf\pm} {\boldsymbol\pi}^{\bf +} {\boldsymbol\pi}^{\bf -}} $ with ${{\boldsymbol a}_{\bf 0}^{\bf 0}{\bf (980)-}{\boldsymbol f}_{\bf 0}{\bf (980)}} $ mixing * Supported by the National Natural Science Foundation of China (12405115, 12105149, 11805153, 12275024), and the High-Level Scientific Research Fund of Ningbo University (GJPY2026032)

We constructed a four-Higgs-doublet model (4HDM) invariant under $\textit{D}$ $_{5}$ symmetry and investigated its complete neutral vacuum structure in detail. Assuming explicit CP conservation in the scalar potential, we examined whether CP symmetry can be spontaneously broken. We provided a complete list of all possible real and complex vacua, along with the constraints on the potential parameters required for each vacuum solution to exist. We also discussed the positive-definiteness conditions that the Hessian must satisfy for each vacuum to be a local minimum of the potential. The results show that, after spontaneous symmetry breaking, some complex vacua lead to spontaneous CP violation in the potential, whereas the remaining complex vacua still preserve CP conservation. Among these CP-violating complex vacua, one can be regarded as the most general form. Furthermore, we discussed the relationship between real and complex vacua.

Dong-Ping Fu

Michihisa Takeuchi

Spontaneous CP violation in the $\textit{D}$ $_{5}$-symmetric four-Higgs-doublet models * Supported by the Fundamental Research Funds for the Central Universities, the One Hundred Talent Program of Sun Yat-sen University, China, and the Guangdong Natural Science Foundation (2026A1515012641)

Hadron-hadron interactions, being nonperturbative in nature, play a significant role in addressing phenomenological questions in particle physics. Femtoscopy is a powerful tool in heavy-ion collision experiments, enabling the extraction of hadron-hadron interactions via momentum-correlation functions (CFs). These CFs are typically expressed as a convolution of source functions and hadron-hadron wave functions, with the latter encoding information about the interactions. However, source functions remain poorly constrained and are commonly approximated by a Gaussian form. Reconstructing source functions from experimental correlation data constitutes an 'inverse problem.' To address this, we propose a toy model based on Tikhonov regularization. Using a square-well potential with four distinct strengths, we calculate the CFs for inputs of single Gaussian source functions and mixed Gaussian source functions. The resulting CFs are then used to reconstruct the source functions via Tikhonov regularization. Our results show that the Gaussian source function can be successfully reconstructed, highlighting the potential of this approach for extracting realistic source functions from hadron pairs of interest.

Ao-Sheng Xiong

Qi-Wei Yuan

Ming-Zhu Liu

Fu-Sheng Yu

Zhi-Wei Liu

Li-Sheng Geng

Solving the inverse source problem in femtoscopy with a toy model * Supported in part by the Fundamental and Interdisciplinary Disciplines Breakthrough Plan of the Ministry of Education of China (JYB2025XDXM204) and the National Natural Science Foundation of China (W2543006, 12435007). Ming-Zhu Liu acknowledges support from the National Natural Science Foundation of China (12575086). Zhi-Wei Liu acknowledges support from the National Natural Science Foundation of China (12405133) and from the Shenzhen Science and Technology Program (ZDSYS20230626091501002). Fu-Sheng Yu and Ao-Sheng Xiong acknowledge support from the Scientific Research Innovation Capability Support Project for Young Faculty (ZYGXQNJSKYCXNLZCXM-P2) and from the Fundamental Research Funds for the Central Universities (lzujbky-2023-stlt01, lzujbky-2024-oy02, lzujbky-2025-eyt01)

In this work, we extend Herrera’s concept of complexity for spherically symmetric self-gravitating static fluid distributions to arbitrary $$(n+2)$$ -dimensional spacetimes. By performing the orthogonal splitting of the Riemann tensor in higher dimensions, we derive a generalized scalar measure that quantifies the combined effects of energy density inhomogeneity and pressure anisotropy. This generalized complexity factor incorporates the dimensional dependence through the gravitational coupling constant and the geometry of the $$n$$ -sphere. We further analyze the vanishing complexity condition, identifying the specific balance between anisotropy and density gradients that yields structurally simple configurations in higher dimensions. Our results offer a foundational framework for investigating gravitational complexity in theories extending beyond four-dimensional general relativity.

India

Bikramarka Choudhury

Shyam Das

South Africa

Megan Govender

Kevin Reddy

Farook Rahaman

A generalized complexity formalism for $$(n+2)$$ -dimensional spacetime

Belgium

A. Sánchez-Fernández

S. Bara

W. Ryssens

S. Goriely

Corrigendum to “Accurate spontaneous fission half-lives from a microscopic large-scale nuclear structure model” [Physics Letters B 140287 (2026)]

Recently, based on the curve-integral formulation for stringy Tr$\textit{ϕ}$ amplitudes, a combinatorial formulation for Yang-Mills amplitudes has been proposed which describes gluons using pairs of scalars and produces the $\textit{n}$-gluon amplitude from simple kinematical shift of stringy Tr$\textit{ϕ}$ amplitudes with 2$\textit{n}$ scalars. It has revealed a variety of new properties and structures even for tree-level gluon amplitudes such as hidden zeros and splits, and in this note we provide another example: we study differential operators acting on Yang-Mills amplitudes with respect to 2$\textit{n}$-scalar kinematic variables, which convert such scalar-scaffolded gluons into scalars. In particular, we find ($\textit{n}$ − 1)-fold differential operators (using 2$\textit{n}$-scalar variables) that turn the $\textit{n}$-gluon amplitude into a single planar $\textit{ϕ}$ diagram; we then generalize such operators to those that convert $\textit{n}$ gluons to mixed amplitudes with $\textit{r}$ scalars and $\textit{n}$ − $\textit{r}$ gluons (the latter can be viewed as insertions on $\textit{ϕ}$ diagrams). We also show that the number of linearly independent mixed amplitudes with $\textit{r}$ scalars and $\textit{n}$ − $\textit{r}$ gluons is given by the number of $\textit{ϕ}$ diagrams, the Catalan number 𝒞 , which can be viewed as a generalization of the “uniqueness” theorem of gluon amplitudes (with $\textit{r}$ = 0). Finally, our construction leads to a planar version of the universal expansion of Yang-Mills amplitudes into a sum of gauge-invariant prefactors built from nested commutators, each accompanied by a mixed amplitude in the natural basis. This formulation significantly reduces the redundancy present in the original expansion.

Germany

Jin Dong

Yong-Xiang Su

Dongyu Yang

On differential operators for scalar-scaffolded gluons

This paper presents a detailed description of a model-independent method for the direct measurement of the Υ(4$\textit{S}$) → $\textit{B}$ $\textit{B}$ and Υ(4$\textit{S}$) → $$ {B}^0{\overline{B}}^0 $$ production fractions at $\textit{B}$ factories. The method is based on counting single- and double-inclusive charmed meson production at the Υ(4$\textit{S}$) resonance, providing statistical tagging of $$ {B}^0{\overline{B}}^0 $$ and $\textit{B}$ $\textit{B}$ events. A feasibility study indicates that a precision comparable to the current world average can be achieved without making any underlying assumptions, as the calculations rely solely on event yields.

Russia

M. Yasaveev

P. Pakhlov

N. Peters

A. Mufazalova

A model independent method for measurement of $\textit{B}$ ± and $\textit{B}$ 0 meson production fractions at Υ(4$\textit{S}$)

We present the first comprehensive study of the rare Dalitz decay $$K^*(892) \rightarrow K \ell ^+ \ell ^- (\ell = e, \mu )$$ , providing a prediction for the branching fraction and the dilepton mass spectrum. This decay involves the emission of a virtual photon which converts into a lepton pair, offering a probe of the transition form factor $$F_{K^*K}(q^2)$$ and underlying meson structure. Using a single pole approximation for the form factor, we present the calculation of the branching fraction for this rare decay channel for the first time. Furthermore, we also investigate the potential to search for a light $$A'$$ boson (dark photon) appearing as a narrow resonance in the dilepton spectrum, and discuss the experimental sensitivity and new physics opportunities at the dedicated BESIII experiment. Our results establish $$K^*(892) \rightarrow K \ell ^+ \ell ^- (\ell = e, \mu )$$ as a new laboratory for hadronic structure and dark-sector searches.

Benhou Xiang

Wanling Chang

Shuangshi Fang

Jingqing Zhang

Dalitz decay of $$K^*(892) \rightarrow K \ell ^+\ell ^-$$ : a new probe for hadronic structure and dark photon searches

A study of retardation models for the hadronic quark interaction is performed starting from a coordinate-space calculation that elaborates a classical electrodynamics procedure. The possibility of constructing a corresponding quantum operator is critically analyzed also performing some numerical matrix element calculations. A comparison of the developed model with the Feynman diagram interaction at tree-level is studied, showing a substantial physical correspondence of the two models. Possible applications and generalizations are discussed. Abstract Published by the Jagiellonian University 2026 authors

Colombia

M. De Sanctis

A study of Retardation Models for Phenomenological Interactions in Hadronic Physics