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)

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)

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

We develop a novel model utilizing the forward <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>K</mi><mo>*</mo></msup></math> production reaction off the nucleon, <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>π</mi><mi>N</mi><mo>→</mo><msup><mi>K</mi><mo>*</mo></msup><mi>M</mi><mi>B</mi></mrow></math>, induced by a high-momentum <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>π</mi></math> beam, as a tool to study low-lying <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>Y</mi><mo>*</mo></msup></math> resonances below and just above the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mover accent="true"><mi>K</mi><mo>¯</mo></mover><mi>N</mi></mrow></math> threshold. Because conventional <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>K</mi><mo>−</mo></msup><mi>p</mi></mrow></math> scattering experiments face difficulties in directly accessing this kinematic region, the proposed reaction offers a valuable complementary approach for <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>Y</mi><mo>*</mo></msup></math> spectroscopy. The constructed model is based on the one-meson exchange mechanism, which is known to dominate forward-angle production at high energies, and the half-off-shell scattering amplitudes from the ANL-Osaka dynamical coupled-channels models (Model A and Model B). We predict various observables, including differential cross sections and angular distributions. Our results demonstrate significant enhancements in the sub-threshold region of the invariant mass spectra. Notably, we show that overlapping resonances, such as a potential new <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mn>3</mn><mo>/</mo><msup><mn>2</mn><mo>+</mo></msup></mrow><mo> </mo><mi mathvariant="normal">Σ</mi></math> state and the well-established <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="normal">Σ</mi><mrow><mo>(</mo><mn>1385</mn><mo>)</mo></mrow><mn>3</mn><mo>/</mo><msup><mn>2</mn><mo>+</mo></msup></mrow></math>, can constitute a single peak in the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>π</mi><mi mathvariant="normal">Λ</mi></mrow></math> mass spectrum, indicating that the existence of previously unconfirmed subthreshold states cannot be ruled out by analyzing only the existing mass spectrum data. Furthermore, we find that angular distributions provide strong discriminatory power to disentangle such overlapping states through partial-wave interference effects, while the <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>t</mi><mo>′</mo></msup></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup><mi>ϕ</mi><mi>M</mi><mo>*</mo></msubsup></math> dependencies provide crucial constraints on the high-energy production mechanisms. Our predictions for these highly sensitive observables can facilitate high-statistics measurements, which are accessible at modern hadron facilities such as J-PARC, to unravel the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>S</mi><mo>=</mo><mo>−</mo><mn>1</mn></mrow><mo> </mo><msup><mi>Y</mi><mo>*</mo></msup></math> mass spectrum.

Japan

H. Kamano

United States

T.S.H. Lee

Low-lying <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">Λ</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">Σ</mi></math> resonances studied with the forward <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>K</mi><mo>*</mo></msup></math> productions off the proton induced by a high-momentum <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>π</mi></math> beam

We examine scattering amplitudes for an arbitrary number of photons in a class of nonnull background electromagnetic fields, studying tree-level and one-loop amplitudes in scalar and spinor quantum-electrodynamics in backgrounds defined by a gauge field <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>A</mi><mi>μ</mi></msub><mo stretchy="false">(</mo><mi mathvariant="fraktur">n</mi><mo>·</mo><mi>x</mi><mo stretchy="false">)</mo></math> for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi mathvariant="fraktur">n</mi><mn>2</mn></msup><mo>≠</mo><mn>0</mn></math>. Motivated to account for more physically realistic laser-plasma dispersive properties, our approach overcomes prior work studying such amplitudes in a constant background field and relaxes the familiar null criterion assumed for plane waves. Master formulas for the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>N</mi></math>-photon amplitudes dressed by the nonnull background are constructed using the first-quantized worldline formalism, which can systematically account for all orders in the nonnull parameter, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi mathvariant="fraktur">n</mi><mn>2</mn></msup></math>, treated here as an expansion parameter. These are derived from worldline representations of the coordinate and momentum space propagators (and their LSZ-truncated amplitudes) and the effective action, each incorporating the nonnull background nonperturbatively. We then outline a partial resummation of their expansions in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi mathvariant="fraktur">n</mi><mn>2</mn></msup></math>. A special exactly solvable case of nonnull constant crossed fields without photon insertion in the effective action is explored to test the master formulas that result. The validity of the presented master formulas is further checked against known expressions for the wave function and nonlinear Compton scattering in a nonnull background to lowest order in the nonnull parameter.

United Kingdom

Patrick Copinger

James P. Edwards

Karthik Rajeev

Scattering in strong field QED in a nonnull background

Purely baryonic weak decays of heavy baryons are investigated within the framework of the Skyrme model. These decays belong to a new class of unobserved decay channels, which would help us to test the standard model, particularly potential sources of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi mathvariant="italic">CP</mi></mrow></math> violation in the baryonic sector. By interpreting the heavy baryon as a bound state of a heavy meson and a baryon (Skyrmion), a direct calculation of the decay process <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msub><mi mathvariant="normal">Λ</mi><mi>b</mi></msub><mo>→</mo><mi>p</mi><mover accent="true"><mi>p</mi><mo>¯</mo></mover><mi>n</mi></mrow></math> is performed. The resulting branching fraction is of <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>O</mi><mo>(</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>6</mn></mrow></msup><mo>)</mo></mrow></math>, in agreement with previous estimates.

Chao-Qiang Geng

Chao Han

Purely baryonic weak decays of heavy baryons in a Skyrme model

This letter considers 3d $$ \mathcal{N} $$ = 4 (unitary-)orthosymplectic quiver gauge theories originating from Type IIA and Type IIB brane systems with ON planes. Such theories lie outside the scope of present combinatorial techniques for Coulomb branch symmetry and symplectic stratification. It turns out that the correct prescription involves ‘symmetry mitosis’: a common subset of nodes in two linear balanced chains source $\textit{two}$ factors of a Coulomb branch global symmetry instead of one; the correct Coulomb branch Hasse diagram is obtained by a ‘doubling’ procedure on that computed by naive quiver subtraction. Input from 6d SQFTs and little string theories allows for the construction of various ‘mitotic’ magnetic quivers. The full Higgs branch Hasse diagram of minimal ($\textit{E}$ , $\textit{E}$ ) conformal matter is given. Additionally, a new Type I brane system using eight full D8 branes, negatively charged D6 branes, and ON planes is found corresponding to a product of Spin(32) instantons on $\textit{ℂ}$ . The corresponding 6d theory uses Sp(−1) gauge nodes which have the interpretation of bi-spinor matter of O($\textit{a}$) and O(12 − $\textit{a}$) for $\textit{a}$ = 0, 1, · · · , 12.

Sam Bennett

Amihay Hanany

Guhesh Kumaran

Germany

Lorenzo Mansi

Symmetry mitosis and Hasse diagram diamonds: a note on brane configurations with ON0 planes

We investigate non-abelian branes in curved space. We discuss solutions to the equations of motion of the transverse scalars when they are constant along the world-volume directions and obey an 𝔰𝔲(2) or an 𝔰𝔲(2) ⊕ 𝔰𝔲(2) algebra. Motivated by the membrane version of the weak gravity conjecture, we specialise our results to non-abelian domain-wall D($\textit{d}$ − 2) branes embedded in AdS flux vacua. We find that they can be less self-attractive than their abelian counterpart, opening up a new decay-channel for vacua that resist all abelian domain-wall destabilisations. These branes come in two types, depending on whether their fuzziness involves the radial direction, or is purely internal. Only the latter can develop in vacua free from abelian decays. We illustrate our construction by embedding these branes in a variety of AdS vacua, destabilising some of them.

Vincent Menet

Alessandro Tomasiello

A weakly non-abelian decay channel

Conformal blocks in odd spacetime dimensions are not known in closed analytic form. To facilitate efficient computations in the conformal bootstrap, we introduce goblocks: a novel conformal-block generator implemented in the Go programming language, designed for rapid, on-the-fly, parallel evaluation in general spacetime dimensions using recursive relations. The package supports both multipoint and derivative-based bootstrap approaches and allows flexible control over accuracy and performance. We benchmark goblocks against the scalar_blocks package, finding significant speed improvements in applications where computational speed and moderate accuracy are critical, but ultrahigh precision is not essential. As an illustration, we apply goblocks to the mixed-correlator bootstrap of the three-dimensional Ising model, formulated as a nonconvex optimization problem in a suitable truncation scheme. We simultaneously optimize over external scaling dimensions and OPE CFT data. In addition, we discuss how the approach scales as we increase the number of mixed correlators in more general <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>O</mi><mo stretchy="false">(</mo><mi>N</mi><mo stretchy="false">)</mo></mrow></math> vector models.