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

The weak decays of charmonium states such as $ J/\psi $ and $ \psi(2S) $ are instrumental in probing both nonperturbative QCD dynamics and the flavor structure of the Standard Model (SM). The extreme rarity of charmonium weak decays renders them highly sensitive to physics beyond the SM, particularly in channels that are heavily suppressed in the SM, such as flavor-changing neutral-current (FCNC) decays. This review highlights the critical role of the BESIII experiment, which leverages an unprecedented data sample of over $ 10^{10} $ $ J/\psi $ and $ 2.7\times10^{9} $ $ \psi(2S) $ events to achieve leading sensitivity in searches for charmonium weak decays. We present the latest and most stringent upper limits established by BESIII on various semileptonic, nonleptonic, and FCNC charmonium weak decay channels.

China

Xu-Ze Li

Kai-Xin Fan

Zheng-Yun You

Yu Zhang

Minggang Zhao

Mini-review of charmonium weak decays at BESIII * Supported in part by the National Key R&D Program of China (2023YFA1606000); the National Natural Science Foundation of China (NSFC) (12035009, 12175321, U1932101), and the National College Students' Science and Technology Innovation Project of Sun Yat-sen University

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.

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)

In the present work, the strong decays of the discovered $ P_c(4380) $ , $ P_c(4440) $ , $ P_c(4457) $ and their possible isospin cousins are systematically studied via the assignment that they are meson-baryon molecular states. In detail, the strong decay constants and partial decay widths of their decay channels are calculated under the framework of QCD sum rules. The decay widths of the discovered $ P_c(4380) $ , $ P_c(4440) $ , and $ P_c(4457) $ are in good agreement with the experiments. The predictions of the decays of these three related possible isospin cousins are presented, which would shed light on their findings in experiments. In return, this may testify to the assignments of the discovered $ P_c $ states.

Xiu-Wu Wang

Xin Li

Zhi-Gang Wang

Systematic study of the strong decays of the $\textit{P}$ $\textit{c}$ states and their possible isospin cousins via the QCD sum rules * Supported by the National Natural Science Foundation of China (12575083) and the Natural Science Foundation of Hebei Province (A2024502002)

In this work, we investigate three representative new-physics resonances that couple to Standard Model (SM) quarks through flavor-changing interactions involving the top quark. We identify the possible SMEFT operators at the electroweak scale and analyze their phenomenology.

Min Huang

Yandong Liu

Hao Zhang

Exploring new resonances with direct top flavor changing interactions * Min Huang and Hao Zhang is supported in part by the National Science Foundation of China (12575114, 12235001, 12075257)

We present a comprehensive study of warm hybrid inflation within the framework of $\textit{α}$-attractor models, where an axionic inflaton is coupled to a waterfall field in the presence of thermal dissipation. The model is analyzed for both linear ( $ \Upsilon \propto T $ ) and cubic ( $ \Upsilon \propto T^{3} $ ) dissipation regimes. Confronting the theoretical predictions with the latest observational data from Planck+BICEP/Keck, P-ACT-LB-BK18, and SPT, we find that in the weak dissipative regime ( $ Q_{*} \lesssim 10^{-5} $ ), the scalar spectral index $ n_{s} \simeq 0.965 $ lies at the boundary of the combined P-ACT-LB-BK18 constraints, while the tensor-to-scalar ratio $\textit{r}$ remains within observable ranges. For stronger dissipation ( $ Q_{*} \gtrsim 10^{-2} $ ), the model predicts values of $ n_{s} $ well within the $ 1-2\sigma $ confidence region of all datasets, with tensor modes remaining fully observable in both dissipation scenarios. These results indicate that forthcoming CMB polarization experiments may be capable of detecting primordial gravitational waves, thereby providing a robust observational test of warm hybrid inflation across different dissipative regimes.

Waqas Ahmed

Pakistan

Waqar Ahmad

Ahsan Illahi

M. Junaid

Warm hybrid axion inflation in $\textit{α}$-attractor models constrained by ACT and future plan experiments

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)

<p>We unveil a remarkable interplay between rigid field theories (RFTs), charge-to-mass ratios <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi></math>, and scalar curvature divergences <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi mathvariant="sans-serif">R</mi></mrow><mrow><mi>div</mi></mrow></msub></mrow></math> in the vector multiplet moduli space of 4D <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">N</mi><mo>=</mo><mn>2</mn></math> supergravities, obtained upon compactifying type II string theory on Calabi–Yau threefolds. We show that the condition to obtain an RFT that decouples from gravity implies a divergence in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi></math> of (would-be) BPS particles charged under the rigid theory and vice-versa. For weak coupling limits, where the scalar curvature diverges, we argue that such BPS particles exist and that <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="sans-serif">R</mi><mrow><mi>div</mi></mrow></msub><mo>≲</mo><msup><mi>γ</mi><mn>2</mn></msup></math>, implying that all these divergences are a consequence of RFT limits. More precisely, along geodesics we find that <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi mathvariant="sans-serif">R</mi></mrow><mrow><mi>div</mi></mrow></msub><mo>∼</mo><mo stretchy="false">(</mo><msub><mrow><mi mathvariant="normal">Λ</mi></mrow><mrow><mi>wgc</mi></mrow></msub><mo>/</mo><msub><mrow><mi mathvariant="normal">Λ</mi></mrow><mrow><mi>g</mi></mrow></msub><msup><mrow><mo stretchy="false">)</mo></mrow><mrow><mn>2</mn></mrow></msup></mrow></math>, where <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="normal">Λ</mi><mrow><mi>wgc</mi></mrow></msub><mo>≡</mo><msub><mi>g</mi><mi>rigid</mi></msub><msub><mi>M</mi><mi>Pl</mi></msub></math> is the RFT cutoff estimate of the weak gravity conjecture and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="normal">Λ</mi><mi>g</mi></msub><mo>=</mo><msubsup><mi>g</mi><mi>rigid</mi><mrow><mo>−</mo><mn>2</mn></mrow></msubsup><msub><mi mathvariant="normal">Λ</mi><mrow><mi>RFT</mi></mrow></msub></math> the electrostatic energy integrated up to its actual cutoff <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="normal">Λ</mi><mrow><mi>RFT</mi></mrow></msub></math>.</p>

United States

Alberto Castellano

Fernando Marchesano

Luca Melotti

Lorenzo Paoloni

Moduli space curvature and the weak gravity conjecture

<p>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.</p>

Japan

H. Kamano

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