Investigating the electromagnetic characteristics of unconventional states may offer new insights into their internal structures. In particular, the magnetic moment attributes may serve as a crucial physical observable for differentiating exotic states with disparate configurations or spin-parity quantum numbers. As a promising avenue for research, encompassing both opportunities and challenges, an in-depth examination of the electromagnetic properties of exotic states is crucial for advancing our understanding of unconventional states. Motivated by this, in this study, the magnetic moments of ${I(J^{P})} = 1(1^{+})$ $ Z_{\bar{b} c} $ tetraquark states are analyzed in the framework of QCD light-cone sum rules by considering the diquark-antidiquark approximation, designated as type $ 3_c \otimes \bar{3}_c $ . Although the tetraquark states examined in this study have nearly identical masses, their magnetic moment results exhibit noticeable discrepancies. This may facilitate the differentiation between quantum numbers associated with states with identical quark content. The results show that heavy quarks overcoming light quarks can determine both the sign and magnitude of the magnetic moments of these tetraquark states. The numerical results obtained in this study suggest that the magnetic moments of $ Z_{\bar{b} c} $ tetraquark states may reveal aspects of their underlying structure, which could distinguish between their spin-parity quantum numbers and internal structure. The results obtained regarding the magnetic moments of the $ Z_{\bar{b} c} $ tetraquark states may be checked within the context of different phenomenological approaches.

Ulaş Özdem

Elucidating the nature of axial-vector charm-antibottom tetraquark states

The Schwinger effect, a non-perturbative mechanism for particle production in strong fields, plays a crucial role in understanding quantum vacuum decay and high-energy phenomena, including heavy-ion collisions (HIC). Although holographic quantum chromodynamics (QCD) models have been widely used to study this effect, most treatments assume isotropy or consider only a single type of anisotropy, neglecting the interplay between spatial and magnetic anisotropies that arise in realistic HIC scenarios. A unified framework accounting for both anisotropies is needed to accurately model particle production. We investigate the Schwinger effect in a twice anisotropic holographic QCD model incorporating both spatial and magnetic anisotropies. Using the anti-de Sitter/conformal field theory correspondence, we compute the total potential of a particle-antiparticle pair to quantify how these anisotropies influence pair production. Our results show that the magnetic field (parameterized by $c_B$ and $q_3$ ) enhances the Schwinger effect by lowering and narrowing the potential barrier, while increasing spatial anisotropy (controlled by $\nu$ ) suppresses the process by raising and widening the barrier. These findings demonstrate that magnetic and spatial anisotropies exert competing effects on particle production, emphasizing the necessity of treating both concurrently in holographic models. This work advances the theoretical description of the Schwinger effect in anisotropic environments, with implications for understanding non-equilibrium dynamics in HIC and other strongly coupled systems.

China

Wen-Bin Chang

Defu Hou

Schwinger effect in a twice anisotropic holographic model * Defu Hou's research is supported in part by the National Key Research and Development Program of China (2022YFA1604900). Additionally, Defu Hou receives partial support from the National Natural Science Foundation of China (NSFC) (12435009, 12275104). Wen-Bin Chang is supported by the Ph.D. Research Startup Project at Hubei Minzu University (RZ2500000857)

We examine the sensitivity of the beam normal spin asymmetry in Bhabha scattering to beyond the Standard Model mediators, in the context of the JLab polarized positron program. A key property of this observable is that the Standard Model contribution exhibits a zero crossing at a fixed scattering angle, providing a clean, effectively background-free point for these searches. We consider scalar, vector, and axial vector mediators and present projected bounds, finding that scalar and vector scenarios allow a significant extension of the search ranges beyond existing constraints.

Aleksandr Pustyntsev

Muthubharathi S. Ramasamy

Marc Vanderhaeghen

New physics searches via beam normal spin asymmetry in Bhabha scattering

We present a study of the rare baryonic decay $$\Lambda _b \rightarrow \Lambda \tau ^+ \tau ^-$$ as a probe of new physics (NP) coupled preferentially to third-generation fermions. Within the Standard Model, we evaluate the branching ratio and the lepton-flavour-universality (LFU) ratio $$R_{\Lambda }^{\tau /\mu },$$ including both perturbative and long-distance charm contributions. We show that the LFU ratio can be predicted with an uncertainty below 10%. Possible NP effects arising from lepton non-universal dynamics are analysed within an effective field theory framework motivated by the current anomalies in $$b \rightarrow c\tau \nu $$ and $$b \rightarrow s\mu ^+\mu ^-$$ transitions. In this context, $$R_{\Lambda }^{\tau /\mu }$$ can be enhanced by several orders of magnitude, offering a clear target for upcoming searches. The implications for the related mode $$\Lambda _b \rightarrow pK\tau ^+\tau ^-$$ are also briefly discussed.

Switzerland

Marzia Bordone

Gino Isidori

Christiane Mayer

Jan-Niklas Toelstede

Probing lepton flavour universality with $$\Lambda _b$$ decays to $$\tau ^+\tau ^-$$ final states

We present possible strategies for anomaly detection of rare particle decays and exotic hadrons, such as pentaquarks, in low-background environments such as those characteristic of diffractive events and ultraperipheral pp, p-A, or A-A collisions at the CERN Large Hadron Collider (LHC). Our models are trained with toy samples representing the UPC processes measured until now by the ALICE Collaboration. When samples containing rare processes such as J/$\textit{ψ}$ → 4$\textit{π}$ and pentaquark production, where the number of injected pentaquark events is estimated based on current experimentally available upper limits, and those for J/$\textit{ψ}$ → 4$\textit{π}$ are estimated through the branching ratio of the decay channel, are analyzed, the rare processes are flagged as anomalous by the models. This approach demonstrates the applicability of such a technique for searches for new physics in the current and future data sets at collider experiments with high purity, while also allowing for the measurement of upper limits for the production of exotica.

United States

S. Ragoni

B. Kinkaid

J. Seger

C. Anson

D. Tlusty

AI-powered full-data set search for new physics in ultraperipheral and diffractive events

In this work, we conduct a systematic investigation of the electromagnetic properties, specifically the magnetic moments and the M1 radiative decay behavior, of the predicted $$\Xi _c^{(',*)}D^{(*)}_s$$ -type double-charm hidden-strangeness molecular pentaquarks. The study is carried out within the framework of the constituent quark model to evaluate these electromagnetic observables, and our analysis incorporates three distinct scenarios: single-channel analysis, $\textit{S}$–$\textit{D}$ wave mixing analysis, and coupled-channel analysis. The calculated magnetic moments reveal characteristic patterns that reflect their underlying constituent configurations and provide sensitive probes for their quantum number assignments. Furthermore, we identify several M1 radiative decay channels with sizable widths that may offer promising signatures for future experimental detection. These M1 transitions also act as sensitive probes into their inner structures, displaying distinctive features that help differentiate between their constituent configurations and quantum number assignments. We anticipate that this study will stimulate experimental interest in exploring the electromagnetic properties of the $$\Xi _c^{(',*)}D^{(*)}_s$$ molecular states, thereby advancing our structural understanding of these exotic hadronic states.

Sheng-He Zhu

Fu-Lai Wang

Xiang Liu

Electromagnetic characteristics as probes into the inner structures of the predicted $$\Xi _c^{(',*)}D^{(*)}_s$$ molecular states

Within the framework of nonrelativistic QCD (NRQCD) factorization, and based on the Collins-Soper operator definition of fragmentation functions, we present a systematic calculation of the fragmentation functions for a heavy quark fragmenting into color-singlet $\textit{P}$-wave quarkonium states. After reproducing and confirming the known leading-order results, we further compute the relativistic corrections up to order $$ \mathcal{O}\left({v}^2\right) $$ . Our analysis applies both to quarkonium systems composed of heavy quarks with the same flavor and to $\textit{B}$ -type mesons formed by heavy quarks of different flavors. Numerical results show that, for all color-singlet $\textit{P}$-wave channels, the $$ \mathcal{O}\left({v}^2\right) $$ relativistic corrections give sizable negative contributions over most of the momentum-fraction $\textit{z}$ region. We further compute inclusive cross sections for $\textit{P}$-wave quarkonium plus charmed hadrons in $\textit{e}$ $\textit{e}$ annihilation via the single photon process up to $$ \mathcal{O}\left({v}^2\right) $$ by applying our obtained fragmentation functions, and the resulting predictions are consistent with the full fixed-order results in the high-energy region.

Sai Cui

Sheng-Juan Jiang

Guang-Zhi Xu

Kui-Yong Liu

Order-$\textit{v}$ 2 relativistic corrections to heavy-quark fragmentation into $\textit{P}$-wave quarkonium states

The Giant Dipole Resonance (GDR) in 51V has been a long-term conflicting interpretation, with existing photoneutron cross section data suggesting either a single peak or a pronounced splitting, leading to opposite conclusions on nuclear deformation. A new measurement of the 51V( <italic>&#947;</italic>,1n) cross section, performed at the Shanghai Laser Electron Gamma Source (SLEGS) facility, employs a refined monochromatic cross section extraction method. By integrating Polynomial Regression and Support Vector Regression (SVR) for robust interpolation and extrapolation, the new extracted monoenergetic cross sections exhibit a single, broad peak with no evidence of GDR splitting. Re-analysis of the reported splitting shows that any deformation extracted from such a structure would be relatively weaker than those of neighboring nuclei, providing a support for a spherical or near-spherical shape of 51V. Furthermore, we found that deliberately overfitting the data using an SVR model reproduces multi-peak structures similar to those reported in historical datasets, implying that the previously claimed splitting might originated from analysis artifacts rather than physical phenomena.

Zi-Rui Hao

Gong-Tao Fan

Chen Chen

Qian-Kun Sun

Hong-Wei Wang

Yi-Fei Niu

Hang-Hua Xu

Long-Xiang Liu

Yue Zhang

Yu-Xuan Yang

Kai-Jie Chen

Zhi-Cai Li

Pu Jiao

Meng-Die Zhou

Shan Ye

Zhen-Wei Wang

Xiang-Fei Wang

Meng-Ke Xu

Yu-Long Shen

Chang Yang

Jia-Wen Ding

New measurement of 51V( <italic>&#947;</italic>,1n) cross section through the refined monochromatic cross section extraction method

We construct a new family of type IIB supergravity solutions corresponding to states of the D1-D5-P-KKm system that carry the same charges and energy as the non-extremal four-charge black hole and are asymptotic to AdS × $$ \left({S}^3/{\mathbb{Z}}_{N_k}\right)\times $$ T . The solutions consist of static binaries of two extremal D1-D5-P black holes with S horizons and charges of opposite signs, held in equilibrium by a topological bubble supporting $\textit{N}$ units of KKm charge. Although dynamically unstable, the spacetimes remain smooth on and outside the horizons. The equilibrium condition discretizes the black hole separation, producing a quantized spectrum labeled by the number of antibranes and antimomenta at the anti-BPS center. Strikingly, the lowest-energy states lie within an energy window smaller than the dual CFT mass gap. We also show that these solutions admit regular finite-temperature deformations, which slightly lift the two black holes above extremality while remaining within the gap.

Spain

Roberto Emparan

Pierre Heidmann

Branes and antibranes in AdS3: the impossible states in the CFT gap

Given the 3 × 3 Cabibbo-Kobayashi-Maskawa (CKM) quark flavor mixing matrix <italic>V</italic>, we define a new set of rephasing invariants in terms of the &#8220;trios&#8221; of its nine elements: <math altimg='si1.svg'><mrow><msubsup><mi>&#9674;</mi><mrow><mi>&#945;</mi><mi>&#946;</mi><mi>&#947;</mi></mrow><mrow><mi>i</mi><mi>j</mi><mi>k</mi></mrow></msubsup><mo>&#8801;</mo><mrow><mo>(</mo><msub><mi>V</mi><mrow><mi>&#945;</mi><mi>i</mi></mrow></msub><msub><mi>V</mi><mrow><mi>&#946;</mi><mi>j</mi></mrow></msub><msub><mi>V</mi><mrow><mi>&#947;</mi><mi>k</mi></mrow></msub><mo>)</mo></mrow><mo linebreak='goodbreak'>/</mo><mi>det</mi><mi>V</mi></mrow></math> with <italic>&#945;</italic>&#8239;&#8800;&#8239; <italic>&#946;</italic>&#8239;&#8800;&#8239; <italic>&#947;</italic> and <italic>i</italic>&#8239;&#8800;&#8239; <italic>j</italic>&#8239;&#8800;&#8239; <italic>k</italic> running respectively over ( <italic>u, c, t</italic>) and ( <italic>d, s, b</italic>). We find that <math altimg='si2.svg'><mrow><mrow><mrow><mi mathvariant='normal'>I</mi></mrow><mi>m</mi></mrow><msubsup><mi>&#9674;</mi><mrow><mi>&#945;</mi><mi>&#946;</mi><mi>&#947;</mi></mrow><mrow><mi>i</mi><mi>j</mi><mi>k</mi></mrow></msubsup><mo linebreak='goodbreak'>=</mo><mo>&#8722;</mo><mi mathvariant='script'>J</mi></mrow></math> holds, where <math altimg='si3.svg'><mi mathvariant='script'>J</mi></math> is the well-known Jarlskog invariant of weak CP violation. Analogous rephasing invariants <math altimg='si4.svg'><mrow><msubsup><mi>&#10731;</mi><mrow><mi>&#945;</mi><mi>&#946;</mi><mi>&#947;</mi></mrow><mrow><mi>i</mi><mi>j</mi><mi>k</mi></mrow></msubsup><mo>&#8801;</mo><mrow><mo>(</mo><msub><mi>U</mi><mrow><mi>&#945;</mi><mi>i</mi></mrow></msub><msub><mi>U</mi><mrow><mi>&#946;</mi><mi>j</mi></mrow></msub><msub><mi>U</mi><mrow><mi>&#947;</mi><mi>k</mi></mrow></msub><mo>)</mo></mrow><mo linebreak='goodbreak'>/</mo><mi>det</mi><mi>U</mi></mrow></math> can be defined for the 3&#8239;&#215;&#8239;3 Pontecorvo-Maki-Nakagawa-Sakata (PMNS) lepton flavor mixing matrix <italic>U</italic>, where <italic>&#945;</italic>&#8239;&#8800;&#8239; <italic>&#946;</italic>&#8239;&#8800;&#8239; <italic>&#947;</italic> and <italic>i</italic>&#8239;&#8800;&#8239; <italic>j</italic>&#8239;&#8800;&#8239; <italic>k</italic> run respectively over ( <italic>e, &#956;, &#964;</italic>) and (1, 2, 3). Taking into account small non-unitarity of <italic>U</italic> based on the canonical seesaw mechanism for neutrino mass generation, we calculate <math altimg='si5.svg'><mrow><mrow><mrow><mi mathvariant='normal'>I</mi></mrow><mi>m</mi></mrow><msubsup><mi>&#10731;</mi><mrow><mi>&#945;</mi><mi>&#946;</mi><mi>&#947;</mi></mrow><mrow><mi>i</mi><mi>j</mi><mi>k</mi></mrow></msubsup></mrow></math> with the help of a full Euler-like block parametrization of the seesaw flavor structure and demonstrate that their leading terms converge to a universal invariant <math altimg='si6.svg'><msub><mi mathvariant='script'>J</mi><mi>&#957;</mi></msub></math> in the unitarity limit of <italic>U</italic>.

Shu Luo

Zhi-zhong Xing

New rephasing invariants and CP violation built from the trios of the CKM or PMNS matrix elements