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 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

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

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

Several proposed future lepton colliders are capable of producing trillions of Z-bosons, including FCC-ee, CEPC, LEP3 and LEP-Z. Such Tera-Z factories can discover new elementary particles with couplings to the Z-boson that are orders of magnitude smaller than current bounds. For couplings near the currently excluded parameter regions they could produce sufficiently large samples to study the new particles’ properties in detail, thereby serving as both a discovery and precision machine in one. Using simple analytic estimates, we quantify the dependence of the expected event yield in long-lived particle searches on the number of produced Z-bosons and on the detector dimensions. From this, we derive estimates for both the discovery reach and the measurement precision attainable at such facilities. While the precision of such estimates of course falls short of proper simulations, the analytic approach is suitable for a quick assessment of the sensitivity for a given design. We illustrate this with two examples, heavy neutral leptons and axion-like particles. Under optimistic assumptions, these could be produced in the millions and billions, respectively, effectively turning future lepton colliders into exotics factories.

Belgium

Germany

Marco Drewes

Croatia

Juraj Klarić

Yuan-Zhen Li

New particles at the Z-pole:

We consider dijet production in $\textit{e}$ $\textit{e}$ collisions and in $$ H\to b\overline{b} $$ decays at next-to-next-to-leading order (NNLO) in perturbative QCD. A new non-local subtraction scheme is applied, for the first time, to obtain the fully differential cross section for these benchmark processes. We discuss and explicitly evaluate the perturbative ingredients needed in the computation, and we compare the performance of different slicing variables to obtain the NNLO corrections.

Switzerland

Luca Buonocore

Massimiliano Grazzini

Flavio Guadagni

Jürg Haag

Stefan Kallweit

Italy

Luca Rottoli

Jet production at NNLO: exploring a new scheme

In this study, we investigate the possibility of enhancing the di-jet resonance searches by tagging the final state radiation (FSR) jet using an event-level deep neural network. It is found that solely relying on the 4-momenta of the leading three jets allows the algorithm to achieve good discriminating power that can identify the hardest FSR jet in the signal while rejecting other soft jets. Once the invariant mass is corrected with the tagged FSR jet, the mass resolution of the signal is greatly enhanced, and the sensitivity of the search is also improved by more than 10%. By crafting the input variables carefully, the algorithm introduces minimal mass sculpting for the background, and its applicability extends to a broad mass range. This work proves that FSR jet tagging can potentially enhance di-jet resonance searches, suiting various stages of the physics programmes at the Large Hadron Collider (LHC) and High-Luminosity LHC (HL-LHC).

Bingxuan Liu

Yuxuan Shen

Yuanshunzi Sui

Enhancing di-jet resonance searches via a final-state radiation jet tagging algorithm * Bingxuan Liu is supported by Shenzhen Campus of the Sun Yat-sen University under project 74140-12255011, and by the Young Scientists Fund (C Class) of the National Natural Science Foundation of China (12405122). Both Yuxuan Shen and Yuanshunzi Sui are supported by College Students’ Innovative Entrepreneurial Training Plan Program

We investigate the collider signatures of a maximally flavor-violating $ U(1)_{L_\mu-L_\tau} $ model, where a new gauge boson $ Z^\prime $ and scalar triplets induce lepton flavor-changing interactions in the $\textit{μ}$-$\textit{τ}$ sector. Focusing on four-lepton final states at multi-TeV lepton colliders, we conduct a detailed analysis of cross sections, asymmetries, and polarization effects. We show that the signal cross section is highly sensitive to $ m_{Z^\prime} $ and the effective parameters $ \tilde{g}/m_{Z^\prime} $ , whereas it remains largely insensitive to the triplet Yukawa couplings within the phenomenologically allowed region. The forward-backward asymmetry exhibits a characteristic monotonic dependence on $ m_{Z^\prime} $ , and beam polarization can significantly suppress the Standard Model backgrounds while enhancing new physics contributions. We find that, in the phenomenologically allowed parameter space, the predicted observables remain highly sensitive to the underlying model parameters. These results show that multi-lepton final states are powerful probes of the $ U(1)_{L\mu - L_\tau} $ framework and can offer valuable guidance for future searches at muon and electron-positron colliders.

Jianing Qin

Fei Huang

Honglei Li

Zhi-Long Han

Jin Sun

Collider probes of four-lepton final states in maximally flavor-violating ${U(1)_{L_\mu-L_\tau}} $ model * Supported by National Natural Science Foundation of China (12505112, 11805081), Shandong Province Natural Science Foundation (ZR2024QA138, ZR2022MA056) and State Key Laboratory of Dark Matter Physics, University of Jinan Disciplinary Cross-Convergence Construction Project 2024 (XKJC- 202404) and Jin Sun is supported by IBS under the project code, (IBS-R018-D1)

Over the last few years, the CMS and ATLAS Collaborations at the Large Hadron Collider (LHC) have reported excesses that could hint at several new scalar resonances. Although none of them have touched the discovery level, at least two of them, at about 95 and 650 GeV, have been indicated by more than one experiment and have reached statistical significance worthy of a serious investigation. Conservatively using only the numbers given by the experimental collaborations, we find combined global significances around <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>3</mn><mi>σ</mi></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>4</mn><mi>σ</mi></mrow></math>, respectively, for the 95 and 650 GeV putative resonances. There are some more, like the one at 320 GeV, which have also been hinted at. We show that the data on only the 650 GeV resonance, assuming they stand the test of time, predict the existence of a doubly charged scalar and make the more common extensions of the scalar sector like those by gauge singlet scalars, the two-Higgs doublet models, or the Georgi-Machacek model highly disfavored. We provide the readers with a minimalistic model that may possibly explain all the indications. Such a model can also accommodate the hints of a singly charged scalar at about 375 GeV and a doubly charged scalar at about 450 GeV, as found by both the major LHC collaborations, the combined global significance for each of them being above <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>2.5</mn><mi>σ</mi></math>. We show that even the scant data, with large error bars, have the potential to strongly constrain our model containing four scalar multiplets, which makes the model easily testable and falsifiable. Our analysis comes with the obvious caveat that the allowed parameter space that we find depends on the available data on all the new resonances and may change in future. One may also note that this is an exploratory exercise that illustrates the difficulties when it comes to fitting several resonances simultaneously, even for next-to-minimal extensions of the Standard Model.

Anirban Kundu

Poulami Mondal

Gilbert Moultaka

Indications for new scalar resonances at the LHC and a possible interpretation

We investigate and update observational constraints on cosmological parameters within the $$\Lambda $$ CDM and dynamical dark energy frameworks, using a new compilation of the transverse (or 2D) BAO data, measurements that provide a relatively model-independent estimate of the BAO angular scale at a given redshift. Firstly, we assess the consistency of this compilation with CMB-Planck data and recent BAO results from the DESI collaboration. After confirming minimal tension with CMB data, we perform a series of joint analyses combining CMB data with the 2D BAO compilation, as well as with several recent Type Ia supernova (SNIa) samples. In all cases, we compare the constraining power of the 2D BAO data with that of DESI DR2 data (3D BAO). Our results indicate that combining 2D BAO with CMB and SNIa data provides observational constraints that are in agreement with those obtained using DESI DR2 data. Although the precision of DESI DR2 results remains higher, as expected due to the more accurate 3D measurements, the 2D BAO compilation combined with other probes yields strong constraints. For example, in the $$\Lambda $$ CDM context, we find (CMB + 2D BAO): $$H_0 = 68.16^{+0.41}_{-0.37} \,\,\, \text {km s}^{-1}\,\text {Mpc}^{-1}$$ and $$\Sigma m_{\nu } < 0.081~\textrm{eV}$$ (95% CL). These results are consistent with analogous analyses using DESI DR2. Several other cases are investigated and discussed in the main text. Our results show that this new 2D BAO compilation is robust and delivers meaningful cosmological constraints. Parameters from 2D BAO alone agree with CMB-only results, with no significant tension. Overall, 2D and 3D BAO provide consistent and complementary information when combined with other probes.

Brazil

Miguel Sabogal

Rafael Nunes

Felipe Avila

Armando Bernui

Updated cosmological constraints from 2D BAO measurements: a new compilation and comparison with DESI DR2