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 investigate the possibility of $\textit{freeze-in}$ dark matter production and baryogenesis via leptogenesis in a $$\psi '$$ SM model, which is an $$E_6$$ extension of the Standard Model, featuring a residual $$U(1)_{\psi '}$$ gauge symmetry. This symmetry arises from a linear combination of $$U(1)_\chi $$ and $$U(1)_{\psi }$$ , both of which are subgroups of the $$E_6$$ . The spontaneous breaking of $$U(1)_{\psi '}$$ symmetry governs the dynamics of a singlet fermion, which serves as a freeze-in dark matter candidate. The dark matter mass arises from dimension-five operators, and a discrete symmetry ensures its stability. We show that freeze-in production from scalar decay can yield the correct relic abundance for dark matter masses between a few MeV to a few hundred GeV. Simultaneously, heavy right-handed neutrinos generate light neutrino masses via the type-I seesaw and produce the observed baryon asymmetry via leptogenesis.

Pakistan

Russia

Adeela Afzal

United Kingdom

Rishav Roshan

Freeze-in dark matter and leptogenesis: a $$\psi '$$ SM route

We construct exact static, spherically symmetric charged fluid solutions within the framework of Einstein–Cartan–Maxwell (ECM) theory, in which intrinsic spin and spacetime torsion are incorporated through the Weyssenhoff spin fluid. Starting from the general ECM field equations, a single master differential equation for the gravitational potential $$Z=e^{\nu /2}$$ is derived. This equation forms the basis of a simple and systematic algorithm for generating charged extensions of known uncharged perfect-fluid solutions. By introducing a deformation of the temporal metric potential, two distinct classes of charged configurations are obtained, depending on whether the deformation parameters $$\alpha $$ or $$\beta $$ vanish. The algorithm is applied explicitly to Adler’s interior solution, yielding closed-form expressions for the electric field, charge density, and matter variables, including explicit spin–torsion contributions. Matching the resulting charged Einstein–Cartan (EC) interior solutions to the exterior Reissner–Nordström spacetime fixes all integration constants uniquely in terms of the mass–radius ratio $$\epsilon =m/a$$ and the dimensionless charge parameter $$n^{2}=q^{2}/a^{2}$$ . In the limit $$n^{2}\rightarrow 0$$ , the charged EC configurations reduce smoothly to Adler’s original uncharged interior solution, ensuring the internal consistency of the construction.

India

L. Katkar

D. Phadatare

Charged Weyssenhoff fluid spheres in Einstein–Cartan–Maxwell theory: a general algorithm

In this paper, we will present a local study of star boundaries along three different routes. Firstly, we will develop a local algorithm based on curvature scalars for identifying invariantly the boundary of a star; we will distinguish between the cases of stars supported by fluids with either isotropic or anisotropic pressure, and we will successfully test our proposal for a number of available analytical spacetimes not necessarily stationary. Our method will be based on the trace anomaly, the variation of volume along a geodesic and the skewness of the matter content. Next, restricting to some Tolman’s metrics, we will recast the Buchdahl’s bound for global and physical quantities, as the mass and radius of the star, into a local inequality between Weyl and Ricci curvature scalars at the boundary: our results will allow to inspect the required interplay between pure gravitational and pure matter energy in supporting the equilibrium. Lastly, we will relate the non-local complexity factor of the matter content for those Tolman’s solutions to a local Weyl scalar in a unified manner. We will compare and contrast our paradigm with the geometric horizon conjecture for black holes also in the context of the no-hair theorem and holographic principle. From the physical perspective, our present research scrutinizes which global properties of bounded compact objects can actually be fully accounted for by local measurements, while from the mathematical side, it provides a transparent foundation via the formalism of differential geometry to some numerical relativity techniques adopted in astrophysical simulations.

Daniele Gregoris

On a local study of star boundaries

We systematically investigate the electromagnetic properties of exotic states whose internal structures remain uncertain and for which different models have been proposed. In this work, we focus on the magnetic dipole moments of hidden-charm pentaquark states using QCD light-cone sum rules with four distinct interpolating currents. The analysis accounts for contributions from both light and charm quark sectors, as well as higher-dimensional operators, ensuring convergence of the operator product expansion and dominance of the ground-state pole. Our results demonstrate a strong dependence of the magnetic moments on the internal quark configurations and spin alignments, revealing substantial variations among the different currents despite identical quark content and quantum numbers. Comparisons with existing studies indicate that while molecular-type predictions show general agreement, compact configurations yield markedly different values, including significant differences in sign and magnitude. These findings therefore underscore the sensitivity of electromagnetic observables to the internal structure of exotic hadrons and highlight their potential as probes to discriminate between competing structural models for spin–parity assignments and underlying quark dynamics.

Türkiye

Ulaş Özdem

Hidden-charm pentaquarks: electromagnetic structure in a diquark–diquark–antiquark model

We provide an elementary pedagogical introduction to some basic concepts and techniques of soft (or Sudakov) resummation, specifically in QCD, paying particular attention to simple but useful tricks of the trade. We briefly review collinear (Altarelli–Parisi) and infrared (eikonal) factorization, cancellation of infrared singularities, and factorization of mass singularities. We recall basic concepts on renormalization group invariance and the solution of renormalization group equations. We then show how threshold resummation can be derived from a renormalization group argument following from the cancellation of infrared singularities. We discuss various equivalent forms of the resummed result, and we briefly present transverse momentum resummation. Abstract Published by the Jagiellonian University 2026 authors

Italy

S. Forte

G. Ridolfi

A Simple Introduction to Soft Resummation

In the presence of a strong electric field, the vacuum is unstable to the production of pairs of charged particles—the Schwinger effect. The created pairs extract energy from the electric field, resulting in nontrivial backreaction. In this paper, we study <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>1</mn><mo>+</mo><mn>1</mn><mi mathvariant="normal">D</mi></mrow></math> massive QED subject to strong external electric fields in a self-consistent and fully quantum manner. We use the bosonized version of the theory, which attains a cosine interaction term in the presence of nonzero fermion mass <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>m</mi></math>. However, the assumption of a strong electric field justifies a perturbative treatment of the cosine interaction, i.e., an expansion in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>m</mi></math>. We calculate the vacuum expectation value of the electric field to first order in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>m</mi></math> and show that—surprisingly—it satisfies a classical nonlinear partial differential equation (related to the sine-Gordon equation). We show that the electric field exhibits dissipation-free oscillations (analogous to ordinary plasma oscillations) and calculate the plasma frequency analytically. We also compare to the semiclassical approximation commonly used to study backreaction, showing that it fails to capture the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>O</mi><mo stretchy="false">(</mo><mi>m</mi><mo stretchy="false">)</mo></math> shift in the plasma frequency.

Samuel E. Gralla

Morifumi Mizuno

Schwinger effect with backreaction in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>1</mn><mo>+</mo><mn>1</mn><mi mathvariant="normal">D</mi></mrow></math> massive QED with a strong external field

Based on the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><mn>2712.4</mn><mo>±</mo><mn>14.4</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>6</mn></mrow></msup><mtext> </mtext><mi>ψ</mi><mo stretchy="false">(</mo><mn>3686</mn><mo stretchy="false">)</mo></mrow></math> events collected with the BESIII detector, we present a high-precision study of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup></math> mass spectrum in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ψ</mi><mo stretchy="false">(</mo><mn>3686</mn><mo stretchy="false">)</mo><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><mi>J</mi><mo>/</mo><mi>ψ</mi></math> decays. A clear resonancelike structure is observed near the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup></math> mass threshold for the first time. A fit with a Breit-Wigner function yields a mass of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>285.6</mn><mo>±</mo><mn>2.5</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> and a width of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>16.3</mn><mo>±</mo><mn>0.9</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math> with a statistical significance exceeding <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>10</mn><mi>σ</mi></mrow></math>. To interpret the data, we incorporate final-state interactions (FSI) within two theoretical frameworks: chiral perturbation theory (ChPT) and QCD multipole expansion (QCDME). ChPT describes the spectrum above <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0.3</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>/</mo><msup><mi>c</mi><mn>2</mn></msup></math> but fails to reproduce the threshold enhancement. In contrast, the QCDME model—assuming the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ψ</mi><mo stretchy="false">(</mo><mn>3686</mn><mo stretchy="false">)</mo></math> is an admixture of S- and D-wave charmonium—reproduces the data well. The pronounced dip near <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0.3</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>/</mo><msup><mi>c</mi><mn>2</mn></msup></math> offers new insight into the interplay between chiral dynamics and low-energy QCD.

M. Ablikim

M.N. Achasov

P. Adlarson

X.C. Ai

R. Aliberti

A. Amoroso

Q. An

Y. Bai

O. Bakina

Y. Ban

H.R. Bao

V. Batozskaya

K. Begzsuren

N. Berger

M. Berlowski

M.B. Bertani

D. Bettoni

F. Bianchi

E. Bianco

A. Bortone

I. Boyko

R.A. Briere

A. Brueggemann

H. Cai

M.H. Cai

X. Cai

A. Calcaterra

G.F. Cao

N. Cao

S.A. Cetin

X.Y. Chai

J.F. Chang

T.T. Chang

G.R. Che

Y.Z. Che

C.H. Chen

Chao Chen

G. Chen

H.S. Chen

H.Y. Chen

M.L. Chen

S.J. Chen

S.M. Chen

T. Chen

X.R. Chen

X.T. Chen

X.Y. Chen

Y.B. Chen

Y.Q. Chen

Z.K. Chen

J.C. Cheng

L.N. Cheng

S.K. Choi

X. Chu

G. Cibinetto

F. Cossio

J. Cottee-Meldrum

H.L. Dai

J.P. Dai

X.C. Dai

A. Dbeyssi

R.E. de Boer

D. Dedovich

C.Q. Deng

Z.Y. Deng

A. Denig

I. Denisenko

M. Destefanis

F. De Mori

X.X. Ding

Y. Ding

Y.X. Ding

J. Dong

L.Y. Dong

M.Y. Dong

X. Dong

M.C. Du

S.X. Du

X.L. Du

Y.Y. Duan

Z.H. Duan

P. Egorov

G.F. Fan

J.J. Fan

Y.H. Fan

J. Fang

S.S. Fang

W.X. Fang

Y.Q. Fang

L. Fava

F. Feldbauer

G. Felici

C.Q. Feng

J.H. Feng

L. Feng

Q.X. Feng

Y.T. Feng

M. Fritsch

Observation of a Threshold Enhancement in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup></math> Spectrum in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>ψ</mi><mo stretchy="false">(</mo><mn>3686</mn><mo stretchy="false">)</mo><mo stretchy="false">→</mo><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow></math> Decays

In recent years, the resistive cylindrical chamber (RCC) has been introduced as a novel gaseous detector, extending the well-established resistive plate chambers (RPCs) to the case of cylindrical electrode geometry. Preliminary experimental studies, although still limited in number and performed under experimental conditions not always fully controlled, have nevertheless highlighted several promising features of this detector configuration, motivating the need for further systematic investigations of its operation. In contrast, from the simulation perspective, detailed studies of the RCC have not been performed yet, despite the fact that the cylindrical geometry introduces new degrees of freedom – such as cylinder electrodes radii and voltage polarity – which lead to asymmetric behaviour of the avalanche development according to the polarity of the applied voltage between the electrodes. In this work we present a standalone simulation program specifically designed to model avalanche growth and signal induction in both RPC and RCC geometries. The code implements a stepwise transport model for electron multiplication, includes approximate space-charge effects, and evaluates the induced signals on an external electrode. The simulation has been validated against experimental data for planar RPCs and subsequently applied to RCC geometries with the primary goal of investigating the underlying physical features of the cylindrical detector configuration. The results show that key observables such as induced charge and efficiency are well reproduced in the planar case, and they highlight the role of the electric-field asymmetry in shaping avalanche dynamics in the cylindrical geometry. A first comparison with available RCC experimental data is also presented, providing an initial assessment of the model performance in realistic operating conditions.

M. Abbrescia

United States

S. Colafranceschi

M. Serio

B. Liberti

S. Meola

A. Paoloni

A. Pastore

D. Piccolo

A. Rocchi

G. Saviano

C. Vendittozzi

A standalone simulation program for resistive cylindrical chamber (RCC)

The lattice QCD results for the temperature-dependent magnetic susceptibility of the medium below the crossover temperature cannot be reconciled with the widely used Hadron Resonance Gas model, also amended with the physical magnetic moments of hadrons or the pion–vector-meson loops. As noticed earlier, one observes a substantially too strong diamagnetism at temperatures in the range above <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mo>≈</mo><mn>120</mn><mspace width="0.16em"></mspace><mi>MeV</mi></mrow></math> compared to the lattice. This hints at a presence of quarks significantly below the QCD crossover temperature, which are needed as a source of paramagnetism. However, the pions must be retained to describe the diamagnetism data at low temperatures. Therefore, we consider here a quark-meson approach, where the temperature-dependent quark masses are fixed in a model-free way using the baryon-baryon and baryon-strangeness susceptibilities from the lattice at zero magnetic field. The constituent quarks possess anomalous magnetic moments estimated from the octet baryon magnetic moments. The vacuum quark-loop and meson-loop contributions are duly incorporated. We show that in such a framework, one can describe the magnetic susceptibility up to the crossover point. The qualitative conclusion is that the QCD degrees of freedom must extend far below the crossover temperature, down to <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mo>≈</mo><mn>120</mn><mspace width="0.16em"></mspace><mi>MeV</mi></mrow></math>.

Rupam Samanta

Wojciech Broniowski

Magnetic susceptibility of a hot hadronic medium and quark degrees of freedom near the QCD crossover point