In our previous studies, we calculated the cross section for the production of free \(\mu ^{+}\mu ^{-}\) pairs using a probability function dependent on the impact parameter, and also, we computed bound-free \(e^{+}e^{-}\) pair production cross section. In this study, unlike the others, we obtained the cross section for the production of bound-free \(e^{+}e^{-}\) pairs using the probability function dependent on the impact parameter. Here also, we simultaneously calculated the cross sections for producing free \(\mu ^{+}\mu ^{-}\) with bound-free \(e^{+}e^{-}\) pairs in relativistic Pb+Pb collisions at the LHC using Lorentz factors \(\gamma =1500\) and \(\gamma =3000\) reported in the literature. Our calculation is based on second-order perturbation theory, implemented by using Monte Carlo integration techniques. We present impact-parameter-dependent pair production probabilities for free \(\mu ^{+}\mu ^{-}\) and bound-free \(e^{+}e^{-}\) pair production processes. Notably, the bound-free \(e^{+}e^{-}\) pair production was evaluated by using a formalism adapted from that of free \(\mu ^{+}\mu ^{-}\) pair production. Our results obtained here for the free \(\mu ^{+}\mu ^{-}\) with bound-free \(e^{+}e^{-}\) pair production cross sections are compared with those from other theoretical methods available in the literature. This study aims to provide predictions that can be tested against future experimental data, thereby offering a valuable test of quantum electrodynamics (QED) in strong electromagnetic fields. Abstract Published by the Jagiellonian University 2026 authors

Türkiye

M. Yilmaz Şengül

Free \(\mu ^{+}\mu ^{-}\) and Bound-free \(e^{+}e^{-}\) Pair Production in Relativistic Heavy-ion Collisions

We investigate the properties of exotic Strange Quark Matter (SQM) with spin polarization and the complex configuration of Strange Quark Stars (SQSs) using a phenomenological MIT Bag Model, enhanced by incorporating a QCD-informed running strange-quark mass dependent on the chemical potential. The effective mass using quasiparticle approach is utilized to understand the framework of SQM. The resulting Equation of State (EoS) is constructed for two distinct parameter sets, yielding an energy per baryon below the iron limit for stable configurations and thus supporting the Bodmer–Witten–Terazawa hypothesis that SQM could be the actual ground state of exotic matter. This framework is then used to address the Tolman–Oppenheimer–Volkoff (TOV) equations to study the effect of spin polarization on stellar properties. The model predicts that the maximum stellar mass increases with the degree of spin polarization, a result that diverges from previous constant-mass models. Furthermore, the model’s predictions for mass, radius, and surface redshift are in excellent agreement with observational constraints for the compact object Vela X-1. This agreement validates our theoretical approach and strengthens the candidacy of Vela X-1 as a Strange Quark Star. Overall, the model results highlight the importance of in-medium QCD effects in describing dense matter. Abstract Published by the Jagiellonian University 2026 authors

India

M. Lohani

Y. Kumar

P. Jain

O. Prakash

S. Tyagi

V. Kumar

Egypt

T.A. Nahool

Revisiting In-medium QCD Effects on Spin-polarized Strange-quark Stars

We analyze the effect of using the Fermi–Dirac statistics, rather than its Boltzmann approximation, in numerical simulations of perfect spin hydrodynamics of particles with spin \(1/2\). The system considered is boost invariant, transversely homogeneous, with corrections to the baryon current and the energy–momentum tensor that are second order in the spin polarization tensor ω, and the spin tensor considered is first order in ω. The study shows the feasibility of this approach, as the special functions defined by integrals that appear in the coefficients in the Fermi–Dirac case can be conveniently parametrized. For sets of initial conditions used in previous works, the differences in parameter evolution between the two underlying particle statistics are about one order of magnitude smaller than corrections coming from spin feedback. We also discuss when and why the numerical solutions of the equations of perfect spin hydrodynamics break down for very large values of spin polarization in one of the geometric configurations considered. Abstract Published by the Jagiellonian University 2026 authors

Poland

Z. Drogosz

N. Łygan

Boost-invariant Perfect Fermi–Dirac Spin Hydrodynamics

We determine the minimum value of thrust for a number of \(N\)-particle configurations. For \(N=5\) in three dimensions, an exact result is found for the first time. For larger \(N\), we obtain numerical results through optimisation. When a definite value cannot be reliably identified, the results are analysed in the context of Extreme Value Theory, using a Maximum Likelihood Estimate and a Bayesian analysis. Results are given for three spatial dimensions, two dimensions, and selected cases in \(d\) dimensions. Abstract Published by the Jagiellonian University 2026 authors

France

M. Cacciari

A Thrust to Trust Minimum Thrust

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 study free open fermionic strings on a non-commutative phase-space. Modified super-Virasoro algebras in both the Ramond and Neveu–Schwarz sectors acquire non-commutativity anomalies, and this non-commtativity breaks also the Lorentz symmetry and give a non-diagonal mass operator. Redefining the Fock space diagonalizes the mass operator. Extra constraints on non-commutativity parameters cancel the anomalies, restore the standard spectrum, and make the GSO projection possible. Abstract Published by the Jagiellonian University 2026 authors

Algeria

M.A. Abdelmoumene

N. Belaloui

Non-commutative Phase-space Effects in Fermionic String Theory

We study the thermodynamics of the quark–gluon plasma using an effective 2-flavor Polyakov–Nambu–Jona-Lasinio (PNJL) model extended by a quasiparticle description for quarks and gluons, incorporating temperature-dependent quark masses within the PNJL framework. Two variants, Quasiparticle Model-I and Quasiparticle Model-II, are implemented to investigate bulk thermodynamic observables such as pressure, energy density, entropy density, specific heat, and the speed of sound. The combined framework yields a robust baseline for the description of hot QGP dynamics in the high-temperature regime at vanishing chemical potential and zero magnetic field. Systematic comparison with lattice QCD results shows excellent agreement and a clear improvement over conventional PNJL implementations. We observe that both variants complement each other, offering mutually consistent insight into quasiparticle mass effects and medium response in the deconfined phase. This mutual consistency validates the physical foundation of the overall quasiparticle mechanism, reinforcing the credibility of the calculated Equation of State. Finally, the quasiparticle model extension improves PNJL from a descriptive tool to a more qualitative phenomenological approach, enabling an improved description of the strongly interacting quark–gluon plasma. Abstract Published by the Jagiellonian University 2026 authors

H. Aggarwal

R.S. Laishram

P. Bangotra

Y. Goswami

M.K. Sahu

Thermodynamical Analysis of QGP Using Effective PNJL Model with Quasiparticle Approach

Where do gauge symmetries come from? This article develops the idea that the Standard Model might be emergent, with its gauge symmetries dissolving in some phase transition deep in the ultraviolet. The (meta)stability of the Higgs vacuum may be pointing to some new critical phenomena at very high energy scales, with the Higgs connecting physics at LHC laboratory energies to that in the deep ultraviolet. In the emergence scenario, the dark energy scale comes out similar to the size of light Majorana neutrino masses. These two quantities appear at the same order in a low-energy expansion in inverse powers of the scale of emergence, about \(10^{16}\) GeV. Dark matter candidates include axions and phonon-like excitations of degrees of freedom above the scale of emergence. Possible tests of these ideas involve neutrinos as well as gravitational-waves-related signals from the early Universe observables, which are sensitive to physics at very high energy scales. Abstract Published by the Jagiellonian University 2026 authors

S.D. Bass

Emergent Gauge Symmetries in Particle Physics and Cosmology

The internal structure of hadrons is characterized by form factors which correspond to matrix elements of currents. Among those, the stress-energy-momentum tensor is a universally conserved quantity providing the gravitational form factors, from which mechanical properties may be derived via the response to the space-time fluctuations. They have received much attention due to their role as moments of the Generalized Parton Distributions, where the stress-energy-momentum tensor couples to two photons, and more recently, due to the explicit lattice QCD determination for the pion and nucleon. In these lectures, we attempt a pedagogical review of the topic from a purely hadronic point of view, based on the notion of dispersion relations, meson dominance, and parton–hadron duality. We show that despite the overwhelming simplicity of the approach, a rather successful description of the lattice QCD data is achieved. Abstract Published by the Jagiellonian University 2026 authors

Spain

E. Ruiz Arriola

W. Broniowski

Particle Seismology: Mechanical and Gravitational Properties from Parton–Hadron Duality

This year marks the \(350^{\mathrm {th}}\) anniversary of the discovery of the first animalcula (little animals) by van Leeuwenhoek in 1676. Flavour physics makes it possible to search for new animalcula at distance scales far shorter than those resolved by van Leeuwenhoek in 1676, and even shorter than those directly accessible at the Large Hadron Collider and the planned colliders in this century. I summarize various strategies for achieving this goal. While precise measurements of a wide variety of observables and their precise theoretical calculations, both within the Standard Model (SM) and beyond it, are indispensable in this context, in my view, it is crucial to develop strategies for the search for New Physics (NP) that go beyond the global fits that are very popular today. While effective field theories such as WET and SMEFT are formulated in terms of Wilson coefficients of the relevant operators, with correlations characteristic of the SM and of specific NP scenarios, the most direct tests of the SM and its extensions are, in my opinion, correlations among different observables, like branching ratios of numerous decays, that are characteristic of particular new animalcula at work. Abstract Published by the Jagiellonian University 2026 authors

Germany

A.J. Buras

Hunting New Animalcula with Flavour Changing Processes