Stanisław Mrówczyński

For a long time, studies of femtoscopic correlations have provided information about space-time characteristics of particle sources in high-energy collisions. Recently, the correlation functions have also been used to determine interaction parameters of correlated particles, which is especially important for short-lived particles, for which scattering experiments are impossible. The abundance of experimental data and their high accuracy require an improved theoretical approach to femtoscopic correlations. The aim of this paper is to systematically discuss relativistic effects and their role in femtoscopy. Since a general relativistic approach is currently unavailable due to serious theoretical difficulties, the correlation functions must be computed in the center-of-mass frame where the correlated particles are mostly nonrelativistic. This requires transforming the source function to this frame, the consequences of which are discussed. Since the deuteron formation has a similar physical origin to femtoscopic correlations, relativistic effects are also discussed in the former process. The considerations are illustrated with calculations of some correlation functions and the deuteron coalescence coefficient to demonstrate the magnitude of relativistic effects. It is also argued that a discrepancy between the coalescence coefficient computed with the source radii inferred from the baryon-baryon correlation functions and the experimental data can be removed by taking into account the relativistic elongation of the source radius in the center of mass of correlated particles.

Potential and corresponding electric and magnetic fields of a moving point-like charge are computed in several ways. The subtle limit of the charge velocity equal to the speed of light is taken either in the final formulas or in the equation of motion. The results are discussed. Published by the Jagiellonian University 2026 authors

At the earliest stage of ultrarelativistic heavy-ion collisions the produced matter is a highly populated system of gluons called glasma which can be approximately described in terms of classical chromodynamic fields. Although the system's dynamics is governed by Yang-Mills equations, glasma evolution is shown to strongly resemble hydrodynamic behavior.

A system of gluon fields produced in the earliest phase of relativistic heavy-ion collisions, which is called glasma, can be described in terms of classical fields. Initially there are chromoelectric and chromomagnetic fields along the collision axis. A linear stability analysis of these fields is performed, assuming that the fields are space-time uniform and using the SU(2) gauge group. We apply Milne coordinates and the gauge condition, which are usually used in studies of glasma. The chromoelectric field is in the Abelian configuration with the corresponding potential linearly depending on coordinates, but the chromomagnetic field is in the non-Abelian configuration generated by the potential of noncommuting components. The chromomagnetic field is found to be unstable, and the growth rate of the unstable mode is derived. Our findings are critically debated and confronted with the numerical simulations by Romatschke and Venugopalan, who found that the evolving glasma is unstable due to the Weibel instability, which is well known in electromagnetic plasma.

A system of gluon fields produced in the earliest phase of relativistic heavy-ion collisions, which is called `glasma', can be described in terms of classical fields. Initially there are chromoelectric and chromomagnetic fields along the collision axis. A linear stability analysis of these fields is performed, assuming that the fields are space-time uniform and using the SU(2) gauge group. We apply Milne coordinates and the gauge condition which are usually used in studies of glasma. The chromoelectric field is in the Abelian configuration with the corresponding potential linearly depending on coordinates but the chromomagnetic field is in the nonAbelian configuration generated by the potential of non-commuting components. The chromomagnetic field is found to be unstable and the growth rate of the unstable mode is derived. Our findings are critically debated and confronted with the numerical simulations by Romatschke and Venugopalan who found that the evolving glasma is unstable due to the Weibel instability well-known in electromagnetic plasma.

In a series of works by two of us, various characteristics of the glasma from the earliest phase of relativistic heavy-ion collisions have been studied using a proper-time expansion. These characteristics include energy density, longitudinal and transverse pressures, collective flow, angular momentum, and parameters of jet quenching. In this paper we extend the proper-time interval where our results are reliable by working at higher order in the expansion. We also generalize our previous study of jet quenching by extending our calculations to consider inhomogeneous glasma. Inhomogeneities are an important aspect of physically realistic systems that are difficult to include in calculations and are frequently ignored.