arXiv subjects

Agnieszka Wierzchucka

Publications and source records attributed to Agnieszka Wierzchucka.

4 recordsLinked to original sources

arXiv2026

Double-Adiabatic Equations of State for Relativistic Plasmas

The adiabatic equation of state $P \propto n^Γ$ describes the pressure evolution of highly collisional, isotropic plasmas in terms of their density, providing a possible closure of the fluid moment hierarchy in the absence of heat fluxes and dissipation. An analogous closure exists for collisionless, magnetised plasmas, whose pressure tensor is anisotropic with respect to the magnetic field, and the closure is therefore double adiabatic, prescribing the evolution of the parallel and perpendicular pressures in terms of the magnetic-field strength and density. Here, we present a general first-principle formalism to derive adiabatic laws using the symmetries of the system. With this theory we recover the adiabatic equation of state $P \propto n^Γ$ for isotropic plasmas and the double-adiabatic equations of state for collisionless, magnetised plasmas. We extend the latter to the relativistic regime, finding that their exact functional form depends on the pressure anisotropy and is not a simple power law. Our double-adiabatic equations of state describe simple geometries, like magnetic mirrors or compressed homogeneous plasmas, as well as complex high-energy astrophysical processes, such as the evolution of plasmoid structures formed during magnetic reconnection.

astro-ph.HE↗

arXiv2026

Two-Phase Structure of Synchrotron-Cooling-Unstable Relativistic Plasma

Using analytic theory, radiative particle-in-cell (PIC) simulations, and fluid simulations, we show that relativistic, synchrotron-cooling, collisionless, high-$β$ pair plasmas filament into a two-phase medium. This process occurs through the interplay of the synchrotron cooling instability (SCI) with the synchrotron firehose instability (SFHI). One phase has high plasma~$β$ and is infested with small-scale firehose fluctuations, which scatter particles and pin the pressure anisotropy to the firehose-marginal level. The other phase has much lower~$β$, causing the suppression of firehose modes and thus allowing large pressure anisotropies. We propose a fluid model for this two-phase plasma, which we use to study the linear and nonlinear evolution of the SCI and SFHI, and to predict the emergence time of the two-phase structure.

astro-ph.HE↗

arXiv2026

Quantum state tomography, entanglement detection and Bell violation prospects in weak decays of massive particles

A rather general method for determining the spin density matrix of a multi-particle system from angular decay data is presented. The method is based on a Bloch parameterisation of the $d$-dimensional generalised Gell-Mann representation of $ρ$ and exploits the associated Wigner- and Weyl-transforms on the sphere. Each parameter of a (possibly multipartite) spin density matrix can be measured from a simple average over an appropriate set of experimental angular decay distributions. The general procedures for both projective and non-projective decays are described, and the Wigner $P$ and $Q$ symbols calculated for the cases of spin-half, spin-one, and spin-3/2 systems. The methods are used to examine Monte Carlo simulations of $pp$ collisions for bipartite systems: $pp\rightarrow W^+W^-$, $pp\rightarrow ZZ$, $pp\rightarrow ZW^+$, $pp\rightarrow W^+\bar{t}$, $t\bar{t}$, and those from the Higgs boson decays $H\rightarrow WW^{*}$ and $H\rightarrow ZZ^*$. Measurements are proposed for entanglement detection and Bell inequality violation in bipartite systems.

quant-ph↗

arXiv2023

Integrability, multifractality, and two-photon dynamics in disordered Tavis-Cummings models

The Tavis-Cummings model is a paradigmatic central-mode model where a set of two-level quantum emitters (spins) are coupled to a collective cavity mode. Here we study the eigenstate spectrum, its localization properties and the effect on dynamics, focusing on the two-excitation sector relevant for nonlinear photonics. These models admit two sources of disorder: in the coupling between the spins and the cavity and in the energy shifts of the individual spins. While this model was known to be exactly solvable in the limit of a homogeneous coupling and inhomogeneous energy shifts, we here establish the solvability in the opposite limit of a homogeneous energy shift and inhomogeneous coupling, presenting the exact solution and corresponding conserved quantities. We identify three different classes of eigenstates, exhibiting different degrees of multifractality and semilocalization closely tied to the integrable points, and study their stability to perturbations away from these solvable points. The dynamics of the cavity occupation number away from equilibrium, exhibiting boson bunching and a two-photon blockade, is explicitly related to the localization properties of the eigenstates and illustrates how these models support a collective spin description despite the presence of disorder.

cond-mat.dis-nn↗