arXiv subjects

Matthias Carosi

Publications and source records attributed to Matthias Carosi.

7 recordsLinked to original sources

arXiv2026

On the relaxation dynamics of non-equilibrium quantum systems

We investigate the relaxation of an approximately conserved charge in interacting quantum systems close to local equilibrium. To this end, we provide a pedagogical review of Zubarev's non-equilibrium statistical operator approach in the minimal setting of a single non-conserved charge and apply it to the problem at hand. We explicitly highlight the physical assumptions that lead to a local relaxation law: weak charge violation, a separation between the short timescale of microscopic correlations and the much longer timescale of charge relaxation, and the resulting loss of microscopic memory. Under these conditions, the leading relaxation rate is determined by an equilibrium correlation function of the charge-violating operator. We show that the same result follows from a simpler local-equilibrium construction based on the system's evolution over an intermediate timescale, providing a direct alternative for practical calculations and making the common physical ingredients of the two approaches explicit. Beyond the decay law itself, we relate the relaxation rate to the equilibrium diffusion of the same charge. We then allow the charge density to vary in space, which leads to a diffusion-relaxation equation. Finally, we illustrate the formalism through electroweak $\mathrm{B+L}$ washout and a perturbative scalar model, where agreement with the linearized Boltzmann equation establishes a direct connection between equilibrium-correlator and kinetic descriptions.

hep-th↗

arXiv2026

On equivalent methods for functional determinants

Computing functional determinants of differential operators is central to any field-theoretical calculation relying on a saddle-point expansion. A variety of approaches is available for the computation that avoid having to know the eigenspectrum of the operator, and in particular the Gel'fand-Yaglom theorem and the Green's function method. In this note, we show how both approaches can be constructed using a contour integral argument and conclude that these are completely equivalent for computing ratios of determinants of one-dimensional operators. Furthermore, we comment on the presence of vanishing as well as negative eigenvalues and show how the Green's function method provides a natural prescription for handling them.

hep-th↗

arXiv2026

Time irreversibility and entropy production in non-Hermitian Model A field theories

We develop a systematic framework to quantify irreversibility in scalar Model A field theories with a generic non-Hermitian term driving the dynamics. Using the stochastic path-integral formalism, we perform a controlled small-noise expansion, allowing the computation of the entropy production rate (EPR) and violations of the fluctuation-dissipation theorem (FDT). We show that the local EPR is entirely determined by the anti-Hermitian part of the linearised Langevin equation. Around steady states, the non-Hermitian component produces linear corrections to FDT violations and contributes quadratically to the EPR. As an illustration of the applicability of our approach, we analyse a minimal non-Hermitian extension of the Ginzburg-Landau $ψ^4$ theory describing a non-reciprocal Ising model at coarse-grained scales, for which we obtain explicit expressions of the local EPR, showing that it localises at interfaces in non-uniform states. Our results provide a general characterisation of TRS breaking in non-Hermitian scalar field theories.

cond-mat.stat-mech↗

arXiv2025

Bubble wall dynamics from nonequilibrium quantum field theory

We derive the coupled dynamics between the bubble wall and the plasma from first principles using nonequilibrium quantum field theory. The commonly used equation of motion of the bubble wall in the kinetic approach is shown to be incomplete. In the language of the two-particle-irreducible effective action, the conventional equation misses higher-loop terms generated by the condensate-particle type vertices (e.g.,~$φϕχ^2$, where $φ$ is the background field describing the bubble wall, $ϕ$ the corresponding particle excitation and $χ$ another particle species in the plasma). From the missing terms, we identify an additional dissipative friction which is contributed by particle production processes from the condensate-particle type vertices. We also show how other transmission processes beyond the 1-to-1 elementary transmission studied in the literature for ultrarelativistic bubble walls, e.g., 1-to-1 mixing and 1-to-2 transition radiation, can be understood from the kinetic approach.

hep-ph↗

arXiv2025

False vacuum decay beyond the quadratic approximation: summation of non-local self-energies

Using the 2PI effective action formalism, we study false vacuum decay beyond the quadratic approximation of the path integral. We derive a coupled system of equations for the bounce and the propagator, and we compute a semi-analytic expression for the self-energy of a real scalar field with cubic and quartic interactions from the 2PI effective action truncated at two loops and without further approximations. Deriving numerical results, we can show that the Hartree approximation, where non-local contributions to the self-energy are neglected, is generally not justified. The procedure we develop is a key step towards the explicit computation of the quantum corrected bounce, the determinant of fluctuations about it and the decay rate in the presence of classical zero-modes that are lifted by quantum effects, e.g. classically scale-invariant models relevant for assessing the Higgs stability.

hep-th↗

arXiv2024

Double-well instantons in finite volume

Assuming a toroidal space with finite volume, we derive analytically the full one-loop vacuum energy for a scalar field tunnelling between two degenerate vacua, taking into account discrete momentum. The Casimir energy is computed for an arbitrary number of dimensions using the Abel-Plana formula, while the one-loop instanton functional determinant is evaluated using the Green's functions for the fluctuation operators. The resulting energetic properties are non-trivial: both the Casimir effect and tunnelling contribute to the Null Energy Condition violation, arising from a non-extensive true vacuum energy. We discuss the relevance of this mechanism to induce a cosmic bounce, requiring no modified gravity or exotic matter.

hep-th↗

arXiv2021

Proca Theory from the Spinning Worldline

We obtain Proca field theory from the quantisation of the $\mathcal{N}=2$ supersymmetric worldline upon supplementing the graded BRST-algebra with an extra multiplet of oscillators. The linearised theory describes the BV-extended spectrum of Proca theory, together with a Stückelberg field. When coupling the theory to background fields we derive the Proca equations, arising as consistency conditions in the BRST procedure. We also explore non-abelian modifications, complexified vector fields as well as coupling to a dilaton field. We propose a cubic action on the space of BRST-operators which reproduces the known Proca action.

hep-th↗