arXiv subjects

A. Kovtun

Publications and source records attributed to A. Kovtun.

4 recordsLinked to original sources

arXiv2022

Breaking BEC: Quantum evolution of unstable condensates

In this work we numerically explore the quantum behavior of a classically unstable relativistic Bose-Einstein condensate (BEC). The main goal is to study the phenomenon of so-called quantum break time which amounts to a significant departure from a semiclassical mean-field description. It has been suggested previously that the existence of Lyapunov instability is crucial for a fast quantum breaking, chaos, and scrambling. In order to clarify the issue, we work within the 2-PI effective action formalism and introduce a simple and very widely applicable dynamical criterion for identifying the timescale of quantumbreaking. We indeed observe that the fast quantum break time is controlled by the Lyapunov exponent of the unstable BEC.

hep-th↗

arXiv2020

Monitoring morphological and chemical properties during silver solid-state dewetting

Solid-state dewetting phenomenon in silver thin films offers a straightforward method to obtain structures having controlled shape or size -this latter in principle spanning several orders of magnitudes -- with potentially strong interest in many applications involving high-tech industry and biomedicine. In this work nanostructured silver is deposited by pulsed electron ablation technique and its surface modified upon thermal treatments in air at increasing temperatures. Surface chemistry and morphology are then monitored simultaneously by X-ray photoemission spectroscopy and atomic force microscopy; in particular, the power spectral density of surface heights is used to analyze the alteration of morphology induced by annealing. It is shown that this approach adds a level of information about the dewetting process since it allows to separate between long- and short-range surface behavior and to retrieve statistical quantities relevant to a description of the features in view of applications. Our results are presented in the framework of a multidisciplinary approach, advantages and limits of which are deepened and discussed.

cond-mat.mtrl-sci↗

arXiv2020

Breaking BEC

In this work quantum corrections to the classical evolution of a relativistic scalar condensate are studied. The problem is approached by means of two different perturbative approaches: the 2-particle-irreducible (2PI) effective action and the expansion in the self-coupling. In the weak coupling regime, the decoherence of the classical state is observed. The corresponding timescale is identified with the quantum break-time.

hep-th↗

arXiv2018

Vibrational modes of Q-balls

We study linear perturbations of classically stable Q-balls in theories admitting analytic solutions. Although the corresponding boundary value problem is non-Hermitian, the analysis of perturbations can also be performed analytically in certain regimes. We show that in theories with the flat potential, large Q-balls possess soft excitations. We also find a specific vibrational mode for Q-balls with a near-critical charge, where the perturbation theory for excitations can be developed. Comparing with the results on stability of Q-balls provides additional checks of our analysis.

hep-th↗