arXiv subjects

Tomasz Romanczukiewicz

Publications and source records attributed to Tomasz Romanczukiewicz.

11 recordsLinked to original sources

arXiv2025

Quasi Q-Balls in massless scalar fields

We study long-term evolution of radiating quasi-Q-balls in 1+1 dimensional models without mass threshold. Two different models are considered, the model with a rational modification of the usual Q-ball sextic potential and the model of a Q-ball in a box with outgoing boundary conditions. We find that the outgoing boundary conditions modify the angular frequency of quasi-Q-balls which becomes complex-valued. The quasi-Q-balls decay initially very similarly, but in the last stage quasi-Q-balls in a box become linear resonances, whereas in the rationally modified model, they decay according to some power law.

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arXiv2024

Normal Modes of the Small-Amplitude Oscillon

Consider a classical (1+1)-dimensional oscillon of small amplitude $ε$. To all orders in $ε$, the oscillon solution is exactly periodic. We study small perturbations of such periodic configurations. These perturbations are themselves periodic up to a monodromy matrix. We explicitly find the eigenvectors of the monodromy matrix, which are the analogues of normal modes for oscillons. Dashen, Hasslacher and Neveu used such eigenvectors to quantize the sine-Gordon breather, and we suspect that they will be necessary to quantize the oscillon. Our results, regardless of the chosen model, suggest that low amplitude oscillons do not reflect small amplitude radiation.

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arXiv2023

Moduli Space for Kink Collisions with Moving Center of Mass

We apply the collective coordinate model framework to describe collisions of a kink and an antikink with nonzero total momentum, i.e., when the solitons possess different velocities. The minimal moduli space with only two coordinates (the mutual distance and the position of the center of mass) is of a wormhole type, whose throat shrinks to a point for symmetric kinks. In this case, a singularity is formed. For non-zero momentum, it prohibits solutions where the solitons pass through each other. We show that this unphysical feature can be cured by enlarging the dimension of the moduli space, e.g., by the inclusion of internal modes.

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arXiv2022

Spectral Walls at One Loop

A spectral wall is a surface in a moduli space of classically BPS solitons where an internal excitation crosses the continuum mass threshold. It has recently been shown that spectral walls in classical field theory repel solitons whose corresponding internal excitations are excited. We investigate, for the first time, the fate of spectral walls in a quantum theory, calculating the instantaneous acceleration of a wave packet of classically BPS antikinks in the presence of an impurity. We find that, in the quantum theory, the antikinks are repelled even when the bound mode is not excited. Perhaps due to this repulsive force, the dramatic classical effects of the spectral wall are not seen in our quantum calculation.

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arXiv2020

Staccato radiation from the decay of large amplitude oscillons

We study the decay of large amplitude, almost periodic breather-like states in a deformed sine-Gordon model in one spatial dimension. We discover that these objects decay in a staggered fashion via a series of transitions, during which higher harmonics are released as short, staccato bursts of radiation. Further, we argue that this phenomenon is not restricted to one particular model, and that similar mechanisms of radiative decay of long-lived oscillating states can be observed for a wide class of physical systems, including the $ϕ^6$ model.

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arXiv2018

Some Recent Developments on Kink Collisions and Related Topics

We review recent works on modeling of dynamics of kinks in 1+1 dimensional $ϕ^4$ theory and other related models, like sine-Gordon model or $ϕ^6$ theory. We discuss how the spectral structure of small perturbations can affect the dynamics of non-perturbative states, such as kinks or oscillons. We describe different mechanisms, which may lead to the occurrence of the resonant structure in the kink-antikink collisions. We explain the origin of the radiation pressure mechanism, in particular, the appearance of the negative radiation pressure in the $ϕ^4$ and $ϕ^6$ models. We also show that the process of production of the kink-antikink pairs, induced by radiation is chaotic.

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arXiv2017

Boundary scattering in the phi^4 model

We study boundary scattering in the $ϕ^4$ model on a half-line with a one-parameter family of Neumann-type boundary conditions. A rich variety of phenomena is observed, which extends previously-studied behaviour on the full line to include regimes of near-elastic scattering, the restoration of a missing scattering window, and the creation of a kink or oscillon through the collision-induced decay of a metastable boundary state. We also study the decay of the vibrational boundary mode, and explore different scenarios for its relaxation and for the creation of kinks.

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arXiv2011

Kink-antikink collisions in the phi^6 model

We study kink-antikink collisions in the one-dimensional non-integrable scalar phi^6 model. Although the single-kink solutions for this model do not possess an internal vibrational mode, our simulations reveal a resonant scattering structure, thereby providing a counterexample to the standard belief that existence of such a mode is a necessary condition for multi-bounce resonances in general kink-antikink collisions. We investigate the two-bounce windows in detail, and present evidence that this structure is caused by existence of bound states in the spectrum of small oscillations about a combined kink-antikink configuration.

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arXiv2008

Negative radiation pressure in case of two interacting fields

We study a simple toy model, which although probably does not have any direct physical applications, can serve as a nice pedagogical example for explanation strange phenomenon of negative radiation pressure and can also give some insight for understanding the interaction between radiation and a vortex. The model discussed is a classical field theory of two interacting scalar fields in 1+1 d. Without coupling one of the fields is governed by the ordinary $ϕ^4$ equation and the second one obeys the Klein-Gordon equation. The possibility of existence of the {\it negative radiation pressure} with a respect to the mass ratio of those two fields is discussed.

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arXiv2005

Creation of Kink and Antikink Pairs Forced By Radiation

The interaction between kink and radiation in nonlinear one-dimensional real scalar field is investigated. The process of discrete vibrational mode excitation in $ϕ^4$ model is considered. The role of this oscillations in creation of kink and antikink is discussed. Numerical results are presented as well as some attempts of analytical explanations. An intriguing fractal structure in parameter space dividing regions with creation and without is also presented.

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arXiv2003

Interaction Between Kink and Radiation in $ϕ^4$ Model

The radiation from oscillating kink in (1+1) dimensional relativistic $ϕ^4$ model is considered. Both analytical and numerical approaches are presented and the comparison between these methods is discussed. Acceleration of the kink in external radiation is calculated and numerical results are also presented.

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