arXiv subjects

P. Klimas

Publications and source records attributed to P. Klimas.

At least 19 recordsLinked to original sources

arXiv2026

Compact Q-balls and Q-shells within a $CP^N$ Skyrme-Faddeev type model

While $CP^N$ models with analytic potentials are known to support finite-energy compact Q-ball and Q-shell solutions, their behavior in more complex Lagrangian frameworks remains a subject of active research. This work explores these non-topological structures within an extended Skyrme-Faddeev-type model that incorporates quartic derivative terms. In this context, harmonic time dependence and the presence of quartic terms constitute two independent stabilization mechanisms that allow the configurations to circumvent Derrick's scaling argument. We investigate the necessary conditions for the existence of these solutions and analyze the influence of quartic terms on the properties of the resulting compactons, specifically examining the $E(Q)$ relationship between energy and Noether charge. Our findings provide valuable insights into the stability and characteristics of compact boson stars within $CP^N$ models featuring higher-order derivative terms.

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arXiv2024

Kink-antikink collisions in hyper-massive models

We study topological kinks and their interactions in a family of scalar field models with a double well potential parametrized by the mass of small perturbations around the vacua, ranging from the mass of the $\phi^4$ Klein-Gordon model all the way to the limit of infinite mass, which is identified with a non-analytic potential. In particular, we look at the problem of kink-antikink collisions and analyze the windows of capture and escape of the soliton pair as a function of collision velocity and model mass. We observe a disappearance of the capture cases for intermediary masses between the $\phi^4$ and non-analytic cases. The main features of the kink-antikink scattering are reproduced in a collective coordinates model, including the disappearance of the capture cases.

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arXiv2023

Gauged compact $Q$-balls and $Q$-shells in a multi-component $CP^N$ model

We study a multicomponent $CP^N$ model's scalar electrodynamics. The model contains $Q$-balls and $Q$-shells, which are nontopological compact solitons with time dependency $e^{i\omega t}$. Two coupled $CP^N$ models can decouple locally if one of their $CP^N$ fields takes the vacuum value. Because of the compacton nature of solutions, $Q$-shells can shelter another compact $Q$-ball or $Q$-shell within their hollow region. Even if compactons do not overlap, they can interact through the electromagnetic field. We investigate how the size of multicompacton formations is affected by electric charge, with a focus on structures with nonzero or zero total net charge.

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arXiv2023

Scattering of compact kinks

We study the scattering processes of kink-antikink and kink-kink pairs in a field theory model with non-differentiable potential at its minima. The kink-antikink scattering includes cases of capture and escape of the soliton pair separated by a critical velocity, without windows of multi bounce followed by escape. Around the critical velocity, the behavior is fractal. The emission of radiation strongly influences the small velocity cases, with the most radiative cases being also the most chaotic. The radiation appears through the emission of compact oscillons and the formation of compact shockwaves. The kink-kink scattering happens elastically, with no emission of radiation. Some features of both the kink-antikink and the kink-kink scattering are explained using a collective coordinate model, even though the kink-kink case exhibits a null-vector problem.

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arXiv2022

Compact kink and its interaction with compact oscillons

We study compact kinks and its interaction with compact oscillons in models with non-analytic potentials. Oscillon-like excitations are the main ingredients of the radiation field. We look at the problem of scattering which involves topological compact kinks and non-topological oscillons. We also look at the problem of propagation of small perturbation at the kink bulk.

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arXiv2022

Nodal compact $Q$-ball/$Q$-shell in the $\mathbb{C}P^N$ nonlinear sigma model

Nodal, excited compactons in the $\mathbb{C}P^N$ models with V-shaped potentials are analyzed. It is shown that the solutions exist as compact $Q$-balls and $Q$-shells. The solutions have a discontinuity in the second derivative associated with the character of the potential, however, their energy and charge densities are both continuous. The excited $Q$-balls and $Q$-shells are analyzed as electrically neutral and electrically charged objects.

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arXiv2021

Compact Q-balls and Q-shells in a multi-component $\mathbb{C}P^N$ model

Coupled multi-component $\mathbb{C}P^N$ models with V-shaped potentials are analyzed. It is shown that the model has solutions being combinations of compact Q-balls and Q-shells. The compact nature of solutions permits the existence of novel harbor-type solutions having the form of Q-balls sheltered by Q-shells. The relation between the energy $E$ and Noether charge $Q$ is discussed both analytically and numerically. The energy of the solutions behaves as $E\sim |Q|^\alpha,~\alpha<1$, i.e., as for the standard Q-ball. Furthermore, the ratio $E/Q$ for various configurations in the multi-component model suggests that the solutions are at least classically stable.

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arXiv2019

Scattering of compact oscillons

We study various aspects of the scattering of generalized compact oscillons in the signum-Gordon model in (1+1) dimensions. Using covariance of the model we construct traveling oscillons and study their interactions and the dependence of these interactions on the oscillons initial velocities and their relative phases. The scattering processes transform the two incoming oscillons into two outgoing ones and lead to the generation of extra oscillons which appear in the form of jet-like cascades. Such cascades vanish for some values of free parameters and the scattering processes, even though our model is non-integrable, resemble typical scattering processes normally observed for integrable or quase-integrable models. Occasionally, in the intermediate stage of the process, we have seen the emission of shock waves and we have noticed that, in general, outgoing oscillons have been more involved in their emission than the initial ones i.e. they have a border in form of curved world-lines. The results of our studies of the scattering of oscillons suggest that the radiation of the signum-Gordon model has a fractal-like nature.

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arXiv2019

On decay of shock-like waves into compact oscillons

The signum-Gordon model in 1+1 dimensions possesses the exact shockwave solution with discontinuity of the field at the light cone and infinite gradient energy. The energy of a regular part of the wave inside the light cone is finite and it grows linearly with time. The initial data for such waves contain a field configuration which is null in the space and has time derivative proportional to the Dirac delta. We study regularized initial data that lead to shock-like waves with finite gradient energy. We found that such waves exist in the finite time intervals and finally they decay and produce a cascade of oscillon-like structures. A pattern of the decay is very similar to the one observed in process of scattering of compact oscillons.

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arXiv2019

Further comments on BPS systems

We look at BPS systems involving two interacting Sine-Gordon like fields both when one of them has a kink solution and the second one either a kink or an antikink solution. The interaction between the two fields is controlled by a parameter $λ$ which has to satisfy $| λ|< 2$. We then take these solitonic static solutions (with solitons well localised) and construct from them systems involving two solitons in each field (kinks and antikinks) and then use them as initial conditions for their evolution in Lorentz covariant versions of such models. This way we study their interactions and compare them with similar interactions involving only one Sine-Gordon field. In particular, we look at the behaviour of two static kinks in each field (which for one field repel each other) and of a system involving kinks and anti-kinks (which for one field attract each other) and look how their behaviour depends on the strength of the interaction $λ$ between the two fields. Our simulations have led us to look again at the static BPS solutions of systems involving more fields. We have found that such ostensibly 'static' BPS solutions can exhibit small motions due to the excitation of their zero modes. These excitations arise from small unavoidable numerical errors (the overall translation is cancelled by the conservation of momentum) but as systems of two or more fields have more that one zero mode such motions can be generated and are extremely small. The energy of our systems has been conserved to within $10^{-5}\%$.

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arXiv2019

Some Comments on BPS systems

We look at simple BPS systems involving more than one field. We discuss the conditions that have to be imposed on various terms in Lagrangians involving many fields to produce BPS systems and then look in more detail at the simplest of such cases. We analyse in detail BPS systems involving 2 interacting Sine-Gordon like fields, both when one of them has a kink solution and the second one either a kink or an antikink solution. We take their solitonic static solutions and use them as initial conditions for their evolution in Lorentz covariant versions of such models. We send these structures towards themselves and find that when they interact weakly they can pass through each other with a phase shift which is related to the strength of their interaction. When they interact strongly they repel and reflect on each other. We use the method of a modified gradient flow in order to visualize the solutions in the space of fields.

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arXiv2018

Self-dual sectors for scalar field theories in (1 + 1) dimensions

We use ideas of generalized self-duality conditions to construct real scalar field theories in (1 + 1)-dimensions with exact self dual sectors. The approach is based on a pre-potential U that defines the topological charge and the potential energy of these theories. In our algebraic method to construct the required pre-potentials we use the representation theory of Lie groups. This approach leads naturally to an infinite set of degenerate vacua and so to topologically non-trivial self-dual solutions of these models. We present explicit examples for the groups SU(2), SU(3) and SO(5) and discuss some properties of these solutions.

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arXiv2018

Oscillons in a perturbed signum-Gordon model

We study various properties of a perturbed signum-Gordon model, which has been obtained through the dimensional reduction of the called `first BPS submodel of the Skyrme model'. This study is motivated by the observation that the first BPS submodel of the Skyrme model may be partially responsible for the good qualities of the rational map ansatz approximation to the solutions of the Skyrme model. We investigate the existence, stability and various properties of oscillons and other time-dependent states in this perturbed signum-Gordon model.

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arXiv2017

Compact Q-balls and Q-shells in the CPN type models

We show that the CPN model with odd number of scalar fields and V-shaped potential possesses finite energy compact solutions in the form of Q-balls and Q-shells. The solutions were obtained in 3+1 dimensions. Q-balls appears for N=1 and N=3 whereas Q-shells are present for higher odd values of N. We show that energy of these solutions behaves as E~|Q|^5/6, where Q is the Noether charge.

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arXiv2015

Static multi-soliton solutions in the affine su(N+1) Toda models

We study some static multi-soliton configurations in the su(N + 1) Toda models. Such configurations exist for N > 1. We construct explicitly a multi-soliton solution for any N and study conditions for having such solutions. The number of static solitons is limited by the rank of the su(N + 1) Lie algebra. We give some examples of non-static multi-soliton solutions with static components.

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arXiv2012

Numerical vortex solutions in (3+1) dimensions for the extended $CP^N$ Skyrme-Faddeev model

We construct numerical vortex solutions in a (3+1) dimensional Minkowski space-time for the extended version of the Skyrme-Faddeev model with target space $CP^N$. The solutions are essentially composed of $N$-th single vortex which does not belong to the integrable sector. They have finite energy per unit length and contain waves propagating along vortices with the speed of light. In this Letter we report on the case N=2 and show existence of the solutions with the charges $(n_1,n_2)=(1,2)$.

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arXiv2011

Some properties of (3+1) dimensional vortex solutions in the extended CP^N Skyrme-Faddeev model

We look at properties of vortex solutions of the extended CP^N Skyrme-Faddeev model. We show that only holomorphic solutions of the CP^N model are also solutions of the Skyrme-Faddeev model. As the total energy of these solutions is infinite these solutions should be interpreted as describing time dependent vortices. We describe their dynamics and, in partcular, point out that one of the terms in the energy density is related to the Noether charge of the model.

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arXiv2011

Properties of some (3+1) dimensional vortex solutions of the CP^N model

We construct new classes of vortex-like solutions of the CP^N model in (3+1) dimensions and discuss some of their properties. These solutions are obtained by generalizing to (3+1) dimensions the techniques well established for the two dimensional CP^N models. We show that as the total energy of these solutions is infinite, they describe evolving vortices and anti-vortices with the energy density of some configurations varying in time. We also make some further observations about the dynamics of these vortices.

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