arXiv subjects

Yakov Shnir

Publications and source records attributed to Yakov Shnir.

49 records · Page 3Linked to original sources

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.

hep-th↗

arXiv2019

Kinks bounded by fermions

We present and study new mechanism of interaction between the solitons based on the exchange interaction mediated by the localized fermion states. As particular examples, we consider solutions of simple 1+1 dimensional scalar field theories with self-interaction potentials, including sine-Gordon model and the polynomial $ϕ^4$, $ϕ^6$ models, coupled to the Dirac fermions with back-reaction. We discover that there is an additional fermion exchange interaction between the solitons, it leads to the formation of static multi-soliton bound states. Further, we argue that similar mechanisms of formation of stable coupled multi-soliton configurations can be observed for a wide class of physical systems.

hep-th↗

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.

hep-th↗

arXiv2018

Soliton solutions of the fermion-Skyrmion system in (2+1) dimensions

We study effects of backreaction of the fermionic modes localized by the baby Skyrmion in the (2+1)-dimensional Skyrme model. It is shown that there is a tower of fermionic modes of two different types, localized by the soliton, however there is only one fermionic level, which flows from positive to negative value as coupling increases. Considering the strong coupling regime we observe that the coupling of the bosonic field to the fermions may strongly deform the Skyrmion, in particular the regions of negative topological charge density appear.

hep-th↗

arXiv2018

$SU(2)$ Yang-Mills solitons in $R^2$ gravity

We construct new family of spherically symmetric regular solutions of $SU(2)$ Yang-Mills theory coupled to pure $R^2$ gravity. The particle-like field configurations possess non-integer non-Abelian magnetic charge. A discussion of the main properties of the solutions and their differences from the usual Bartnik-McKinnon solitons in the asymptotically flat case is presented. It is shown that there is continuous family of linearly stable non-trivial solutions in which the gauge field has no nodes.

hep-th↗

arXiv2017

Oscillons in the presence of external potential

We discuss similarity between oscillons and oscillational mode in perturbed $ϕ^4$. For small depths of the perturbing potential it is difficult to distinguish between oscillons and the mode in moderately long time evolution, moreover one can transform one into the other by adiabatically switching on and off the potential. Basins of attraction are presented in the parameter space describing the potential and initial conditions.

hep-th↗

arXiv2017

Spinning gravitating Skyrmions in generalized Einstein-Skyrme model

We investigate properties of self-gravitating isorotating Skyrmions in the generalized Einstein-Skyrme model with higher-derivative terms in the matter field sector. These stationary solutions are axially symmetric, regular and asymptotically flat. We provide a detailed account of the branch structure of the spinning solutions in the topological sector of degree one. We show that additional branches of solutions appear, as the angular frequency increases above some critical value, these "cloudy" configurations can be considered as a bound system of the spinning Skyrmions and "pion" excitations in the topologically trivial sector. Considering the critical behavior of the isorotating solitons in the general Einstein-Skyrme model, we point out that there is no isospinning regular solutions in the reduced self-dual $\mathcal{L}_6+\mathcal{L}_0$ submodel for any non zero value of the angular frequency.

hep-th↗

arXiv2017

Crystal structures in generalized Skyrme model

We investigate the properties of triply-periodic Skyrme crystals in the generalized Skyrme model $\mathcal{L}_6 + \mathcal{L}_4 + \mathcal{L}_2+ \mathcal{L}_0$ with higher-derivative terms up to sixth order. Three different symmetry breaking potential terms $\mathcal{L}_0$ are considered, the generalized pion mass term, double vacuum potential and mixed potential. Various scenario of phase transitions from the low density phase to the high density phase are examined for different choices of the parameters of the model. In particular, we investigated limiting behavior of the Skyrme crystals in the truncated submodel without the Skyrme term $\mathcal{L}_4$ and/or without the $\mathcal{L}_2$ term. We show that the Skyrme crystal may exist in the pure $\mathcal{L}_4$ and $\mathcal{L}_6$ models and investigated the phase structure of these solutions. Considering the near-BPS submodel, we found that there are indications of the phase transition from a low density quasi-liquid phase to the high density symmetric phase of the Skyrmionic matter.

hep-th↗

arXiv2016

Generalized Skyrmions and hairy black holes in asymptotically AdS$_4$ spacetime

We investigate the properties of spherically symmetric black hole solutions in the generalized Einstein-Skyrme model theory in four-dimensional asymptotically anti-de Sitter space-time. The dependencies of the Skyrmion fields on the cosmological constant and on the strength of the effective gravitational coupling are examined. We show that the increase of the absolute value of the cosmological constant qualitatively yields the same effect as increasing of the effective gravitational coupling. We confirm that, similar to the model in the asymptotically flat space-time, a necessary condition for the existence of black holes with Skyrmionic hair is the inclusion of the Skyrme term.

hep-th↗

arXiv2014

Spontaneous symmetry breaking in dual-core baby-Skyrmion systems

We introduce a system composed of two (2+1)-dimensional baby-skyrmion models (BSMs) set on parallel planes and linearly coupled by tunneling of fields. This system can be realized in a dual-layer ferromagnetic medium. Unlike dual-core models previously studied\ in nonlinear optics and BEC, here the symmetry-breaking bifurcation (SBB) in solitons (baby skyrmions) occurs with the increase of the inter-core coupling ($κ$), rather than with its decrease, due to the fact that even in the uncoupled system neither core may be empty. Prior to the onset of the symmetry breaking between the two components of the solitons, they gradually separate in the lateral direction, due to the increase of $κ$, which is explained in an analytical form by means of an effective interaction potential. Such evolution scenario are produced for the originally symmetric states with topological charges in the two cores $\left(B^{(1)},B^{(2)}\right)$, with $% B^{(1)}=B^{(2)}=1,2,3,4$. The evolution of mixed states, of the $\left(1,2\right)$ and $\left(2,4\right)$ types, with the variation of $κ$ is studied too.

hep-th↗

arXiv2013

Isorotating Baby Skyrmions

We discuss how internal rotation with fixed angular frequency can affect the solitons in the baby Skyrme model in which the global O(3) symmetry is broken to the SO(2). Two particular choices of the potential term are considered, the "old" potential and the "new" double vacuum potential, We do not impose any assumptions about the symmetry on the fields. Our results confirm existence of two types of instabilities determined by the relation between the mass parameter of the potential and the angular frequency.

hep-th↗

arXiv2013

Isospinning hopfions

The problem of constructing internally rotating solitons of fixed angular frequency $ω$ in the Faddeev-Skyrme model is reformulated as a variational problem for an energy-like functional, called pseudoenergy, which depends parametrically on $ω$. This problem is solved numerically using a gradient descent method, without imposing any spatial symmetries on the solitons, and the dependence of the solitons' energy on $ω$, and on their conserved total isospin $J$, studied. It is found that, generically, the shape of a soliton is independent of $ω$, and that its size grows monotonically with $ω$. A simple elastic rod model of time-dependent hopfions is developed which, despite having only one free parameter, accounts well for most of the numerical results.

hep-th↗

arXiv2012

Spontaneous symmetry breaking of binary fields in a nonlinear double-well structure

We introduce a one-dimensional two-component system with the self-focusing cubic nonlinearity concentrated at a symmetric set of two spots. Effects of the spontaneous symmetry breaking (SSB) of localized modes were previously studied in the single-component version of this system. In this work, we study the evolution (in the configuration space of the system) and SSB scenarios for two-component modes of three generic types, as concerns the spatial symmetry of each component: symmetric-symmetric (Sm-Sm), antisymmetric-antisymmetric (AS-AS), and symmetric-antisymmetric (S-AS) ones. In the limit case of the nonlinear potential represented by two $% δ$-functions, solutions are obtained in a semi-analytical form. They feature novel properties, in comparison with the previously studied single-component model. In particular, the SSB of antisymmetric modes is possible solely in the two-component system, and, obviously, S-AS states exist only in the two-component system too. In the general case of the symmetric pair of finite-width nonlinear potential wells, evolution scenarios are very complex. In this case, new results are reported, first, for the single-component model. These are pairs of broken-antisymmetry modes, and of twin-peak symmetric ones, which are generated by saddle-mode bifurcations separated from the transformations previously studied in the the single-component setting. With regard to these findings, complex scenarios of the evolution of the two-component solution families are realized in terms of links connecting pairs of modes of three simplest types: (A) two-component ones with unbroken symmetries; (B) single-component modes featuring density peaks in both potential wells; (C) single-component modes which are trapped, essentially, in a single well.

nlin.PS↗