arXiv subjects

Yakov Shnir

Publications and source records attributed to Yakov Shnir.

At least 19 recordsLinked to original sources

arXiv2026

The Non-Relativistic Limit of Five-Dimensional Boson Stars and Scale Invariance Violation

We investigate the non-relativistic limit of spherically symmetric boson stars in (4+1)-dimensional general relativity (GR). In this limit, the resulting Newtonian theory exhibits an exact scale invariance, leading to a critical boson star configuration with a fixed global U(1) charge and vanishing binding energy. We identify the origin of these properties in the restored scale symmetry and analyze how relativistic and gravitational corrections break this symmetry. By comparing the full (4+1)-dimensional Einstein-Klein-Gordon system with the Wick-Cutkosky model, we quantify the effects of these corrections on the energy-charge relation and the kinematic stability of the configurations. Our results demonstrate how weak violation of scale invariance lifts the degeneracy of the non-relativistic solutions and determines the behavior of boson stars away from the critical limit.

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arXiv2026

Two types of hairy black holes in the (3+1)-dimensional $O(3)$ sigma-model

We construct stationary axially symmetric black holes with scalar hair in the gravitating nonlinear $O(3)$ sigma model with a partly negative symmetry-breaking potential. Our results show that it supports two qualitatively different types of asymptotically flat hairy black holes, distinguished by their connection to the corresponding solitonic branches and by the structure of their scalar hair; the type I black holes are connected to the vacuum branch and type II black holes are connected to regular scalaron-supported spinning solitons. The type II black holes have a strongly deformed scalar field structure, with the scalar field taking its vacuum value on the symmetry axis and approaching the anti-vacuum in the near-horizon equatorial region. We analyze their global charges, horizon properties, and dependence on the model parameters, comparing the solutions with Kerr black holes. For sufficiently weak gravitational coupling, the branch connectivity changes: the fundamental branches of types I and II reconnect to form one continuous family, while their corresponding second branches form another. We find that, in contrast to the vacuum-connected type I family, the scalaron-supported type II black holes extend to substantially larger horizon radii while preserving a nontrivial scalar configuration outside the horizon.

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arXiv2026

Stress stability criterion of the isospinning $\mathbb{C}P^2$ solitons

We study the energy-momentum tensor of stationary rotating topological solitons in a (2 + 1)-dimensional $\mathbb{C}P^2$ nonlinear sigma model with a stabilizing potential term. We evaluate the distributions of the corresponding shear forces and pressure and study the stability criteria for these solutions. Our results suggest that these solitons become classically unstable for some range of values of the parameters of the system.

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arXiv2026

Linearized Q-Ball Perturbations

Linearized deformations of the thick-walled (low-amplitude) (1+1)-dimensional Q-ball may be decomposed into relativistic modes, which are roughly plane waves, and also long-wavelength corotating and counterrotating Floquet modes. Each mode oscillates at a pair of mirror frequencies which average to the Q-ball frequency. The corotating modes are those of a breather or oscillon plus a very loosely bound mode. The counterrotating modes are described by an irrational-level Pöschl-Teller potential, with two discrete modes which mix with their unbound mirrors, unbinding them and turning them into Feshbach-type quasinormal modes. Expanding to leading order in the Q-ball amplitude, we present all of these modes in closed form, except for the bound mode which does not exist at leading order.

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arXiv2026

Stress stability criterion of $U(1)$ gauged non-topological solitons in the 3+1 dimensional O(3) sigma-model

We study the energy-momentum tensor of the spherically symmetric non-topological solitons of the $O(3)$ non-linear sigma-model with a standard kinetic term and with a symmetry breaking potential in 3+1 dimensional flat space-time. We evaluate the distributions of the corresponding energy density, shear forces and pressure and study the stability criteria for these solutions. We argue that the presence of domains with negative energy density and violation of the energy conditions most likely do not lead to destabilization of solitons.

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arXiv2026

Towards spinning $U(1)$ gauged non-topological solitons in the model with Chern-Simons term

We obtain localized field configurations with finite energy in a ($2+1$)-dimensional model with Maxwell and Chern-Simons gauge terms coupled to a massive complex scalar field. These non-topological solitons are characterized by the $U(1)$ frequency and a winding number. Thus, the solutions possess Noether charge and non-trivial angular momentum, which is not quantized in contrast to the topological case. We study the solitons and their integral characteristics numerically and demonstrate that they are kinematically stable. The obtained solutions allow for the thin-wall approximation in some region of frequencies. For each winding number, the Noether charge has a lower bound that coincides with an isolated point, where the non-relativistic conformal symmetry seems to be restored.

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arXiv2026

Two types of boson stars in $U(1)$ gauged $3+1$-dimensional $O(3)$ sigma-model

We investigate boson stars in an $O(3)$ scalar field theory with a symmetry-breaking potential. By constructing numerically spherically symmetric solutions, we demonstrate that the model gives rise to a rich set of field configurations. The negative coupling constant of the scalar self-interactions allows for two types of boson stars: Type I solutions represent the usual boson stars, that emerge from the vacuum as the boson frequency is decreased below the boson mass, whereas type II boson stars emerge from a set of static soliton solutions. Depending on the strengths of the gravitational and the electric coupling constants, both types or only one type is present. At a critical set of coupling constants, both types undergo a bifurcation. There the spirals of both types disconnect from their branches and reconnect with each other, while the remaining branches of both types also reconnect with each other.

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arXiv2025

Generalized Models for Spinning Field Lumps on Plane

We study planar non-topological solitons in models with nonlinear potentials that are bounded from below. These models provide consistent completion for the classical consideration at any energy scale. The properties of our solutions indicate the kinematical stability, which is unachievable in the previously studied model with negative quartic self-interaction. Remarkably, our generalization preserves restoration of the full Schrödinger symmetry at low energies, including scale invariance (dilatation) and special conformal symmetry. Our numerical calculations and analytical approximations demonstrate that the details of non-relativistic regime are defined by the lowest nonlinear $U(1)$-invariant term.

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arXiv2025

CFT-approach to Rotating Field Lumps in Attractive Potential

We demonstrate the importance of relativistic corrections for the study of the stability of $(2+1)$-dimensional non-topological solitons with quartic self-interaction in the low-energy limit. This result is explained by the restoration of conformal symmetry in the non-relativistic limit. Particularly, the corresponding cubic Gross-Pitaevskii equation supports scale-free non-topological solitons. An unbroken conformal symmetry provides the additional degeneration that allows for the exact result for the energy and angular momentum of the stationary classical solutions. We study the violation of conformal symmetry by relativistic corrections. The emergence of exponentially growing modes on the classical background is demonstrated using analytical approximations and numerical calculations.

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arXiv2025

Properties of Non-topological Solitons in Two-dimensional Model With Resurrected Conformal Symmetry

We study properties of non-topological solitons in two-dimensional conformal field theory. The spectrum of linear perturbations on these solutions is found to be trivial, containing only symmetry-related zero modes. The interpretation of this feature is given by considering the relativistic generalization of our theory in which the conformal symmetry is violated. It is explicitly seen that the restoration of this symmetry leads to the absence of decay/vibrational modes.

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arXiv2025

$U(1)$ gauged non-topological solitons in the 3+1 dimensional $O(3)$ sigma-model

We present and study new non-topological soliton solutions in the $U(1)$ gauged non-linear $O(3)$ sigma model with a symmetry breaking potential in 3+1 dimensional flat space-time. The configurations are endowed with an electric and magnetic field and also carry a nonvanishing angular momentum density. We discuss properties of these solitons and investigate the domains of their existence.

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arXiv2025

Boson stars in the $U(1)$ gauged 3+1 dimensional $O(3)$ sigma-model

We study regular self-gravitating non-topological soliton solutions of the $U(1)$ gauged non-linear $O(3)$ sigma model with the usual kinetic term and a simple symmetry breaking potential in 3+1 dimensional asymptotically flat spacetime. Both parity-even and parity-odd configurations with an angular node of the scalar field are considered. Localized solutions are endowed with an electric charge, spinning configurations are also coupled to the toroidal flux of magnetic field. We confirm that such solutions do not exist in the flat space limit. Similar to the usual boson stars, a spiral-like frequency dependence of the mass and the Noether charge of the gauged solutions is observed. Depending on the relative strength of gravity and the electromagnetic interaction, the resulting gauged $O(3)$ boson stars at the mass threshold either possess the usual Newtonian limit, or they are linked to a regular strongly gravitating critical configuration. We explore domain of existence of the solutions and investigate some of their physical properties.

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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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arXiv2025

Fermions localized on $U(1)$ gauged Q-balls

The axially symmetric $U(1)$ gauged self-interacting Q-balls are shown to support normalizable fermionic bound state, minimally coupled to the electromagnetic field of the Q-ball. It is shown that the effects of the backreaction of the fermionic mode are very small. We explore the domain of existence of the solutions and address some of their physical properties. Among other properties, we observe that the eigenvalue of the Dirac operator remains positive, there is no zero mode in the spectrum.

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arXiv2024

Hairy dyonic Reissner-Nordström black holes in an Einstein-Maxwell-Friedberg-Lee-Sirlin type model

We construct spherically symmetric dyonic black holes in a generalized Maxwell-Friedberg-Lee-Sirlin type model with a complex scalar doublet and a symmetry breaking potential {for the real scalar field}, minimally coupled to Einstein gravity in asymptotically flat space. We analyze the properties of the hairy black holes and determine their domain of existence. Our discussion focuses mostly on the case of a long-ranged massless real scalar field. Our results indicate that in this case, depending on the coupling constants, the resonant hairy dyonic black holes may bifurcate from Reissner-Nordström black holes at maximal chemical potential, while the limiting solutions at minimal chemical potential may be related to the Penney solution.

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arXiv2024

Localized Electromagnetic Perturbations on Vector Solitons

Using effective field theory approach one can describe localization of electromagnetic field on a non-topological soliton. Pursuing this aim we consider the U(1) gauge theory with gauge kinetic coupling to a self-interacting complex neutral Proca field. The model possesses single energy scale given by the vector boson mass. Considering spherically symmetric stationary configurations, we study vibrational modes of the Proca field on the background of the soliton and discuss their properties.

hep-ph↗

arXiv2024

Gravitating Skyrmions with localized fermions

We consider self-gravitating Skyrmions in the presence of Dirac fermions, that carry spin and isospin. By varying the gravitational and the Yukawa coupling constants, we investigate the spectral flow of the fermion eigenvalue associated with a zero mode in the absence of gravity. We demonstrate that the backreaction of the fermion can strongly influence the Skyrmion-fermion configurations. In particular, the energy conditions may be violated, and regular anti-gravitating asymptotically flat solutions with negative ADM mass may emerge.

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arXiv2024

Fermion states localized on a self-gravitating Skyrmion

We investigate self-gravitating solutions of the Einstein-Skyrme theory coupled to spin-isospin Dirac fermions and consider the dependence of the spectral flow on the effective gravitational coupling constant and on the Yukawa coupling. It is shown that the effects of the backreaction of the fermionic mode may strongly deform the configuration. Depending on the choice of parameters, solutions with positive, negative and zero ADM mass may arise. The occurrence of regular anti-gravitating asymptotically flat solutions with negative ADM mass is caused by the violation of the energy conditions.

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