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Yu. A. Kubyshin

Publications and source records attributed to Yu. A. Kubyshin.

15 recordsLinked to original sources
arXiv2016

Stability of the phase motion in race-track microtons

We model the phase oscillations of electrons in race-track microtrons by means of an area preserving map with a fixed point at the origin, which represents the synchronous trajectory of a reference particle in the beam. We study the nonlinear stability of the origin in terms of the synchronous phase -- the phase of the synchronous particle at the injection. We estimate the size and shape of the stability domain around the origin, whose main connected component is enclosed by the last rotational invariant curve. We describe the evolution of the stability domain as the synchronous phase varies. Besides, we approximate some rotational invariant curves by level sets of certain Hamiltonians. Finally, we clarify the role of the stable and unstable invariant curves of some hyperbolic (fixed or periodic) points.

math.DS↗
arXiv2006

The variation of the gravitational constant inferred from the Hubble diagram of Type Ia supernovae

We consider a cosmological model with a variable gravitational constant, G, based on a scalar-tensor theory. Using the recent observational data for the Hubble diagram of type Ia supernovae (SNeIa) we find a phenomenological expression describing the variation of G. The corresponding variation of the fine structure constant αwithin multidimensional theories is also computed and is shown not to support known constraints on Δα/ α.

gr-qc↗
arXiv2003

Time variation of G and αwithin models with extra dimensions

We derive the formulae for the time variation of the gravitational "constant" G and of the fine structure "constant" αin various models with extra dimensions and analyze their consistency with the available observational data for distant supernovae. We find that the reported variation of αtranslates into a small variation of G that makes distant supernovae to appear brighter, in contradiction with recent observations of high z supernovae. The significance of these results within the framework of some cosmological scenarios is also discussed. We find, however, that the magnitude of the effect is not large enough to safely discard the models with extra dimensions studied here.

astro-ph↗
arXiv2002

Solutions of the Polchinski ERG equation in the O(N) scalar model

Solutions of the Polchinski exact renormalization group equation in the scalar O(N) theory are studied. Families of regular solutions are found and their relation with fixed points of the theory is established. Special attention is devoted to the limit $N=\infty$, where many properties can be analyzed analytically.

hep-th↗
arXiv2001

A gauge invariant regulator for the ERG

A gauge invariant regularisation for dealing with pure Yang-Mills theories within the exact renormalization group approach is proposed. It is based on the regularisation via covariant higher derivatives and includes auxiliary Pauli-Villars fields which amounts to a spontaneously broken SU(N|N) super-gauge theory. We demonstrate perturbatively that the extended theory is ultra-violet finite in four dimensions and argue that it has a sensible limit when the regularization cutoff is removed.

hep-th↗
arXiv2001

Gauge invariant regularisation in the ERG approach

A gauge invariant regularisation which can be used for non-perturbative treatment of Yang-Mills theories within the exact renormalization group approach is constructed. It consists of a spontaneously broken SU(N|N) super-gauge extension of the initial Yang-Mills action supplied with covariant higher derivatives. We demonstrate that the extended theory in four dimensions is ultra-violet finite perturbatively and argue that it has a sensible limit when the regularisation cutoff is removed.

hep-th↗
arXiv2000

Instanton propagator and instanton induced processes in scalar model

The propagator in the instanton background in the $(- λϕ^{4})$ scalar model in four dimensions is studied.Leading and sub-leading terms of its asymptotics for large momenta and its on-shell double residue are calculated analytically. These results are applied to the analysis of the initial-state and initial-final-state corrections and the calculation of the next-to-leading (propagator) correction to the exponent of the cross section of instanton induced multiparticle scattering processes.

hep-ph↗
arXiv2000

Instanton propagator in scalar model: exact expression and contribution to instanton induced processes

The propagator in the instanton background in the -lambda phi^4 scalar model in four dimensions is studied. Leading and sub-leading terms of its asymptotics for large momenta and its on-shell double residue are calculated. These results are applied to the analysis of the initial state and initial-final state corrections and the calculation of the next-to-leading (propagator) correction to the exponent of the cross section of multiparticle scattering processes.

hep-ph↗
arXiv1999

A classification of fibre bundles over 2-dimensional spaces

The classification problem for principal fibre bundles over two-dimensional CW-complexes is considered. Using the Postnikov factorization for the base space of a universal bundle a Puppe sequence that gives an implicit solution for the classification problem is constructed. In cases, when the structure group $G$ is path-connected or $π_{1}(G) = 0$, the classification can be given in terms of cohomology groups.

math.AT↗
arXiv1998

Propagator in the Instanton Background and Instanton-Induced Processes in Scalar Model

The cross section of the multiparticle scattering processes in the non-perturbative sector of the scalar -lambda * phi^4 model is studied within the semiclassical approximation. For this purpose the exact formula for the residue of the propagator in the instanton background is derived. The exponent of the cross section is calculated at small energies both analytically and numerically in the leading and next-to-leading orders in energy. The results are in agreement with the numerical calculations of ref.[1].

hep-ph↗
arXiv1998

Study of Wilson loop functionals in 2D Yang-Mills theories

The derivation of the explicit formula for the vacuum expectation value of the Wilson loop functional for an arbitrary gauge group on an arbitrary orientable two-dimensional manifold is considered both in the continuum case and on the lattice. A contribution to this quantity, coming from the space of invariant connections, is also analyzed and is shown to be similar to the contribution of monopoles.

hep-th↗
arXiv1993

Manifestations of Space-Time Multidimensionality in Scattering of Scalar Particles

We analyze a possibility of experimental detection of the contribution of the Kaluza-Klein tower of heavy particles to scattering cross-section in a six-dimensional scalar model with two dimensions being compactified to the torus with the radii $R$. It is shown that there is a noticeable effect even for the energies of colliding particles below $R^{-1}$ which may be observed in future collider experiments if $R^{-1}$ is of the order of $1 TeV$.

hep-th↗
arXiv1993

Compactification to Non-symmetric Homogeneous Space in Multidimensional Einstein-Yang-Mills Theory

We study ten-dimensional Einstein-Yang-Mills model with the space of extra dimensions being a non-symmetric homogeneous space with the invariant metric parametrized by two scales. Dimensional reduction of the model is carried out and the scalar potential of the reduced theory is calculated. In a cosmological setting minima of the potential in the radiation-dominated period that followed the inflation are found and their stability is analyzed. The compactifying solution is shown to be stable for the appropriate values of parameters.

gr-qc↗
arXiv1993

Invariant Connections with Torsion on Group Manifolds and Their Application in Kaluza-Klein Theories

Invariant connections with torsion on simple group manifolds $S$ are studied and an explicit formula describing them is presented. This result is used for the dimensional reduction in a theory of multidimensional gravity with curvature squared terms on $M^{4} \times S$. We calculate the potential of scalar fields, emerging from extra components of the metric and torsion, and analyze the role of the torsion for the stability of spontaneous compactification.

gr-qc↗