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Eugene M. Maslov

Publications and source records attributed to Eugene M. Maslov.

9 recordsLinked to original sources
arXiv2026

Dynamics of the inflaton scalar field for a certain class of E-model potentials

We investigate the dynamics of the inflaton scalar field in a certain class of inflationary E-models that combine the properties of the Starobinsky model and the $α$-attractor model. The inflaton potential we are dealing with has an exponentially flat plateau at high field values and a sharply defined minimum at zero. Using the slow-roll approximation, we obtain the analytic expressions describing evolution of the background inflaton field at the inflationary stage. To describe the nonlinear field oscillations at the preheating stage, we use the technique of separation of fast (oscillation phase) and slow (field energy density) variables. The obtained expressions are in good agreement with the results of direct numerical integration of the field equations. These expressions are then used to study the evolution of perturbations at the preheating stage. Based on the Mukhanov-Sasaki equation, we derive the Hill equation with slowly varying parameters, which describes the scalar perturbation modes taking into account the anharmonicity of the background oscillations. Using Floquet theory, we analyze the structure of the resonance zones of this equation and then integrate it numerically. We show that the cosmological expansion limits the resonant growth of scalar modes, making their amplitudes nearly constant at late times. We also derive the corresponding Hill equation for tensor modes. We show that resonant amplification of tensor fluctuations of the metric does not occur.

astro-ph.CO↗
arXiv2024

Resonant phenomena in finite motions of test particles in oscillating dark matter configurations

Nonlinear differential equations are derived that describe the time evolution of the test particle coordinates during finite motions in the gravitational field of oscillating dark matter. It is shown that in the weak field approximation, the radial oscillations of a test particle and oscillations in orbital motion are described by the Hill equation and the nonhomogeneous Hill equation, respectively. In the case of scalar dark matter with a logarithmic self-interactions, these equations are integrated numerically, and the solutions are compared with the corresponding solutions of the original nonlinear system to identify possible resonance effects.

gr-qc↗
arXiv2022

Passage of test particles through oscillating spherically-symmetric dark matter configurations

Applying the perturbative approach to geodesic equations, we study motion of the test particles in time-dependent spherically symmetric spacetimes created by oscillating dark matter. Assuming the weakness of the gravitational field, we derive general formulas that describe infinite trajectories of the test particles and determine the total deflection angle in the leading order approximation. The obtained formulas are valid for both time-dependent and static matter configurations. Using these results, we calculate the deflection angle of a test particle passing through a spherically symmetric oscillating distribution of a self-gravitating scalar field with a logarithmic potential. It turned out that, in a wide range of amplitudes, oscillations in the deflection angle are sinusoidal and become small for ultrarelativistic particles.

gr-qc↗
arXiv2020

Deflection of light in time-periodic spherically symmetric gravitational fields

Using the geodesic method and the perturbative approach, we study the deflection of light by time-periodic spherically symmetric gravitational fields. Assuming the weakness of the gravitational field, we derive general formulas that determine the deflection angle in the leading order approximation. The formulas are valid for both time-periodic and static metrics. Using these results, we calculate the deflection angle of a light ray passing through a spherically symmetric oscillating distribution of a self-gravitating scalar field with a logarithmic potential. It turned out that in this case the deflection angle does not depend on time in the leading order.

gr-qc↗
arXiv2019

Analytical study of the parametric instability of an oscillating scalar field in an expanding universe

We investigate the dynamics of the perturbations of the inflaton scalar field oscillating around a minimum of its effective potential in an expanding universe. With the assumption of smallness of the ratio of the Hubble parameter to the oscillation frequency we apply the technique of separation of fast and slow motions. Considering the oscillation phase and the energy density as fast and slow variables we derive the Hill equation for the fluctuation modes in which the energy density is treated as a slowly varying parameter. We develop a general perturbative approach to solving the equations of this type, which is based on the Floquet theory and asymptotic expansions in the vicinity of the solutions with the "frozen" parameters. As an example, we consider the $ϕ^{2}-ϕ^{4}$ potential and construct the approximate solutions of the corresponding Lamé equation. The obtained solutions are found to be in a good agreement with the results of the direct numerical integration.

gr-qc↗
arXiv2016

On the oscillation-driven cosmological expansion at the post-inflation stage

Dynamics of the inflaton scalar field oscillating around a minimum of the singular potentials in the expanding Universe is investigated. Asymptotic formulas are obtained describing the cosmological expansion at the late times. The problem of stability of the oscillations considered and the related phenomenon of the field fragmentation are briefly discussed.

gr-qc↗
arXiv2011

Gravipulsons

We search for self-gravitating oscillating field lumps (pulsons) in the scalar model with logarithmic potential. With the use of a Krylov-Bogoliubov-type asymptotic expansion in the gravitational constant, the pulson solutions of the Einstein-Klein-Gordon system are obtained in the Schwarzschild coordinates. They are expressed in terms of solutions of the singular Hill's equation. The masses of the obtained pulsons are calculated. The initial conditions are found under which the pulson solutions become periodic. These conditions are then used in direct numerical integration of the Einstein-Klein-Gordon system. It is shown that they do evolve into a very long-lived periodic pulson. Stability of the self-gravitating pulsons and their possible astrophysical applications are briefly discussed.

hep-ph↗
arXiv2005

Instability of coherent states of a real scalar field

We investigate stability of both localized time-periodic coherent states (pulsons) and uniformly distributed coherent states (oscillating condensate) of a real scalar field satisfying the Klein-Gordon equation with a logarithmic nonlinearity. The linear analysis of time-dependent parts of perturbations leads to the Hill equation with a singular coefficient. To evaluate the characteristic exponent we extend the Lindemann-Stieltjes method, usually applied to the Mathieu and Lame equations, to the case that the periodic coefficient in the general Hill equation is an unbounded function of time. As a result, we derive the formula for the characteristic exponent and calculate the stability-instability chart. Then we analyze the spatial structure of the perturbations. Using these results we show that the pulsons of any amplitudes, remaining well-localized objects, lose their coherence with time. This means that, strictly speaking, all pulsons of the model considered are unstable. Nevertheless, for the nodeless pulsons the rate of the coherence breaking in narrow ranges of amplitudes is found to be very small, so that such pulsons can be long-lived. Further, we use the obtaned stability-instability chart to examine the Affleck-Dine type condensate. We conclude the oscillating condensate can decay into an ensemble of the nodeless pulsons.

hep-th↗