arXiv subjects

Polina Petriakova

Publications and source records attributed to Polina Petriakova.

8 recordsLinked to original sources

arXiv2026

Taming the infrared in de Sitter space: autonomous equations, stochastic approach, and Borel resummation

We investigate the divergent perturbative series of correlation functions for a massless, self-interacting scalar field in de Sitter space. First, we use our previously proposed method of autonomous equations to obtain finite time-dependent functions, and show that these functions approximate the time evolution of the correlation functions of the stochastic theory reasonably well. Second, we apply the technique of autonomous equations to the Borel-Le Roy transforms of correlation functions, and use solutions of these equations to perform Borel resummation. The results match the time evolution obtained in the stochastic picture substantially better. In addition, we propose an alternative method for extracting perturbative coefficients and provide a new derivation of our autonomous equation by truncating a system of Schwinger-Dyson-type differential equations.

hep-th↗

arXiv2026

IR finite correlation functions in de Sitter space, a smooth massless limit, and an autonomous equation

We explore two-point and four-point correlation functions of a massive scalar field on the flat de Sitter background in the long-wavelength approximation. By employing the Yang-Feldman-type equation, we compute the two-point correlation function up to $λ^3$ order and the four-point correlation function up to $λ^2$ order. In contrast to the standard theory of a massive scalar field based on the de Sitter-invariant vacuum, we develop a vacuum-independent reasoning that may not possess de Sitter invariance but results in a smooth massless limit of the correlation function's infrared part. Our elaboration allows us to calculate correlation functions of a free massive scalar field and to proceed with quantum corrections, relying only on the known infrared part of the two-point correlation function of a free massless one. Remarkably, the two-point correlation function of a free massive scalar field coincides with that of the Ornstein-Uhlenbeck stochastic process and has a clear physical interpretation. We compare our results with those obtained using the Schwinger-Keldysh diagrammatic technique, Starobinsky's stochastic approach, and the Hartree-Fock approximation. At last, we construct a renormalization group-inspired autonomous equation for the two-point correlation function. Integrating its approximate version, one obtains the non-analytic expression with respect to a self-interaction coupling constant $λ$. That solution reproduces the correct perturbative series up to the two-loop level. In the late-time limit, it almost coincides with the result of Starobinsky's stochastic approach over the whole interval of a new dimensionless parameter $0 \leq \tfrac{π^2 m^4}{3λH^4} < \infty$.

hep-th↗

arXiv2025

From the Fokker-Planck equation to perturbative QFT's results in de Sitter space

A technique to build perturbative series for the spectator field's correlation functions in de Sitter space through the Fokker-Planck equation is proposed. We derive from the first-order differential equation the iterative integral relation for equal- and multi-time correlation functions. With an appropriate integration, the obtained two-point and four-point correlation functions are in agreement with quantum field theory's ones.

hep-th↗

arXiv2024

Regular Friedmann Universes and Matter Transformations

We apply a very simple procedure to construct non-singular cosmological models for flat Friedmann universes filled with minimally coupled scalar fields or by tachyon Born-Infeld-type fields. Remarkably, for the minimally coupled scalar field and the tachyon field, the regularity of the cosmological evolution, or in other words, the existence of bounce, implies the necessity of the transition between scalar fields with standard kinetic terms to those with phantom ones. In both cases, the potentials in the vicinity of the point of the transition have a non-analyticity of the cusp form that is characterized by the same exponent and is equal to 2/3. If, in the tachyon models evolution, the pressure changes its sign, then another transformation of the Born-Infeld-type field occurs: the tachyon transforms into a pseudotachyon, and vice versa. We also undertake an analysis of the stability of the cosmological evolution in our models; we rely on the study of the speed of sound squared.

gr-qc↗

arXiv2023

Bianchi-I cosmologies, magnetic fields and singularities

We study the effects of a spatially homogenous magnetic field in Bianchi-I cosmological models. The cases of a pure magnetic field and two models with additional dust and a massless scalar field (stiff matter) are also considered. At the beginning of the cosmological evolution,i.e., in the neighborhood of the singularity, the universe is described by one of Kasner's solutions, and asymptotically by another Kasner solution when the volume of the universe tends to infinity. The transition law between these two Kasner regimes is established, and shown to coincide with the analogous law for the empty Bianchi-II universe. The universe filled with dust and a magnetic field undergoes the process of isotropization, while the presence of a massless scalar field induces a modification of the relations between Kasner indices in the two asymptotic regimes. In all of these cases, we analyze the approach to the singularity in some detail and comment on the issue of the possible singularity crossing.

gr-qc↗

arXiv2023

Newman-Janis algorithm's application to regular black hole models

We examine the Newman-Janis algorithm's application to an exact regular static solution sustained by a minimally coupled scalar field with a non-standard kinetic term. Although coordinate complexification leads to a regular Kerr-like black hole, we are facing discrepancies in Einstein's equations in a fairly small domain, for which the regularizing parameter is responsible. Outside this most intriguing region, the geometry is nothing but the standard Kerr spacetime.

gr-qc↗

arXiv2023

Flexible extra dimensions

This paper discusses the origin of the small parameters with the aim of explaining the Hierarchy problem. The flexible extra dimensions are an essential tool in the process by which physical parameters are formed. The evolution of a multidimensional metric starts at the Planck scale and is completed with the static extra-dimensional metric and the 4-dim de Sitter space at high energies, where the exponential production of causally disconnected universes begins. Quantum fluctuations independently distort the metric within these universes, causing inflationary processes within them. Some of these universes tend asymptotically towards states characterised by small Hubble parameters. The effective parameter reduction applied to the Higgs sector of the Standard Model is explained by the presence of small-amplitude distributions of a scalar field in a fraction of these universes.

gr-qc↗

arXiv2022

Self-tuning inflation

We develop an inflationary model without small parameters on the basis of multidimensional $f(R)$ gravity with a minimally coupled scalar field. The model is described by two stages of space expansion. The first one begins at energy scales about the D-dimensional Planck mass and ends with the de Sitter metric of our space and the maximally symmetric extra dimensions. In the following, the quantum fluctuations produce a wide set of inhomogeneous extra metrics in causally disconnected regions quickly generated in the de Sitter space. We find a specific extra space metric that leads to the effective Starobinsky model that fits the observational data.

gr-qc↗