Research Interests:
Research Interests:
We examine long-wavelength correlation functions of massive scalar fields in de Sitter spacetime. For the theory with a quartic self-interaction, the two-point function is calculated up to two loops. Comparing our results with the... more
We examine long-wavelength correlation functions of massive scalar fields in de Sitter spacetime. For the theory with a quartic self-interaction, the two-point function is calculated up to two loops. Comparing our results with the Hartree–Fock approximation and with the stochastic approach shows that the former resums only the cactus type diagrams, whereas the latter contains the sunset diagram as well and produces the correct result. We also demonstrate that the long-wavelength expectation value of the commutator of two fields is equal to zero both for spacelike and timelike separated points.
Research Interests:
We present constraints on inflationary dynamics and features in the primordial power spectrum of scalar perturbations using the Cosmic Microwave Background temperature, polarization data from Planck 2018 data release and updated... more
We present constraints on inflationary dynamics and features in the primordial power spectrum of scalar perturbations using the Cosmic Microwave Background temperature, polarization data from Planck 2018 data release and updated likelihoods. We constrain the slow-roll dynamics using Hilltop Quartic Potential and Starobinsky R + R 2 model in the Einstein frame using the Planck 2018 binned Plik likelihood. Using the Hilltop as base potential, we construct Whipped Inflation potential to introduce suppression in the scalar power spectrum at large angular scales. We notice marginal (68% C.L.) preference of suppression from the large scale temperature angular power spectrum. However, large-scale E-mode likelihood based on high frequency instrument cross spectrum, does not support this suppression and in the combined data the preference towards the suppression becomes negligible. Based on the Hilltop and Starobinsky model, we construct the Wiggly Whipped Inflation potentials to introduce o...
Research Interests:
Motivated by the idea that inflation occurs at the GUT symmetry breaking scale, in this paper we construct a new class of large field inflaton potentials where the inflaton starts with a power law potential; after initial period of... more
Motivated by the idea that inflation occurs at the GUT symmetry breaking scale, in this paper we construct a new class of large field inflaton potentials where the inflaton starts with a power law potential; after initial period of relative fast roll that lasts until after a few e-folds inside the horizon, it transits to the attractor of the slow roll part of the potential with a lower power. Due to the initial fast roll stages of inflation, we find a suppression in scalar primordial power at large scales and at the same time the choice of the potential can provide us a tensor primordial spectrum with high amplitude. This suppression in scalar power with a large tensor-to-scalar ratio helps us to reconcile the Planck and BICEP2 data in a single framework. We find that a transition from a cubic to quadratic form of inflaton potential generates an appropriate suppression in power of scalar primordial spectrum that provides significant improvement in fit compared to power law model whe...
Research Interests:
Emergence of [Formula: see text] inflation, which is the best fit framework for CMB observations till date, comes from the attempts to attack the problem of quantization of gravity which in turn have resulted in the trace anomaly... more
Emergence of [Formula: see text] inflation, which is the best fit framework for CMB observations till date, comes from the attempts to attack the problem of quantization of gravity which in turn have resulted in the trace anomaly discovery. Further developments in trace anomaly and different frameworks aiming to construct quantum gravity indicate an inevitability of nonlocality in fundamental physics at small time and length scales. A natural question would be to employ the [Formula: see text] inflation as a probe for signatures of nonlocality in the early Universe physics. Recent advances of embedding [Formula: see text] inflation in a string theory inspired nonlocal gravity modification provide very promising theoretical predictions connecting the nonlocal physics in the early Universe and the forthcoming CMB observations.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
A novel class of exact solutions of inflationary dynamics with a specific form of a scalar potential is given based on a "fast-roll" ansatz, where the even-order slow-roll parameters approach to a nonnegligible constants while... more
A novel class of exact solutions of inflationary dynamics with a specific form of a scalar potential is given based on a "fast-roll" ansatz, where the even-order slow-roll parameters approach to a nonnegligible constants while the odd ones are asymptotically vanishing in the quasi-de Sitter regime. Due to the rapid evolution of the background dynamics, the would-be decaying mode of the linear curvature perturbation may behave as a growing mode depending on the value of the model parameter, while the other mode remains constant. For the parameters giving a slightly red-tilted primordial power spectrum, the unwanted anomalous growth of the curvature perturbation is inevitable, which is similar to the case of the so-called ultra-slow-roll inflation.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
We discuss the structure of parametric resonance which occurs in the process of reheating after inflation with two interacting scalar fields. It is found that, for the case of a not too large coupling constant, a quasi-homogeneous part of... more
We discuss the structure of parametric resonance which occurs in the process of reheating after inflation with two interacting scalar fields. It is found that, for the case of a not too large coupling constant, a quasi-homogeneous part of the second, initially subdominant scalar field may not be neglected due to its stochastic growth during inflation. This fact has strong consequences for the reheating stage: dynamics of background fields becomes chaotic after inflation -- it consists of subsequent chaotic and regular eras, and a tachyonic instability for inhomogeneous perturbations arises in the quantum reheating problem. This instability may pose a problem for the standard reheating scenario. In order to avoid it, the coupling constant should be either sufficiently small, or very large.
Research Interests:
Research Interests:
Research Interests:
The effect of amplification of electromagnetic and gravitational waves reflected from a rotating black hole (‘superradiance scattering’) is investigated. This effect was proposed by Zel'dovich (1971). It leads, as well as the Penrose... more
The effect of amplification of electromagnetic and gravitational waves reflected from a rotating black hole (‘superradiance scattering’) is investigated. This effect was proposed by Zel'dovich (1971). It leads, as well as the Penrose process, to the energy extraction from a Kerr black hole at the expense of its rotational energy and momentum decrease. The coefficient of wave reflection R>1 if ω<nω, where ω is the wave frequency, n - its angular momentum and ω is the black hole angular velocity. The value of this effect is not small in the case of gravitational waves, for example, if l=n = 2, ω →nω and a = M, then R≈2.38.There also exists a quantum version of the effect, namely, the one of spontaneous pair creation in the Kerr metric, but this quantum effect is exceedingly small in real astrophysical conditions, because its characteristic time is of the order G2M3/hc4, where M is the black hole mass.
Research Interests:
Research Interests:
Research Interests:
It is natural to expect a consistent inflationary model of the very early Universe to be an effective theory of quantum gravity, at least at energies much less than the Planck one. For the moment, R + R 2, or shortly R 2, inflation is the... more
It is natural to expect a consistent inflationary model of the very early Universe to be an effective theory of quantum gravity, at least at energies much less than the Planck one. For the moment, R + R 2, or shortly R 2, inflation is the most successful in accounting for the latest CMB data from the PLANCK satellite and other experiments. Moreover, recently it was shown to be ultra-violet (UV) complete via an embedding into an analytic infinite derivative (AID) non-local gravity. In this paper, we derive a most general theory of gravity that contributes to perturbed linear equations of motion around maximally symmetric space-times. We show that such a theory is quadratic in the Ricci scalar and the Weyl tensor with AID operators along with the Einstein-Hilbert term and possibly a cosmological constant. We explicitly demonstrate that introduction of the Ricci tensor squared term is redundant. Working in this quadratic AID gravity framework without a cosmological term we prove that f...