arXiv subjects

Abbas Altafhussain Tinwala

Publications and source records attributed to Abbas Altafhussain Tinwala.

4 recordsLinked to original sources

arXiv2023

Local momentum space: Scalar field and gravity

We use the local momentum space technique to obtain an expansion of the Feynman propagators for scalar field and graviton up to first order in the background curvature. The expressions for the propagators are cross-checked with the past literature as well as with the expressions for the traced heat kernel coefficients. The propagators so obtained are used to compute one-loop divergences in the Vilkovisky-Dewitt's effective action for a scalar field non-minimally coupled with gravity for an arbitrary spacetime metric background. The Vilkovisky-DeWitt effective action is then compared with the standard effective action in the limit $κ=0$, where $κ= 2/M_P$ in terms of the Planck mass. The comparison yields the important result that taking the limit $κ=0$ after computing the Vikovisky-DeWitt effective action is not equivalent to computing the Vikovisky-DeWitt effective action for the same theory in the absence of gravity.

hep-th↗

arXiv2023

Two-loop Vilkovisky-DeWitt effective action for scalar field minimally coupled with gravity

It is known that Vilkovisky-DeWitt's effective action is gauge invariant off-shell and independent of quantum field parametrization. In this work, we perform the calculation of the divergences in two-loop Vilkovisky-DeWitt's effective action for the theory of a massive scalar field minimally coupled to gravity. We quantize both gravity and scalar field around a flat Minkowski metric and a constant scalar field background. The quantum corrections are computed up to second order in the background scalar field for the purpose of mass renormalization.

hep-th↗

arXiv2023

Ultraviolet Unitarity Violations in Non-minimally Coupled Scalar-Starobinsky Inflation

We perform the calculation for tree-level ultraviolet unitarity violation scales for scalar-$R^2$ inflation models by including an additional $R^2 |Φ|^2$-type term. Due to certain constraints, we resort to the Einstein frame for our calculations, where we separate our analysis between metric and Palatini formulations. We follow recent works in this line that debunk the naive predictions for unitarity violations in Higgs' inflation models to determine how to accurately estimate the behaviour of scattering amplitudes in the UV limit. Later, we work out different cases by assuming potentials corresponding to known inflation scenarios so we could predict the range of coupling parameters for which the theories would remain unitary up to the Planckian regime. We also try to find the behaviour of the scattering amplitudes for these theories during the transition from inflationary to reheating epoch.

gr-qc↗

arXiv2021

Covariant Effective Action for Scalar-Tensor Theories of Gravity

We develop the calculation of the divergent part of one-loop covariant effective action for scalar fields minimally and non-minimally coupled to gravity using the generalized Schwinger-DeWitt technique. We derive the field-space metric using Vilkovisky's prescription and obtain new terms in the one-loop corrections which are absent in past literature with trivial choices of field-space metric. We further calculate the covariant versions of past results, obtained using the standard approach, by applying Barvinsky and Vilkovisky's extension to the ordinary Schwinger-DeWitt approach. For completeness, we study the one-loop gravitational corrections for a dilaton-extended two-field Starobinsky model and compare with known results.

hep-th↗