A Stellar Constraint on Eddington-inspired Born–Infeld Gravity from Cataclysmic Variable Binaries

Pritam Banerjee,Rajibul Shaikh,Debojyoti Garain,Suvankar Paul,Tapobrata Sarkar

doi:10.3847/1538-4357/ac324f

Abstract

Abstract Eddington-inspired Born–Infeld gravity is an important modification of Einstein’s general relativity, which can give rise to nonsingular cosmologies at the classical level, and avoid the end-stage singularity in a gravitational collapse process. In the Newtonian limit, this theory gives rise to a modified Poisson’s equation, as a consequence of which stellar observables acquire model dependent corrections, compared to the ones computed in the low energy limit of general relativity. This can in turn be used to establish astrophysical constraints on the theory. Here, we obtain such a constraint using observational data from cataclysmic variable binaries. In particular, we consider the tidal disruption limit of the secondary star by a white dwarf primary. The Roche lobe filling condition of this secondary star is used to compute stellar observables in the modified gravity theory in a numerical scheme. These are then contrasted with the values obtained by using available data on these objects, via a Monte Carlo error progression method. This way, we are able to constrain the theory within the 5σ confidence level.

Highlights

In spite of the unprecedented success of Einstein’s general relativity (GR), modifications thereof are important, and have been the focus of intense research over the last few decades
Eddington inspired Born-Infeld (EiBI) theories of gravity are very attractive in this sense, as they give rise to non-singular cosmologies as well as predict non-singular collapse processes in the realm of classical gravity, i.e., without invoking quantum effects
The main effects of such modified theories of gravity are expected to set in at strong gravity scales, they often leave their imprint at low energy scales, in this case by a modification of the Poisson’s equation in the Newtonian limit

Summary

INTRODUCTION

In spite of the unprecedented success of Einstein’s general relativity (GR), modifications thereof are important, and have been the focus of intense research over the last few decades. In the beyond-Horndeski class of modified gravity theories (for a recent review, see Kobayashi (2019)), only the radial part of the modified pressure balance equation is known, and it is imperative in such examples to assume spherical symmetry of stellar objects This assumption has to be carefully dealt with, in CV systems where the stellar structure is more complicated due to effects of tidal forces as well as rotations, as discussed by Banerjee et. We use the observational data on CV binaries, with the underlying theory being EiBI gravity This latter fact is inbuilt in our analysis which uses the modified Poisson’s equation, Eq(2), and via this, stellar observables are numerically obtained as a functions of κg, offering ready comparison with data, which allows us to constrain the possible values of κg.

NUMERICAL PROCEDURE

METHODOLOGY

CONSTRAINING THE EIBI GRAVITY PARAMETER