Constraining Einstein-Maxwell-Dilaton-Axion Gravity from The Observed Quasi-Periodic Oscillations in Black Holes

Abstract

The general theory of relativity (GR) plays the the key role to understand cosmology and gravity.GR has been successful to demonstrate the fundamental characteristics of gravity through its appreciable originality and mathematical magnificence.But,despite of its vast applications,GR is incomplete because of the presence of singularity where all the laws of physics breaks down,it’s inconsistency with quantum mechanism,failure to explain dark matter and dark energy.Under this scenario,it is important to search for alternate theories those are able to solve most of the issues of GR.Einstein Maxwell Dilaton Axion (EMDA) gravity is an alternate theory of gravity which originates from compactifying 10 dimensional heterotic string theory on a 6 dimensional torus.It is therefore necessary to examine this theory whether it agrees with the astrophysical observations.Quasi periodic oscillation, observed in the power spectrum of few black holes can be our tool.Kerr-Sen black hole is the solution of EMDA gravity which represents stationary,axisymmetric,charged ,rotating black holes.There are several models those try to explain the QPOs observed from black hole like GRO J1655-40,XTE J1550-564,GRS 1915+105,H 143+322,Sgr A*.We have analysed these models in the background of Kerr-Sen spacetime and tried to see the effectiveness of EMDA gravity by constraining the dilaton charge which is indispensable part of Kerr-Sen spacetime.