Gravastars in f(T, τ) gravity

We propose a stellar model under the f(T, tau) gravity following Mazur-Mottola's conjecture(1,2) known as gravastar which is generally believed as a viable alternative to black hole. The gravastar consists of three regions, viz., (I) interior region, (II) intermediate shell region, and (III) exterior region. The pressure within the interior core region is assumed to be equal to the constant negative matter-energy density which provides a constant repulsive force over the thin shell region. The shell is assumed to be made up of fluid of ultrarelativistic plasma and following the Zel'dovich's conjecture of stiff fluid(3) it is also assumed that the pressure which is directly proportional to the matter-energy density according to Zel'dovich's conjecture, does cancel the repulsive force exerted by the interior region. The exterior region is completely vacuum and it can be described by the Schwarzschild solution. Under all these specifications, we find out a set of exact and singularity-free solutions of the gravastar presenting several physically valid features within the framework of alternative gravity, namely f(T, tau) gravity,(4) where the part of the gravitational Lagrangian in the corresponding action is taken as an arbitrary function of torsion scalar T and the trace of the energy-momentum tensor tau.