Neutron Stars In F(T) Gravity

We investigate the nonrotating neutron stars in f(T)gravity in this thesis,where T is the torsion scalar in the teleparallel formalism of gravity.we use four realistic equations of state and choose a simple f(T)=T+?T~2model to study the effect of f(T)gravity on the realistic model of neutron star numerically.We study the energy density and pressure distribution of neutron stars,the effective density and pressure distribution in the effective f(T)fluid,and the influence of model parameters on the relationship between the mass and radius of neutron stars.When?>0,we find that f(T)gravity exerts a stronger gravitation effect on the neutron stellar material,resutling in a smaller neutron stars mass in comparison to general relativity.In addition,when?>0,the central density of the neutron stars has an upper limit.If the central density of the neutron stars is beyond the upper limit,the effective f(T)fluid would have a steplike phase transition on the effective density and pressure distribution in the effective f(T)fluid,which will cause the numerical system to collapse.For?<0,the f(T)modification provides additional support for neutron stars to gain more mass.We get the relations between mass and radius of the realistic models of neutron stars.Also we need to consider the observed massive pulsars PSR J0030+0451,PSR J0740+6620,and PSR J2215+5135,as well as the gravitational wave events GW170817 and GW190814 to obtain the joint constraints.For BSk19 equation of state,the neutron star model in f(T)gravity is compat-ible with all the mentioned data when??3.5G~2M~2?/c~4.For BSk20,BSk21 and SLy equations of state,the observed data expect model parameter?to be negative.This data group can be excluded if the dense matter in gravitational wave GW190814 is not classified into a neutron star.For BSk20and BSk21 equations of state,the constranints of f(T)gravity model parameter?can be broadened to??0.4G~2M~2?/c~4and??1.9G~2M~2?/c~4,respectively.