Neutron stars as laboratories for gravity physics

Abstract

We study the structure of neutron stars in R + αR 2 gravity model with perturbative method. We obtain mass-radius relations for four representative equations of state (EoS). We find that, for |α| ∼ 10 9 cm 2 , the results differ substantially from the results of general relativity. The effects of modified gravity are seen as mimicking a stiff or soft EoS for neutron stars depending upon whether α is negative or positive, respectively. Some of the soft EoS that are excluded within the framework of general relativity can be reconciled for certain values of α of this order with the 2 solar mass neutron star recently observed. Indeed, if the EoS is ever established to be soft, modified gravity of the sort studied here may be required to explain neutron star masses as large as 2 M . The associated length scale √ α ∼ 10 5 cm is of the order of the the typical radius of neutron stars implying that this is the smallest value we could find by using neutron stars as a probe. We thus conclude that the true value of α is most likely much smaller than 10 9 cm 2 .

Neutron Stars with realistic EoS in f(R) theories of gravity

“…For the polytropic EoS one can choose the boundary conditions such that we can match with Schwarzschild even if α < 0, which is obviously excluded because of the ghost condition [35]. Our approach will also be pragmatic in a sense such that we find some stable solutions with α < 0, as also considered earlier by some authors [8,9,36,37]. In the following paragraphs, we discuss the numerical analysis for both the categories of EoS viz: Nuclear and Strange discussed above.…”

A perturbative approach to neutron stars in $$f(T, \mathcal {T})$$ f ( T , T ) -gravity

“…These also make up the matter functions which, along with the metric functions, A(r ) and B(r ), are also taken to be independent of time [22]. Thus the system is taken to be in equilibrium [5,28]. The equation of conservation of energy is given by…”

“…where ρ(r ) χ and p(r ) χ are the energy density and pressure of the fluid, respectively [28]. These also make up the matter functions which, along with the metric functions, A(r ) and B(r ), are also taken to be independent of time [22].…”

Scalar tensor teleparallel dark gravity via Noether symmetry

“…Lately, f (T ) theory attracted much attention in the literature, and we refer to e.g. [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] for some relevant works.…”