Hydrostatic equilibrium configurations of neutron stars in a non-minimal geometry-matter coupling theory of gravity

Abstract

In this work we analyze hydrostatic equilibrium configurations of neutron stars in a non-minimal geometrymatter coupling (GMC) theory of gravity. We begin with the derivation of the hydrostatic equilibrium equations for the f (R, L) gravity theory, where R and L are the Ricci scalar and Lagrangian of matter, respectively. We assume f (R, L) = R/2 + [1 + σ R]L, with σ constant. To describe matter inside neutron stars we assume a relativistic polytropic equation of state p = Kρ γ , with ρ being the energy density, K and γ = 5/3 being constants. We also consider the more realistic equation of state (EoS) known as SLy4, which is a Skyrme type one based on effective nuclear interaction. We show that in this theory it is possible to reach the mass of massive pulsars, such as PSR J2215 + 5135, for both equations of state. Also, results for mass-radius relation in GMC gravity are strongly dependent on the stiffness of the EoS.

Neutron stars in $f(\mathtt{R,L_m})$ gravity with realistic equations of state: joint-constrains with GW170817, massive pulsars, and the PSR J0030+0451 mass-radius from ${\it NICER}$ data

“…As one increases the σ parameter, i.e., increases the effects of the f (R, L m ) gravity, the maximum mass starts to increase as well. Remarkably, this EoS shows an enhancement in the mass for different values of σ for the same radius (see curves for σ = 0 and σ = 30), which is a similar behavior of the simple barotropic equation of state [38].…”

“…Here, we shall go further than Ref. [38], where the study of NS in f (R, L m ) gravity kicked off, and put a window to constrain parameters from the modified gravity perspective using realistic stellar models and realistic hadronic equations of state (EoS). The neutron star mass-radius obtained with these EoS are subject to a joint constrain from observed massive pulsars, the gravitational wave events GW170817, and the PSR J0030+0451 mass-radius from NASA's Neutron Star Interior Composition Explorer (NICER) data.…”

Massive white dwarfs in $$f(\mathtt {R,L_m})$$ gravity

“…Furthermore, one can note from (3), that the four-divergence of the energy-momentum tensor is conserved, which is a remarkable feature of the f (R, L m ) theory for stars with spherical symmetry. The four-divergence conservation of T μν is a consequence of our choice for the matter Lagrangian [50,51], L m = −p, which is consistent with the on-shell Lagrangian for relativistic perfect fluids [73]. Finally we mention that for L m = 0, i.e., the vacuum case in which we also have T μν = 0 and p = 0, the new Einstein equations reduce to G μν + Rg μν /3 = 0.…”

“…In the present work, we are continuing to investigate compact objects in f (R, L m ) gravity, which we have applied in previous works to neutron stars [50,51]. In those works, we showed that this theory can account for the enhancement of the maximum mass in neutron stars, in better agreement with the observational data from GW170817 and NICER as compared to General Relativity [51].…”

Anti-de Sitter neutron stars in the theory of gravity with nonminimal derivative coupling

“…Generally, neutron stars are compact objects with a mass M ∼ 1.4M ⊙ , a radius R ∼ 12 km, and a central density as high as 5 to 10 times the nuclear equilibrium density n 0 ≈ 0.16 fm −3 of neutrons and protons found in laboratory nuclei (ρ n ≈ 2.3−2.8 × 10 14 g/cm 3 ) [10,11,13]. 2 Neutron stars have been investigated in various modified theories of gravity including, in particular, f (R) gravity [14][15][16][17][18], f (R, T ) gravity [19][20][21][22][23],…”