Modified gravity with logarithmic curvature corrections and the structure of relativistic stars

Odintsov

Cruz-Dombriz

2017

Class. Quantum Grav.

165

104

The realistic models of relativistic stars in f (R) = R + αR 2 gravity In the context of f (R) = R + αR 2 gravity, we study the existence of neutron and quark stars for various α with no intermediate approximation in the system of equations. Analysis shows that for positive α the scalar curvature does not drop to zero at the star surface (as in General Relativity) but exponentially decreases with distance. Also the stellar mass bounded by star surface decreases when the value α increases. Nonetheless distant observers would observe a gravitational mass due to appearance of a so-called gravitational sphere around the star. The non-zero curvature contribution to the gravitational mass eventually is shown to compensate the stellar mass decrease for growing α's. We perform our analysis for several equations of state including purely hadronic configurations as well as hyperons and quark stars. In all cases, we assess that the relation between the parameter α and the gravitational mass weakly depends upon the chosen equation of state. Another interesting feature is the increase of the star radius in comparison with General Relativity for stars with masses close to maximal, whereas for intermediate masses 1.4 − 1.6M⊙ the radius of star depends upon α very weakly. Also the decrease in the mass bounded by star surface may cause the surface redshift to decrease in R 2 -gravity when compared to Einsteinian predictions. This effect is shown to hardly depend upon the observed gravitational mass. Finally, for negative values of α our analysis shows that outside the star the scalar curvature has damped oscillations but the contribution of the gravitational sphere into the gravitational mass increases indefinitely with radial distance putting into question the very existence of such relativistic stars.

Section: And References Therein)mentioning

confidence: 99%

The realistic models of relativistic stars in f ( R ) = R + αR ² gravity

Odintsov

Cruz-Dombriz

2017

Class. Quantum Grav.

165

104

“…[16][17][18] For a perturbative solution, the density, pressure, mass and curvature can be expanded as…”

Section: F (R) = R + αH(r) αH(r) << Rmentioning

confidence: 99%

Neutron and quark stars in f(R) gravity

Int. J. Mod. Phys. Conf. Ser.

2016

The realistic compact star models are considered in f (R) gravity. The main result is that simple modified gravity can be consistent with current observational mass limit of neutron stars, with current data on their masses and radii; also, it simplifies solution of the hyperon problem. The effect of strong magnetic field in R 2 -gravity is also investigated. The existence of more compact (in comparison with General Relativity) stars with large magnetic fields in central regions is possible. In fact the second branch of stability appears.

“…(7), (8), and (9) can be solved numerically for given EOS. In order to get solution, one can use perturbative approach (see for details [57][58][59][60]). In the framework of perturbative approach, terms containing h(R) are assumed to be of first order in the small parameter α, so all such terms should be evaluated at O(α) order.…”

Section: Modified Tov Equations In F (R) Gravitymentioning

confidence: 99%

Magnetic neutron stars in f(R) gravity

Capozziello

Odintsov

2014

Astrophys Space Sci

Neutron stars with strong magnetic fields are considered in the framework of f (R) gravity. In order to describe dense matter in magnetic field, the model with baryon octet interacting through σρω-fields is used. The hyperonization process results in softening the equation of state (EoS) and in decreasing the maximal mass. We investigate the effect of strong magnetic field in models involving quadratic and cubic corrections in the Ricci scalar R to the Hilbert-Einstein action. For large fields, the Mass-Radius relation differs considerably from that of General Relativity only for stars with masses close to the maximal one. Another interesting feature is the possible existence of more compact stable stars with extremely large magnetic fields (∼ 6 × 10 18 G instead of ∼ 4 × 10 18G as in General Relativity) in the central regions of the stars. Due to cubic terms, a significant increasing of the maximal mass is possible.