Late-times asymptotic equation of state for a class of nonlocal theories of gravity

Leonardo Giani; Oliver F. Piattella

doi:10.1103/physrevd.100.123508

Late-times asymptotic equation of state for a class of nonlocal theories of gravity

Physical Review D ◽

10.1103/physrevd.100.123508 ◽

2019 ◽

Vol 100 (12) ◽

Author(s):

Leonardo Giani ◽

Oliver F. Piattella

Keyword(s):

Equation Of State ◽

Asymptotic Equation ◽

Theories Of Gravity

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Concept of Gravito-Rotational Acceleration and its Consequences for Compact Stellar Objects

10.20944/preprints202104.0163.v1 ◽

2021 ◽

Author(s):

Mohamed Hassani

Keyword(s):

Magnetic Field ◽

Neutron Star ◽

Equation Of State ◽

Orbital Motion ◽

Rotational Acceleration ◽

Material Body ◽

Stellar Objects ◽

Gravitational Action ◽

Theories Of Gravity ◽

Previous Series

In a previous series of papers relating to the Combined Gravitational Action (CGA), we have exclusively studied orbital motion without spin. In the present paper, we apply CGA to any self-rotating material body, i.e., an axially spinning massive object, which itself may be locally seen as a gravito-rotational source because it is capable of generating the gravito-rotational acceleration, which seems to be unknown to previously existing theories of gravity. The consequences of such an acceleration are very interesting, particularly for Compact Stellar Objects. Independently of the equation of state, it is found that the critical and maximum internal magnetic field strength of a stable neutron star cannot exceed the value of 3x1018G.

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Neutron stars in Palatini $$R+\alpha R^2$$ and $$R+\alpha R^2+\beta Q$$ theories

The European Physical Journal C ◽

10.1140/epjc/s10052-021-09662-z ◽

2021 ◽

Vol 81 (10) ◽

Author(s):

Georg Herzog ◽

Hèlios Sanchis-Alepuz

Keyword(s):

General Relativity ◽

Equation Of State ◽

Neutron Stars ◽

Equations Of State ◽

Stellar Structure ◽

Modified Theories Of Gravity ◽

State Uncertainty ◽

Structure Equations ◽

Theories Of Gravity

AbstractWe study solutions of the stellar structure equations for spherically symmetric objects in modified theories of gravity, where the Einstein-Hilbert Lagrangian is replaced by $$f(R)=R+\alpha R^2$$ f ( R ) = R + α R 2 and $$f(R,Q)=R+\alpha R^2+\beta Q$$ f ( R , Q ) = R + α R 2 + β Q , with R being the Ricci scalar curvature, $$Q=R_{\mu \nu }R^{\mu \nu }$$ Q = R μ ν R μ ν and $$R_{\mu \nu }$$ R μ ν the Ricci tensor. We work in the Palatini formalism, where the metric and the connection are assumed to be independent dynamical variables. We focus on stellar solutions in the mass-radius region associated to neutron stars. We illustrate the potential impact of the $$R^2$$ R 2 and Q terms by studying a range of viable values of $$\alpha $$ α and $$\beta $$ β . Similarly, we use different equations of state (SLy, FPS, HS(DD2) and HS(TMA)) as a simple way to account for the equation of state uncertainty. Our results show that for certain combinations of the $$\alpha $$ α and $$\beta $$ β parameters and equation of state, the effect of modifications of general relativity on the properties of stars is sizeable. Therefore, with increasing accuracy in the determination of the equation of state for neutron stars, astrophysical observations may serve as discriminators of modifications of General Relativity.

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