TY - JOUR

T1 - Neutron stars in the Starobinsky model

AU - Ganguly, Apratim

AU - GANNOUJI , RADOUANE

AU - Goswami, Rituparno

AU - Ray, Subharthi

PY - 2014/3/7

Y1 - 2014/3/7

N2 - We study the structure of neutron stars in the f(R)=R+αR2 theory of gravity (the Starobinsky model) in an exact and nonperturbative approach. In this model, apart from the standard general relativistic junction conditions, two extra conditions - namely, the continuity of the curvature scalar and its first derivative - need to be satisfied. For an exterior Schwarzschild solution, the curvature scalar and its derivative must be zero at the stellar surface. We show that for some equation of state (EoS) of matter, matching all conditions at the surface of the star is impossible. Hence the model brings two major fine-tuning problems: (i) only some particular classes of EoS are consistent with Schwarzschild at the surface, and (ii) given the EoS, only a very particular set of boundary conditions at the center of the star will satisfy the given boundary conditions at the surface. Hence we show that this model [and subsequently many other f(R) models where the uniqueness theorem is valid] is highly unnatural for the existence of compact astrophysical objects. This is because the EoS of a compact star should be completely determined by the physics of nuclear matter at high density and not the theory of gravity.

AB - We study the structure of neutron stars in the f(R)=R+αR2 theory of gravity (the Starobinsky model) in an exact and nonperturbative approach. In this model, apart from the standard general relativistic junction conditions, two extra conditions - namely, the continuity of the curvature scalar and its first derivative - need to be satisfied. For an exterior Schwarzschild solution, the curvature scalar and its derivative must be zero at the stellar surface. We show that for some equation of state (EoS) of matter, matching all conditions at the surface of the star is impossible. Hence the model brings two major fine-tuning problems: (i) only some particular classes of EoS are consistent with Schwarzschild at the surface, and (ii) given the EoS, only a very particular set of boundary conditions at the center of the star will satisfy the given boundary conditions at the surface. Hence we show that this model [and subsequently many other f(R) models where the uniqueness theorem is valid] is highly unnatural for the existence of compact astrophysical objects. This is because the EoS of a compact star should be completely determined by the physics of nuclear matter at high density and not the theory of gravity.

UR - http://www.scopus.com/inward/record.url?scp=84897011311&partnerID=8YFLogxK

U2 - 10.1103/PhysRevD.89.064019

DO - 10.1103/PhysRevD.89.064019

M3 - Article

AN - SCOPUS:84897011311

VL - 89

JO - Physical Review D - Particles, Fields, Gravitation and Cosmology

JF - Physical Review D - Particles, Fields, Gravitation and Cosmology

SN - 1550-7998

IS - 6

M1 - 064019

ER -