TY - JOUR

T1 - Neutron stars in f(R) gravity and scalar-tensor theories

AU - Kase, Ryotaro

AU - Tsujikawa, Shinji

N1 - Publisher Copyright:
© 2019 IOP Publishing Ltd and Sissa Medialab.

PY - 2019/9/26

Y1 - 2019/9/26

N2 - In f(R) gravity and Brans-Dicke theory with scalar potentials, we study the structure of neutron stars on a spherically symmetric and static background for two equations of state: SLy and FPS . In massless BD theory, the presence of a scalar coupling Q with matter works to change the star radius in comparison to General Relativity, while the maximum allowed mass of neutron stars is hardly modified for both SLy and FPS equations of state. In Brans-Dicke theory with the massive potential V(φ)=m2 φ2/2, where m2 is a positive constant, we show the difficulty of realizing neutron star solutions with a stable field profile due to the existence of an exponentially growing mode outside the star. As in f(R) gravity with the R2 term, this property is related to the requirement of extra boundary conditions of the field at the surface of star. For the self-coupling potential V(φ)=λ φ4/4, this problem can be circumvented by the fact that the second derivative V,φ φ=3λφ2 approaches 0 at spatial infinity. In this case, we numerically show the existence of neutron star solutions for both SLy and FPS equations of state and discuss how the mass-radius relation is modified as compared to General Relativity.

AB - In f(R) gravity and Brans-Dicke theory with scalar potentials, we study the structure of neutron stars on a spherically symmetric and static background for two equations of state: SLy and FPS . In massless BD theory, the presence of a scalar coupling Q with matter works to change the star radius in comparison to General Relativity, while the maximum allowed mass of neutron stars is hardly modified for both SLy and FPS equations of state. In Brans-Dicke theory with the massive potential V(φ)=m2 φ2/2, where m2 is a positive constant, we show the difficulty of realizing neutron star solutions with a stable field profile due to the existence of an exponentially growing mode outside the star. As in f(R) gravity with the R2 term, this property is related to the requirement of extra boundary conditions of the field at the surface of star. For the self-coupling potential V(φ)=λ φ4/4, this problem can be circumvented by the fact that the second derivative V,φ φ=3λφ2 approaches 0 at spatial infinity. In this case, we numerically show the existence of neutron star solutions for both SLy and FPS equations of state and discuss how the mass-radius relation is modified as compared to General Relativity.

KW - modified gravity

KW - neutron stars

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U2 - 10.1088/1475-7516/2019/09/054

DO - 10.1088/1475-7516/2019/09/054

M3 - Article

AN - SCOPUS:85075926639

VL - 2019

JO - Journal of Cosmology and Astroparticle Physics

JF - Journal of Cosmology and Astroparticle Physics

SN - 1475-7516

IS - 9

M1 - 054

ER -