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Cosmic stringlike objects in hybrid metric-Palatini gravity

T. Harko, F. S. N. Lobo, H. M. R. Silva

Abstract
We consider static and cylindrically symmetric interior string-type solutions in the scalar-tensor representation of the hybrid metric-Palatini modified theory of gravity. As a first step in our study, we obtain the gravitational field equations and further simplify the analysis by imposing Lorentz invariance along the t and z axes, which reduces the number of unknown metric tensor components to a single function W2(r). In this case, the general solution of the field equations can be obtained, for an arbitrary form of the scalar field potential, in an exact closed parametric form, with the scalar field ϕ taken as a parameter. We consider in detail several exact solutions of the field equations, corresponding to a null and constant potential, and to a power-law potential of the form V(ϕ)=V0ϕ3/4, in which the behaviors of the scalar field, of the metric tensor components, and of the string tension can be described in a simple mathematical form. We also investigate the string models with exponential and Higgs-type scalar field potentials by using numerical methods. In this way, we obtain a large class of novel stable stringlike solutions in the context of hybrid metric-Palatini gravity, in which the basic parameters, such as the scalar field, metric tensor components, and string tension, depend essentially on the initial values of the scalar field, and of its derivative, on the r=0 circular axis.

Keywords
General Relativity and Quantum Cosmology; Astrophysics - High Energy Astrophysical Phenomena; High Energy Physics - Theory

Physical Review D
Volume 101, Issue 1240, Page 15
2020 June

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia