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Neutron stars in Scalar-Tensor-Vector Gravity

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Abstract

Scalar-Tensor-Vector Gravity (STVG), also referred as Modified Gravity (MOG), is an alternative theory of the gravitational interaction. Its weak field approximation has been successfully used to describe Solar System observations, galaxy rotation curves, dynamics of clusters of galaxies, and cosmological data, without the imposition of dark components. The theory was formulated by John Moffat in 2006. In this work, we derive matter-sourced solutions of STVG and construct neutron star models. We aim at exploring STVG predictions about stellar structure in the strong gravity regime. Specifically, we represent spacetime with a static, spherically symmetric manifold, and model the stellar matter content with a perfect fluid energy-momentum tensor. We then derive the modified Tolman–Oppenheimer–Volkoff equation in STVG and integrate it for different equations of state. We find that STVG allows heavier neutron stars than General Relativity (GR). Maximum masses depend on a normalized parameter that quantifies the deviation from GR. The theory exhibits unusual predictions for extreme values of this parameter. We conclude that STVG admits suitable spherically symmetric solutions with matter sources, relevant for stellar structure. Since recent determinations of neutron stars masses violate some GR predictions, STVG appears as a viable candidate for a new gravity theory.

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Notes

  1. Actually, there is discussion about these statements. For instance, Lasky argued that new generalizations of TeVeS, with equivalent solutions, may solve instability problems (see [16, 17]).

  2. Compared to Moffat’s original action at Ref. [11], we nullify the cosmological constant because its effects are negligible over stellar structure, we ignore the scalar field nature of \(\omega \) and set \(\omega =1/\sqrt{12}\), as suggested by Moffat [20, 21], and we set the potential \(W(\phi )=0\) as is usually stated (see Ref. [11]). Also, we propose a slight modification: we change the sign of vector field action \(S_{\phi }\) in order to find agreement with the analogous Einstein–Maxwell formalism.

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Authors and Affiliations

  1. Instituto Argentino de Radioastronomía CCT La Plata (CONICET), C.C.5 1894 Villa Elisa, Buenos Aires, Argentina

    Federico G. Lopez Armengol & Gustavo E. Romero

  2. Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, 1900, La Plata, Buenos Aires, Argentina

    Gustavo E. Romero

Authors
  1. Federico G. Lopez Armengol
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  2. Gustavo E. Romero
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Correspondence to Federico G. Lopez Armengol.

Additional information

This work was supported by Grants PICT 2012-00878 (Agencia Nacional de Promoción Científica y Tecnológica, Argentina) and AYA 2013-47447-C3-1-P (Ministro de Educación, Cultura y Deporte, España). We would like to thank Federico García and Santiago del Palacio for helpful comments.

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Lopez Armengol, F.G., Romero, G.E. Neutron stars in Scalar-Tensor-Vector Gravity. Gen Relativ Gravit 49, 27 (2017). https://doi.org/10.1007/s10714-017-2184-0

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