Abstract
Screening mechanisms are often deployed by dark energy models to conceal the effects of their new degrees of freedom from the scrutiny of terrestrial and solar system experiments. However, the extreme properties of nuclear matter may lead to a partial failure of screening mechanisms inside the most massive neutron stars observed in nature, opening up the possibility of probing these theories with neutron star observations. In this work, we explore equilibrium and stability properties of neutron stars in two variants of the symmetron model. We show that around sufficiently compact neutron stars, the symmetron is amplified with respect to its background (cosmological) value by several orders of magnitude, and that the properties of such unscreened stars are sensitive to corrections to the leading linear coupling between the symmetron and matter.
Highlights
Due to their high compactness, neutron stars (NSs) offer a unique environment to probe the strong-field regime of Einstein’s general relativity (GR) and constrain possible modifications
Tensor theories of this kind offer a suitable framework for cosmology [10–12], since a judicious choice of V (φ) and A(φ) may lead to a model behaving as dark energy [13,14] at cosmological scales, but still reproducing the successes of general relativity in explaining solar system and other observational data [15,16]
This is accomplished through the suppression, or screening, of scalar field effects at solar system scales, which exploits the fact that the scalar field dynamics is governed by a density-dependent effective potential, Veff (φ) ≡ V (φ) − T ln A(φ), where T is the trace of the energy–momentum tensor of matter fields
Summary
Due to their high compactness, neutron stars (NSs) offer a unique environment to probe the strong-field regime of Einstein’s general relativity (GR) and constrain possible modifications Their core is characterized by extreme densities and pressures, which may lead to additional, matter-induced phenomenology in alternative theories of gravity, as compared, e.g., to the case of black holes. The field becomes massive and short-ranged in highdensity environments (such as the solar system), but light and long-ranged at cosmological scales, possibly behaving as dark energy Another example of a screening mechanism, which is the focus of the present work, occurs in the symmetron model [19,20]
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