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Astrophysical and local constraints on string theory: Runaway dilaton models

C. J. A. P. Martins, L. Vacher

Abstract
One of the clear predictions of string theory is the presence of a dynamical scalar partner of the spin-2 graviton, known as the dilaton. This will violate the Einstein equivalence principle, leading to a plethora of possibly observable consequences which in a cosmological context include dynamical dark energy and spacetime variations of nature’s fundamental constants. The runaway dilaton scenario of Damour, Piazza, and Veneziano is a particularly interesting class of string theory inspired models which can in principle reconcile a massless dilaton with experimental data. Here we use the latest background cosmology observations, astrophysical and laboratory tests of the stability of the fine-structure constant, and local tests of the weak equivalence principle to provide updated constraints on this scenario, under various simplifying assumptions. Overall we find consistency with the standard ΛCDM paradigm. We improve the existing constraints on the coupling of the dilaton to baryonic matter by a factor of 6 and to the dark sector by a factor of 2. At the one-sigma level the current data already exclude dark sector couplings of order unity, which would be their natural value.

Keywords
particles, fields, gravitation, cosmology, dark energy, string phenomenology

Physical Review D
Volume 100, Issue 12
2019 December

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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