Astrophysical and local constraints on string theory: Runaway dilaton models

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 is 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, and we improve the existing constraints on the coupling of the dilaton to baryonic matter by a factor of six, and to the dark sector by a factor of two. At the one sigma level the current data already excludes dark sector couplings of order unity, which would be their natural value.

ESPRESSO at VLT

“…pepe_final damental physics and theoretical cosmology. While the impact of confirmed spacetime variations is self-evident, more stringent upper bounds on these variations are also important and will lead to improved constraints on the parameter space of various theoretical paradigms that predict their variability (Martins 2017;Alves et al 2017;Martins & Vacher 2019).…”

ESPRESSO@VLT -- On-sky performance and first results

“…The proposed observations, a first version of which is summarized in Leite et al (2016), will test the universality of physical laws in an unexplored regime, which directly impacts fundamental physics and theoretical cosmology. While the impact of confirmed spacetime variations is self-evident, more stringent upper bounds on these variations are also important and will lead to improved constraints on the parameter space of various theoretical paradigms that predict their variability (Martins 2017;Alves et al 2017;Martins & Vacher 2019).…”

Varying-$α$ in scalar-tensor theory: Implications in light of the supernova absolute magnitude tension and forecast from GW standard sirens

“…In this work we will focus on the so-called Runaway Dilaton Model, a string theory-inspired model capable of delineating a time-variation of α close to the present day [49][50][51][52]70]. Such a model is a particular case of scalar-tensor theories of gravity inspired by a multiplicative coupling between an extra scalar-field and the usual matter Lagrangian [52].…”

“…In such a framework the entire electromagnetic sector of the theory is also affected, leading to α variation. In this line, a particular class of string theory inspired-models that produce a temporal variation of alpha is the so-called runaway dilaton model [49][50][51][52] (string theories at low energy predict the existence of dilaton, a scalar partner of Spin-2 graviton). In order to check a possible temporal variation of the finestructure constant in runaway dilaton scenarios, some methods using astronomical data have been developed in recent years [52][53][54][55][56][57][58].…”