skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Dark matter relics and the expansion rate in scalar-tensor theories

Abstract

We study the impact of a modified expansion rate on the dark matter relic abundance in a class of scalar-tensor theories. The scalar-tensor theories we consider are motivated from string theory constructions, which have conformal as well as disformally coupled matter to the scalar. We investigate the effects of such a conformal coupling to the dark matter relic abundance for a wide range of initial conditions, masses and cross-sections. We find that exploiting all possible initial conditions, the annihilation cross-section required to satisfy the dark matter content can differ from the thermal average cross-section in the standard case. We also study the expansion rate in the disformal case and find that physically relevant solutions require a nontrivial relation between the conformal and disformal functions. We study the effects of the disformal coupling in an explicit example where the disformal function is quadratic.

Authors:
;  [1];  [2]
  1. Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843 (United States)
  2. Department of Physics, Swansea University, Singleton Park, Swansea, SA2 8PP (United Kingdom)
Publication Date:
OSTI Identifier:
22676152
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2017; Journal Issue: 06; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ABUNDANCE; ANNIHILATION; COMPUTERIZED SIMULATION; COUPLING; CROSS SECTIONS; EXPANSION; FIELD THEORIES; MASS; MATHEMATICAL SOLUTIONS; NONLUMINOUS MATTER; STRING THEORY

Citation Formats

Dutta, Bhaskar, Jimenez, Esteban, and Zavala, Ivonne, E-mail: dutta@physics.tamu.edu, E-mail: este1985@physics.tamu.edu, E-mail: e.i.zavalacarrasco@swansea.ac.uk. Dark matter relics and the expansion rate in scalar-tensor theories. United States: N. p., 2017. Web. doi:10.1088/1475-7516/2017/06/032.
Dutta, Bhaskar, Jimenez, Esteban, & Zavala, Ivonne, E-mail: dutta@physics.tamu.edu, E-mail: este1985@physics.tamu.edu, E-mail: e.i.zavalacarrasco@swansea.ac.uk. Dark matter relics and the expansion rate in scalar-tensor theories. United States. doi:10.1088/1475-7516/2017/06/032.
Dutta, Bhaskar, Jimenez, Esteban, and Zavala, Ivonne, E-mail: dutta@physics.tamu.edu, E-mail: este1985@physics.tamu.edu, E-mail: e.i.zavalacarrasco@swansea.ac.uk. Thu . "Dark matter relics and the expansion rate in scalar-tensor theories". United States. doi:10.1088/1475-7516/2017/06/032.
@article{osti_22676152,
title = {Dark matter relics and the expansion rate in scalar-tensor theories},
author = {Dutta, Bhaskar and Jimenez, Esteban and Zavala, Ivonne, E-mail: dutta@physics.tamu.edu, E-mail: este1985@physics.tamu.edu, E-mail: e.i.zavalacarrasco@swansea.ac.uk},
abstractNote = {We study the impact of a modified expansion rate on the dark matter relic abundance in a class of scalar-tensor theories. The scalar-tensor theories we consider are motivated from string theory constructions, which have conformal as well as disformally coupled matter to the scalar. We investigate the effects of such a conformal coupling to the dark matter relic abundance for a wide range of initial conditions, masses and cross-sections. We find that exploiting all possible initial conditions, the annihilation cross-section required to satisfy the dark matter content can differ from the thermal average cross-section in the standard case. We also study the expansion rate in the disformal case and find that physically relevant solutions require a nontrivial relation between the conformal and disformal functions. We study the effects of the disformal coupling in an explicit example where the disformal function is quadratic.},
doi = {10.1088/1475-7516/2017/06/032},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 06,
volume = 2017,
place = {United States},
year = {Thu Jun 01 00:00:00 EDT 2017},
month = {Thu Jun 01 00:00:00 EDT 2017}
}
  • Scalar-tensor theories of gravity provide a consistent framework to accommodate an ultralight quintessence scalar field. While the equivalence principle is respected by construction, deviations from general relativity and standard cosmology may show up at nucleosynthesis, cosmic microwave background, and solar system tests of gravity. After imposing all the bounds coming from these observations, we consider the expansion rate of the Universe at weakly interacting massive particle decoupling, showing that it can lead to an enhancement of the dark matter relic density up to few orders of magnitude with respect to the standard case. This effect can have an impact onmore » supersymmetric candidates for dark matter.« less
  • We find exact power-law solutions for scalar-tensor theories and clarify the conditions under which they can account for an accelerated expansion of the Universe. These solutions have the property that the signs of both the Hubble rate and the deceleration parameter in the Jordan frame may be different from the signs of their Einstein-frame counterparts. For special parameter combinations we identify these solutions with asymptotic attractors that have been obtained in the literature through dynamical-system analysis. We establish an effective general-relativistic description for which the geometrical equivalent of dark energy is associated with a time dependent equation of state. Themore » present value of the latter is consistent with the observed cosmological 'constant'. We demonstrate that this type of power-law solution for accelerated expansion cannot be realized in f(R) theories.« less
  • In the Horndeski's most general scalar-tensor theories with second-order field equations, we derive the conditions for the avoidance of ghosts and Laplacian instabilities associated with scalar, tensor, and vector perturbations in the presence of two perfect fluids on the flat Friedmann-Lema├«tre-Robertson-Walker (FLRW) background. Our general results are useful for the construction of theoretically consistent models of dark energy. We apply our formulas to extended Galileon models in which a tracker solution with an equation of state smaller than -1 is present. We clarify the allowed parameter space in which the ghosts and Laplacian instabilities are absent and we numerically confirmmore » that such models are indeed cosmologically viable.« less
  • Cited by 3
  • We study models of late-time cosmic acceleration in terms of scalar-tensor theories generalized to include a certain class of nonlinear derivative interaction of the scalar field. The nonlinear effect suppresses the scalar-mediated force at short distances to pass solar-system tests of gravity. It is found that the expansion history until today is almost indistinguishable from that of the {Lambda}CDM model or some (phantom) dark energy models, but the fate of the universe depends clearly on the model parameter. The growth index of matter density perturbations is computed to show that its past asymptotic value is given by 9/16, while themore » value today is as small as 0.4.« less