Modified Gravity and the CMB

Abstract

We consider the effect of modified gravity on the peak structure of the Cosmic Microwave Background (CMB) spectrum. We focus on simple models of modified gravity mediated by a massive scalar field coupled to both baryons and cold dark matter. This captures the features of chameleon, symmetron, dilaton and $f(R)$ models. We find that the CMB peaks can be affected in three independent ways provided the Compton radius of the massive scalar is not far-off the sound horizon at last scattering. When the coupling of the massive scalar to Cold Dark Matter (CDM) is large, the anomalous growth of the CDM perturbation inside the Compton radius induces a change in the peak amplitudes. When the coupling to baryons is moderately large, the speed of sound is modified and the peaks shifted to higher momenta. Finally when both couplings are non-vanishing, a new contribution proportional to the Newton potential appears in the Sachs-Wolfe temperature and increases the peak amplitudes. We also show how, given any temporal evolution of the scalar field mass, one can engineer a corresponding modified gravity model of the chameleon type. This opens up the possibility of having independent constraints on modified gravity from the CMB peaks and large scale structures at low redshifts.

15 pages, 10 figures, published version

References in corpus (5)

• Evading Equivalence Principle Violations, Cosmological and other Experimental Constraints in Scalar Field Theories with a Strong Coupling to Matter
• Environmental Dependence of Masses and Coupling Constants
• Strongly Coupled Chameleon Fields: New Horizons in Scalar Field Theory
• Modified gravity a la Galileon: Late time cosmic acceleration and observational constraints
• Adiabatic instability in coupled dark energy-dark matter models

Cited by in corpus (8)

• Tests of Chameleon Gravity
• A Unified Description of Screened Modified Gravity
• The minimally extended Varying Speed of Light (meVSL)
• Modified Gravity and the Radiation Dominated Epoch
• Early Modified Gravity: Implications for Cosmology
• How CMB and large-scale structure constrain chameleon interacting dark energy
• Phi Zeta Delta: Growth of Perturbations in Parameterized Gravity for an Einstein-de Sitter Universe
• Quantum corrections to symmetron fifth-force profiles