Journal
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
Volume -, Issue 10, Pages -Publisher
IOP Publishing Ltd
DOI: 10.1088/1475-7516/2021/10/085
Keywords
cosmology of theories beyond the SM; dark energy theory
Funding
- U.K. Science and Technology Facilities Council [ST/M503836/1]
- Science and Technology Facilities Council [ST/T000473/1]
- STFC [ST/M503836/1, ST/T000473/1] Funding Source: UKRI
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The study explores a disformal coupling between Standard Model matter and a cubic Galileon scalar sector, which evades strict constraints from the integrated Sachs-Wolfe effect. Despite the presence of a cosmological 'screening-like' phenomenon, the disformal coupling is too weak to be constrained by recent events such as GW170817 or by the dispersion of electromagnetic radiation at different wavelengths.
We consider a disformal coupling between Standard Model matter and a cubic Galileon scalar sector, assumed to be a relict of some other physics that solves the cosmological constant problem rather than a solution in its own right. This allows the energy density carried by the Galileon scalar to be sufficiently small that it evades stringent constraints from the integrated Sachs-Wolfe effect, which otherwise rules out the cubic Galileon theory. Although the model with disformal coupling does not exhibit Vainshtein screening, we show there is a cosmological 'screening-like' phenomenon in which the energy density carried by the Galileon scalar is suppressed during matter domination when the quadratic and cubic Galileon operators are both relevant. We obtain the explicit 3+1 form of Maxwell's equations in the presence of the disformal coupling, and the wave equations that govern electromagnetic waves. The disformal coupling is known to generate a small mass that modifies their velocity of propagation. We use the WKB approximation to study electromagnetic waves in this theory and show that, despite remarkable recent constraints from the LIGO/Virgo observatories that restrict the difference in propagation velocity between electromagnetic and gravitational radiation to roughly 1 part in 10(15), the disformal coupling is too weak to be constrained by events such as GW170817 or by the dispersion of electromagnetic radiation at different wavelengths.
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