Disformal transformations on the CMB

Abstract

In this work we study the role of disformal transformation on cosmological backgrounds and its relation to the speed of sound for tensor modes. A speed different from one for tensor modes can arise in several contexts, such as Galileons theories or massive gravity, nevertheless the speed is very constrained to be one by observations of gravitational wave emission. It has been shown that in inflation a disformal trans- formation allows to set the speed for tensor modes to one without making changes to the curvature power spectrum. Here we show that this invariance does not hold when considering the CMB anisotropy power spectrum. It turns out that the after doing the transformation there is an imprint on the acoustic peaks and the diffusion damping. This has interesting consequences; here we explore quartic galileon theories which allow a modified speed for tensor modes. For these theories the transformation can be used to constraint the parameter space in different regimes.

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Cited by in corpus (8)

• Cosmological Backgrounds of Gravitational Waves
• Black Hole Gravitational Waves in the Effective Field Theory of Gravity
• Primordial Gravitational Wave Signals in Modified Cosmologies
• Invertible disformal transformations with higher derivatives
• Generalized non-local $R^2$-like inflation
• Non-Gaussianity in multi-sound-speed disformally coupled inflation
• Disformal transformations as a change of units
• Constraints on a cubic Galileon disformally coupled to Standard Model matter