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arXiv · 1810.01047

Phenomenology in type-I minimally modified gravity

Katsuki Aoki·Antonio De Felice·Chunshan Lin·Shinji Mukohyama·Michele Oliosi
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Abstract

We study cosmology in a class of minimally modified gravity (MMG) with two local gravitational degrees of freedom. We classify modified gravity theories into type-I and type-II: theories of type-I have an Einstein frame and can be recast by change of variables as general relativity (GR) with a non-minimal matter coupling, while theories of type-II have no Einstein frame. Considering a canonical transformation of the lapse, the 3-dimensional induced metric and their conjugate momenta we generate type-I MMG. We then show that phenomenological deviations from GR, such as the speed of gravitational waves $c_T$ and the effective gravitational constant for scalar perturbations $G_{\rm eff}$, are characterized by two functions of an auxiliary variable. We study the phenomenology of several models all having $c_T=1$. We obtain a scenario with $c_T=1$ in which the effective equation-of-state parameter of dark energy is different from $-1$ even though the cosmic acceleration is caused by a bare cosmological constant, and we find that it is possible to reconstruct the theory on choosing a selected time-evolution for the effective dark energy component.

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Katsuki Aoki, Antonio De Felice, Chunshan Lin, Shinji Mukohyama, Michele Oliosi. 2019-01-04. Phenomenology in type-I minimally modified gravity. https://doi.org/10.1088/1475-7516%2F2019%2F01%2F017

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