### 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
_{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.

Original language | English |
---|---|

Article number | 017 |

Journal | Journal of Cosmology and Astroparticle Physics |

Volume | 2019 |

Issue number | 1 |

DOIs | |

Publication status | Published - 2019 Jan 7 |

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### ASJC Scopus subject areas

- Astronomy and Astrophysics

### Cite this

*Journal of Cosmology and Astroparticle Physics*,

*2019*(1), [017]. https://doi.org/10.1088/1475-7516/2019/01/017

**Phenomenology in type-I minimally modified gravity.** / Aoki, Katsuki; Felice, Antonio De; Lin, Chunshan; Mukohyama, Shinji; Oliosi, Michele.

Research output: Contribution to journal › Article

*Journal of Cosmology and Astroparticle Physics*, vol. 2019, no. 1, 017. https://doi.org/10.1088/1475-7516/2019/01/017

}

TY - JOUR

T1 - Phenomenology in type-I minimally modified gravity

AU - Aoki, Katsuki

AU - Felice, Antonio De

AU - Lin, Chunshan

AU - Mukohyama, Shinji

AU - Oliosi, Michele

PY - 2019/1/7

Y1 - 2019/1/7

N2 - 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 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.

AB - 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 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.

UR - http://www.scopus.com/inward/record.url?scp=85062290865&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85062290865&partnerID=8YFLogxK

U2 - 10.1088/1475-7516/2019/01/017

DO - 10.1088/1475-7516/2019/01/017

M3 - Article

VL - 2019

JO - Journal of Cosmology and Astroparticle Physics

JF - Journal of Cosmology and Astroparticle Physics

SN - 1475-7516

IS - 1

M1 - 017

ER -