# Healthy imperfect dark matter from effective theory of mimetic cosmological perturbations

## Abstract

We study the stability of a recently proposed model of scalar-field matter called mimetic dark matter or imperfect dark matter. It has been known that mimetic matter with higher derivative terms suffers from gradient instabilities in scalar perturbations. To seek for an instability-free extension of imperfect dark matter, we develop an effective theory of cosmological perturbations subject to the constraint on the scalar field's kinetic term. This is done by using the unifying framework of general scalar-tensor theories based on the ADM formalism. We demonstrate that it is indeed possible to construct a model of imperfect dark matter which is free from ghost and gradient instabilities. As a side remark, we also show that mimetic F (R) theory is plagued with the Ostrogradsky instability.

- Authors:

- Department of Physics, Rikkyo University, Toshima, Tokyo 171-8501 (Japan)

- Publication Date:

- OSTI Identifier:
- 22676120

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2017; Journal Issue: 07; Other Information: Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMPUTERIZED SIMULATION; COSMOLOGICAL MODELS; DISTURBANCES; INSTABILITY; NONLUMINOUS MATTER; PERTURBATION THEORY; SCALAR FIELDS; STABILITY

### Citation Formats

```
Hirano, Shin'ichi, Nishi, Sakine, and Kobayashi, Tsutomu, E-mail: s.hirano@rikkyo.ac.jp, E-mail: sakine@rikkyo.ac.jp, E-mail: tsutomu@rikkyo.ac.jp.
```*Healthy imperfect dark matter from effective theory of mimetic cosmological perturbations*. United States: N. p., 2017.
Web. doi:10.1088/1475-7516/2017/07/009.

```
Hirano, Shin'ichi, Nishi, Sakine, & Kobayashi, Tsutomu, E-mail: s.hirano@rikkyo.ac.jp, E-mail: sakine@rikkyo.ac.jp, E-mail: tsutomu@rikkyo.ac.jp.
```*Healthy imperfect dark matter from effective theory of mimetic cosmological perturbations*. United States. doi:10.1088/1475-7516/2017/07/009.

```
Hirano, Shin'ichi, Nishi, Sakine, and Kobayashi, Tsutomu, E-mail: s.hirano@rikkyo.ac.jp, E-mail: sakine@rikkyo.ac.jp, E-mail: tsutomu@rikkyo.ac.jp. Sat .
"Healthy imperfect dark matter from effective theory of mimetic cosmological perturbations". United States.
doi:10.1088/1475-7516/2017/07/009.
```

```
@article{osti_22676120,
```

title = {Healthy imperfect dark matter from effective theory of mimetic cosmological perturbations},

author = {Hirano, Shin'ichi and Nishi, Sakine and Kobayashi, Tsutomu, E-mail: s.hirano@rikkyo.ac.jp, E-mail: sakine@rikkyo.ac.jp, E-mail: tsutomu@rikkyo.ac.jp},

abstractNote = {We study the stability of a recently proposed model of scalar-field matter called mimetic dark matter or imperfect dark matter. It has been known that mimetic matter with higher derivative terms suffers from gradient instabilities in scalar perturbations. To seek for an instability-free extension of imperfect dark matter, we develop an effective theory of cosmological perturbations subject to the constraint on the scalar field's kinetic term. This is done by using the unifying framework of general scalar-tensor theories based on the ADM formalism. We demonstrate that it is indeed possible to construct a model of imperfect dark matter which is free from ghost and gradient instabilities. As a side remark, we also show that mimetic F (R) theory is plagued with the Ostrogradsky instability.},

doi = {10.1088/1475-7516/2017/07/009},

journal = {Journal of Cosmology and Astroparticle Physics},

number = 07,

volume = 2017,

place = {United States},

year = {Sat Jul 01 00:00:00 EDT 2017},

month = {Sat Jul 01 00:00:00 EDT 2017}

}