# Bigravity from gradient expansion

## Abstract

We discuss how the ghost-free bigravity coupled with a single scalar field can be derived from a braneworld setup. We consider DGP two-brane model without radion stabilization. The bulk configuration is solved for given boundary metrics, and it is substituted back into the action to obtain the effective four-dimensional action. In order to obtain the ghost-free bigravity, we consider the gradient expansion in which the brane separation is supposed to be sufficiently small so that two boundary metrics are almost identical. The obtained effective theory is shown to be ghost free as expected, however, the interaction between two gravitons takes the Fierz-Pauli form at the leading order of the gradient expansion, even though we do not use the approximation of linear perturbation. We also find that the radion remains as a scalar field in the four-dimensional effective theory, but its coupling to the metrics is non-trivial.

- Authors:

- Yukawa Institute for Theoretical Physics, Kyoto University,606-8502, Kyoto (Japan)
- (Japan)

- Publication Date:

- Sponsoring Org.:
- SCOAP3, CERN, Geneva (Switzerland)

- OSTI Identifier:
- 22572072

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2016; Journal Issue: 05; Other Information: PUBLISHER-ID: JCAP05(2016)011; OAI: oai:repo.scoap3.org:15476; cc-by Article funded by SCOAP3. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 License. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.; Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACTION INTEGRAL; BRANES; COSMOLOGY; COUPLING; FOUR-DIMENSIONAL CALCULATIONS; GRAVITONS; METRICS; PARTICLE INTERACTIONS; QUANTUM FIELD THEORY

### Citation Formats

```
Yamashita, Yasuho, Tanaka, Takahiro, and Department of Physics, Kyoto University,606-8502, Kyoto.
```*Bigravity from gradient expansion*. United States: N. p., 2016.
Web. doi:10.1088/1475-7516/2016/05/011.

```
Yamashita, Yasuho, Tanaka, Takahiro, & Department of Physics, Kyoto University,606-8502, Kyoto.
```*Bigravity from gradient expansion*. United States. doi:10.1088/1475-7516/2016/05/011.

```
Yamashita, Yasuho, Tanaka, Takahiro, and Department of Physics, Kyoto University,606-8502, Kyoto. Wed .
"Bigravity from gradient expansion". United States.
doi:10.1088/1475-7516/2016/05/011.
```

```
@article{osti_22572072,
```

title = {Bigravity from gradient expansion},

author = {Yamashita, Yasuho and Tanaka, Takahiro and Department of Physics, Kyoto University,606-8502, Kyoto},

abstractNote = {We discuss how the ghost-free bigravity coupled with a single scalar field can be derived from a braneworld setup. We consider DGP two-brane model without radion stabilization. The bulk configuration is solved for given boundary metrics, and it is substituted back into the action to obtain the effective four-dimensional action. In order to obtain the ghost-free bigravity, we consider the gradient expansion in which the brane separation is supposed to be sufficiently small so that two boundary metrics are almost identical. The obtained effective theory is shown to be ghost free as expected, however, the interaction between two gravitons takes the Fierz-Pauli form at the leading order of the gradient expansion, even though we do not use the approximation of linear perturbation. We also find that the radion remains as a scalar field in the four-dimensional effective theory, but its coupling to the metrics is non-trivial.},

doi = {10.1088/1475-7516/2016/05/011},

journal = {Journal of Cosmology and Astroparticle Physics},

number = 05,

volume = 2016,

place = {United States},

year = {Wed May 04 00:00:00 EDT 2016},

month = {Wed May 04 00:00:00 EDT 2016}

}