# Primordial perturbations from dilaton-induced gauge fields

## Abstract

We study the primordial scalar and tensor perturbations in inflation scenario involving a spectator dilaton field. In our setup, the rolling spectator dilaton causes a tachyonic instability of gauge fields, leading to a copious production of gauge fields in the superhorizon regime, which generates additional scalar and tensor perturbations through gravitational interactions. Our prime concern is the possibility to enhance the tensor-to-scalar ratio r relative to the standard result, while satisfying the observational constraints. To this end, we allow the dilaton field to be stabilized before the end of inflation, but after the CMB scales exit the horizon. We show that for the inflaton slow roll parameter ε ∼> 10{sup −3}, the tensor-to-scalar ratio in our setup can be enhanced only by a factor of O(1) compared to the standard result. On the other hand, for smaller ε corresponding to a lower inflation energy scale, a much bigger enhancement can be achieved, so that our setup can give rise to an observably large r∼> 10{sup −2} even when ε|| 10{sup −3}. The tensor perturbation sourced by the spectator dilaton can have a strong scale dependence, and is generically red-tilted. We also discuss a specific model to realize our scenario, and identify the parameter regionmore »

- Authors:

- Center for Theoretical Physics of the Universe, Institute for Basic Science (IBS), Daejeon 305-811 (Korea, Republic of)
- Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of)
- Department of Phyiscs, KAIST, Daejeon 305-701 (Korea, Republic of)
- New High Energy Theory Center, Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854 (United States)

- Publication Date:

- OSTI Identifier:
- 22525230

- Resource Type:
- Journal Article

- Journal Name:
- Journal of Cosmology and Astroparticle Physics

- Additional Journal Information:
- Journal Volume: 2015; Journal Issue: 10; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1475-7516

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMPARATIVE EVALUATIONS; COSMOLOGICAL INFLATION; DILATONS; DISTURBANCES; GAUGE INVARIANCE; GRAVITATIONAL INTERACTIONS; INFLATIONARY UNIVERSE; INSTABILITY; LIMITING VALUES; SCALARS; TACHYONS; TENSORS

### Citation Formats

```
Choi, Kiwoon, Choi, Ki-Young, Kim, Hyungjin, and Shin, Chang Sub, E-mail: kchoi@ibs.re.kr, E-mail: kiyoungchoi@kasi.re.kr, E-mail: hjkim06@kaist.ac.kr, E-mail: changsub@physics.rutgers.edu.
```*Primordial perturbations from dilaton-induced gauge fields*. United States: N. p., 2015.
Web. doi:10.1088/1475-7516/2015/10/046.

```
Choi, Kiwoon, Choi, Ki-Young, Kim, Hyungjin, & Shin, Chang Sub, E-mail: kchoi@ibs.re.kr, E-mail: kiyoungchoi@kasi.re.kr, E-mail: hjkim06@kaist.ac.kr, E-mail: changsub@physics.rutgers.edu.
```*Primordial perturbations from dilaton-induced gauge fields*. United States. doi:10.1088/1475-7516/2015/10/046.

```
Choi, Kiwoon, Choi, Ki-Young, Kim, Hyungjin, and Shin, Chang Sub, E-mail: kchoi@ibs.re.kr, E-mail: kiyoungchoi@kasi.re.kr, E-mail: hjkim06@kaist.ac.kr, E-mail: changsub@physics.rutgers.edu. Thu .
"Primordial perturbations from dilaton-induced gauge fields". United States. doi:10.1088/1475-7516/2015/10/046.
```

```
@article{osti_22525230,
```

title = {Primordial perturbations from dilaton-induced gauge fields},

author = {Choi, Kiwoon and Choi, Ki-Young and Kim, Hyungjin and Shin, Chang Sub, E-mail: kchoi@ibs.re.kr, E-mail: kiyoungchoi@kasi.re.kr, E-mail: hjkim06@kaist.ac.kr, E-mail: changsub@physics.rutgers.edu},

abstractNote = {We study the primordial scalar and tensor perturbations in inflation scenario involving a spectator dilaton field. In our setup, the rolling spectator dilaton causes a tachyonic instability of gauge fields, leading to a copious production of gauge fields in the superhorizon regime, which generates additional scalar and tensor perturbations through gravitational interactions. Our prime concern is the possibility to enhance the tensor-to-scalar ratio r relative to the standard result, while satisfying the observational constraints. To this end, we allow the dilaton field to be stabilized before the end of inflation, but after the CMB scales exit the horizon. We show that for the inflaton slow roll parameter ε ∼> 10{sup −3}, the tensor-to-scalar ratio in our setup can be enhanced only by a factor of O(1) compared to the standard result. On the other hand, for smaller ε corresponding to a lower inflation energy scale, a much bigger enhancement can be achieved, so that our setup can give rise to an observably large r∼> 10{sup −2} even when ε|| 10{sup −3}. The tensor perturbation sourced by the spectator dilaton can have a strong scale dependence, and is generically red-tilted. We also discuss a specific model to realize our scenario, and identify the parameter region giving an observably large r for relatively low inflation energy scales.},

doi = {10.1088/1475-7516/2015/10/046},

journal = {Journal of Cosmology and Astroparticle Physics},

issn = {1475-7516},

number = 10,

volume = 2015,

place = {United States},

year = {2015},

month = {10}

}