# Matter bounce cosmology with a generalized single field: non-Gaussianity and an extended no-go theorem

## Abstract

We extend the matter bounce scenario to a more general theory in which the background dynamics and cosmological perturbations are generated by a k -essence scalar field with an arbitrary sound speed. When the sound speed is small, the curvature perturbation is enhanced, and the tensor-to-scalar ratio, which is excessively large in the original model, can be sufficiently suppressed to be consistent with observational bounds. Then, we study the primordial three-point correlation function generated during the matter-dominated contraction stage and find that it only depends on the sound speed parameter. Similar to the canonical case, the shape of the bispectrum is mainly dominated by a local form, though for some specific sound speed values a new shape emerges and the scaling behaviour changes. Meanwhile, a small sound speed also results in a large amplitude of non-Gaussianities, which is disfavored by current observations. As a result, it does not seem possible to suppress the tensor-to-scalar ratio without amplifying the production of non-Gaussianities beyond current observational constraints (and vice versa). This suggests an extension of the previously conjectured no-go theorem in single field nonsingular matter bounce cosmologies, which rules out a large class of models. However, the non-Gaussianity results remain as amore »

- Authors:

- CAS Key Laboratory for Researches in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Chinese Academy of Sciences, Hefei, Anhui 230026 (China)
- Department of Physics, McGill University, 3600 rue University, Montréal, QC, H3A 2T8 (Canada)
- Leiden Observatory, Leiden University, 2300 RA Leiden (Netherlands)

- Publication Date:

- OSTI Identifier:
- 22679973

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2017; Journal Issue: 03; Other Information: Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMPLITUDES; CORRELATION FUNCTIONS; CORRELATIONS; COSMOLOGY; DISTURBANCES; PERTURBATION THEORY; SCALAR FIELDS; VELOCITY

### Citation Formats

```
Li, Yu-Bin, Cai, Yi-Fu, Quintin, Jerome, and Wang, Dong-Gang, E-mail: lyb2166@mail.ustc.edu.cn, E-mail: jquintin@physics.mcgill.ca, E-mail: wdgang@strw.leidenuniv.nl, E-mail: yifucai@ustc.edu.cn.
```*Matter bounce cosmology with a generalized single field: non-Gaussianity and an extended no-go theorem*. United States: N. p., 2017.
Web. doi:10.1088/1475-7516/2017/03/031.

```
Li, Yu-Bin, Cai, Yi-Fu, Quintin, Jerome, & Wang, Dong-Gang, E-mail: lyb2166@mail.ustc.edu.cn, E-mail: jquintin@physics.mcgill.ca, E-mail: wdgang@strw.leidenuniv.nl, E-mail: yifucai@ustc.edu.cn.
```*Matter bounce cosmology with a generalized single field: non-Gaussianity and an extended no-go theorem*. United States. doi:10.1088/1475-7516/2017/03/031.

```
Li, Yu-Bin, Cai, Yi-Fu, Quintin, Jerome, and Wang, Dong-Gang, E-mail: lyb2166@mail.ustc.edu.cn, E-mail: jquintin@physics.mcgill.ca, E-mail: wdgang@strw.leidenuniv.nl, E-mail: yifucai@ustc.edu.cn. Wed .
"Matter bounce cosmology with a generalized single field: non-Gaussianity and an extended no-go theorem". United States.
doi:10.1088/1475-7516/2017/03/031.
```

```
@article{osti_22679973,
```

title = {Matter bounce cosmology with a generalized single field: non-Gaussianity and an extended no-go theorem},

author = {Li, Yu-Bin and Cai, Yi-Fu and Quintin, Jerome and Wang, Dong-Gang, E-mail: lyb2166@mail.ustc.edu.cn, E-mail: jquintin@physics.mcgill.ca, E-mail: wdgang@strw.leidenuniv.nl, E-mail: yifucai@ustc.edu.cn},

abstractNote = {We extend the matter bounce scenario to a more general theory in which the background dynamics and cosmological perturbations are generated by a k -essence scalar field with an arbitrary sound speed. When the sound speed is small, the curvature perturbation is enhanced, and the tensor-to-scalar ratio, which is excessively large in the original model, can be sufficiently suppressed to be consistent with observational bounds. Then, we study the primordial three-point correlation function generated during the matter-dominated contraction stage and find that it only depends on the sound speed parameter. Similar to the canonical case, the shape of the bispectrum is mainly dominated by a local form, though for some specific sound speed values a new shape emerges and the scaling behaviour changes. Meanwhile, a small sound speed also results in a large amplitude of non-Gaussianities, which is disfavored by current observations. As a result, it does not seem possible to suppress the tensor-to-scalar ratio without amplifying the production of non-Gaussianities beyond current observational constraints (and vice versa). This suggests an extension of the previously conjectured no-go theorem in single field nonsingular matter bounce cosmologies, which rules out a large class of models. However, the non-Gaussianity results remain as a distinguishable signature of matter bounce cosmology and have the potential to be detected by observations in the near future.},

doi = {10.1088/1475-7516/2017/03/031},

journal = {Journal of Cosmology and Astroparticle Physics},

number = 03,

volume = 2017,

place = {United States},

year = {Wed Mar 01 00:00:00 EST 2017},

month = {Wed Mar 01 00:00:00 EST 2017}

}