# The coincidence problem and the Swampland conjectures in the Ijjas-Steinhardt cyclic model of the universe

## Abstract

In the Ijjas-Steinhardt cyclic model, the universe passes through phases dominated by radiation, matter, and a dark energy scalar field, with the value of the scale factor increasing with each cycle. Since each cycle terminates in a finite time, it is straightforward to calculate the fraction of time that the universe spends in a state for which the matter and dark energy densities have comparable magnitudes; when this fraction is large, it can be taken as a solution of the coincidence problem. This solution of the coincidence problem requires a relatively short lifetime for each cycle, but unlike in the case of phantom models, there is no fixed upper bound on this lifetime. However, scalar field models satisfying the Swampland conjectures yield sufficiently short lifetimes to provide a satisfactory resolution of the coincidence problem.

- Authors:

- Publication Date:

- Research Org.:
- Vanderbilt Univ., Nashville, TN (United States)

- Sponsoring Org.:
- USDOE Office of Science (SC), High Energy Physics (HEP)

- OSTI Identifier:
- 1567721

- Alternate Identifier(s):
- OSTI ID: 1599597

- Grant/Contract Number:
- SC0019207

- Resource Type:
- Published Article

- Journal Name:
- Physics Letters B

- Additional Journal Information:
- Journal Name: Physics Letters B Journal Volume: 798 Journal Issue: C; Journal ID: ISSN 0370-2693

- Publisher:
- Elsevier

- Country of Publication:
- Netherlands

- Language:
- English

- Subject:
- 79 ASTRONOMY AND ASTROPHYSICS; dark energy; swampland conjecture; cosmological constant coincidence problem; cyclic universe

### Citation Formats

```
Scherrer, Robert J. The coincidence problem and the Swampland conjectures in the Ijjas-Steinhardt cyclic model of the universe. Netherlands: N. p., 2019.
Web. doi:10.1016/j.physletb.2019.134981.
```

```
Scherrer, Robert J. The coincidence problem and the Swampland conjectures in the Ijjas-Steinhardt cyclic model of the universe. Netherlands. doi:10.1016/j.physletb.2019.134981.
```

```
Scherrer, Robert J. Fri .
"The coincidence problem and the Swampland conjectures in the Ijjas-Steinhardt cyclic model of the universe". Netherlands. doi:10.1016/j.physletb.2019.134981.
```

```
@article{osti_1567721,
```

title = {The coincidence problem and the Swampland conjectures in the Ijjas-Steinhardt cyclic model of the universe},

author = {Scherrer, Robert J.},

abstractNote = {In the Ijjas-Steinhardt cyclic model, the universe passes through phases dominated by radiation, matter, and a dark energy scalar field, with the value of the scale factor increasing with each cycle. Since each cycle terminates in a finite time, it is straightforward to calculate the fraction of time that the universe spends in a state for which the matter and dark energy densities have comparable magnitudes; when this fraction is large, it can be taken as a solution of the coincidence problem. This solution of the coincidence problem requires a relatively short lifetime for each cycle, but unlike in the case of phantom models, there is no fixed upper bound on this lifetime. However, scalar field models satisfying the Swampland conjectures yield sufficiently short lifetimes to provide a satisfactory resolution of the coincidence problem.},

doi = {10.1016/j.physletb.2019.134981},

journal = {Physics Letters B},

number = C,

volume = 798,

place = {Netherlands},

year = {2019},

month = {11}

}

DOI: 10.1016/j.physletb.2019.134981