# Can compactifications solve the cosmological constant problem?

## Abstract

Recently, there have been claims in the literature that the cosmological constant problem can be dynamically solved by specific compactifications of gravity from higher-dimensional toy models. These models have the novel feature that in the four-dimensional theory, the cosmological constant Λ is much smaller than the Planck density and in fact accumulates at Λ=0. Here we show that while these are very interesting models, they do not properly address the real cosmological constant problem. As we explain, the real problem is not simply to obtain Λ that is small in Planck units in a toy model, but to explain why Λ is much smaller than other mass scales (and combinations of scales) in the theory. Instead, in these toy models, all other particle mass scales have been either removed or sent to zero, thus ignoring the real problem. To this end, we provide a general argument that the included moduli masses are generically of order Hubble, so sending them to zero trivially sends the cosmological constant to zero. We also show that the fundamental Planck mass is being sent to zero, and so the central problem is trivially avoided by removing high energy physics altogether. On the other hand, bymore »

- Authors:

- Institute of Cosmology, Department of Physics and Astronomy, Tufts University,574 Boston Ave, Medford, MA 02155 (United States)
- (United States)

- Publication Date:

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

- OSTI Identifier:
- 22572109

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2016; Journal Issue: 06; Other Information: PUBLISHER-ID: JCAP06(2016)053; OAI: oai:repo.scoap3.org:16246; 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; COMPACTIFICATION; COSMOLOGICAL CONSTANT; COSMOLOGY; FOUR-DIMENSIONAL CALCULATIONS; GRAVITATION; MASS; MATHEMATICAL SOLUTIONS; NONLUMINOUS MATTER

### Citation Formats

```
Hertzberg, Mark P., Center for Theoretical Physics, Department of Physics,Massachusetts Institute of Technology,77 Massachusetts Ave, Cambridge, MA 02139, and Masoumi, Ali.
```*Can compactifications solve the cosmological constant problem?*. United States: N. p., 2016.
Web. doi:10.1088/1475-7516/2016/06/053.

```
Hertzberg, Mark P., Center for Theoretical Physics, Department of Physics,Massachusetts Institute of Technology,77 Massachusetts Ave, Cambridge, MA 02139, & Masoumi, Ali.
```*Can compactifications solve the cosmological constant problem?*. United States. doi:10.1088/1475-7516/2016/06/053.

```
Hertzberg, Mark P., Center for Theoretical Physics, Department of Physics,Massachusetts Institute of Technology,77 Massachusetts Ave, Cambridge, MA 02139, and Masoumi, Ali. Thu .
"Can compactifications solve the cosmological constant problem?". United States.
doi:10.1088/1475-7516/2016/06/053.
```

```
@article{osti_22572109,
```

title = {Can compactifications solve the cosmological constant problem?},

author = {Hertzberg, Mark P. and Center for Theoretical Physics, Department of Physics,Massachusetts Institute of Technology,77 Massachusetts Ave, Cambridge, MA 02139 and Masoumi, Ali},

abstractNote = {Recently, there have been claims in the literature that the cosmological constant problem can be dynamically solved by specific compactifications of gravity from higher-dimensional toy models. These models have the novel feature that in the four-dimensional theory, the cosmological constant Λ is much smaller than the Planck density and in fact accumulates at Λ=0. Here we show that while these are very interesting models, they do not properly address the real cosmological constant problem. As we explain, the real problem is not simply to obtain Λ that is small in Planck units in a toy model, but to explain why Λ is much smaller than other mass scales (and combinations of scales) in the theory. Instead, in these toy models, all other particle mass scales have been either removed or sent to zero, thus ignoring the real problem. To this end, we provide a general argument that the included moduli masses are generically of order Hubble, so sending them to zero trivially sends the cosmological constant to zero. We also show that the fundamental Planck mass is being sent to zero, and so the central problem is trivially avoided by removing high energy physics altogether. On the other hand, by including various large mass scales from particle physics with a high fundamental Planck mass, one is faced with a real problem, whose only known solution involves accidental cancellations in a landscape.},

doi = {10.1088/1475-7516/2016/06/053},

journal = {Journal of Cosmology and Astroparticle Physics},

number = 06,

volume = 2016,

place = {United States},

year = {Thu Jun 30 00:00:00 EDT 2016},

month = {Thu Jun 30 00:00:00 EDT 2016}

}