## Can compactifications solve the cosmological constant problem?

##### Author(s)

Masoumi, Ali; Hertzberg, Mark Peter
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Creative Commons Attribution

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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.

##### Date issued

2016-06##### Department

Massachusetts Institute of Technology. Center for Theoretical Physics; Massachusetts Institute of Technology. Department of Physics##### Journal

Journal of Cosmology and Astroparticle Physics

##### Publisher

Institute of Physics Publishing/SISSA

##### Citation

Hertzberg, Mark P., and Ali Masoumi. “Can Compactifications Solve the Cosmological Constant Problem?” Journal of Cosmology and Astroparticle Physics 2016.06 (2016): 053–053. © Copyright 2017 IOP Publishing

Version: Final published version

##### ISSN

1475-7516

1475-7508