Brans-Dicke supergravity and the Lambda naturalness problem

Hewitt, M. (2015) Brans-Dicke supergravity and the Lambda naturalness problem. In: COSMO 15 - 19th International Conference on Particle Physics and Cosmology, 7th-11th September, 2015, University of Warsaw, Poland. (Unpublished)

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The successful $\Lambda CDM$ cosmological model requires a small but nonzero $\Lambda$ which appears to have an unnaturally small value compared to the supersymmetry breaking scale, typically $O(10^{-60}) m_{3/2}^4$ for $m_{3/2} \sim 10 TeV$. We explore the possibility of solving this naturalness problem in a special class of no-scale supergravity models which arise from a supersymmetric version of Brans-Dicke gravity, in which the Volkov and Brans-Dicke multiplets may be identified. These may be embedded in compactified string models, with the Brans-Dicke scalar given by the combination of dilaton and compactification breathing modes which leaves the 4 dimensional gauge couplings fixed. Assuming that 4 dimensional physics has an approximate symmetry under changes in this mode broken only by couplings between the low energy and gravitational or string sectors, the main one loop contribution to $\Lambda$ cancels between Brans-Dicke and gravitational (conformal compensator) F terms, and the leading contributions to $\Lambda$ now appear to be $O(m_{3/2}^8 m_{p}^{-4)}$, enabling a natural reconciliation between observational and particle physics estimates for $\Lambda$.
The Brans-Dicke scalar has a range $O(m_{3/2}^{-1})$, lifting observational constraints on scalar gravity in this scenario.

Item Type: Conference or Workshop Item (Paper)
Uncontrolled Keywords: Dark energy; cosmological constant
Subjects: Q Science > QC Physics
Divisions: Faculty of Social and Applied Sciences > School of Law, Criminal Justice and Computing
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Depositing User: Mr Mike Hewitt
Date Deposited: 17 Sep 2015 11:18
Last Modified: 18 May 2016 09:37

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Last edited: 29/06/2016 12:23:00