Some Remarks on Anthropic Approaches to the Strong CP Problem

Abstract

The peculiar value of $\theta$ is a challenge to the notion of an anthropic landscape. We briefly review the possibility that a suitable axion might arise from an anthropic requirement of dark matter. We then consider an alternative suggestion of Kaloper and Terning that $\theta$ might be correlated with the cosmological constant. We note that in a landscape one expects that $\theta$ is determined by the expectation value of one or more axions. We discuss how a discretuum of values of $\theta$ might arise with an energy distribution dominated by QCD, and find the requirements to be quite stringent. Given such a discretuum, we find limited circumstances where small $\theta$ might be selected by anthropic requirements on the cosmological constant.

arXiv comment18 pages, 2 figures

References in corpus (9)

• Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant
• Quantization of Four-form Fluxes and Dynamical Neutralization of the Cosmological Constant
• Dimensionless constants, cosmology and other dark matters
• Constraining Light Dark Matter with Diffuse X-Ray and Gamma-Ray Observations
• Is There A String Theory Landscape
• Irrational Axions as a Solution of The Strong CP Problem in an Eternal Universe
• R Symmetries in the Landscape
• Axionic Band Structure of the Cosmological Constant
• Discrete R Symmetries and Anomalies

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