Searching for Composite Neutrinos in the Cosmic Microwave Background

Abstract

We analyze signals in the Cosmic Microwave Background (CMB) in theories where the small Dirac neutrino masses arise as a consequence of the compositeness of right-handed neutrinos. In such theories, the right-handed neutrinos are massless ``baryons'' of a new strong gauge interaction. We find that the results crucially depend on whether or not the new strong sector undergoes chiral symmetry breaking. In the case with chiral symmetry breaking, we find that there are indeed signals in the CMB, but none of them is a direct consequence of neutrino compositeness. In contrast, if the underlying theory does not undergo chiral symmetry breaking, the large scattering cross-section among the composites gives rise to a sizable CMB signal over a wide region of the parameter space, and it can potentially probe whether the neutrino mass spectrum is hierarchical, inverse hierarchical, or degenerate. We also discuss collider constraints on the compositeness in the context of the CMB signals.

26 pages. References and clarifying comments added. Version appearing to JHEP

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• A Dynamical Framework for KeV Dirac Neutrino Warm Dark Matter
• Composite Dirac Neutrinos
• Mini Z' Burst from Relic Supernova Neutrinos and Late Neutrino Masses
• Light Neutrinos from a Mini-Seesaw Mechanism in Warped Space
• Probing Late Neutrino Mass Properties with Supernova Neutrinos
• KeV Warm Dark Matter and Composite Neutrinos
• Small neutrino masses due to R-symmetry breaking for a small cosmological constant
• Neutrino Constraints on Spontaneous Lorentz Violation
• Neutrino Masses from Low Scale Partial Compositeness
• Constraints on composite Dirac neutrinos from observations of galaxy clusters
• Neutrino Mass and $\mu \to e+\gamma$ from a Mini-Seesaw
• Emergent neutrinos from heavy messengers
• Composite Dark Matter and Neutrino Masses from a Light Hidden Sector