Abstract
We point out a novel role for the Standard Model neutrino in dark matter phenomenology where the exchange of neutrinos generates a long-range potential between dark matter particles. The resulting dark matter self interaction could be sufficiently strong to impact small-scale structure formation, without the need of any dark force carrier. This is a generic feature of theories where dark matter couples to the visible sector through the neutrino portal. It is highly testable with improved decay rate measurements at future $Z$, Higgs, and $\tau$ factories, as well as precision cosmology.
Highlights
Dark matter (DM) is a key ingredient throughout the evolution of our universe, yet its identity remains unknown
We demonstrate that DM self-interactions can be mediated exclusively by Standard Model (SM) neutrinos, without
For asymmetric DM, the interaction is repulsive, and the low-energy scattering can be solved within quantum mechanics, independent of short distance physics
Summary
We first explore DM self interaction of relevance to structure formation. Because the DM particles are already nonrelativistic when they self interact in galaxies and clusters, the heavier φ field could be integrated out from Eq (2), leading to. A direct comparison shows Vðr 1⁄4 m−ν 1Þ=K ∼ 10−37ð10 MeV=mχÞ5 for an order one coupling y, where K 1⁄4 mχv2=2 ∼ 10−6mχ is the typical dark matter kinetic energy in galaxies Based on these observations, we conclude it is a good approximation to consider the potential in Eq (5) for the discussions here. The resulting cross section goes as jyαj8=3 rather than jyαj, indicating the importance of resumming multiple neutrino bubble exchange contributions [71]. This is the key for generating a sizable DM interaction in spite of FIG. When mφ and mχ are closer, the effective coupling in Eq (3) is more enhanced, allowing for smaller values of yα
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