Resolving Hubble Tension by Self-Interacting Neutrinos with Dirac Seesaw

Understand

Self-interacting neutrinos that begin to free-stream at close to matter-radiation equality can reduce the physical size of photon sound horizon at last scattering surface.

• This mechanism can be the reason why standard $\Lambda$CDM cosmology sees a lower value of the Hubble constant than local measurements from distance ladder.
• We propose a new realization of self-interacting Dirac neutrinos (SID$\nu$) with light-dark-photon mediator for a viable interaction mechanism.
• Our model is UV completed by a Dirac seesaw with anomaly-free dark $U(1)_X^{}$ gauge group which charges the right-handed neutrinos.