Neutrinos, B-L Symmetry and the Dark Dimension
Miguel Montero, Cumrun Vafa, Irene Valenzuela
TL;DR
The paper addresses how to realize a gauged $U(1)_{B-L}$ in the Dark Dimension framework, where the SM resides on a brane in a 5d spacetime with a mesoscopic extra dimension. It analyzes three routes to neutrino masses: anomaly inflow with a Green-Schwarz mechanism (pseudovector case), a bulk vector with anomaly cancellation by bulk fermions, and a Higgsing of B-L via a bulk scalar (Phi). The Higgsing scenario emerges as the most predictive, yielding $m_{B-L} \sim 100$ GeV and $g_{B-L} \sim 10^{-10}$, naturally supplying three bulk RH neutrinos and a neutrino mass relation $m_\nu \sim m_{KK} \sim \Lambda^{1/4}$, along with a keV-scale sterile neutrino tower; it also provides a potential collider signature and motivates further tests, while two large extra dimensions fail to reproduce the same neutrino-dark energy coincidence. Overall, the work links neutrino physics to the Dark Dimension scale without excessive fine-tuning and highlights collider-accessible predictions for the bulk B-L scenario.
Abstract
We consider realizations of a gauged B-L symmetry in the context of the Dark Dimension scenario, where the SM lives on a codimension one brane in 5d spacetime. The B-L can naturally be a bulk gauge symmetery leading to a global symmetry on the SM brane, and have its gauge anomaly canceled by charged bulk modes. This naturally leads to the existence of 3 right-handed neutrinos propagating in the dark dimension. Allowing for Higgsing of B-L by a bulk scalar at the Higgs scale, results in a massive gauge field with $m_{B-L}\sim 100$ GeV and weak coupling $g_{B-L}\sim 10^{-10}$ which is allowed by current bounds. The model also predicts a natural matching $m_ν\sim m_{KK}\simΛ^{1/4}$, thereby providing a theoretical explanation for the observed coincidence between neutrino masses and the Dark Energy scale. It also predicts a tower of sterile right-handed neutrinos in the $keV$ mass range.