Do neutrinos dream in 5D? Towards a comprehensive extra-dimensional neutrino phenomenology

TL;DR

The work analyzes neutrino masses and mixing in a five-dimensional LED framework with a bulk fermion, producing a KK tower that couples to brane-localised SM neutrinos. It develops analytic KK spectra and active–sterile mixing patterns for four benchmark scenarios (Dirac/Majorana, bulk/brane), and formulates vacuum and matter oscillation formalisms incorporating the KK states. By confronting MINOS/MINOS+ and Daya Bay data, it derives bounds on the compactification scale $R^{-1}=\mu_1$ and bulk parameters, highlighting resonant structures in the Majorana bulk case and the seesaw-like limits in Majorana/brane scenarios. The results demonstrate rich phenomenology with clear experimental signatures and outline paths for strengthening constraints with upcoming neutrino experiments and potential warped extra-dimensional generalisations.

Abstract

This paper provides a comprehensive overview of neutrino masses and mixing in Large Extra Dimension scenarios, focusing on the phenomenological impact of a five-dimensional (5D) bulk fermion. In a flat extra dimension compactified on an $S^1/\mathbb{Z}_2$ orbifold, this fermion manifests as a Kaluza-Klein tower of right-handed neutrinos in the 4D effective theory. We systematically investigate four distinct scenarios for mass generation, considering both Dirac and Majorana mass terms originating from either the bulk or the 3-brane. For each case, we analyse the consequences for neutrino oscillations in a vacuum and in matter, deriving the resulting mass spectra and mixing patterns. By comparing these theoretical predictions with experimental data, we explore the constraints on the large extra dimensions' parameters.

Figures (13)

• Figure 1: Brane-Dirac spectrum for representative values of $\mu_1$ in units of $m_D=1$. The dashed lines and the dots represent $\mathcal{N}_\lambda$ of Eq. \ref{['eq:brane-dirac-N']} as a continuous function of $m_\lambda$ and the physical masses stemming from Eq. \ref{['eq:DBrane-eigenvalues']}, respectively.
• Figure 2: Bulk-Dirac spectrum for representative values of $\mu_1$ in units of $m_D=1$. The dashed lines and the dots represent $\mathcal{N}_\lambda$ of Eq. \ref{['eq:normalisation-bulk-dirac']} as a continuous function of $m_\lambda$ and the physical masses stemming from Eq. \ref{['eq:masses-bulk-dirac']}, respectively.
• Figure 3: Bulk-Majorana spectrum for representative values of $\mu_1$ in units of $m_D=1$. The dashed lines and the dots represent $\mathcal{N}_\lambda$ of Eq. \ref{['eq:eigeq-2']} as a continuous function of $m_\lambda$ and the physical masses stemming from Eq. \ref{['eq:eigeq-1']}, respectively.
• Figure 4: Brane-Majorana spectrum for representative values of $\mu_1$ in units of $m_D=1$. The dashed lines and the dots represent $\mathcal{N}_\lambda$ of Eq. \ref{['eq:brane-majorana-eigen2']} as a continuous function of $m_\lambda$ and the physical masses stemming from Eq. \ref{['eq:brane-majorana-eigen1']}, respectively.
• Figure 5: 90% C.L. exclusion contours for the Dirac brane scenario from MINOS/MINOS+ and Daya Bay. Solid lines correspond to exclusion from Daya Bay, and dotted lines MINOS/MINOS+.