[Paper Review] Common Origin of Active and Sterile Neutrino Masses with Dark Matter

Rathin Adhikari, Debasish Borah+1 more|arXiv (Cornell University)|Nov 17, 2014

Dark Matter and Cosmic Phenomena3 citations

TL;DR

This paper proposes a U(1)ₐ extension of the Standard Model that simultaneously explains eV-scale masses and mixings for three active and one sterile neutrino via one-loop radiative mechanisms, while preserving a residual Z₂ symmetry that stabilizes a cold dark matter candidate. The model naturally unifies sterile neutrino physics with dark matter, allowing for viable phenomenology within current experimental constraints.

ABSTRACT

We propose an abelian extension of the Standard Model which can explain the origin of eV scale masses and mixing for active and sterile neutrinos and at the same time providing a natural cold dark matter candidate. One of the three active neutrinos acquires mass at tree level through seesaw mechanism whereas the other two active neutrinos and one sterile neutrino acquire eV scale masses at one-loop level. The model also allows non-trivial mixing between active and sterile neutrinos at one-loop level which could have interesting signatures at neutrino experiments. After the abelian gauge symmetry gets spontaneously broken down to a $Z_2$ symmetry, the lightest $Z_2$ odd particle can naturally give rise to the cold dark matter of the Universe. The phenomenology of both fermionic and scalar dark matter is briefly discussed by incorporating latest experimental constraints.

Motivation & Objective

• To provide a unified framework for eV-scale masses of three active and one sterile neutrino within a single renormalizable model.
• To preserve a residual Z₂ symmetry after U(1)ₐ gauge symmetry breaking to stabilize a dark matter candidate.
• To allow non-trivial mixing between active and sterile neutrinos at one-loop level, addressing short-baseline neutrino anomalies.
• To incorporate both fermionic and scalar dark matter candidates in the low mass range (10–100 GeV), consistent with relic density and direct detection constraints.
• To explore the possibility of a mixed dark matter scenario including keV-scale sterile neutrinos as warm dark matter candidates.

Proposed method

• Introduce an abelian U(1)ₐ gauge symmetry with anomaly-free hypercharge assignments for all new particles.
• Implement spontaneous breaking of U(1)ₐ down to a residual Z₂ symmetry, ensuring stability of the lightest Z₂-odd particle.
• Realize one-loop radiative neutrino masses via scalar and fermionic loop diagrams involving new scalar doublets and right-handed neutrinos.
• Construct a scalar sector with two complex scalar doublets and two real singlets to mediate neutrino mass generation and dark matter stability.
• Use the Standard Model Higgs boson to mediate spin-independent dark matter-nucleon scattering, with coupling strength constrained by LUX data.
• Perform relic density calculations for scalar and fermionic dark matter candidates, focusing on the low-mass region (10–100 GeV) to satisfy observed dark matter abundance.

Experimental results

Research questions

• RQ1 Can a single model simultaneously explain eV-scale masses for three active and one sterile neutrino through a common radiative mechanism?
• RQ2 How can a residual Z₂ symmetry be preserved in a U(1)ₐ extension to stabilize a cold dark matter candidate?
• RQ3 What is the role of one-loop diagrams in generating non-zero active-sterile neutrino mixing at the eV scale?
• RQ4 Can the model accommodate both fermionic and scalar dark matter candidates within the 10–100 GeV mass range while satisfying relic density and direct detection bounds?
• RQ5 Is it possible to extend the model to include keV-scale sterile neutrinos as warm dark matter without destabilizing the cold dark matter candidate?

Key findings

• One active neutrino acquires mass at tree level via the type I seesaw mechanism, while the other two active and one sterile neutrino gain eV-scale masses through one-loop diagrams.
• Non-zero mixing between active and sterile neutrinos is generated at one-loop level, providing a viable explanation for reactor and accelerator-based short-baseline neutrino anomalies.
• The lightest Z₂-odd particle is stable and can serve as a cold dark matter candidate, with both fermionic and scalar realizations satisfying the observed relic density within the 10–100 GeV mass window.
• The scalar doublet dark matter candidate satisfies the LUX direct detection constraint of σ_SI < 7.6×10⁻⁴⁶ cm² for dark matter masses below 100 GeV.
• The model allows for a mixed dark matter scenario with a Z₂-stabilized cold dark matter candidate and a keV-scale sterile neutrino as a warm dark matter component, with a lifetime exceeding the age of the Universe.
• The new physics scale is naturally at the TeV scale due to loop suppression, avoiding fine-tuning of dimensionless couplings.