[Paper Review] Radiative Seesaw Model with Non-zero $ heta_{13}$ and Warm Dark Matter Scenario

Ping-Kai Hu|arXiv (Cornell University)|Aug 13, 2012

Cosmology and Gravitation Theories3 citations

TL;DR

This paper revisits Ma's radiative seesaw model with updated experimental data, particularly non-zero θ₁₃, to explore its viability for both cold (CDM) and warm dark matter (WDM) scenarios. It shows that relic abundance can be achieved via thermal production followed by entropy dilution from N₂ decay, requiring M₁ < M₂ < m₀, and imposes strong constraints from μ → eγ and relic density, while finding the model insufficient to explain the muon g−2 anomaly.

ABSTRACT

With updated experiment result, we study Ma's radiative seesaw model. We try to use fewer assumptions to study the feasibility of this model. Both CDM and WDM scenario are taken into consideration. In CDM scenario, the fitting of relic abundance shows that a mass spectrum M_1 < m_0 < M_2 is preferred if theory remains perturbability. By studying the flavour violation process \mu ightarrow e \gamma and relic density abundance, we get very strong constraint for the model. In addition, we try to explain muon anomaly a_{\mu} \equiv (g-2)/2 within the model, but the contribution induced by new particles is too small to account for the discrepancy. In WDM scenario, We show that relic abundance can be produced by thermal production with subsequent entropy dilution process. The entropy dilution can be attained by N_2 decay in which a mass spectrum M_1 < M_2 < m_0 is required.

Motivation & Objective

• To re-evaluate Ma's radiative seesaw model in light of the non-zero θ₁₃ measurement from Daya Bay.
• To assess the model's viability in both cold and warm dark matter (CDM and WDM) scenarios.
• To constrain the model's parameter space using flavor-violating processes like μ → eγ and relic density measurements.
• To examine whether the model can account for the observed muon g−2 anomaly.
• To demonstrate that entropy dilution for WDM can be achieved within the model without additional particles, via N₂ decay.

Proposed method

• Reconstructs the neutrino mass matrix using updated θ₁₃ data and the PMNS mixing matrix.
• Applies thermal production and entropy dilution mechanisms to generate correct relic abundance in the WDM scenario.
• Uses the Z₂ symmetry to stabilize the lightest Majorana fermion N₁ as a dark matter candidate.
• Performs numerical fitting of the relic density under CDM and WDM assumptions, considering coannihilation and mixing effects.
• Evaluates flavor-violating processes such as μ → eγ using one-loop diagrams involving N₁, N₂, and the scalar doublet η.
• Analyzes the contribution to the muon anomalous magnetic moment (g−2) from new particles in the model.

Experimental results

Research questions

• RQ1 Can the radiative seesaw model with non-zero θ₁₃ reproduce the correct relic abundance in both CDM and WDM scenarios?
• RQ2 What mass hierarchy (M₁ < m₀ < M₂ or M₁ < M₂ < m₀) is favored by relic density and perturbativity constraints?
• RQ3 How strong are the constraints from the μ → eγ decay process on the model's parameter space?
• RQ4 Can the model account for the observed discrepancy in the muon g−2 anomaly?
• RQ5 Is entropy dilution for WDM achievable within the model without introducing additional particles, and what decay mechanism enables it?

Key findings

• A mass spectrum with M₁ < m₀ < M₂ is preferred in the CDM scenario to maintain perturbativity and fit the observed relic density.
• The μ → eγ process imposes very strong constraints on the model, significantly limiting the allowed parameter space.
• The contribution to the muon g−2 from new particles in the model is too small to explain the observed discrepancy.
• In the WDM scenario, correct relic abundance is achieved via thermal production followed by entropy dilution from N₂ decay, requiring M₁ < M₂ < m₀.
• Entropy dilution can be realized within the model itself via N₂ decay, eliminating the need for additional scalar singlets or reheating particles.
• The model's viability is significantly constrained by flavor-changing processes and relic density, especially with non-zero θ₁₃.