[Paper Review] Bound-state dark matter with Majorana neutrinos

Mario Reig, Diego Restrepo+2 more|arXiv (Cornell University)|Jun 23, 2018

Particle physics theoretical and experimental studies38 references3 citations

TL;DR

This paper proposes a bound-state dark matter model where dark matter arises from a stable color-octet Dirac fermion $ ilde{\mathcal{Q}}$ stabilized by a $\operatorname{U}(1)_D$ symmetry, while neutrinos acquire radiative Majorana masses via exchange of colored scalar doublets $\eta_a$. The model unifies dark matter and neutrino mass generation, predicts a lower bound on neutrinoless double beta decay, and is viable up to the Planck scale with no Landau poles if scalars are heavier than fermions.

ABSTRACT

We propose a simple scenario in which dark matter (DM) emerges as a stable neutral hadronic thermal relics, its stability following from an exact $\operatorname{U}(1)_D$ symmetry. Neutrinos pick up radiatively induced Majorana masses from the exchange of colored DM constituents. There is a common origin for both dark matter and neutrino mass, with a lower bound for neutrinoless double beta decay. Direct DM searches at nuclear recoil experiments will test the proposal, which may also lead to other phenomenological signals at future hadron collider and lepton flavour violation experiments.

Motivation & Objective

• To propose a viable, UV-complete framework where dark matter and neutrino masses arise from a common origin via radiative mechanisms.
• To stabilize bound-state dark matter through a $\operatorname{U}(1)_D$ symmetry rather than $B-L$, allowing Majorana neutrinos.
• To ensure consistency with neutrino oscillation data by generating at least two non-zero neutrino masses.
• To explore phenomenological signals in direct dark matter detection, lepton flavor violation, and future hadron colliders.
• To demonstrate that the model remains perturbative up to the Planck scale, avoiding Landau poles when scalar masses exceed fermion masses.

Proposed method

• Introduce a heavy Dirac fermion $\mathcal{Q}$ transforming as a color octet under $\operatorname{SU}(3)_c$ and charged under $\operatorname{U}(1)_D$, ensuring its stability via the global symmetry.
• Introduce two colored $\operatorname{SU}(2)_L$ doublet scalars $\eta_a$ with opposite $\operatorname{U}(1)_D$ charges to mediate neutrino mass generation.
• Implement a one-loop Feynman diagram with $\mathcal{Q}$ and $\eta_a$ circulating to generate Majorana neutrino masses at one-loop order.
• Construct a Higgs potential $\mathcal{V}(H,\eta_a)$ that respects $\operatorname{U}(1)_D$ and CP conservation, forbidding tree-level neutrino masses.
• Use the one-loop effective neutrino mass matrix $\mathcal{M}_\nu \sim \frac{N_c M_{\mathcal{Q}}}{32\pi^2} (h_i y_j + h_j y_i)$ to compute radiatively induced Majorana masses.
• Ensure asymptotic freedom and absence of Landau poles by requiring $M_{\eta_a} > M_{\mathcal{Q}}$, with $n_\eta = 2$ scalar octets.

Experimental results

Research questions

• RQ1 Can a bound-state dark matter candidate be stabilized by a $\operatorname{U}(1)_D$ symmetry instead of $B-L$, while allowing Majorana neutrinos?
• RQ2 What is the one-loop mechanism for generating radiative Majorana neutrino masses in a model with colored dark matter constituents?
• RQ3 What are the cosmological and collider constraints on the mass scale of the dark matter fermion and its scalar partners?
• RQ4 How does the model predict a lower bound on the effective Majorana neutrino mass in neutrinoless double beta decay?
• RQ5 Can the colored scalar and fermion states in this model produce distinctive signatures in future hadron colliders or lepton flavor violation experiments?

Key findings

• The model generates radiative Majorana neutrino masses via a one-loop diagram involving $\mathcal{Q}$ and $\eta_a$, with the effective mass matrix $\mathcal{M}_\nu \sim \frac{N_c M_{\mathcal{Q}}}{32\pi^2} (h_i y_j + h_j y_i)$.
• The model predicts a lower bound on the effective Majorana neutrino mass $\langle m_{\nu} \rangle \gtrsim 0.02$ eV for normal neutrino mass ordering, depending on Yukawa couplings.
• Direct dark matter detection experiments are expected to probe the model, as the $\mathcal{Q}\mathcal{Q}$ bound state can induce nuclear recoils.
• The model is UV-complete up to the Planck scale without Landau poles, provided the scalar masses $M_{\eta_a}$ exceed the fermion mass $M_{\mathcal{Q}}$.
• The pair production cross sections for $\mathcal{Q}\bar{\mathcal{Q}}$ and $\eta_1\bar{\eta}_1$ are comparable at a 100 TeV collider, leading to similar signatures with additional charged leptons or missing energy.
• Charged lepton flavor violation processes mediated by $\mathcal{Q}$ and $\eta_a$ may reach detectable levels depending on scalar masses and Yukawa couplings.