[Paper Review] Inverse neutrinoless double beta decay (and other Delta L=2 processes)

David London|ArXiv.org|Jul 19, 1999

Particle physics theoretical and experimental studies1 references3 citations

TL;DR

This paper investigates the feasibility of detecting lepton-number-violating processes like inverse neutrinoless double beta decay at future colliders, focusing on ΔL = 2 processes such as e⁻e⁻ → W⁻W⁻ and μ⁻μ⁻ → W⁻W⁻. It shows that while e⁻e⁻ → W⁻W⁻ is constrained by neutrinoless double beta decay unless √s ≳ 2 TeV, μ⁻μ⁻ → W⁻W⁻ could be observable at lower energies due to the absence of analogous constraints on the muon neutrino mass.

ABSTRACT

I review the prospects for the detection of Delta L=2 processes at future colliders. Except in contrived models, the process e- e- -> W- W- is unobservable at future linear colliders unless $\sqrt{s} \gsim 2$ TeV, due to constraints from neutrinoless double beta decay. As there are no analogous constraints on the Majorana mass of the $ν_μ$, mu- mu- -> W- W- could be observed at a muon collider with considerably lower $\sqrt{s}$. One can also consider esoteric processes such as gamma gamma -> mu+ mu+ W- W-. Such processes may be observable if $\sqrt{s} \gsim 4$ TeV.

Motivation & Objective

• To assess the detectability of ΔL = 2 processes, particularly inverse neutrinoless double beta decay, at future linear and muon colliders.
• To evaluate the constraints imposed by existing neutrinoless double beta decay limits on the observation of e⁻e⁻ → W⁻W⁻ at linear colliders.
• To explore whether muon colliders could enable the observation of μ⁻μ⁻ → W⁻W⁻ at lower center-of-mass energies than electron colliders.
• To examine the potential for observing exotic processes such as γγ → μ⁺μ⁺W⁻W⁻ at high-energy colliders.
• To determine the energy thresholds required for observing these lepton-number-violating processes under realistic model constraints.

Proposed method

• Analyzes the constraints from neutrinoless double beta decay on the effective Majorana mass of the electron neutrino.
• Applies these constraints to the process e⁻e⁻ → W⁻W⁻ at future linear colliders, showing that observation requires √s ≳ 2 TeV.
• Considers the absence of analogous constraints on the muon neutrino Majorana mass, enabling lower-energy observation of μ⁻μ⁻ → W⁻W⁻.
• Evaluates the cross-sections and kinematic feasibility of higher-multiplicity processes like γγ → μ⁺μ⁺W⁻W⁻ at high-energy colliders.
• Uses effective field theory techniques to model ΔL = 2 interactions in the context of lepton-number violation.
• Compares the sensitivity of different collider types (electron vs. muon) to ΔL = 2 signals based on available experimental constraints.

Experimental results

Research questions

• RQ1 What is the minimum center-of-mass energy required for observing e⁻e⁻ → W⁻W⁻ at a linear collider, given constraints from neutrinoless double beta decay?
• RQ2 Why is the μ⁻μ⁻ → W⁻W⁻ process potentially observable at lower energies than e⁻e⁻ → W⁻W⁻?
• RQ3 What are the kinematic and cross-section constraints on exotic ΔL = 2 processes such as γγ → μ⁺μ⁺W⁻W⁻?
• RQ4 How do the limits from neutrinoless double beta decay affect the viability of observing ΔL = 2 processes in e⁻e⁻ collisions?
• RQ5 Can a muon collider provide a more favorable environment for probing lepton-number-violating interactions than an electron collider?

Key findings

• The process e⁻e⁻ → W⁻W⁻ is unobservable at future linear colliders unless √s ≳ 2 TeV, due to stringent constraints from neutrinoless double beta decay on the electron neutrino Majorana mass.
• In contrast, μ⁻μ⁻ → W⁻W⁻ could be observed at a muon collider with significantly lower center-of-mass energy, as no analogous constraints exist for the muon neutrino Majorana mass.
• Exotic processes such as γγ → μ⁺μ⁺W⁻W⁻ may be observable at √s ≳ 4 TeV, depending on the model parameters and cross-sections.
• The absence of strong bounds on the muon neutrino Majorana mass allows for a broader discovery reach in μ⁻μ⁻ → W⁻W⁻ at lower energies.
• The study highlights the complementary role of muon colliders in probing lepton-number-violating physics beyond the reach of electron-based colliders.
• The results suggest that future colliders, especially muon colliders, offer a viable pathway to test ΔL = 2 processes if the underlying physics is realized at accessible energy scales.