[Paper Review] Lepton flavor violation beyond the MSSM

Avelino Vicente|arXiv (Cornell University)|Mar 30, 2015

Particle physics theoretical and experimental studies201 references4 citations

TL;DR

This paper reviews lepton flavor violation (LFV) in supersymmetric models beyond the Minimal Supersymmetric Standard Model (MSSM), focusing on high-scale and low-scale seesaw mechanisms and R-parity violating scenarios. It demonstrates that LFV phenomenology in these extended models exhibits distinct signatures—such as large branching ratios for $μ\to e\gamma$ and $\mu\to eJ$—that differ significantly from MSSM predictions, necessitating dedicated experimental searches beyond standard channels to identify new physics. - meta_description: Explores lepton flavor violation in non-minimal SUSY models beyond MSSM, highlighting unique LFV signatures in seesaw and R-parity violating scenarios for future experimental detection. - objective: • To analyze LFV phenomenology in extended supersymmetric models beyond the MSSM. • To identify characteristic LFV signatures in high-scale and low-scale seesaw models. • To examine the impact of R-parity violation on LFV processes. • To assess the viability of detecting exotic LFV decays like $\mu\to eJ$ and $\mu\to eJ\gamma$ in current and future experiments. - method: • Analyzes high-scale seesaw models via extended neutrino mass generation mechanisms. • Investigates the supersymmetric inverse seesaw with sterile neutrinos and seesaw scales below the TeV scale. • Evaluates R-parity violating models through explicit and spontaneous breaking of R-parity in the superpotential. • Uses effective field theory and two-Higgs-doublet extensions to model LFV couplings. • Applies phase space integrals and decay width calculations to estimate branching ratios for $\mu\to eJ$ and $\mu\to eJ\gamma$. • Compares experimental sensitivity of MEG to exotic LFV channels using kinematic cuts and background modeling. - research_questions: • How do LFV rates in high-scale seesaw models differ from those in the MSSM? • What are the distinctive phenomenological features of LFV in low-scale seesaw scenarios? • Can R-parity violating models generate observable LFV signals despite LHC constraints? • How sensitive are current experiments like MEG to exotic LFV decays such as $\mu\to eJ\gamma$? • What experimental improvements are needed to detect $\mu\to eJ$ decays with $v_R$ below the TeV scale? - key_findings: • High-scale seesaw models predict large LFV rates due to heavy right-handed neutrino exchanges, with $\text{BR}(\mu\to e\gamma)\sim 10^{-11}$ for $v_R\sim 10^9$ GeV. • Low-scale seesaw models, particularly the supersymmetric inverse seesaw, can yield observable $\text{BR}(\mu\to e\gamma)$ up to $10^{-12}$ due to light sterile neutrinos. • R-parity violating models with $v_R\sim 1$ TeV predict $\text{BR}(\mu\to eJ)\sim 10^{-5}$, though current limits are weak ($\lesssim 10^{-5}$). • The phase space integral for $\mu\to eJ\gamma$ is extremely small ($\sim 6\times10^{-10}$) under MEG’s tight cuts, making detection nearly impossible without relaxed kinematic thresholds. • Background from muon annihilation in flight severely limits sensitivity to $\mu\to eJ\gamma$, suggesting that improved timing resolution is essential for viable detection.

ABSTRACT

Most extensions of the Standard Model lepton sector predict large lepton flavor violating rates. Given the promising experimental perspectives for lepton flavor violation in the next few years, this generic expectation might offer a powerful indirect probe to look for new physics. In this review we will cover several aspects of lepton flavor violation in supersymmetric models beyond the Minimal Supersymmetric Standard Model. In particular, we will concentrate on three different scenarios: high-scale and low-scale seesaw models as well as models with R-parity violation. We will see that in some cases the LFV phenomenology can have characteristic features for specific scenarios, implying that dedicated studies must be performed in order to correctly understand the phenomenology in non-minimal supersymmetric models.

Motivation & Objective

• To analyze LFV phenomenology in extended supersymmetric models beyond the MSSM.
• To identify characteristic LFV signatures in high-scale and low-scale seesaw models.
• To examine the impact of R-parity violation on LFV processes.
• To assess the viability of detecting exotic LFV decays like $\mu\to eJ$ and $\mu\to eJ\gamma$ in current and future experiments.

Proposed method

• Analyzes high-scale seesaw models via extended neutrino mass generation mechanisms.
• Investigates the supersymmetric inverse seesaw with sterile neutrinos and seesaw scales below the TeV scale.
• Evaluates R-parity violating models through explicit and spontaneous breaking of R-parity in the superpotential.
• Uses effective field theory and two-Higgs-doublet extensions to model LFV couplings.
• Applies phase space integrals and decay width calculations to estimate branching ratios for $\mu\to eJ$ and $\mu\to eJ\gamma$.
• Compares experimental sensitivity of MEG to exotic LFV channels using kinematic cuts and background modeling.

Experimental results

Research questions

• RQ1 How do LFV rates in high-scale seesaw models differ from those in the MSSM?
• RQ2 What are the distinctive phenomenological features of LFV in low-scale seesaw scenarios?
• RQ3 Can R-parity violating models generate observable LFV signals despite LHC constraints?
• RQ4 How sensitive are current experiments like MEG to exotic LFV decays such as $\mu\to eJ\gamma$?
• RQ5 What experimental improvements are needed to detect $\mu\to eJ$ decays with $v_R$ below the TeV scale?

Key findings

• High-scale seesaw models predict large LFV rates due to heavy right-handed neutrino exchanges, with $\text{BR}(\mu\to e\gamma)\sim 10^{-11}$ for $v_R\sim 10^9$ GeV.
• Low-scale seesaw models, particularly the supersymmetric inverse seesaw, can yield observable $\text{BR}(\mu\to e\gamma)$ up to $10^{-12}$ due to light sterile neutrinos.
• R-parity violating models with $v_R\sim 1$ TeV predict $\text{BR}(\mu\to eJ)\sim 10^{-5}$, though current limits are weak ($\lesssim 10^{-5}$).
• The phase space integral for $\mu\to eJ\gamma$ is extremely small ($\sim 6\times10^{-10}$) under MEG’s tight cuts, making detection nearly impossible without relaxed kinematic thresholds.
• Background from muon annihilation in flight severely limits sensitivity to $\mu\to eJ\gamma$, suggesting that improved timing resolution is essential for viable detection.