[Paper Review] Flavour Physics and Grand Unification

A. Masiero, Sudhir K. Vempati+1 more|ArXiv.org|Nov 19, 2007

Space Science and Extraterrestrial Life2 references18 citations

TL;DR

This paper explores the interplay between flavor physics and grand unification in supersymmetric grand unified theories (SUSY-GUTs), showing how low-energy flavor and CP violation observables—such as electric dipole moments, lepton flavor violation, and anomalous magnetic moments—can serve as indirect probes of GUT-scale physics. It demonstrates that SUSY-GUTs naturally generate flavor-violating soft terms, linking high-scale unification to measurable low-energy effects.

ABSTRACT

In spite of the enormous success of the Standard Model (SM), we have strong reasons to expect the presence of new physics beyond the SM at higher energies. The idea of the Grand Unification of all the known interactions in nature is perhaps the main reason behind these expectations. Low-energy Supersymmetry is closely linked with grand unification as a solution of the hierarchy problem associated with the ratio M_GUT / M_Z. In these lectures we will provide a general overview of Grand Unification and Supersymmetry with special emphasis on their phenomenological consequences at low energies. We will analyse the flavour and CP problems of Supersymmetry and try to identify in these associated low-energy observables possible indications of the existence of a Grand Unified theory at high energies.

Motivation & Objective

• To examine the theoretical and phenomenological motivations for physics beyond the Standard Model, particularly grand unification and supersymmetry.
• To analyze the flavor and CP problems in supersymmetric grand unified theories (SUSY-GUTs), focusing on how these issues constrain or signal new physics.
• To identify low-energy observables—such as electric dipole moments, lepton flavor violation, and anomalous magnetic moments—that can indirectly probe GUT-scale dynamics.
• To investigate the role of seesaw mechanisms and right-handed neutrinos in connecting flavor structure to GUT-scale physics.
• To assess the complementarity between direct collider searches (LHC/ILC), flavor experiments, and dark matter detection in probing SUSY-GUT models.

Proposed method

• Analyzes gauge coupling unification in minimal SU(5) and SO(10) GUTs, including the role of supersymmetry in stabilizing the hierarchy.
• Applies renormalization group evolution (RGE) techniques to study the generation of flavor-violating soft terms from GUT-scale breaking patterns.
• Evaluates flavor-changing neutral currents (FCNCs) and electric dipole moments (EDMs) in the MSSM, using mass insertion approximations and RGE-improved effective Lagrangians.
• Considers the seesaw mechanism in GUTs to explain small neutrino masses and its implications for lepton flavor violation and CP violation.
• Assesses the interplay between SUSY-GUTs, dark matter phenomenology, and leptogenesis, particularly in SO(10) models.
• Uses indirect constraints from precision electroweak observables (e.g., (g-2)μ, Z→bb̄ asymmetry) to probe the viability of SUSY-GUT scenarios.

Experimental results

Research questions

• RQ1 How do flavor-violating soft terms arise in SUSY-GUTs, and what constraints do low-energy flavor observables impose on the GUT scale?
• RQ2 To what extent can electric dipole moments (EDMs) and lepton flavor violation (LFV) in SUSY-GUTs serve as indirect signals of grand unification?
• RQ3 What role does the seesaw mechanism play in linking neutrino masses to flavor structure and CP violation in GUT models?
• RQ4 In what regions of parameter space do indirect flavor probes (e.g., (g-2)μ, LFV) outperform direct LHC searches for SUSY?
• RQ5 Can CP violation in SUSY-GUTs provide a viable mechanism for leptogenesis and explain the baryon asymmetry of the universe?

Key findings

• SUSY-GUTs naturally generate flavor-violating soft terms through RGE evolution, making low-energy flavor observables sensitive probes of GUT-scale physics.
• Electric dipole moments (EDMs) in the MSSM are strongly constrained by CP-violating phases in the soft-breaking sector, with current bounds disfavoring large CP phases unless R-symmetry or other protections are present.
• Lepton flavor violation (LFV) processes such as μ→eγ are enhanced in SUSY-GUTs with right-handed neutrinos, particularly in SO(10) models, due to mixing in the right-handed slepton sector.
• The (g-2)μ anomaly persists in many SUSY-GUT models, suggesting that new physics contributions may be relevant, especially in the focus point region of the parameter space.
• In certain SUSY-GUT scenarios—particularly SO(10) with the seesaw mechanism—flavor experiments can be more sensitive than LHC direct searches, especially in the focus point region.
• SUSY-GUTs can modify the dark matter parameter space, and flavor and dark matter constraints can act as complementary probes of the underlying GUT structure.