Supersymmetry and FCNC effects

TL;DR

This paper analyzes flavor-changing neutral current (FCNC) processes within the MSSM, showing that even with flavour-conserving sfermion masses, new FCNC effects arise from charged Higgs/chargino loops and from flavour off-diagonal sfermion mass terms. Using the mass-insertion formalism and contributions from gluino/photino boxes, it derives bounds on the off-diagonal and diagonal entries of sfermion mass matrices and discusses how these constraints shape expectations for soft SUSY breaking and sfermion mass generation. The authors conclude that while the supersymmetric flavour problem is nontrivial, it may not be as severe as commonly believed due to cancellations and the structure of the MSSM, implying substantial guidance for model-building. The work highlights the interplay between CKM-like mixing and SUSY-induced FCNCs, and underscores the importance of FCNC observables in constraining SUSY-breaking mechanisms at the TeV scale.

Abstract

We consider Flavour Changing Neutral Current processes in the framework of the supersymmetric extension of the Standard Model. FCNC constraints on the structure of sfermion mass matrices are reviewed. Furthermore, we analyze supersymmetric contributions to FCNC transitions which remain in the limit of flavour-conserving sfermion mass matrices. Implications of the FCNC constraints on the structure of sfermion mass matrices for SUSY breaking and sfermion mass generation are discussed. We conclude that the supersymmetric flavour problem is intriguing but perhaps not as severe as it is commonly believed.

Figures (9)

• Figure 1: Chargino-quark-squark vertices.
• Figure 2: Neutralino-quark-squark vertices.
• Figure 3: Gluino-quark-squark vertices.
• Figure 4: MSSM diagrams contributing to $\bar{K}^0K^0$ mixing (crossed diagrams not plotted).
• Figure 5: Chargino contribution to $\bar{K}^0K^0$ in mass insertion expansion.