Minimal Flavor Violation

by Christopher Smith (Université de Berne)

Tuesday 18 Mar 2008, 11:00 → 12:30 Europe/Brussels

Fynu Seminar

The reason why quarks and leptons appear in three generations (or flavors) is one of the most mysterious aspect of the Standard Model (SM). Further, the three up-quarks, down-quarks and charged leptons have highly non-generic masses and mixings, with e.g. the top mass about 105 times larger than the up. These peculiar patterns have several important phenomenological consequences, which have been confirmed extensively in B and K physics experiments. At the same time, New Physics around the TeV scale could be discovered soon at the LHC. If this is the case, the presence of new particles so close to the electroweak scale immediately collides with the results of precision experiments, typically over-producing quark flavor transitions measured in B or K decays, lepton flavor transitions like mu --> e gamma, or inducing very rapid proton decay. Therefore, the dynamics of flavored particles must be highly non-generic also within New Physics. The Minimal Flavor Violation (MFV) hypothesis is designed to enforce such non-generic structures, and can do this by systematically exporting the patterns exhibited in the SM to the New Physics. In the course, after a short introduction on flavor dynamics in the SM, the MFV hypothesis is introduced to solve the New Physics flavor puzzle in a model-independent way. Then, the implementations of this hypothesis in presence of two Higgs doublets with very different vacuum expectation values (the so-called large tan(beta) limit), and when neutrinos are massive (e.g., through the seesaw mechanism) are detailed. After those mostly model-independent developments, the last part of the course concerns the Minimal Supersymmetric Standard Model (MSSM). There, MFV will be seen to be essential to prevent TeV-scale supersymmetric particles from spoiling the delicate patterns needed to pass experimental constraints on flavor-transitions. In addition, a peculiar aspect of the MSSM is that baryon and lepton numbers are not automatically conserved in the Lagrangian. Therefore, to avoid rapid proton decay, the MSSM is usually defined including an extra symmetry, the R-parity, but this at the cost of deeply altering its phenomenology, and making the experimental search strategies more involved. We will see that MFV naturally suppresses proton decay, and thus that R-parity can be avoided altogether. Some phenomenological consequences for the search for supersymmetry at the LHC will then be illustrated. Finally, if time permits, a few aspect of MFV beyond the MSSM will be presented, taking the supersymmetric SU(5) theory as an example. ___________________________________________________ References: Some notes are still under construction but should be available soon (see Table of Content below). The various aspects of MFV we will introduce in the course were originally developed in: - D'Ambrosio, Giudice, Isidori, Strumia, hep-ph/0207036, - Cirigliano, Grinstein, Isidori, Wise, hep-ph/0507001, hep-ph/0608123, - Isidori, Mescia, Paradisi, Smith, Trine, hep-ph/0604074, - Cirigliano, Isidori, Porretti, hep-ph/0607068, - Nikolidakis, Smith, arXiv:0710.3129. ___________________________________________________ 1 Introduction 2 The flavors in the Standard Model 2.1 Gauge sector, Yukawa couplings and flavor-changing currents 2.2 How to exploit the flavor symmetry in a clever way? 2.3 The accidental conservation of the baryon and lepton numbers 3 New Physics and the flavor puzzle 3.1 How to define naturalness in flavor physics? 3.1.1 Naturalness and the scale of New Physics 3.1.2 Naturalness and the Minimal Flavor Violation hypothesis 3.2 Reconstruction and MFV expansion 3.3 The two Higgs doublet model 3.4 Turning on neutrino masses 3.4.1 The light neutrino masses and mixings 3.4.2 Neutrino spurions in the Dirac neutrino case 3.4.3 Neutrino spurions in the Majorana neutrino case 3.4.4 Neutrino spurions from the seesaw mechanism 3.4.5 Conclusion: MFV in the leptonic sector 4 Flavors in the Minimal Supersymmetric Standard Model 4.1 Flavor puzzles in the MSSM 4.2 Squark masses and Flavor Changing Neutral Currents 4.3 Super-seesaw and Lepton Flavor Violation 4.4 R-parity, proton decay and the LHC 4.4.1 R-parity and its violation 4.4.2 Enforcing MFV and proton decay 4.4.5 Phenomenological consequences for LHC, FCNC, LFV. 5 Conclusion