New physics in CP violation experiments

CP violation plays a privileged role in our quest for new physics beyond the electroweak standard model (SM). In the SM the violation of CP in the weak interactions has a single source: the phase of the quark mixing matrix (the CKM matrix, for Cabibbo-Kobayashi-Maskawa). Most extensions of the SM exhibit new sources of CP violation. For instance, the truly minimal supersymmetric extension of the SM (CMSSM) has two new phases in addition to the CKM phase. Given that CP violation is so tiny in the kaon system, is still largely unexplored in B physics and is negligibly small in the electric dipole moments, it is clear that new physics may have a good chance to manifest some departure from the SM in this particularly challenging class of rare phenomena. On the other hand, it is also apparent that CP violation generally represents a major constraint on any attempt at model building beyond the SM. In this review we tackle these two sides of the relation between CP violation and new physics. Our focus will be on the potentialities to use CP violation as a probe on Supersymmetric (SUSY) extensions of the SM. We wish to clarify the extent to which such indirect signals for SUSY are linked to a fundamental theoretical issue: is there a relation between the mechanism that originates the whole flavor structure and the mechanism that is responsible for the breaking of supersymmetry? Different ways to answer this question lead to quite different expectations for CP violation in B physics.Comment: 47 pages, 3 figures. Invited contribution to appear in Annual Reviews of Nuclear and Particle Science Vol. 51, December 200

Flavor Structure and Supersymmetric CP-Violation

In this talk, we address the possibility of finding supersymmetry through indirect searches in the K and B systems. We prove that, in the absence of the Cabibbo-Kobayashi-Maskawa phase, a general Minimal Supersymmetric Standard Model with all possible phases in the soft-breaking terms, but no new flavor structure beyond the usual Yukawa matrices, can never give a sizeable contribution to $\epsilon_K$, $\epsilon^\prime/\epsilon$ or hadronic B^0 CP asymmetries. However, Minimal Supersymmetric models with additional flavor structures in the soft-supersymmetry breaking terms can produce large deviations from the Standard Model predictions. Hence, observation of supersymmetric contributions to CP asymmetries in B decays would be the first sign of the existence of new flavor structures in the soft-terms and would hint at a non-flavor blind mechanism of supersymmetry breaking.Comment: 15 pages, 3 eps figures. Invited talks given by A. Masiero at the 8th International Symposium on Heavy Flavour Physics (Heavy Flavors 8), Southampton, 25-29 July 1999 and Workshop on Physics and Detectors for DAFNE (Dafne99), Frascati, 16-10 Nov. 199

Flavoured leptogenesis: a successful thermal leptogenesis with N_1 mass below 10^8 GeV

We prove that taking correctly into account the lepton flavour dependence of the CP asymmetries and washout processes, it is possible to obtain successful thermal leptogenesis from the decays of the second right-handed neutrino. The asymmetries in the muon and tau-flavour channels are then not erased by the inverse decays of the lightest right-handed neutrino, N_1. In this way, we reopen the possibility of ``thermal leptogenesis'' in models with a strong hierarchy in the right-handed Majorana masses that is typically the case in models with up-quark--neutrino Yukawa unification.Comment: 5 pages, no figures. References added, referencing correcte

Invariant approach to flavour-dependent CP-violating phases in the MSSM

We use a new weak basis invariant approach to classify all the observable phases in any extension of the Standard Model (SM). We apply this formalism to determine the invariant CP phases in a simplified version of the Minimal Supersymmetric SM with only three non-trivial flavour structures. We propose four experimental measures to fix completely all the observable phases in the model. After these phases have been determined from experiment, we are able to make predictions on any other CP-violating observable in the theory, much in the same way as in the Standard Model all CP-violation observables are proportional to the Jarlskog invariant.Comment: 25 pages, 12 figure

Eviction of a 125 GeV "heavy"-Higgs from the MSSM

We prove that the present experimental constraints are already enough to rule out the possibility of the ~125 GeV Higgs found at LHC being the second lightest Higgs in a general MSSM context, even with explicit CP violation in the Higgs potential. Contrary to previous studies, we are able to eliminate this possibility analytically, using simple expressions for a relatively small number of observables. We show that the present LHC constraints on the diphoton signal strength, tau-tau production through Higgs and BR(B -> X_s gamma) are enough to preclude the possibility of H_2 being the observed Higgs with m_H~125 GeV within an MSSM context, without leaving room for finely tuned cancellations. As a by-product, we also comment on the difficulties of an MSSM interpretation of the excess in the gamma-gamma production cross section recently found at CMS that could correspond to a second Higgs resonance at m_H~136 GeV.Comment: 38 pages, 9 figures. Final version accepted at JHEP. Sections 2, 3 and appendices simplified. Experimental results updated, several references added. Small typos corrected and a new comparison of approximate formulas with full expressions include

METing SUSY on the Z peak

Recently the ATLAS experiment announced a 3 $\sigma$ excess at the Z-peak consisting of 29 pairs of leptons together with two or more jets, $E_T^{\rm miss}> 225$ GeV and $H_T \geq 600$ GeV, to be compared with $10.6 \pm 3.2$ expected lepton pairs in the Standard Model. No excess outside the Z-peak was observed. By trying to explain this signal with SUSY we find that only relatively light gluinos, $m_{\tilde g} \lesssim 1.2$ TeV, together with a heavy neutralino NLSP of $m_{\tilde \chi} \gtrsim 400$ GeV decaying predominantly to Z-boson plus a light gravitino, such that nearly every gluino produces at least one Z-boson in its decay chain, could reproduce the excess. We construct an explicit general gauge mediation model able to reproduce the observed signal overcoming all the experimental limits. Needless to say, more sophisticated models could also reproduce the signal, however, any model would have to exhibit the following features, light gluinos, or heavy particles with a strong production cross-section, producing at least one Z-boson in its decay chain. The implications of our findings for the Run II at LHC with the scaling on the Z peak, as well as for the direct search of gluinos and other SUSY particles, are pointed out.Comment: 24 pages, 17 figures, simulation improved, Checkmate analysis added, new benchmark point included. Typos corrected, conclusions unchange

Kaon vs. Bottom: Where to look for a general MSSM?

We analyze CP violation and Flavor Changing effects in a general Minimal Supersymmetric extension of the Standard Model with arbitrary non-universal soft-breaking terms. We show that, in this conditions, large FCNC effects are naturally expected in the Kaon system, even in the absence of quark-squark flavor misalignment. On the other hand, the B system is only sensitive to new supersymmetric contributions if the non-universality implies, not only different soft term for the three generations but also the presence of a quark-squark misalignment much larger that the corresponding CKM mixing. The only exception to this rule are processes where the chirality changing contributions proportional to tan beta are leading (for instance b -> s gamma)

General Flavor Blind MSSM and CP Violation

We study the implications on flavor changing neutral current and CP violating processes in the context of supersymmetric theories without a new flavor structure (flavor blind supersymmetry). The low energy parameters are determined by the running of the soft breaking terms from the grand unified scale with SUSY phases consistent with the EDM constraints. We find that the CP asymmetry in b --> s gamma can reach large values potentially measurable at B factories, especially in the low BR(b --> s gamma) region. We perform a fit of the unitarity triangle including all the relevant observables. In this case, no sizeable deviations from the SM expectations are found. Finally we analyze the SUSY contributions to the anomalous magnetic moment of the muon pointing out its impact on the b --> s gamma CP asymmetry and on the SUSY spectrum including chargino and stop masses.Comment: 40 pages, 8 figures, typos corrected, references adde