We investigate the consequences of replacing the global flavour symmetry of Minimal Flavour Violation (MFV) SU(3)_QxSU(3)_UxSU(3)_Dx..., by a discrete D_QxD_UxD_Dx.. symmetry. Goldstone bosons resulting from the breaking of the flavour symmetry generically lead to bounds on new flavour structure many orders of magnitude above the TeV-scale. The absence of Goldstone bosons for discrete symmetries constitute the \emph{primary} motivation of our work. Less symmetry implies further invariants and renders the mass flavour basis transformation observable in principle and calls for a hierarchy in the Yukawa matrix expansion. We show, through the dimension of the representations, that the (discrete) symmetry in principle does allow for additional Delta F = 2 operators. If though the Delta F = 2 transitions are generated by two subsequent Delta F = 1 processes, as for example in the Standard Model, then the four crystal-like groups Sigma(168) ~ PSL(2,7), Sigma(72phi), Sigma(216phi) and especially Sigma(360phi) do provide enough protection for a TeV-scale discrete MFV scenario. Models where this is not the case have to be investigated case by case. Interestingly Sigma(216phi) has a (non-faithful) representation corresponding to an A4-symmetry. Moreover we argue that the, apparently often omitted, (D)-groups are subgroups of an appropriate Delta(6g^2). We would like to stress that we do not provide an actual model that realizes the MFV scenario nor any other theory of flavour.
We review aspects of the phenomenology of the MSSM with non-minimal flavour violation, including a discussion of important constraints and the sensitivity to fundamental scales.
We summarize the results on patterns of flavour violation in a Randall-Sundrum model with custodial protection (RSc) and compare them with those identified in the Littlest Higgs Model with T--parity (LHT) and in a number of SUSY Flavour Models. While K decays play in this presentation a prominent role, the inclusion of B physics and lepton flavour violation is crucial in the distinction between these three popular extensions of the Standard Model (SM) by means of flavour physics.
We analyze CP violation in supersymmetry with Effective Minimal Flavour Violation, as recently proposed in arXiv:1011.0730. Unlike the case of standard Minimal Flavour Violation, we show that all the phases allowed by the flavour symmetry can be sizable without violating existing Electric Dipole Moment constraints, thus solving the SUSY CP problem. The EDMs at one and two loops are precisely analyzed as well as their correlations with the expected CP asymmetries in B physics.
The Little Higgs model with T-parity (LHT) belongs to the non-minimal flavour violating model. This model has new sources of flavour and CP violation both in quark and leptonic sectors. These new sources of flavour violation originates by the interaction of Standard Model (SM) fermions with heavy gauge bosons and heavy (or mirror) fermions. In this work we will present the impact of the new flavour structure of T-parity models on flavour violations in leptonic sector.
We analyze lepton flavour violation (LFV) and the generation of the observed baryon-antibaryon asymmetry of the Universe (BAU) within a generalized minimal lepton flavour violation framework with three quasi-degenerate heavy Majorana neutrinos. The BAU which is obtained through radiative resonant leptogenesis can successfully be generated widely independent of the Majorana scale in this scenario and flavour effects are found to be relevant. Then we discuss the specific case in which CP violation is exclusively present at low-energies (a real R matrix) in the flavour sensitive temperature regim…
We give a pedagogical review of flavour and CP violation in the lepton sector, with a particular emphasis on new physics - and in particular supersymmetric - contributions to flavour and CP violating observables involving leptons.
The SUSY flavour problem is deeply related to the origin of flavour and hence to the origin of the SM Yukawa couplings themselves. Since all CP-violation in the SM is restricted to the flavour sector, it is possible that the SUSY CP problem is related to the origin of flavour as well. In this work, we present three variations of an SU(3) flavour model with spontaneous CP violation. Such models explain the hierarchy in the fermion masses and mixings, and predict the structure of the flavoured soft SUSY breaking terms. In such a situation, both SUSY flavour and CP problems do not exist. We use e…
We analyse the violations of lepton-flavour universality in the ratios B(P -> l nu)/B(P -> l' nu) using a general effective theory approach, discussing various flavour-symmetry breaking patterns of physics beyond the SM. We find that in models with Minimal Lepton Flavour Violation the effects are too small to be observed in the next generations of experiments in all relevant meson systems (P = Pi, K, B). In a Grand Unified framework with a minimal breaking of the flavour symmetry, the effects remain small in Pi and K decays while large violations of lepton-flavour universality are possible in …
The MSSM with $R$-Parity violation allows flavour changing neutral currents through two mechanisms, directly through one loop diagrams, and indirectly through the generation of flavour violation in the sparticle sector. We discuss the use of these mechanisms for constraining $R$-Parity violation, and show that the indirect mechanism parametrised in terms of the running of the soft masses from the unification or Planck scale typically dominates previously calculated effects. We discuss neutrino mass generation, $μ\to eγ$, $b\to sγ$, and $K^0-\bar K^0$ mixing as examples.
The tree-level flavour-changing neutral currents in the two-Higgs-doublet models can be suppressed by protecting the breaking of either flavour or flavour-blind symmetries, but only the first choice, implemented by the application of the Minimal Flavour Violation hypothesis, is stable under quantum corrections. Moreover, a two-Higgs-doublet model with Minimal Flavour Violation enriched with flavour-blind phases can explain the anomalies recently found in the Delta F = 2 transitions, namely the large CP-violating phase in B_s mixing and the tension between epsilon_K and S_ψ_K.
We explore the possibility of detecting lepton flavour violation, now a well established experimental fact, at the International Linear Collider. Using a model independent approach we conclude that, given all experimental constraints available, there is still room to detect lepton flavour violation at the ILC.
We present the first exact and most general neutralino-neutralino annihilation cross sections in the presence of flavor violation. The existing set of calculations in literature do not include flavour violation. These calculations are important for the calculation of relic density and indirect detection of dark matter in various experiments.
We investigate the phenomenological impact of different sources of lepton flavour violation arising from realistic models based on supergravity mediated supersymmetry breaking with Yukawa operators. We discuss four distinct sources of lepton flavour violation in such models: minimum flavour violation, arising from neutrino masses and the see-saw mechanism with RG running; supergravity flavour violation due to the non-universal structure of the supergravity model; flavour violation due to Froggatt-Nielsen (FN) fields appearing in Yukawa operators developing supersymmetry breaking F-terms and co…
I discuss theoretical and phenomenological aspects of flavour violation in charged lepton transitions. This includes minimal extensions of the Standard Model within effective-theory approaches, as well as an incomplete selection of concrete new physics models.
If observed, charged lepton flavour violation is a clear sign of new physics - beyond the Standard Model minimally extended to accommodate neutrino oscillation data. We briefly review several extensions of the Standard Model which could potentially give rise to observable signals, also emphasising the rôle of charged lepton flavour violation in probing such new physics models.
The flavour-changing neutral currents (FCNC) are derived at tree level if the electroweak gauge group depends on the fermion family, which are absent in the standard model. We study the lepton flavour violation (LFV) through the FCNC interactions in a nonuniversal gauge interaction model where the third generation fermions are subjected to the separate SU(2)$_L$ gauge group.
We study the implications of a successful leptogenesis within the framework of Minimal Lepton Flavour Violation combined with radiative resonant leptogenesis and the PMNS matrix being the only source of CP violation, which can be obtained provided flavour effects are taken into account. We find that the right amount of the baryon asymmetry of the universe can be generated under the conditions of a normal hierarchy of the light neutrino masses, a non-vanishing Majorana phase, sin(theta_{13})>0.13 and m_{nu,lightest}<0.04 eV. If this is fulfilled, we find strong correlations among ratios of char…
In supersymmetric models new sources of lepton flavour violation (LFV) may enhance the rates of charged lepton flavour violating processes, like mu to e gamma, and generate distinct final states at future colliders, e.g. tau mu + jets + missing energy. We discuss the role of chargino pair production for the LFV signals at e+e- colliders.
After a brief review of the minimal flavour violation hypothesis and its implementation in the MSSM, the most general parametrisation of the soft supersymmetry-breaking terms by means of the charged lepton and neutrino spurions is constructed. Thereby a type I seesaw mechanism is assumed to generate neutrino masses. This expansion introduces several new CP-violating phases, whose effects on the leptonic electric dipole moments are investigated.
These lecture notes provide an introduction to the theoretical concepts of flavour physics and CP violation, based on a series of lectures given at the ESHEP 2016 summer school. In the first lecture we review the basics of flavour and CP violation in the Standard Model. The second lecture is dedicated to the phenomenology of K and B meson decays, where we focus on a few representative observables. In the third lecture we give an introduction to flavour physics beyond the Standard Model, both within the framework of Minimal Flavour Violation and beyond.
We briefly review flavour violation in the lepton sector: starting from neutrino oscillations and their implications, we consider several charged lepton flavour violating observables at high and low energies. We present new physics models and discuss the rôle of the latter in disentangling them. In particular, we show how the interplay of different observables allows to derive important information on the underlying mechanism of lepton flavour violation. As an example, we discuss the impact of a type-I SUSY seesaw concerning lepton flavour violation at low energies and at colliders (LHC and a …
We investigate the implications of $R$-Parity violation (RPV) for quark flavour violation both by constraining the sneutrino masses to be positive and by studying the processes $b\to sγ$ and $K^0-\bar K^0$ mixing. In the latter there are two major contributions, one from ``direct'' one loop diagrams involving RPV couplings, and one from the ``indirect'' contributions generated by the renormalisation group. We compare the effects and discuss the implications of our results.
Little Higgs models with T-parity have a new source of lepton flavour violation. In this paper we consider the anomalous magnetic moment of the muon \gmtwo and the lepton flavour violating decays \mutoeg and \tautomug in Little Higgs model with T-parity \cite{Goyal:2006vq}. Our results shows that present experimental constraints of \mutoeg is much more useful to constrain the new sources of flavour violation which are present in T-parity models.
Combining Pati-Salam (PS) and flavour symmetries in a renormalisable setup, we devise a scenario which produces realistic masses for the charged leptons. Flavour-symmetry breaking scalar fields in the adjoint representations of the PS gauge group are responsible for generating different flavour structures for up- and down-type quarks as well as for leptons. The model is characterised by new heavy fermions which mix with the Standard Model quarks and leptons. In particular, the partners for the third fermion generation induce sizeable sources of flavour violation. Focusing on the charged-lepton…
Starting from the effective-theory framework for Minimal Flavour Violation, we give a systematic definition of next-to-minimal (quark) flavour violation in terms of a set of spurion fields exhibiting a particular hierarchy with respect to a small (Wolfenstein-like) parameter. A few illustrative examples and their consequences for charged and neutral decays with different quark chiralities are worked out in some detail. Our framework can be used as a model-independent classification scheme for the parameterization of flavour structure from physics beyond the Standard Model.
We present an extensive analysis of gauge-mediated supersymmetry breaking models with minimal and non-minimal flavour violation. We first demonstrate that low-energy, precision electroweak, and cosmological constraints exclude large "collider-friendly" regions of the minimal parameter space. We then discuss various possibilities how flavour violation, although naturally suppressed, may still occur in gauge-mediation models. The introduction of non-minimal flavour violation at the electroweak scale is shown to relax the stringent experimental constraints, so that benchmark points, that are also…
If observed, charged lepton flavour violation is a clear sign of new physics - beyond the Standard Model minimally extended to accommodate neutrino oscillation data. After a brief review of several charged lepton flavour violation observables and their current experimental status, we consider distinct extensions of the Standard Model which could potentially give rise to observable signals, focusing on the case of models in which the mechanism of neutrino mass generation is the common source of neutral and charged lepton flavour violation.
This note is a concise theoretical summary of the first session on new physics searches at the high-intensity frontier of the IFAE2017 Conference. Recent theoretical developments related to muonic lepton-flavour violation and $g-2$ are reviewed.
The branching ratio for the mu-->e+gamma decay in the framework of the minimal flavour violation in the MSSM is calculated for various regions of the MSSM parameter space. The lepton flavour violation goes through the PMNS mixing matrix. The dependence on tanbeta is studied in comparison with experimental data. The results crucially depend on the mixing angle theta_{13}. Observation of this decay would serve as a manifestation of new physics beyond the SM.
We propose an extension of the hypothesis of Minimal Flavour Violation (MFV) to general multi-Higgs Models without the assumption of Natural Flavour Conservation in the Higgs sector. We study in detail under what conditions the neutral Higgs couplings are only functions of $V_{CKM}$ and propose a MFV expansion for the neutral Higgs couplings to fermions.
These notes represent a summary of three lectures on flavour and CP violation, given at the CERNs European School of High Energy Physics in 2014. They cover flavour physics within the standard model, phenomenology of CP violation in meson mixing and decays, as well as constraints of flavour observableson physics beyond the standard model. In preparing the lectures (and consequently this summary) I drew heavily from several existing excellent and exhaustive sets of lecture notes and reviews on flavour physics and CP violation [1]. The reader is encouraged to consult those as well as the origina…
In the absence of a fundamental principle preventing charged lepton flavour violation, one expects that extensions of the Standard Model accommodating neutrino masses and mixings should also allow for charged lepton flavour violating processes such as $\ell_i \to \ell_jγ$, $\ell_i \to \ell_j \ell_k \ell_m $ and $μ- e$ conversion in nuclei, for which the rates depend in general on the mechanism of neutrino mass generation. In addition to low-energy experiments, there are also searches for lepton flavour violation at colliders, where new physics can be directly probed through flavour violating p…
We construct lepton flavour-dependent and basis-independent measures of R-parity violation in the minimal supersymmetric extension of the Standard Model (MSSM). We work in the context of exact supersymmetry, neglecting the effects of Higgs vacuum expectation values and soft supersymmetry-breaking terms. We devote particular attention to appropriate choices of flavour eigenstates, and to the counting and enumeration of R-violating invariants in two- and three-generation models. We also make an indicative application of our results to derive possible basis-independent cosmological upper bounds o…
We review the main aspects of Flavour Physics and CP Violation in the Standard Model. After presenting a grand view of the field including a Master Formula for weak decays we discuss i) Standard analysis of the unitarity triangle, ii) The ratio epsilon'/epsilon, iii) Rare decays K^+ -> pi^+ nu barnu and K_L -> pi^0 nu barnu, iv) CP violation in B decays and v) Models with Minimal Flavour Violation. Our review ends with 20 questions that hopefully will be answered in the coming years.
Neutrino masses imply the violation of lepton flavour and new physics beyond the Standard Model. However, flavour change has only been observed in oscillations. In analogy with the quark sector, we could deduce the existence of a principle of Minimal Flavour Violation also for Leptons. Such an extension is not straightforward, since the mechanisms generating neutrino masses are unknown and many scenarios can be envisaged. Thus, we explore some possible definitions of MFVL and propose a notion that can include many models. We build an R-parity violating neutrino mass model in agreement with our…
This is a written version of a series of lectures aimed at graduate students in particle theory/string theory/particle experiment familiar with the basics of the Standard Model. We explain the many reasons for the interest in flavour physics. We describe flavour physics and the related CP violation within the Standard Model, and explain how the B-factories proved that the Kobayashi-Maskawa mechanism dominates the CP violation that is observed in meson decays. We explain the implications of flavour physics for new physics. We emphasize the "new physics flavour puzzle". As an explicit example, w…
The sources of lepton flavour and lepton number violation in the left-right symmetric models are reviewed and the most sensitive processes to these violations are discussed. Both the non-SUSY and SUSY versions of the theories are considered. Present and future experimental constraints at low as well as at high energies are discussed. Some emphasis has been put on the doubly charged particle production at future colliders.
We consider the approximate U(2)^3 flavour symmetry exhibited by the quark sector of the Standard Model and all its possible breaking terms appearing in the quark Yukawa couplings. Taking an Effective Field Theory point of view, we determine the current bounds on these parameters, assumed to control the breaking of flavour in a generic extension of the Standard Model at a reference scale Lambda. In particular, a significant bound from epsilon'/epsilon is derived, which is relevant to Minimal Flavour Violation as well. In the up-quark sector, the recently observed CP violation in D -> pi+ pi-, …
In these three lectures, I overview the theoretical framework of the flavour physics and CP violation. The first lecture is the introduction to the flavour physics. Namely, I give theoretical basics of the weak interaction. I follow also some historical aspect, discovery of the CP violation, phenomenological studies of charged and neutral currents and the success of the GIM mechanism. In the second lecture, I describe the flavour physics and CP violating phenomena in the Standard Model (SM). I also give the latest experimental observation of the CP Violation at the B factories and the LHC and …
The future of flavour physics and CP violation in the quark, lepton and Higgs sectors are discussed, particularly from the viewpoint of physics beyond the Standard Model, such as supersymmetry. Current issues in B to pi^+ pi^-, phi K_s and D^*+ D^*-, B_s physics and rare B decays are reviewed. The prospects for seeing flavour and CP violation in the charged-lepton sector are discussed, using the minimal supersymmetric seesaw model as a guide. Finally, the possible consequences of CP violation in the Higgs sector are mentioned.
We discuss several manifestations of charged lepton flavour violation at high energies. Focusing on a supersymmetric type I seesaw, considering constrained and semi-constrained supersymmetry breaking scenarios, we analyse different observables, both at the LHC and at a future Linear Collider. We further discuss how the synergy between low- and high-energy observables can shed some light on the underlying mechanism of lepton flavour violation.
In supersymmetric extensions of the Standard Model, the Yukawa and/or mass terms of the heavy neutrinos can generate lepton flavour violating slepton mass terms. These new supersymmetric sources of lepton flavour violation may both enhance the rates of charged lepton flavour violating processes, l_a -> l_b y, and generate distinct final states, like l_b l_a + jets + missing E_T, at future colliders. First, we discuss the sensitivity of future e^+e^- colliders to the SLFV independently of the lepton flavour violating mechanism. Second, we study lepton flavour violating slepton pair production a…
We investigate the viability of leptogenesis in models with three heavy right-handed neutrinos, where the charged-lepton and the neutrino Yukawa couplings are the only irreducible sources of lepton-flavour symmetry breaking (Minimal Lepton Flavour Violation hypothesis). We show that in this framework a specific type of resonant leptogenesis can be successfully accomplished. For natural values of the free parameters, this mechanism requires a high right-handed neutrino mass scale ($M_ν\gsim 10^{12}$ GeV). By means of a general effective field theory approach, we analyse the impact of the CP vio…
We review the formulation of the Minimal Flavour Violation (MFV) hypothesis in the quark sector, as well as some "variations on a theme" based on smaller flavour symmetry groups and/or less minimal breaking terms. We also review how these hypotheses can be tested in B decays and by means of other flavour-physics observables. The phenomenological consequences of MFV are discussed both in general terms, employing a general effective theory approach, and in the specific context of the Minimal Supersymmetric extension of the SM.
After a summary of the motivations for searching flavour violating decays and electric dipole moments in the leptonic sector, I briefly sketch the present status of the limits on lepton-slepton misalignement and discuss the potentialities of the planned experimental improvements. Candidates for theories beyond the Standard Model have to satisfy all these experimental constraints; I will discuss in particular how the supersymmetric SM extended with the see-saw faces the flavour problem.
We derive a strong bound on the chromo-electric dipole moment of the charm quark, and we quantify its impact on models that allow for a sizeable flavour violation in the up quark sector. In particular we show how the constraints coming from the charm and up CEDMs limit the size of new physics contributions to direct flavour violation in D meson decays. We also specialize our analysis to the cases of split-families Supersymmetry and composite Higgs models. The results we expose motivate an increase in experimental sensitivity to fundamental hadronic dipoles, and a further exploration of the SM …
In this talk I review the status of B mixing in the Standard Model and the room for new physics in B_s and B_d mixing in the light of recent LHCb data.
We suppose that the observed neutrino masses can be parametrised by a lepton number violating dimension-five operator, and calculate the mixing of double insertions of this operator into lepton flavour changing dimension-six operators of the standard model effective theory. This allows to predict the log-enhanced, but $m_ν^2$-suppressed lepton flavour violation that is generic to high-scale Majorana neutrino mass models. We also consider the Two Higgs Doublet Model, where the second Higgs allows the construction of three additional dimension-five operators, and evaluate the corresponding anoma…
The Minimal Lepton Flavour Violation (MLFV) framework is discussed after the recent indication for CP violation in the leptonic sector. Among the three distinct versions of MLFV, the one with degenerate right-handed neutrinos will be disfavoured, if this indication is confirmed. The predictions for leptonic radiative rare decays and muon conversion in nuclei are analysed, identifying strategies to disentangle the different MLFV scenarios. The claim that the present anomalies in the semi-leptonic $B$-meson decays can be explained within the MLFV context is critically re-examined concluding that…
The experimental success of the predictions of the Standard Model in the flavour sector suggests that New Physics should possess a highly non-generic flavour structure. Different approaches to this idea of Minimal Flavour Violation have been proposed and studied during the last years. At last, the LHC provides the possibility to test these patterns from different points of view, i.e. through the direct search of New Physics at the high energy frontier, and through the indirect constraints at the intensity frontier of precision measurements.
We consider the supersymmetric seesaw mechanism induced by the exchange of heavy SU(2)_W triplet states, rather than `right-handed' neutrino singlets, to generate neutrino masses. We show that in this scenario the neutrino flavour structure tested at low-energy in the atmospheric and solar neutrino experiments is directly inherited from the neutrino Yukawa couplings to the triplets. This allows us to predict the ratio of the tau --> mu gamma (or tau --> e gamma) and mu --> e gamma decay rates in terms of the low-energy neutrino parameters. Moreover, once the model is embedded in a grand unifie…
A discrepancy between the experimental and theoretical results was reported for the anomalous magnetic moment of the muon. In leptogenesis scenarios which are due to a decay of right-handed neutrinos, this anomaly leads to large violations of lepton flavour within the framework of supersymmetric see-saw models. It is shown that for a hierarchical right-handed neutrino mass spectrum, we generically expect to observe μ\to e γin the near future experiment.
In supersymmetric extensions of the Standard Model, the lepton flavour violation (LFV) is closely related to the structure of slepton masses and mixing. Allowing for the most general flavour structure of the slepton sector, consistent with the experimental limits on rare lepton decays, large and distinct signals of LFV at future colliders can be expected. A case study of mixing of second and third generation of sleptons at an e+e- collider is presented and compared to that of tau to mu+gamma rare decay.
We discuss the tension between discrete flavour symmetries and extended scalar sectors arising from lepton flavour violation experiments. The key point is that extended scalar sectors will generically lead to flavour changing neutral currents, which are strongly constrained by experiments. Due to the large parameter space in the scalar sector such models will, however, usually have no big problems with existing and future bounds (even though the models might be constrained). This changes considerably once a flavour symmetry is imposed in addition: Due to the symmetry, additional relations betw…
In these proceedings we review the flavour phenomenology of 2HDMs with generic Yukawa structures. We first consider the quark sector and find that despite the stringent constraints from FCNC processes large effects in tauonic B decays are still possible. We then consider lepton flavour observables, show correlations between μ-> eγand μ^- -> e^-e^+e^- in the 2HDM of type III and give upper bounds on the lepton flavour violating B decay B_d -> μe.
