It is widely believed that existing electroweak data requires a Standard Model Higgs to be light while electroweak and flavour physics constraints require other scalars charged under the Standard Model gauge couplings to be heavy. We analyze the robustness of these beliefs within a general scalar sector and find both to be incorrect, provided that the scalar sector approximately preserves custodial symmetry and minimal flavour violation (MFV). We demonstrate this by considering the phenomenology of the Standard Model supplemented by a scalar having SU(3)_c x SU(2)_L x U(1)_Y quantum numbers (8,2)_(1/2) which has been argued to be the only kind of exotic flavour singlet scalar allowed by MFV that couples to quarks. We examine constraints coming from electroweak precision data, direct production from LEPII and the Tevatron, and from flavour physics, and find that the observations allow both the Standard Model Higgs and the new scalars to be simultaneously light, with masses ~ 100 GeV, and in some cases lighter. The discovery of such light coloured scalars could be a compelling possibility for early LHC runs, due to their large production cross section, ~100 pb. But the observations equally allow all the scalars to be heavy (including the Higgs), with masses ~ 1 TeV, with the presence of the new scalars removing the light-Higgs preference that normally emerges from fits to the electroweak precision data.
The lightest baryon octet is studied within a covariant and confining Nambu--Jona-Lasinio model. By solving the relativistic Faddeev equations including scalar and axialvector diquarks, we determine the masses and axial charges for ΔS = 0 transitions. For the latter the degree of violation of SU(3) symmetry arising because of the strange spectator quark(s) is found to be up to 10%.
We perform a lattice computation of the flavour octet contribution to the average quark momentum in a nucleon, $\la x\ra^{(8)}_{μ^2 = 4 \gev^2}$. In particular, we fully take the disconnected contributions into account in our analysis for which we use a generalization of the technique developed in \cite{Dinter:2012tt}. We investigate systematic effects with a particular emphasis on the excited states contamination. We find that in the renormalization free ratio $\frac{\la x \ra^{(3)}}{\la x \ra^{(8)}}$ (with $\la x \ra^{(3)}$ the non-singlet moment) the excited state contributions cancel to a …
The value of the nucleon's flavour-singlet axial-charge extracted from polarised deep inelastic scattering is sensitive to the value of the octet axial-charge g_A^8 which is usually taken from an analysis of hyperon beta-decays within the framework of SU(3) symmetry, namely 0.58 \pm 0.03. Using the Cloudy Bag model we find that the value of g_A^8 is reduced by as much as 20% below the usual phenomenological value. This increases the value of the flavour singlet axial charge (g_A^0|_inv) derived from deep inelastic data and significantly reduces the difference between it and g_A^8.
We discuss neutrinoless double beta decay and lepton flavor violating decays such as $μ-> eγ$ in the colored seesaw scenario. In this mechanism, neutrino masses are generated at one-loop via the exchange of TeV-scale fermionic and scalar color octets. The same particles mediate lepton number and flavor violating processes. We show that within this framework a dominant color octet contribution to neutrinoless double beta decay is possible without being in conflict with constraints from lepton flavor violating processes. We furthermore compare the "direct" color octet contribution to neutrinoles…
Octet baryon magnetic moments are calculated within \chiQM, respecting color spin spin forces (Szczepaniak et al., PRL 87, 072001(2001)), incorporating the orbital angular momentum as well as the quark sea contribution through the Cheng and Li mechanism (PRL 80, 2789(1998)). Using configuration mixing generated by color spin spin forces as well as the concept of ``effective'' quark mass to include the effects of confinement, we are able to get an excellent fit to the octet magnetic moments as well as the violation of Coleman Glashow Sum Rule (CGSR) without any further input except for the ones…
We consider the phenomenology of CP violation in a color-octet extended scalar sector for t\bar{t} production and decay at the LHC. In particular we study the effect of the two neutral color-octet scalars S_I and S_R that occur in the model. There are two new sources of CP violation: a phase in the couplings of S_{I,R} to top-quarks; and two phases in the quartic couplings of the scalar potential. In resonant production of a single S_{I,R} followed by its decay into t\bar{t} pairs through the parton level process gg to S_{I,R} to t\bar{t}, we find large raw CP asymmetries which can reach 12%. …
Octet baryon axial, induced pseudoscalar, and pseudoscalar form factors are computed using a symmetry-preserving treatment of a vector$\,\times\,$vector contact interaction (SCI), thereby unifying them with an array of other baryon properties and analogous treatments of semileptonic decays of pseudoscalar mesons. The baryons are treated as quark--plus--interacting-diquark bound states, whose structure is obtained by solving a Poincaré-covariant Faddeev equation. The approach is marked by algebraic simplicity, involves no free parameters, and since it is symmetry preserving, all consequences of…
We reappraise the flavour changing neutral currents (FCNC) problem in string--derived supergravity models. We overview and classify possible sources of flavour violation and find that the problem often does not arise in classes of models which generate hierarchical Yukawa matrices. In such models, constraints from the K- and D-meson systems leave room for substantial flavour non-universality of the soft terms. The current B-physics experiments only begin to probe its natural range. Correlations among different observables can allow one to read off the chirality structure of flavour violating s…
Baryon octet magnetic moments when calculated within the chiral quark model, incorporating the orbital angular momentum as well as the quark sea contribution through the Cheng-Li mechanism, not only show improvement over the non relativistic quark model results but also gives a non zero value for the right hand side of Coleman-Glashow sum rule. When effects due to spin-spin forces between constituent quarks as well as `mass adjustments' due to confinement are added, it leads to an excellent fit for the case of p, Σ^+, Ξ^o and violation of Coleman-Glashow sum rule, whereas in almost all the oth…
We study $c \bar c$ color-octet contribution to $B\to ψ(ψ') X$. When this contribution is included, the theoretical predictions for the branching ratios become in much better agreement with the experiment. This mechanism also enhances the partial rate asymmetries by about a factor of five. The inclusive $ψ(ψ')$ resulting from $b\to d+{}$gluon can have asymmetry around a few percent whereas those from $b\to s+{}$gluon has it around $4\times 10^{-4}$. The asymmetry in the former modes should be observable, to a significance of $3σ$, with about $(1-10)\times 10^8B$ mesons.
We show how a mass mixing matrix can be generated dynamically, for two massless fermion flavours coupled to a Lorentz invariance violating (LIV) gauge field. The LIV features play the role of a regulator for the gap equations, and the non-analytic dependence of the dynamical masses, as functions of the gauge coupling, allows to consider the limit where the LIV gauge field eventually decouples from the fermions. Lorentz invariance is then recovered, to describe the oscillation between two free fermion flavours, and we check that the finite dynamical masses are the only effects of the original L…
Using an SU(3) flavour symmetry breaking expansion in the quark mass, we determine the QCD component of the nucleon, Sigma and Xi mass splittings of the baryon octet due to up-down (and strange) quark mass differences in terms of the kaon mass splitting. Provided the average quark mass is kept constant, the expansion coefficients in our procedure can be determined from computationally cheaper simulations with mass degenerate sea quarks and partially quenched valence quarks. Both the linear and quadratic terms in the SU(3) flavour symmetry breaking expansion are considered; it is found that the…
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.
We explore the electromagnetic contribution to the charge symmetry breaking in the octet baryon masses using a subtracted dispersion relation based on the Cottingham formula. For the proton-neutron mass splitting we report a minor revision of the recent analysis of Walker-Loud, Carlson and Miller. For the electromagnetic structure of the hyperons we constrain our analysis, where possible, by a combination of lattice QCD and SU(3) symmetry breaking estimates. The results for the baryon mass splittings are found to be compatible with recent lattice QCD+QED determinations. The uncertainties in th…
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.
A continuum approach to the three valence-quark bound-state problem in quantum field theory, employing parametrisations of the necessary kernel elements, is used to compute the spectrum and Poincaré-covariant wave functions for all flavour-$SU(3)$ octet and decuplet baryons and their first positive-parity excitations. Such analyses predict the existence of nonpointlike, dynamical quark-quark (diquark) correlations within all baryons; and a uniformly sound description of the systems studied is obtained by retaining flavour-antitriplet--scalar and flavour-sextet--pseudovector diquarks. Thus cons…
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.
In this work we present a minimal parametrization of the light-cone distribution amplitudes of the baryon octet including higher twist contributions. Simultaneously we obtain the quark mass dependence of the amplitudes at leading one-loop accuracy by the use of three-flavor baryon chiral perturbation theory (BChPT), which automatically yields model-independent results for the leading $SU(3)$ flavor breaking effects. For that purpose we have constructed the nonlocal light-cone three-quark operators in terms of baryon octet and meson fields and have carried out a next-to-leading order BChPT calc…
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 …
