The sector of decay constants of the octet of light pseudoscalar mesons in the framework of 'resummed' $SU(3)$ chiral perturbation theory is investigated. A theoretical prediction for the decay constant of $η$-meson is compared to a range of available determinations. Compatibility of these determinations with the latest fits of the $SU(3)$ low energy coupling constants is discussed. Using a Bayesian statistical approach, constraints on the low energy coupling constants $L_4^r$ and $L_5^r$, as well as higher order remainders to the decay constants $F_K$ and $F_η$, are extracted from the most recent experimental and lattice QCD inputs for the values of the decay constants.
We extend a known method to integrate out the strange quark in three flavour chiral perturbation theory to the context of an arbitrary number of flavours. As an application, we present the explicit formulae to one--loop accuracy for the heavy quark mass dependency of the low energy constants after decreasing the number of flavours by one while integrating out the heaviest quark in N--flavour chiral perturbation theory.
A summary of recent progress in Chiral Perturbation Theory (ChPT) at the two-loop level is given. A short introduction to ChPT is included, along with an explanation of the usefulness of developing ChPT for partially quenched QCD. Further, our recent work in partially quenched ChPT is reviewed, and a few comments are given on older work in mesonic ChPT at the two-loop level. In particular, we quote the present best values for the low-energy constants of the $\mathcal{O}(p^4)$ chiral Lagrangian.
We present the scattering lengths for the $ππ$ processes in the three flavour Chiral Perturbation Theory (ChPT) framework at next-to-next-to-leading order. We then combine this calculation with the determination of the parameters from $K_{e4}$ and the masses and decay constants and compare with the results of a dispersive analysis of $ππ$ scattering. The comparison indicates a small but nonzero value for the $1/N_c$ suppressed NLO low energy constants $L_4^r$ and $L_6^r$.
We present the scattering lengths for the $πK$ processes in the three flavour Chiral Perturbation Theory (ChPT) framework at next-to-next-to-leading order (NNLO). The calculation has been performed analytically but we only include analytical results for the dependence on the low-energy constants (LECs) at NNLO due to the size of the expressions. These results, together with resonance estimates of the NNLO LECs are used to obtain constraints on the Zweig rule suppressed LECs at NLO, $L_4^r$ and $L_6^r$. Contrary to expectations from NLO order calculations we find them to be compatible with zero…
Machine learning unveils the quark mass dependence of the pseudoscalar meson decay constants in three-flavour N$^2$LO ChPT
Departamento de Física Teórica and IFIC, Centro Mixto Universidad de Valencia-CSIC（瓦伦西亚大学-西班牙国家科学研究委员会联合中心理论物理系与IFIC）；School of Physics, University of Electronic Science and Technology of China（电子科技大学物理学院）
We present positivity bounds, derived from the principles of analyticity, unitarity and crossing symmetry, that constrain the low-energy constants of chiral perturbation theory. Bounds are produced for 2, 3 or more flavours with equal meson masses, up to and including next-to-next-to-leading order (NNLO), using the second and higher derivatives of the amplitude. We enhance the bounds by using the most general isospin combinations posible (or higher-flavour counterparts thereof) and by analytically integrating the low-energy range of the amplitude. In addition, we present a powerful and general…
We investigate three-flavour chiral perturbation theory including virtual photons in a limit where the strange quark mass is much larger than the external momenta and the up and down quark masses, and where the external fields are those of two-flavour chiral perturbation theory. In particular we work out the strange quark mass dependence of the electromagnetic two-flavour low-energy constants C and k_i. We expect that these relations will be useful for a more precise determination of the electromagnetic low-energy constants.
I present higher loop order results for several calculations in Chiral perturbation Theory. 1) Two-loop results at finite volume for hadronic vacuum polarization. 2) A three-loop calculation of the pion mass and decay constant in two-flavour ChPT. For the pion mass all needed auxiliary parameters can be determined from lattice calculations of $ππ$-scattering. 3) Chiral corrections to neutron-anti-neutron oscillations.
The present status of Chiral Perturbation Theory in the meson sector is discussed concentrating on recent developments. This write-up contains short discussions on a listing a few historical papers, the principles behind ChPT, two-flavour ChPT including some comments about the pion polarizability, three-flavour ChPT with a discussion of the recently found relations as tests of ChPT and preliminary results of a new fit of the NLO low-energy-constants (LECs). It discusses somewhat deeper $η\to3π$ and the arguments for the existence of a ``hard pion ChPT'' and its application to $K\to2π$.
We discuss various aspects of resummed chiral perturbation theory, which was developed recently in order to consistently include the possibility of large vacuum fluctuations of the ss-pairs and the scenario with smaller value of the chiral condensate for N_f=3. The subtleties of this approach are illustrated using a concrete example of observables connected with pi-eta scattering. This process seems to be a suitable theoretical laboratory for this purpose due to its sensitivity to the values of the O(p^4) LEC's, namely to the values of the fluctuation parameters L4 and L6. We discuss several i…
We study three flavour chiral perturbation theory in a limit where the strange quark mass is much larger than the external momenta and the up and down quark masses, and where the external fields are those of two-flavour chiral perturbation theory. In this case, the theory reduces to the one of SU(2)_L x SU(2)_R. Through this reduction, one can work out the strange quark mass dependence of the LECs in the two-flavour case. We present the pertinent relations at two-loop order for F,B and l_i.
We present the results from our two-loop calculations of masses, decay-constants, vacuum-expectation-values and the $K_{\ell4}$ form-factors in three-flavour Chiral Perturbation Theory (CHPT). We use this to fit the $L_i^r$ to two-loops and discuss the ensuing predictions for $ππ$-threshold parameters.
We calculate the leading divergences at NNLO for the octet part of the nonleptonic weak sector of chiral perturbation theory, using renormalization group methods. The role of counterterms which vanish at the equation of motion and their use to simplify the calculation is shown explicitly. The obtained countertem Lagrangian can be employed to calculate the chiral double log contributions of quantities in this sector, most notably the K --> pi pi amplitude. The double log contribution of the latter is discussed in a separate paper.
Multi-flavour (N_f>=3) Chiral Perturbation Theory (ChPT) may exhibit instabilities due to vacuum fluctuations of sea q-bar q pairs. Keeping the fluctuations small would require a very precise fine-tuning of the low-energy constants L_4 and L_6 to L_4[crit](M_rho) = - 0.51 * 10^(-3), and L_6[crit](M_rho) = - 0.26 * 10^(-3). A small deviation from these critical values -- like the one suggested by the phenomenology of OZI-rule violation in the scalar channel -- is amplified by huge numerical factors inducing large effects of vacuum fluctuations. This would lead in particular to a strong N_f-depe…
We derive constraints on combinations of O(p^6) chiral coupling constants by matching a recent two-loop calculation of the pi-K scattering amplitude with a set of sum rules. We examine the validity of the natural expectation that the values of the chiral couplings can be associated with physics properties of the light resonance sector. We focus, in particular, on flavour symmetry breaking of vector resonances. A resonance chiral Lagrangian is constructed which incorporates flavour symmetry breaking more completely than was done before. We use pi-K unsubtracted sum rules as tests of the modelli…
We study lattice QCD determinations of the pion mass and decay constant by means of chiral perturbation theory (ChPT). The lattice data are obtained from large scale simulations with N_f=2 flavours of twisted mass fermions at maximal twist. We perform a scaling test to the continuum limit of these data and use ChPT to perform both the chiral and the infinite volume extrapolations.
The present status of Chiral Perturbation Theory (ChPT) in the strong mesonic sector is discussed. A very short introduction to ChPT is followed by an overview of existing two-loop calculations and the determination of the Low-Energy-Constants (LECs). I discuss the case of $η\toπππ$ decays in somewhat more detail and finish by mentioning some recent work on partially quenched ChPT and on the renormalization group in ChPT.
We discuss finite volume effects and partial quenching for Chiral Perturbation Theory in the mesonic sector. The effects are computed in terms of analytical expressions for masses, decay constants and vacuum expectation values (VEVs) to two-loop order. Numerical examples are presented for a number of interesting and relevant cases. All numerical programs are publically available, the prospects of a combination of these studies with lattice gauge theory computations are discussed briefly.
We calculate the finite volume corrections to meson masses and decay constants in two and three flavour Chiral Perturbation Theory to two-loop order. The analytical results are compared with the existing result for the pion mass in two-flavour ChPT and the partial results for the other quantities. We present numerical results for all quantities.
These lectures provide an elementary introduction to Chiral Perturbation Theory, focused on the sector of pseudoscalar meson interactions. Basic concepts and technical methods of this approach are discussed on general grounds and with the help of a few specific examples.
Experimental information on low energy $πK$ scattering would shed light on the poorly known OZI suppressed sector of ChPT. I describe recent work aimed at generating such information based on available experimental data by setting up and then solving with appropriate boundary conditions a non linear system of equations of the Roy and Steiner type. First results of this analysis are presented.
Chiral perturbation theory in the two-flavour sector allows one to analyse Green functions in QCD in a limit where the strange quark mass is considered to be large in comparison to the external momenta and to the light quark masses. In this framework, the pertinent low-energy constants depend on the value of the heavy quark masses. In a recent article, we have worked out, for the coupling constants which occur at order p^4, the dependence on the strange quark mass at two-loop accuracy. Here, we provide analogous relations for some of the couplings which are relevant at order p^6. To keep the c…
We reanalyse the topological susceptibility assuming the possibility of a significant paramagnetic suppression of the three-flavour quark condensate and a correlated enhancement of vacuum fluctuations of $s\bar{s}$ pairs. Using the framework of resummed ChPT, we point out that simulations performed near the physical point, with a significant mass hierarchy between u,d and s dynamical quarks, are not able to disentangle the contributions from the quark condensate and sea $s\bar{s}$-pair fluctuations, and that simulations with three light quark masses of the same order are better suited for this…
Chiral perturbation theory (ChPT) is the effective field theory of the strong interactions at low energies. We will address the issue of a consistent power counting scheme in a manifestly Lorentz-invariant formulation of baryon ChPT. As applications we show how the inclusion of vector and axial-vector mesons in the calculation of the nucleon electromagnetic and axial form factors, respectively, lead to an improved description of the empirical data. Finally, we will outline a systematic implementation of the Delta(1232) resonance into the effective field theory program.
We present a calculation of the finite volume corrections to meson masses and decay constants in three flavour Partially Quenched Chiral Perturbation Theory (PQChPT) through two-loop order in the chiral expansion for the flavour-charged (or off-diagonal) pseudoscalar mesons. The analytical results are obtained for three sea quark flavours with one, two or three different masses. We reproduce the known infinite volume results and the finite volume results in the unquenched case. The calculation has been performed using the supersymmetric formulation of PQChPT as well as with a quark-flow techni…
Using the example of the elastic $πN$-amplitude, we discuss the low energy expansion of QCD amplitudes in the sector with baryon number one. We show that the chiral expansion of these amplitudes breaks down in certain regions of phase space and present a framework which leads to a coherent description throughout the low energy region, while keeping Lorentz and chiral invariance manifest at every stage of the calculation. We explain how to construct a representation of the pion nucleon scattering amplitude in terms of functions of a single variable, which is valid to $O(q^4)$ and properly accou…
The flavour messenger sectors and their impact on the soft SUSY breaking terms are investigated in SUSY flavour models. In the case when the flavour scale M is below the SUSY breaking mediation scale M_S, the universality of soft terms, even if assumed at M_S, is radiatively broken. We estimate this effect in a broad class of models. In the CKM basis that effect gives flavour off-diagonal soft masses comparable to the tree-level estimate based on the flavour symmetry.
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.
We study different types of radiative decays involving f0(980) and a0(980) mesons within a unified ChPT-based approach at one-loop level. Light scalar resonances which are seen in pi pi, pi eta, K K-bar channels of phi(1020) radiative decays and in J/psi decays are responsible for key questions of low-energy dynamics in the strong interaction sector, and decays phi(1020) -> gamma a0(980), phi(1020) -> gamma f0(980), a0(980) -> gamma gamma, f0(980) -> gamma gamma are of interest for current experimental programs in Juelich, Frascati and Novosibirsk. From theoretical point of view it is importan…
We show that the Hidden Local Symmetry Model, supplemented with well-known procedures for breaking flavor SU(3) and nonet symmetry, provides all the information contained in the standard Chiral Perturbation Theory (ChPT) Lagrangian ${\cal L}^{(0)}+{\cal L}^{(1)}$. This allows to rely on radiative decays of light mesons ($VPγ$ and $P γγ$) in order to extract some numerical information of relevance to ChPT: a value for $Λ_1=0.20 \pm 0.04$, a quark mass ratio of $\simeq 21.2 \pm 2.4$, and a negligible departure from the Gell-Mann--Okubo mass formula. The mixing angles are $θ_8=-20.40^\circ \pm 0.…
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…
Symmetries affected by the anomaly do not survive quantization and cannot be understood classically. They are of fundamental importance and offer an opportunity of expanding the theoretical framework. We examine the theory of the anomalous sector, starting from lowest order Chiral Perturbation Theory (ChPT), leading up to the construction of the recently developed Lagrangian of $\mathcal{O}(p^{6}) $ describing anomalous processes. This Lagrangian contains a set of chiral coefficients that must be determined phenomenologically. Using currently available experimental data, we fit as many of thes…
We present a general class of operators resembling compact tetraquarks which have a range of colour-flavour-spin structures, transform irreducibly under the symmetries of the lattice and respect other relevant symmetries. These constructions are demonstrated in lattice QCD calculations with light quarks corresponding to $m_π=$ 391 MeV. Using the distillation framework, correlation functions involving large bases of meson-meson and tetraquark operators are computed in the isospin-1 hidden-charm and doubly-charmed sectors, and finite-volume spectra are extracted with the variational method. We f…
We present results for the masses of pseudoscalar mesons in twisted mass lattice QCD with a degenerate doublet of u and d quarks and a non-degenerate doublet of s and c quarks in the framework of next-to-leading order chiral perturbation theory, including lattice effects up to O(a^2). The masses depend on the two twist angles for the light and heavy sectors. For maximal twist in both sectors, O(a)-improvement is explicitly exhibited. The mixing of flavour-neutral mesons is also discussed, and results in the literature for the case of degenerate s and c quarks are corrected.
We discuss how flavour GUT models in the context of supergravity can be completed with a simple SUSY breaking sector, such that the flavour-dependent (non-universal) soft breaking terms can be calculated. As an example, we discuss a model based on an SU(5) GUT symmetry and $A_4$ family symmetry, plus additional discrete "shaping symmetries" and a $\mathbb{Z}_4^\mathrm{R}$ symmetry. We calculate the soft terms and identify the relevant high scale input parameters, and investigate the resulting predictions for the low scale observables, such as flavour violating processes, the sparticle spectrum…
We review flavour and CP violations in the lepton sector as probes of new physics beyond the standard model and its minimal extensions accommodating massive neutrinos. After recalling the main experimental bounds and the future perspectives, we summarize the limits on a set of dimension-six gauge-invariant operators, pointing to a scale of new physics much larger than the electroweak scale. If we insist on having new physics at the TeV scale, as demanded by most of the standard model extensions addressing the gauge hierarchy problem, we should rely on special mechanisms to deplete flavour and …
Flavour symmetries are fundamental tools in the search for an explanation to the flavour puzzle: fermion mass hierarchies, the neutrino mass ordering, the differences between the mixing matrices in the quark and lepton sector, can all find an explanation in models where the fermion generations undergo specific geometric relations. An overview on the implementation of continuous symmetries in the flavour sector is presented here, focussing on the lepton sector.
A three Higgs-doublet model admitting an $S_3$-symmetry can predict the observed pattern of the quark masses and their mixings. However the same symmetry also introduces potential flavour-changing neutral currents at the tree level. We assume in this work that the scalar potential contains appropriate \emph{soft} $S_3$-breaking terms in order to keep the choices of the scalar masses flexible. We identify the parameters in the Yukawa Lagrangian in the quark sector responsible for such FCNCs and constrain them using data from some of the flavour physics observables like meson-decays and meson-mi…
It is the purpose of the present manuscript to emphasize those aspects that make the scalar sector with vacuum quantum numbers rather unique. Chiral symmetry is the basic tool for our study together with a resummation of Chiral Perturbation Theory (CHPT) that stresses the role of unitarity but also allows one to include explicit resonance fields and to match with the CHPT expansion at low energies.
We address the question, how general is the gauge sector in extra-dimensional models which explain hierarchies of masses and mixings of quarks, charged leptons and neutrinos in terms of a single family of multidimensional fermions. We give qualitative arguments that though there are a plethora of possible variations, they do not result in drastical changes of phenomenology.
Flavour-Changing-Neutral-Currents (FCNC) play an important r\^ ole in testing the Standard Model (SM) while probing the possibility of having New Physics beyond the SM. In the SM, FCNC are forbidden at three level, but arise through calculable one-loop contributions. We review some of the features of FCNC in two examples of minimal extensions of the SM. In the first example, we consider an extension of the SM consisting of the addition of one vector-like quark either of the up-type ($Q=2/3$) or the down type ($Q=- 1/3$). In this extension there are non-vanishing but naturally suppressed Z-medi…
We extend a previously developed description of the flavour parameters in the charged fermion sector, based on a U(2) flavour symmetry, to include two main features of the neutrino sector seemingly implied by recent data: a large mixing angle $θ_{μτ}$ and a large hierarchy in the neutrino squared mass differences. A unified description of quark and lepton masses and mixings emerges. The neatest quantitative predictions are for elements of the unitary mixing matrix in the lepton sector: |V_{μ1}| = |V_{e 3} / V_{μ3}| = |V_{e 2} / V_{τ3}| = \sqrt{m_e / m_μ}, which go together with the analogous r…
Any supersymmetric mechanism to solve the flavour puzzle would generate mixing both in the superpotential Yukawa couplings and in the Kahler potential. In this paper we study, in a model independent way, the impact of the nontrivial structure of the Kahler potential on the physical mixing matrix, after kinetic terms are canonically normalized. We undertake this analysis both for the quark sector and the neutrino sector. For the quark sector, and in view of the experimental values for the masses and mixing angles, we find that the effects of canonical normalization are subdominant. On the other…
We construct extensions of the Standard Model with two Higgs doublets, where there are flavour changing neutral currents both in the quark and leptonic sectors, with their strength fixed by the fermion mixing matrices $V_{CKM}$ and $V_{PMNS}$. These models are an extension to the leptonic sector of the class of models previously considered by Branco, Grimus and Lavoura, for the quark sector. We consider both the cases of Dirac and Majorana neutrinos and identify the minimal discrete symmetry required in order to implement the models in a natural way.
Flavour physics is currently well described by the Standard Model except for some measurements which could be signalling new physics. We briefly summarize the status of tensions in rare exclusive semi-leptonic $B$ decays and in $R_{K/D^{(\ast)}}$ ratios. We also address the issue of the long standing tension in the $|V_{cb}|$ and $|V_{ub}|$ exclusive/inclusive determinations.
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.
Masses of the dimesonic (meson-antimeson) molecular states are calculated using Yukawa like and meson exchange potential in semi-relativistic approach. The digamma decay width of the dimesonic systems are evaluated using the spectroscopic parameters. Many states such as $f{}_{0}$(980), $h{}_{1}$(1380), $a{}_{0}$(1450), $f{}_{0}$(1500), $f{}_{2}'$(1525), $f{}_{2}$(1565), $a{}_{2}$(1700), $f{}_{0}$(1710), $f{}_{2}$(1810), $f{}_{2}$(2010) have shown the signature of dimesonic molecules. Their masses and digamma widths are in good agreement with other theoretical results as well as experimental me…
We investigate the implications for fermion mass models in heterotic orbifolds of the modular symmetry mixing twisted states localized at different fixed points. We show that, unlike in the case of continuous gauge symmetries, the mass eigenstates do not mix under the symmetry; thus coupling constants in the low-energy theory are invariant functions of the moduli.
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 explore the phenomenology of a QCD-like dark sector which confines around the GeV scale. The dark sector inherits a flavour structure from a coupling between dark quarks and SM quarks via a heavy mediator, which leads to exciting new phenomena. While stable baryonic bound states are the dark matter candidates, the phenomenology is dominated by the lightest composite mesons, the dark pions, which can have decay lengths ranging from millimetres to hundreds of meters. For masses below 1.5 GeV, their exclusive decays to SM mesons are calculated for the first time by matching both dark and visib…
We study the behaviour of the flavour changing neutral currents in the Left-Right Symmetric Model related to the presence of spontaneous CP phases. To do this, we explore four cases corresponding to combinations of maximal and no CP violation in both the lepton and quark sector. We find that we can constrain the flavour changing neutral currents to the experimental limit, by adjusting the CP-violating phase of the quark sector, opening the possibility to obtain a large CP violation in the lepton sector as well as new Higgs bosons at the electroweak scale.
Both discrete flavour symmetries and Grand Unified symmetries explain apparent structures in the mass sector of the Standard Model. A model that combines both symmetries is therefore very appealing. We construct a model with the $S_4$ flavour symmetry and the Pati-Salam unification. We show that this model can indeed explain many observable relations between the masses of the quarks and leptons and that it is predictive in the neutrino sector. However, the combination of the two symmetries leads to new complications in the Higgs sector and in the running of the renormalisation group equations.
The gauging of the lepton flavour group is considered in the Standard Model context and in its extension with three right-handed neutrinos. The anomaly cancellation conditions lead to a Seesaw mechanism as underlying dynamics for all leptons; requiring in addition a phenomenologically viable setup leads to Majorana masses for the neutral sector: the type I Seesaw Lagrangian in the Standard Model case and the inverse Seesaw in the extended model. Within the minimal extension of the scalar sector, the Yukawa couplings are promoted to scalar fields in the bifundamental of the flavour group. The r…
In these proceedings I present a personal perspective of the challenges for new physics (NP) searches in the flavour sector. Since the CKM mechanism of flavour violation has been established to a very high precision, we know that physics beyond the Standard Model can only contribute sub-dominantly. Therefore, any realistic model of physics beyond the Standard Model (SM) must respect the stringent constrains from flavour observables like $b\to s γ$, $B_s\toμ^+μ^-$, $ΔF=2$ processes etc., in a first step. In a second step, it is interesting to ask the question if some deviations from the SM pred…
Several experiments observed deviations from the Standard Model (SM) in the flavour sector: LHCb found a $4-5\,σ$ discrepancy compared to the SM in $b\to sμ^+μ^-$ transitions (recently supported by an Belle analysis) and CMS reported a non-zero measurement of $h\toμτ$ with a significance of $2.4\,σ$. Furthermore, BELLE, BABAR and LHCb founds hints for the violation of flavour universality in $B\to D^{(*)}τν$. In addition, there is the long-standing discrepancy in the anomalous magnetic moment of the muon. Interestingly, all these anomalies are related to muons and taus, while the corresponding…
We demonstrate that flavour-changing neutral currents in the top sector, mediated by leptophilic scalars at the electroweak scale, can easily arise in scenarios of new physics, and in particular in composite Higgs models. We moreover show that such interactions are poorly constrained by current experiments, while they can be searched for at the LHC in rare top decays and, more generally, in the channels $pp\to tS(S)+j$, with $S\to\ell^+\ell^-$. We provide dedicated analyses in this respect, obtaining that cut-off scales as large as $Λ\sim$ 90 TeV can be probed with an integrated luminosity of …
We present the results of an extensive analysis of flavour physics in both quark and lepton sectors, in the Littlest Higgs model with T-parity (LHT). In the quark sector, we identify some interesting scenarios for new mirror quark masses and V_Hd mixing matrix that satisfy the existing experimental constraints from K and B physics and simultaneously allow large New Physics effects in rare decays and CP-violating observables. In the lepton sector, where flavour violation in the Standard Model is highly suppressed by small neutrino masses, LHT effects turn out to be naturally huge and could be s…
The gauge sector of the Standard Model (SM) exhibits a flavour symmetry which allows for independent unitary transformations of the fermion multiplets. In the SM the flavour symmetry is broken by the Yukawa couplings to the Higgs boson, and the resulting fermion masses and mixing angles show a pronounced hierarchy. In this work we connect the observed hierarchy to a sequence of intermediate effective theories, where the flavour symmetries are broken in a step-wise fashion by vacuum expectation values of suitably constructed spurion fields. We identify the possible scenarios in the quark sector…
In this work we study the Lepton Flavour Violating semileptonic tau --> mu f0(980) decay within the context of SUSY-Seesaw Models, where the MSSM spectrum is extended by three right handed neutrinos and their SUSY partners, and where the seesaw mechanism is used to generate the neutrino masses. We estimate its decay rate when it proceeds via the Higgs mediated channel tau --> mu H* --> mu f0(980), where H refers to the CP-even MSSM Higgs bosons h^0 and H^0, and the Lepton Flavour Violating tau mu H vertex is radiatively generated via SUSY loops. In order to describe the f0(980) meson we follow…
