Did one observe couplings of right-handed quarks to W ?

I consider non standard EW couplings of light right-handed quarks to W and Z suggested in a systematic non decoupling bottom-up low-energy effective theory approach to possible extensions of the Standard Model. New experimental tests in K^L_{mu3} decays based on recent measurements and scalar form factor analysis are discussed. A successful NLO fit to the standard set of Z-pole and other NC data is presented as well.Comment: 9 pages, 2 figures. Talk given at the KAON07 International Conference, May 21-25 2007, Frascati, Ital

The role of spurions in Higgs-less electroweak effective theories

Inspired by recent developments of moose models we reconsider low-energy effective theories of Goldstone bosons, gauge fields and chiral fermions applied to low-energy QCD and to Higgs-less electroweak symmetry breaking. Couplings and the corresponding reduction of symmetry are introduced via constraints enforced by a set of non-propagating covariantly constant spurion fields. Relics of the latter are used as small expansion parameters conjointly with the usual low-energy expansion. Certain couplings can only appear at higher orders of the spurion expansion and consequently, they become naturally suppressed independently of the idea of dimensional deconstruction. At leading order this leads to a set of generalized Weinberg sum rules and to the suppression of non-standard couplings to fermions in Higgs-less EWSB models with the minimal particle content. Within the latter, higher spurion terms allow for a fermion mass matrix with the standard CKM structure and CP violation. In addition, Majorana masses for neutrinos are possible. Examples of non-minimal models are briefly mentioned.Comment: Some precisions added to section 3.4. Reference [13] added. To appear in EPJ

Paramagnetic effect of light quark loops on Chiral Symmetry Breaking

We argue that light quark loops produce a paramagnetic suppression of infrared-sensitive order parameters such as , as the number N_f of light fermions increases. The possibly strong dependence of on N_f is related to the observed Zweig rule violation in the scalar channel. Presuming the existence of a chiral phase transition for not too large N_f, we discuss the phenomenological possibilities of separately determining the two-flavour and three-flavour condensates and the quark mass ratio r=2m_s/(m_u+m_d). The issue is closely related to the interpretation of new forthcoming precise pi-pi data at low energy.Comment: 15 pages, Latex, using JHEP.cls (included), 1 PS figur

Lepton-number violation and right-handed neutrinos in Higgs-less effective theories

Following previous work, we identify a symmetry S_nat that generalizes the concept of custodial symmetry, keeping under control deviations from the Standard Model (SM). To realize S_nat linearly, the space of gauge fields has to be extended. Covariant constraints formulated in terms of spurions reduce S_nat back to SU(2)_L x U(1)_Y. This allows for a covariant introduction of explicit S_nat-breaking parameters. We assume that S_nat is at play in a theory of electroweak symmetry-breaking without a light Higgs particle. We describe some consequences of this assumption, using a non-decoupling effective theory in which the loop expansion procedure is based on both momentum and spurion power counting, as in Chiral Perturbation Theory. A hierarchy of lepton-number violating effects follows. Leading corrections to the SM are non-oblique. The effective theory includes stable light right-handed neutrinos, with an unbroken Z_2 symmetry forbidding neutrino Dirac masses. nu_R contribution to dark matter places bounds on their masses.Comment: Corresponds to published version: added subsection VI-D about order-of-magnitude estimate

Chiral Dynamics beyond the Standard Model

The SM Lagrangian without physical scalars is rewritten as the LO of a Low-Energy Effective Theory invariant under a higher non linear symmetry S_{nat} \supset SU(2)_W \times U(1)_Y. Soft breaking of S_{nat} defines a hierarchy of non standard effects dominated by universal couplings of right-handed quarks to W. The interface of corresponding EW tests with non perturbative QCD aspects is briefly discussed.Comment: 6 pages, Tallk given at QCD06 Conference, Montpellier, France, 3-7 July 2006, to appear in the Proceeding