The angular correlation of the electrons emitted in the neutrinoless double beta decay (0ν2β) is presented using a general Lorentz invariant effective Lagrangian for the leptonic and hadronic charged weak currents. We show that the coefficient K in the angular correlation dΓ/d cos θ ∝ (1 − K cos θ) is essentially independent of the nuclear matrix element models and present its numerical values for the five nuclei of interest ( 76 Ge, 82 Se, 100 Mo, 130 Te, and 136 Xe), assuming that the 0ν2β-decays in these nuclei are induced solely by a light Majorana neutrino, νM . This coefficient varies between K = 0.81 (for the 76 Ge nucleus) and K = 0.88 (for the 82 Se and 100 Mo nuclei), calculated taking into account the effects from the nucleon recoil, the S and P -waves for the outgoing electrons and the electron mass. Deviation of K from its values derived here would indicate the presence of New Physics (NP) in addition to a light Majorana neutrino, and we work out the angular coefficients in several νM + NP scenarios for the 76 Ge nucleus. As an illustration of the correlations among the 0ν2β observables (half-life T 1/2 , the coefficient K, and the effective Majorana neutrino mass | m |) and the parameters of the underlying NP model, we analyze the left-right symmetric models, taking into account current phenomenological bounds on the right-handed WR-boson mass and the left-right mixing parameter ζ.It is now established beyond any doubt that the observed neutrinos have tiny but non-zero masses and they mix with each other, with both of these features following from the observation of the atmospheric and solar neutrino oscillations and from the long baseline neutrino oscillation experiments [1]. Theoretically, it is largely anticipated that the neutrinos are Majorana particles. Experimental evidence for the neutrinoless double beta decay (0ν2β) would deliver a conclusive confirmation of the Majorana nature of neutrinos, establishing the existence of physics beyond the standard model. This is the overriding interest in carrying out these experiments and in the related phenomenology [2].We recall that 0ν2β-decays are forbidden in the standard model (SM) by lepton number (LN) conservation, which is a consequence of the renormalizability of the SM. However, being the low energy limit of a more general theory, an extended version of the SM could contain nonrenormalizable terms (tiny to be compatible with experiments), in particular, terms that violate LN and allow the 0ν2β decay. Probable mechanisms of LN violation may include exchanges by: Majorana neutrinos ν M s [3, 4, 5] (the preferred mechanism after the observation of neutrino oscillations [1]), SUSY particles [6,7,8,9,10,11], scalar bilinears (SBs) [12], e.g. doubly charged dileptons (the component ξ −− of the SU (2) L triplet Higgs scalar etc.), leptoquarks (LQs) [13], right-handed W R bosons [5,14] etc. From these particles light νs are much lighter than the electron and others are much heavier than the proton. Therefore, there are two possible classes of mechanis...

Lepton flavor-violating processes offer interesting possibilities to probe new physics at multi-TeV scale. We discuss those in the framework of effective field theory, emphasizing the role of gluonic operators. Those operators are obtained by integrating out heavy quarks that are kinematically inaccessible at the scale where low-energy experiments take place and make those experiments sensitive to the couplings of lepton flavor changing neutral currents to heavy quarks. We discuss constraints on the Wilson coefficients of those operators from the muon conversion µ − + (A, Z) → e − + (A, Z) and from lepton flavor-violating tau decays with one or two hadrons in the final state, e.g. τ → ℓ η (′) and τ → ℓ π + π − with ℓ = µ, e. To illustrate the results we discuss explicit examples of constraining parameters of leptoquark models.

In this letter, we address the question of whether the almost four standard deviations difference between theory and experiment for the muon anomalous magnetic moment aµ can be explained as a higher-order Standard Model perturbation effect in the pion form factor measurements. This question has, until now, remained open, obscuring the source of discrepancies between the measurements. We calculate the last radiative corrections for the extraction of the pion form factor, which were believed to be potentially substantial enough to explain the data within the Standard Model. We find that the corrections are too small to diminish existing discrepancies in the determination of the pion form factor for different kinematical configurations of low-energy BABAR, BESS-III and KLOE experiments. Consequently, they cannot noticeably change the previous predictions for aµ and decrease the deviations between theory and direct measurements. To solve the above issues, new data and better understanding of low-energy experimental setups are needed, especially as new direct aµ measurements at Fermilab and J-PARC will provide new insights and substantially shrink the experimental error.

In a supersymmetric model with hierarchical squark masses we analyze a pattern of flavour symmetry breaking centered on the special role of the top Yukawa coupling and, by extension, of the full Yukawa couplings for the up-type quarks. For sufficiently heavy squarks of the first and second generation this leads to effective Minimal Flavour Violation of the Flavour Changing Neutral Current amplitudes. For this to happen we determine the bounds on the masses of the heavy squarks with QCD corrections taken into account, properly including previously neglected effects. We believe that the view presented in this paper altogether strengthens the case for hierarchical sfermions.