Search Results for « Leptons »

~~In obtaining the expression (11) the mass difference between the charged and neutral has been ignored.~2M.Adernollo and R. Gatto, Nuovo Cimento 44A, 282 (1966); see also J. Pasupathy and H, .E. Marshak, Phys.Rev. Letters 17, 888 (1966).~3The predicted ratio I.eq.|, '12)] from the current alge-bra is slightly larger than that (0.23%) obtained from the p-dominance model of Ref. 2. This seems to be true also in the other case of the ratio &(t) ~+m y}/ &(V V} calculated in Refs.12 and 14.

There is a group-theoretical connection between fermion mixing matrices and minimal horizontal symmetry groups. Applying this connection to the tribimaximal neutrino mixing matrix, we show that the minimal horizontal symmetry group for leptons is uniquely ${S}_{4}$, the permutation group of four objects.

Anomalies in semileptonic B-meson decays present interesting patterns that might be revealing the shape of the new physics to come. Under the assumption that neutrino and charged lepton mass terms are the only sources of flavor violation and given the hierarchy between the two, we find that charged lepton universality violation without charged lepton flavor violation naturally arises. This can account for a deficit of B + → K + μμ over B + → K + ee decays with new physics coupled predominantly to muons and a new physics scale of a few TeV. A generic prediction of this scenario is a large enhacement of tauonic B decay rates that, in particular, could accommodate an excess in B → D (∗) τ ν. For the most part, the study is carried out in an effective field theory framework with an underlying SU(2) L × U(1) Y symmetry that emphasizes the model-independent correlations between low- and high-energy observables. As an example, a connection between B-decays and top physics is pointed out. To complement the discussion, all possible (spin 0 and 1) leptoquark models are matched to the low-energy field theory so that the effective analysis can be used to survey these candidates for new physics.

Quarks and leptons, which have the same electroweak interactions, markedly differ in their masses and mixing patterns. Neutrino masses are very small while quark masses are large and the lepton mixing matrix contains two large angles while quark mixings are small. Concentrating on the lepton sector, this review presents the flavor puzzles with effective field theories. Beyond standard model theories are discussed that contain organizing principles designed to provide natural explanations of neutrino masses and mixings.

Kerson Huang 1982 Singapore: World Scientific x + 281 pp price £24 (£22.50 paperback) Huang presents a concise introduction to quantum chromodynamics and the Weinberg–Salam SU(2) × U(1) electroweak interaction. Other major chapters cover Yang–Mills fields, path integrals, quantisation of gauge fields and renormalisation.

A bstract We investigate the role of leptons in electroweak baryogenesis by studying a relatively simple framework inspired by effective field theory that satisfies all Sakharov conditions. In particular, we study the effectiveness of CP-violating source terms induced by dimension-six Yukawa interactions for quarks and charged leptons. Despite the relatively small Yukawa coupling, CP-violating source terms involving taus are quite effective and can account for the observed matter-antimatter asymmetry. We obtain analytical and numerical expressions for the total baryon asymmetry, the former providing important insight into what makes lepton CP violation relatively effective compared to quark CP violation. Leptons also play an important role if the CP-violating source involves top quarks. While the tau Yukawa coupling in the Standard Model is small, it significantly enhances the baryon asymmetry by transferring the chiral asymmetry in quarks, which is washed out by strong sphalerons, to a chiral asymmetry in leptons. We conclude that leptons should not be ignored even if CP violation is limited to the quark sector. The role of leptons can be further increased in scenarios of new physics with additional chiral-symmetry-breaking interactions between quarks and leptons, as can happen in models with additional Higgs bosons or leptoquarks. Finally, we study CP-violating dimension-six Yukawa interactions for lighter quarks and leptons but conclude that these lead to too small baryon asymmetries.

We present a model for calculating charged-lepton mixing matrices. These matrices are an essential ingredient for predicting lepton flavor-violating rates in the lepton number nonuniversal models recently proposed to explain anomalies in B-meson decays. The model is based on work on “constrained flavor breaking” by Appelquist, Bai and Piai relating the charged-lepton mass matrix, Mℓ, to those for the up- and down-type quarks, Mu,d. We use our recent model of lepton nonuniversality to illustrate the magnitudes of flavor-violating B-decay rates that might be expected. Decays with μτ final states generally have the highest rates by far.