Search

In 3-3-1 models, anomaly cancellation requires that one of the three families of quarks transforms as triplet by SU 3 L , with the other two transforming necessarily as anti-triplet. This is an important feature of the model because, with it, we explain family replication. Thus it is mandatory to discriminate which of the families will transform as triplet by SU 3 L because the main consequence of anomaly cancellation in 3-3-1 models is the arising of processes violating flavor at the tree level by means of neutral currents mediated by gauge and scalar fields, and each case leads to different results. In this work, we consider the 3-3-1 model with right-handed neutrinos. Among the spectrum of 3-3-1 particles that contribute to the flavor changing neutral processes, there is a pseudoscalar that may be the lightest of the 3-3-1 particles, and this then should give the main contribution to such processes. We then calculate its contribution to the K 0 − K ¯ 0 mixing transition and confront it with the current experimental results. We do this for the three cases in which one of the family of quarks transforms as a triplet by SU 3 L . According to our findings, each case leads to different constraints on the mass of the pseudoscalar, and the case in which the third family of quarks transforms as triplet seems to be the favoured one. We also obtain the most stringent bounds on the mass of the pseudoscalar of the model. [ABSTRACT FROM AUTHOR]

In this work we consider scenarios where light sterile neutrinos are mixed with the active ones. The active-sterile neutrino mixings render new contributions to the invisible Z decay width which will depend predominantly on the active-sterile mixing matrix elements. We then use the current experimental value of the invisible Z decay width to obtain bounds on these mixing matrix elements for both (3+1) and (3+2) models. [ABSTRACT FROM AUTHOR]

Theoretical consistency of the 3-3-1 model with right-handed neutrinos demands that the number of family of fermions be exactly equal to three. In this brief report we show that such theoretical requirement results in a clean and severe bound on the Z–Z′ mixing angle: -3.979×10-3<ϕ<1.309×10-4 with 90% CL. [ABSTRACT FROM AUTHOR]

We assume that lepton number is explicitly broken at low energy scale (M) in the framework of the Higgs triplet (Δ) model. The scalar sector of the model is developed considering the particular assumption M = vΔ ≈ eV. We show that such assumption infers a particular mass spectrum for the scalars that compose the triplet and cause a decoupling of these scalars from those that compose the standard scalar doublet. [ABSTRACT FROM AUTHOR]

Although noncommutative QED presents a non-Abelian structure, it does not present structure constants. In view of this we investigate how Ward identity is satisfied in pair annihilation process and γγ → γγ scattering in noncommutative QED. [ABSTRACT FROM AUTHOR]

In models with flat extra dimensions tiny Dirac neutrino masses can be generated via the coupling of four-dimensional Standard Model fields to a higher dimensional fermion. Here we argue that, in spite of the Dirac nature of the neutrino, quantization of the electric charge can still be understood as a result of anomaly cancellation, charge conservation and naturalness requirements. [ABSTRACT FROM AUTHOR]

We study the cosmology of models with four space and one time dimension where our universe is a three-brane and report a few results which extend existing work in several directions. Assuming a stable fifth dimension, we obtain a solution for the metric, which does not depend on any arbitrary parameters. We discuss some implications of this result. [ABSTRACT FROM AUTHOR]

We build a gauge model based on the SU(3)c⊗SU(4)L⊗U(1)X symmetry where the scalar spectrum needed to generate gauge boson and fermion masses has a smaller scalar content than usually assumed in literature. We compute the running of its abelian gauge coupling and show that a Landau pole shows up at the TeV scale, a fact that we use to consistently implement those fermion masses that are not generated by Yukawa interactions, including neutrino masses. This is appropriately achieved by non renormalizable effective operators, suppressed by the Landau pole scale. Also, SU(3)c⊗SU(3)L⊗U(1)N models embedded in this gauge structure are bound to be strongly coupled at this same energy scale, contrary to what is generally believed, and neutrino mass generation is rather explained through the same effective operators used in the larger gauge group. Besides, their nice features, as the existence of cold dark matter candidates and the ability to reproduce the observed standard model Higgs-like phenomenology, are automatically inherited by our model. Finally, our results imply that this model is constrained to be observed or discarded soon, since it must be realized at the currently probed energy scale in LHC. [ABSTRACT FROM AUTHOR]