Inverse Seesaw Neutrino Mass from Lepton Triplets in the U(1)_Sigma Model

The inverse seesaw mechanism of neutrino mass, i.e. m_nu = (m_D^2/m_N^2)epsilon_L where epsilon_L is small, is discussed in the context of the U(1)_Sigma model. This is a gauge extension of the Standard Model of particle interactions with lepton triplets (Sigma^+,Sigma^),Sigma^-) as (Type III) seesaw anchors for obtaining small Majorana neutrino masses.Comment: 7 pages, no figur

A Positive Test for Fermi-Dirac Distributions of Quark-Partons

By describing a large class of deep inelastic processes with standard parameterization for the different parton species, we check the characteristic relationship dictated by Pauli principle: broader shapes for higher first moments. Indeed, the ratios between the second and the first moment and the one between the third and the second moment for the valence partons is an increasing function of the first moment and agrees quantitatively with the values found with Fermi-Dirac distributions.Comment: 15 pages LaTeX, 2 eps figures. Final version, to appear in Mod. Phys. Lett.

Upper Bound on the Mass of the Type III Seesaw Triplet in an SU(5) Model

We investigate correlation between gauge coupling unification, fermion mass spectrum, proton decay, perturbativity and ultraviolet cutoff within an SU(5) grand unified theory with minimal scalar content and an extra adjoint representation of fermions. We find strong correlation between the upper bound on the mass of both the bosonic and fermionic SU(2) triplets and the cutoff. The upper bound on the mass of fermionic triplet responsible for Type III seesaw mechanism is 10^{2.1} GeV for the Planck scale cutoff. In that case both the idea of grand unification and nature of seesaw mechanism could be tested at future collider experiments through the production of those particles. Moreover, the prediction for the proton decay lifetime is at most an order of magnitude away from the present experimental limits. If the cutoff is lowered these predictions change significantly. In the most general scenario, if one does (not) neglect a freedom in the quark and lepton mixing angles, the upper bound on the fermionic triplet mass is at 10^{5.4} GeV (10^{10} GeV). Since the predictions of the model critically depend on the presence of the higher-dimensional operators and corresponding cutoff we address the issue of their possible origin and also propose alternative scenarios that implement the hybrid seesaw framework of the original proposal.Comment: 13 pages, 2 figures, minor changes introduced to match the JHEP versio

Scalar diquark in top-antitop production and constraints on Yukawa sector of grand unified theories

International audienceA colored weak singlet scalar state with hypercharge 4/3 is one of the possible candidates for the explanation of the unexpectedly large forward-backward asymmetry in tt production as measured by the CDF and D0 experiments. We investigate the role of this state in a plethora of flavor chang- ing neutral current processes and precision observables of down-quarks and charged leptons. Our analysis includes tree- and loop-level mediated observables in the K and B systems, the charged lepton sector, as well as the Z → b ¯b width. We perform a fit of the relevant scalar couplings. This approach can explain the (g − 2)µ anomaly while tensions among the CP violating observables in the quark sector, most notably the nonstandard CP phase (and width difference) in the Bs system cannot be fully relaxed. The results are interpreted in a class of GUT models which allow for a light colored scalar with a mass below 1 TeV

Explaining Why the u and d Quark Masses are Similar

An approach is suggested for modeling quark and lepton masses and mixing in the context of grand unified theories that explains the curious fact that m_u ~ m_d even though m_t >> m_b. The structure of the quark mass matrices is such as to allow a non-Peccei-Quinn solution of the Strong CP Problem.Comment: 11 pages, ReVTeX

Renormalization group evolution of neutrino masses and mixing in seesaw models: A review

We consider different extensions of the standard model which can give rise to the small active neutrino masses through seesaw mechanisms, and their mixing. These tiny neutrino masses are generated at some high energy scale by the heavy seesaw fields which then get sequentially decoupled to give an effective dimension-5 operator. The renormalization group evolution of the masses and the mixing parameters of the three active neutrinos in the high energy as well as the low energy effective theory is reviewed in this article.Comment: 54 pages. Invited review submitted to IJMP

Proton Stability, Dark Matter and Light Color Octet Scalars in Adjoint SU(5) Unification

The unification of gauge interactions in the context of Adjoint SU(5) and its phenomenological consequences are investigated. We show the allowed mass spectrum of the theory which is compatible with proton decay, and discuss the possibility to have a cold dark matter candidate. Due to the upper bounds on the proton decay partial lifetimes, tau (p --> K^+ nubar) < 9.3 10^{36} years and tau(p --> pi^+ nubar) < 3.0 10^{35} years, the theory could be tested at future proton decay experiments. The theory predicts also light scalar color octets which could be produced at the Large Hadron Collider.Comment: 20 pages, 8 figures, minor corrections, one reference added, to appear in Physical Review

Zee Model Confronts SNO Data

We reexamine the solution of the minimal Zee model by comparing with the data of the SNO experiment, and conclude that the model is strongly disfavored but not yet excluded by the observations. Two extensions of the Zee model are briefly discussed both of which introduce additional freedom and can accommodate the data.Comment: 16 pages LaTeX including 7 figure