Ilja Dorsner

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 102.1 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 105.4 GeV (1010 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.

Can scalar leptoquarks explain the fDs puzzle

Abstract Motivated by the disagreement between experimental and lattice QCD results on the D s decay constant we systematically reinvestigate role of leptoquarks in charm meson decays. We consider scalar leptoquarks that transform as a weak interaction triplet, doublet, or singlet in a model independent approach, and also argue that in a particular class of SU ( 5 ) GUT models these leptoquark states, contained in the 45-dimensional Higgs representation, could be safe against proton decay bounds. Using the current experimental measurements in τ, kaon and charm sectors, we find that scalar leptoquarks cannot naturally explain the D s → μ ν and D s → τ ν decay widths simultaneously. While any contributions of the triplet leptoquarks are already excluded, the singlets could only contribute significantly to the D s → τ ν width. Finally, a moderate improvement of the experimental upper bound on the D 0 → μ + μ − decay width could exclude the doublet contribution to the D s → μ ν , while present experimental data limits its mass to be below 1.4 TeV . Possible new signatures at present and near future experiments are also briefly discussed.

Fermion Masses and the UV Cutoff of the Minimal Realistic Su (5) model

8 pages, 4 figures.-- PACS nrs.: 12.10.Dm; 12.10.Kt; 12.15.Ff; 14.60.Pq.-- ISI Article Identifier: 000247625400067.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0607208

Heavy and light scalar leptoquarks in proton decay

We list scalar leptoquarks that mediate proton decay via renormalizable couplings to the Standard Model fermions. We employ a general basis of baryon number violating operators to parameterize contributions of each leptoquark towards proton decay. This then sets the stage for investigation of bounds on the leptoquark couplings to fermions with respect to the most current Super Kamiokande results on proton stability. We quantify if, and when, it is necessary to have leptoquark masses close to a scale of grand unification in the realistic SU(5) and flipped SU(5) frameworks. The most and the least conservative lower bounds on the leptoquark masses are then presented. We furthermore single out a leptoquark without phenomenologically dangerous tree-level exchanges that might explain discrepancy of the forward-backward asymmetries in

Predictions from type II see-saw mechanism in SU(5)

t \bar t

Scaling of lepton dipole moments with lepton mass

production observed at Tevatron, if relatively light. The same state could also play significant role in explaining muon anomalous magnetic moment. We identify contributions of this leptoquark to dimension-six operators, mediated through a box diagram, and tree-level dimension-nine operators, that would destabilize proton if sizable leptoquark and diquark couplings were to be simultaneously present.

Scalar leptoquarks from grand unified theories to accommodate the

Abstract We propose a simple, testable, SU ( 5 ) model within the context of the type II neutrino see-saw mechanism. It is based on requiring renormalizability, the absence of any other matter fields besides those already present in the Standard Model and consistency with all experimental data. These “minimal” requirements, together with group-theoretical considerations, uniquely determine the model and lead to interesting implications. The model predicts correlation between a light SU ( 2 ) triplet boson responsible for the type II see-saw mechanism and observable proton decay signatures. It also allows for an enhanced production of doubly charged Higgs particles through the WW fusion process due to a built-in custodial symmetry. This could also have profound impact on the explicit realization of electroweak symmetry breaking. The model also predicts the existence of a light scalar that transforms as a colour octet and electroweak doublet, with interesting phenomenological consequences.

B

The dipole moments of the leptons and quarks are matrices in flavor space, which can potentially reveal as much about the flavor structure of the theory as do the mass matrices. The off-diagonal elements of the dipole matrices lead to flavor-changing decays such as {mu}{yields}e{gamma}, while the imaginary parts of the diagonal elements give rise to electric dipole moments. We analyze the scaling of the leptonic dipole moments with the lepton masses in theories beyond the standard model. While in many models the dipole moments scale roughly as lepton mass, it is shown that simple models exist in which the dipoles scale as the cube of the mass or in other ways. An explicit example with cubic scaling is presented, which is motivated on independent grounds from large angle neutrino oscillation data. Our results have great significance for the observability of the electric dipole moments d{sub e}, d{sub {mu}}, d{sub {tau}}, and the rare decays {mu}{yields}e{gamma}, and {tau}{yields}{mu}{gamma} and will be tested in several forthcoming experiments.

-physics anomalies

We address the

Light vector-like fermions in a minimal SU(5) setup

B