Possible non-decoupling effects of heavy Higgs bosons in e+ e- -> W+ W- within THDM

We discuss the origin of the nondecoupling effects of the heavy Higgs bosons within the two Higgs doublet extension (THDM) of the Standard Model (SM) and illustrate it by means of the one-loop calculation of the differential cross-sections of the process e+ e- -> W+ W- in both the decoupling and the non-decoupling regimes. We argue that there are many regions in the THDM parametric space in which the THDM and SM predictions differ by several percents and such effects could, at least in principle, be testable at the future experimental facilities.Comment: 8 pages, 2 figures; to appear soon in EPJC. v2 - several minor corrections (typos), references adde

Triple gauge vertices at one-loop level in THDM

Renormalized triple gauge vertices (TGV) are examined within the two-Higgs-doublet model of electroweak interactions. Deviations of the TGV from their standard-model values are calculated at the one-loop level, in the on-shell renormalization scheme. As a consistency check, UV divergence cancellations anticipated on symmetry grounds are verified explicitly. Dependence of the TGV finite parts on the masses of possible heavy Higgs scalars is discussed briefly.Comment: 10pages, 13figure

Novel Supersymmetric SO(10) Seesaw Mechanism

We propose a new seesaw mechanism for neutrino masses within a class of supersymmetric SO(10) models with broken D-parity. It is shown that in such scenarios the B-L scale can be as low as TeV without generating inconsistencies with gauge coupling unification nor with the required magnitude of the light neutrino masses. This leads to a possibly light new neutral gauge boson as well as relatively light quasi-Dirac heavy leptons. These particles could be at the TeV scale and mediate lepton flavour and CP violating processes at appreciable levels.Comment: 4 pages, 3 figures, revtex4, references added, typos corrected, sharper discussion of the RGEs give

On CP Violation in Minimal Renormalizable SUSY SO(10) and Beyond

We investigate the role of CP phases within the renormalizable SUSY SO(10) GUT with one 10_H, one 126bar_H one 126_H and one 210_H Higgs representations and type II seesaw dominating the neutrino mass matrix. This framework is non trivially predictive in the fermionic sector and connects in a natural way the GUT unification of b and tau Yukawa couplings with the bi-large mixing scenario for neutrinos. On the other hand, existing numerical analysis claim that consistency with quark and charged lepton data prevents the minimal setup from reproducing the observed CP violation via the Cabibbo-Kobayashi-Maskawa (CKM) matrix. We re-examine the issue and find by inspection of the fermion mass sum rules and a detailed numerical scan that, even though the CKM phase takes preferentially values in the second quadrant, the agreement of the minimal model with the data is actually obtained in a non negligible fraction of the parameter space. We then consider a recently proposed renormalizable extension of the minimal model, obtained by adding one chiral 120-dimensional Higgs supermultiplet. We show that within such a setup the CKM phase falls naturally in the observed range. We emphazise the robust predictivity of both models here considered for neutrino parameters that are in the reach of ongoing and future experiments.Comment: 9 pages, 6 figures. Two refs added, discussion expanded. To appear on Phys. Rev.

Renormalization group running of neutrino parameters in the inverse seesaw model

We perform a detailed study of the renormalization group equations in the inverse seesaw model. Especially, we derive compact analytical formulas for the running of the neutrino parameters in the standard model and the minimal supersymmetric standard model, and illustrate that, due to large Yukawa coupling corrections, significant running effects on the leptonic mixing angles can be naturally obtained in the proximity of the electroweak scale, perhaps even within the reach of the LHC. In general, if the mass spectrum of the light neutrinos is nearly degenerate, the running effects are enhanced to experimentally accessible levels, well suitable for the investigation of the underlying dynamics behind the neutrino mass generation and the lepton flavor structure. In addition, the effects of the seesaw thresholds are discussed, and a brief comparison to other seesaw models is carried out.Comment: 30 pages, 7 figures. Final version published in Phys. Rev. D. v3: Typo in Eq. (33) correcte

Fermion masses in SUSY SO(10) with type II seesaw: a non-minimal predictive scenario

A predictive framework for fermion masses and mixing is given by the supersymmetric SO(10) model with one 10, one bar126, one 126 and one 210 Higgs representations, and type II seesaw dominating the neutrino mass matrix. We investigate the origin of the tension between this model and lepton mixing data and refine previous numerical analyses. We discuss an extension of the minimal model that includes one 120 Higgs chiral superfield representation. This exhausts the possible renormalizable contributions to the Yukawa sector. In spite of the increase in the number of parameters the predictivity of the minimal setting is not spoiled. We argue that the contributions to fermion masses due to the doublet components of 120 can be naturally small compared to those of 10 and 126, thus acting as a perturbation in the fermion mass generation. The antisymmetric nature of the 120 Yukawa coupling affects at leading order the determination of the mixing angles and it allows to remove the inconsistencies between predictions and data on the neutrino parameters. An improvement in the experimental bound on |Ue3| can tell this scenario from the minimal model.Comment: 11 pages, 3 figures; Note and references added on new KamLAND dat

On the vacuum of the minimal nonsupersymmetric SO(10) unification

We study a class of nonsupersymmetric SO(10) grand unified scenarios where the first stage of the symmetry breaking is driven by the vacuum expectation values of the 45-dimensional adjoint representation. Three decade old results claim that such a Higgs setting may lead exclusively to the flipped SU(5) x U(1) intermediate stage. We show that this conclusion is actually an artifact of the tree level potential. The study of the accidental global symmetries emerging in various limits of the scalar potential offers a simple understanding of the tree level result and a rationale for the drastic impact of quantum corrections. We scrutinize in detail the simplest and paradigmatic case of the 45_{H} + 16_{H} Higgs sector triggering the breaking of SO(10) to the standard electroweak model. We show that the minimization of the one-loop effective potential allows for intermediate SU(4)_C x SU(2)_L x U(1)_R and SU(3)_c x SU(2)_L x SU(2)_R x U(1)_{B-L} symmetric stages as well. These are the options favoured by gauge unification. Our results, that apply whenever the SO(10) breaking is triggered by , open the path for hunting the simplest realistic scenario of nonsupersymmetric SO(10) grand unification.Comment: 22 pages, 1 figure. Refs added. To appear in Phys. Rev.

Collider phenomenology of a unified leptoquark model

We demonstrate that in a recently proposed unified leptoquark model based on the gauge group SU(4)C×SU(2)L×U(1)R significant deviations from the Standard Model values of RK and RK∗ can be accommodated without any need of extra heavy fermions. Low energy data, in particular lepton-flavor-violating μ decays and KL→eμ, severely constrain the available parameter space. We show that in the allowed part of the parameter space (i) some of the lepton-flavor-violating tau decay branching ratios are predicted to be close to their current experimental limits. (ii) The underlying scalar leptoquarks can be probed at the LHC via their dominant decay modes into tau leptons and electrons and the third generation quarks. (iii) The constraints from meson oscillations imply that the masses of scalar gluons, another pair of colored multiplets around, have to be bigger than around 15 TeV, and thus, they can be probed only at a future 100 TeV collider. In both neutral and charged variants, these scalars decay predominantly into third generation quarks, with up to O(10%) branching ratios into family-mixed final states. Besides that, we comment on the phenomenology of the scalar gluons in the current scenarios in the case that the B-decay anomalies eventually disappear

A unified leptoquark model confronted with lepton non-universality in B-meson decays

The anomalies in the B-meson sector, in particular RK(⁎) and RD(⁎), are often interpreted as hints for physics beyond the Standard Model. To this end, leptoquarks or a heavy Z′ represent the most popular SM extensions which can explain the observations. However, adding these fields by hand is not very satisfactory as it does not address the big questions like a possible embedding into a unified gauge theory. On the other hand, light leptoquarks within a unified framework are challenging due to additional constraints such as lepton flavor violation. The existing accounts typically deal with this issue by providing estimates on the relevant couplings. In this letter we consider a complete model based on the SU(4)C⊗SU(2)L⊗U(1)R gauge symmetry, a subgroup of SO(10), featuring both scalar and vector leptoquarks. We demonstrate that this setup has, in principle, all the potential to accommodate RK(⁎) and RD(⁎) while respecting bounds from other sectors usually checked in this context. However, it turns out that KL→e±μ∓ severely constraints not only the vector but also the scalar leptoquarks and, consequently, also the room for any sizeable deviations of RK(⁎) from 1. We briefly comment on the options for extending the model in order to conform this constraint. Moreover, we present a simple criterion for all-orders proton stability within this class of models