Upper bound on the scale of Majorana-neutrino mass generation

We derive a model-independent upper bound on the scale of Majorana-neutrino mass generation. The upper bound is $4\pi v^2/\sqrt 3 m_\nu$, where $v \simeq 246$ GeV is the weak scale and $m_\nu$ is the Majorana neutrino mass. For neutrino masses implied by neutrino oscillation experiments, all but one of these bounds are less than the Planck scale, and they are all within a few orders of magnitude of the grand-unification scale.Comment: 6 pages, 3 figures; REVTeX; published versio

On the nature of the fourth generation neutrino and its implications

We consider the neutrino sector of a Standard Model with four generations. While the three light neutrinos can obtain their masses from a variety of mechanisms with or without new neutral fermions, fourth-generation neutrinos need at least one new relatively light right-handed neutrino. If lepton number is not conserved this neutrino must have a Majorana mass term whose size depends on the underlying mechanism for lepton number violation. Majorana masses for the fourth generation neutrinos induce relative large two-loop contributions to the light neutrino masses which could be even larger than the cosmological bounds. This sets strong limits on the mass parameters and mixings of the fourth generation neutrinos.Comment: To be published. Few typos corrected, references update

Pathways to Naturally Small Neutrino Masses

In the minimal standard electroweak gauge model, there is an effective dimension-five operator which generates neutrino masses, and it has only three tree-level realizations. One is the canonical seesaw mechanism with a right-handed neutrino. Another is having a heavy Higgs triplet as recently proposed. The third is to have a heavy Majorana fermion triplet, an example of which is presented here in the context of supersymmetric SU(5) grand unification. The three generic one-loop realizations of this operator are also discussed.Comment: 12 pages including 5 figures; corrected minus signs in Eqs.(5)-(6), no result is affecte

Decoupling property of the supersymmetric Higgs sector with four doublets

In supersymmetric standard models with multi Higgs doublet fields, selfcoupling constants in the Higgs potential come only from the D-terms at the tree level. We investigate the decoupling property of additional two heavier Higgs doublet fields in the supersymmetric standard model with four Higgs doublets. In particular, we study how they can modify the predictions on the quantities well predicted in the minimal supersymmetric standard model (MSSM), when the extra doublet fields are rather heavy to be measured at collider experiments. The B-term mixing between these extra heavy Higgs bosons and the relatively light MSSM-like Higgs bosons can significantly change the predictions in the MSSM such as on the masses of MSSM-like Higgs bosons as well as the mixing angle for the two light CP-even scalar states. We first give formulae for deviations in the observables of the MSSM in the decoupling region for the extra two doublet fields. We then examine possible deviations in the Higgs sector numerically, and discuss their phenomenological implications.Comment: 26 pages, 24 figures, text sligtly modified,version to appear in Journal of High Energy Physic

Kaluza-Klein Induced Gravity Inflation

A D-dimensional induced gravity theory is studied carefully in a $4 + (D-4)$ dimensional Friedmann-Robertson-Walker space-time. We try to extract information of the symmetry breaking potential in search of an inflationary solution with non-expanding internal-space. We find that the induced gravity model imposes strong constraints on the form of symmetry breaking potential in order to generate an acceptable inflationary universe. These constraints are analyzed carefully in this paper.Comment: 10 pages, title changed, corrected some typos, two additional comments adde

Constraints from muon g-2 and LFV processes in the Higgs Triplet Model

Constraints from the muon anomalous magnetic dipole moment and lepton flavor violating processes are translated into lower bounds on v_Delta*m_H++ in the Higgs Triplet Model by considering correlations through the neutrino mass matrix. The discrepancy of the sign of the contribution to the muon anomalous magnetic dipole moment between the measurement and the prediction in the model is clarified. It is shown that mu to e gamma, tau decays (especially, tau to mu e e), and the muonium conversion can give a more stringent bound on v_Delta*m_H++ than the bound from mu to eee which is expected naively to give the most stringent one.Comment: 18 pages, 16 figure

Lepton Number Violation from Colored States at the LHC

The possibility to search for lepton number violating signals at the Large Hadron Collider (LHC) in the colored seesaw scenario is investigated. In this context the fields that generate neutrino masses at the one-loop level are scalar and Majorana fermionic color-octets of SU(3). Due to the QCD strong interaction these states may be produced at the LHC with a favorable rate. We study the production mechanisms and decays relevant to search for lepton number violation signals in the channels with same-sign dileptons. In the simplest case when the two fermionic color-octets are degenerate in mass, one could use their decays to distinguish between the neutrino spectra. We find that for fermionic octets with mass up to about 1 TeV the number of same-sign dilepton events is larger than the standard model background indicating a promising signal for new physics.Comment: minor corrections, added reference

Inflationary Universe in Higher Derivative Induced Gravity

In an induced-gravity model, the stability condition of an inflationary slow-rollover solution is shown to be $\phi_0 \partial_{\phi_0}V(\phi_0)=4V(\phi_0)$. The presence of higher derivative terms will, however, act against the stability of this expanding solution unless further constraints on the field parameters are imposed. We find that these models will acquire a non-vanishing cosmological constant at the end of inflation. Some models are analyzed for their implication to the early universe.Comment: 6 pages, two typos correcte

Effective Lagrangian approach to neutrinoless double beta decay and neutrino masses

Neutrinoless double beta ($0\nu\beta\beta$) decay can in general produce electrons of either chirality, in contrast with the minimal Standard Model (SM) extension with only the addition of the Weinberg operator, which predicts two left-handed electrons in the final state. We classify the lepton number violating (LNV) effective operators with two leptons of either chirality but no quarks, ordered according to the magnitude of their contribution to \znbb decay. We point out that, for each of the three chirality assignments, $e_Le_L, e_Le_R$ and $e_Re_R$, there is only one LNV operator of the corresponding type to lowest order, and these have dimensions 5, 7 and 9, respectively. Neutrino masses are always induced by these extra operators but can be delayed to one or two loops, depending on the number of RH leptons entering in the operator. Then, the comparison of the $0\nu\beta\beta$ decay rate and neutrino masses should indicate the effective scenario at work, which confronted with the LHC searches should also eventually decide on the specific model elected by nature. We also list the SM additions generating these operators upon integration of the heavy modes, and discuss simple realistic examples of renormalizable theories for each case.Comment: Accepted for publication. Few misprints corrected and new references adde

The unexpected resurgence of Weyl geometry in late 20-th century physics

Weyl's original scale geometry of 1918 ("purely infinitesimal geometry") was withdrawn by its author from physical theorizing in the early 1920s. It had a comeback in the last third of the 20th century in different contexts: scalar tensor theories of gravity, foundations of gravity, foundations of quantum mechanics, elementary particle physics, and cosmology. It seems that Weyl geometry continues to offer an open research potential for the foundations of physics even after the turn to the new millennium.Comment: Completely rewritten conference paper 'Beyond Einstein', Mainz Sep 2008. Preprint ELHC (Epistemology of the LHC) 2017-02, 92 pages, 1 figur