Nobuchika Okada

Bulk Standard Model in the Randall-Sundrum Background

We discuss issues in an attempt to put the standard model (SM) in five-dimensional anti\char21{}de Sitter spacetime compactified on

Classically conformal

{S}^{1}{/Z}_{2}.

B^-

The recently proposed approach to the gauge hierarchy problem by using this background geometry, with the SM confined on a boundary, is extended to a situation where (some of) the SM particles reside in the five-dimensional bulk. In particular, we find a localization of zero modes of bulk fermions near the boundary with a negative tension. Unlike the compactification with the flat metric, these fermion zero modes couple to Kaluza-Klein (KK) excitations of the SM gauge bosons. Interestingly, only low-lying modes of such KK gauge bosons have non-negligible couplings. Current electroweak precision data give a constraint that the first KK mode be heavier than

L extended Standard Model

9

The minimal B-L model naturally realized at TeV scale

TeV. We also argue that at least the Higgs field should be confined on the brane to utilize the Randall-Sundrum background as a solution to the gauge hierarchy.

Can WIMP dark matter overcome the nightmare scenario

Abstract Under a hypothesis of classically conformal theories, we investigate the minimal B – L extended Standard Model, which naturally provides the seesaw mechanism for explaining tiny neutrino masses. In this setup, the radiative gauge symmetry breaking is successfully realized in a very simple way: The B – L gauge symmetry is broken through the conformal anomaly induced by quantum corrections in the Coleman–Weinberg potential. Associated with this B – L symmetry breaking, the Higgs mass parameter is dynamically generated, by which the electroweak symmetry breaking is triggered. We find that a wide range of parameter space can satisfy both the theoretical and experimental requirements.

Inverse seesaw neutrino signatures at the LHC and ILC

In a previous paper [S. Iso, N. Okada, and Y. Orikasa, Phys. Lett. B 676, 81 (2009).], we have proposed the minimal B-L extended standard model as a phenomenologically viable model that realizes the Coleman-Weinberg-type breaking of the electroweak symmetry. Assuming the classical conformal invariance and stability up to the Planck scale, we will show in this paper that the model naturally predicts TeV scale B-L breaking as well as a light standard-model singlet Higgs boson and light right-handed neutrinos around the same energy scale. We also study phenomenology and detectability of the model at the Large Hadron Collider and the International Linear Collider.

Neutrino oscillation data versus minimal supersymmetric SO(10) model

Even if new physics beyond the Standard Model (SM) indeed exists, the energy scale of new physics might be beyond the reach at the Large Hadron Collider (LHC) and the LHC could find only the Higgs boson but nothing else. This is the so-called “nightmare scenario”. On the other hand, the existence of the dark matter has been established from various observations. One of the promising candidates for thermal relic dark matter is a stable and electric charge-neutral Weakly Interacting Massive Particle (WIMP) with the mass below the TeV scale. In the nightmare scenario, we introduce a WIMP dark matter singlet under the SM gauge group, which only couples to the Higgs doublet at the lowest order, and investigate a possibility that such WIMP dark matter can be a clue to overcome the nightmare scenario via various phenomenological tests such as the dark matter relic abundance, the direct detection experiments for the dark matter particle, and the production of the dark matter particle at the LHC.

General formulation for proton decay rate in minimal supersymmetric SO(10) GUT

We study the collider signature of pseudo-Dirac heavy neutrinos in the inverse seesaw scenario, where the heavy neutrinos with mass at the electroweak scale can have sizable mixings with the Standard Model neutrinos, while providing the tiny light neutrino masses by the inverse seesaw mechanism. Based on a simple, concrete model realizing the inverse seesaw, we fix the model parameters so as to reproduce the neutrino oscillation data and to satisfy other experimental constraints, assuming two typical flavor structures of the model and the different types of hierarchical light neutrino mass spectra. With the fixed parameters in this way, we analyze the heavy neutrino signal at the LHC through tri-lepton final state with large missing energy and at the ILC through a single lepton plus di-jet with large missing energy. We find that in some cases, the heavy neutrino signal can be observed with a large statistical significance via different flavor charged lepton final states. Therefore, we can not only discover the heavy neutrinos in the future but also obtain a clue to reveal the origin of the small neutrino mass and flavor mixing.

Direct bounds on electroweak scale pseudo-Dirac neutrinos from s=8 TeV LHC data

WereconsidertheminimalsupersymmetricSO(10)model,whereonlyone 10 and one 126 Higgs multiplets have Yukawa couplings with matter multiplets. The model is generalized to include CP-violating phases, and examined how well its predictions can meet the current neutrino oscillation data. Using the electroweak scale data about six quark masses, three angles andone CP-phasein theCabibbo-Kobayashi-Maskawa matrix and three charged-lepton masses and given tanfl (the ratio of vacuum expectation values ofapairofHiggsdoublets),weobtainthePontecorvo-Maki-Nakagawa-Sakata matrixand the ratio, ¢m 2=¢m 2, as functions of only one free parameter in the model. In our analysis, one-loop renormalization group equations for the gauge couplings, the Yukawa couplingsandtheefiectivedimension-flveoperatorareusedtoconnectthedatabetweenthe electroweak scaleandthegranduniflcationscale. Fixingthefreeparameterappropriately, weflnd,forexample,sin 2 2µ12 »0:72, sin 2 2µ23 »0:90,sin 2 2µ13 »0:16and¢m 2 =¢m 2 » 0:19 withtanfl=45, whichare inagreement withthe currentneutrinooscillation data.