Dynamical Electroweak Symmetry Breaking in SO(5)xU(1) Gauge-Higgs Unification with Top and Bottom Quarks

An SO(5)xU(1) gauge-Higgs unification model in the Randall-Sundrum warped space with top and bottom quarks is constructed. Additional fermions on the Planck brane make exotic particles heavy by effectively changing boundary conditions of bulk fermions from those determined by orbifold conditions. Gauge couplings of a top quark multiplet trigger electroweak symmetry breaking by the Hosotani mechanism, simultaneously giving a top quark the observed mass. The bottom quark mass is generated by combination of brane interactions and the Hosotani mechanism, where only one ratio of brane masses is relevant when the scale of brane masses is much larger than the Kaluza-Klein scale (\sim 1.5 TeV). The Higgs mass is predicted to be 49.9 (53.5) GeV for the warp factor 10^{15} (10^{17}). The Wilson line phase turns out \pi/2 and the Higgs couplings to W and Z vanish so that the LEP2 bound for the Higgs mass is evaded. In the flat spacetime limit the electroweak symmetry is unbroken.Comment: 35 pages, 2 figures. A few corrections are mad

Two loop finiteness of Higgs mass and potential in the gauge-Higgs unification

The zero mode of an extra-dimensional component of gauge potentials serves as a 4D Higgs field in the gauge-Higgs unification. We examine QED on $M^4 \times S^1$ and determine the mass and potential of a 4D Higgs field (the $A_5$ component) at the two loop level with gauge invariant reguralization. It is seen that the mass is free from divergences and independent of the renormalization scheme.Comment: 18 pages, 1 figur

Progress in weakly coupled string phenomenology

The weakly coupled vacuum of $E_8\otimes E_8$ heterotic string theory remains an attractive scenario for particle physics. The particle spectrum and the issue of dilaton stabilization are reviewed. A specific model for hidden sector condensation and supersymmetry breaking, that respects known constraints from string theory, is described, and its phenomenological and cosmological implications are discussed.Comment: 15 pages, full postscript also available from http://phyweb.lbl.gov/theorygroup/papers/48640.p

Effects of Fermion Masses and Twisting on Non-Integrable Phases on Compact Extra Dimensions

The effective potential for the Wilson loop in the SU(2) gauge theory with N_f massive fundamental and N_a massive adjoint fermions on S^1 x M^4 is computed at the one-loop level, assuming periodic boundary conditions for the gauge field and general boundary conditions for fermions. It is shown that there are critical values for the bare mass, and the boundary condition parameter for the adjoint fermions, beyond which the symmetry pattern changes. However, neither bare mass, nor the boundary condition parameter for the fundamental fermion play any role on the vacuum structure, thus the symmetry breaking pattern. When the two different types of fermions with equal masses exist together the pattern of the fundamental fermion dominate, and SU(2) gauge symmetry remains intact independent of the fermion masses.Comment: 21 pages, 28 figures, version to appear in Nucl. Phys.

Gauge-Higgs Dark Matter

When the anti-periodic boundary condition is imposed for a bulk field in extradimensional theories, independently of the background metric, the lightest component in the anti-periodic field becomes stable and hence a good candidate for the dark matter in the effective 4D theory due to the remaining accidental discrete symmetry. Noting that in the gauge-Higgs unification scenario, introduction of anti-periodic fermions is well-motivated by a phenomenological reason, we investigate dark matter physics in the scenario. As an example, we consider a five-dimensional SO(5)\timesU(1)_X gauge-Higgs unification model compactified on the $S^1/Z_2$ with the warped metric. Due to the structure of the gauge-Higgs unification, interactions between the dark matter particle and the Standard Model particles are largely controlled by the gauge symmetry, and hence the model has a strong predictive power for the dark matter physics. Evaluating the dark matter relic abundance, we identify a parameter region consistent with the current observations. Furthermore, we calculate the elastic scattering cross section between the dark matter particle and nucleon and find that a part of the parameter region is already excluded by the current experimental results for the direct dark matter search and most of the region will be explored in future experiments.Comment: 16 pages, 2 figure

A possible minimal gauge-Higgs unification

A possible minimal model of the gauge-Higgs unification based on the higher dimensional spacetime M^4 X (S^1/Z_2) and the bulk gauge symmetry SU(3)_C X SU(3)_W X U(1)_X is constructed in some details. We argue that the Weinberg angle and the electromagnetic current can be correctly identified if one introduces the extra U(1)_X above and a bulk scalar triplet. The VEV of this scalar as well as the orbifold boundary conditions will break the bulk gauge symmetry down to that of the standard model. A new neutral zero-mode gauge boson Z' exists that gains mass via this VEV. We propose a simple fermion content that is free from all the anomalies when the extra brane-localized chiral fermions are taken into account as well. The issues on recovering a standard model chiral-fermion spectrum with the masses and flavor mixing are also discussed, where we need to introduce the two other brane scalars which also contribute to the Z' mass in the similar way as the scalar triplet. The neutrinos can get small masses via a type I seesaw mechanism. In this model, the mass of the Z' boson and the compactification scale are very constrained as respectively given in the ranges: 2.7 TeV < m_Z' < 13.6 TeV and 40 TeV < 1/R < 200 TeV.Comment: 20 pages, revised versio

Effective theories of gauge-Higgs unification models in warped spacetime

We derive four-dimensional (4D) effective theories of the gauge-Higgs unification models in the warped spacetime. The effective action can be expressed in a simple form by neglecting subleading corrections to the wave functions. We have shown in our previous works that some Higgs couplings to the other fields are suppressed by factors that depend on $\bar{\theta}_H$ from the values in the standard model. Here $\bar{\theta}_H$ is the Wilson line phase along the fifth dimension, which characterizes the electroweak symmetry breaking. The effective action derived here explicitly shows a nonlinear structure of the Higgs sector, which clarifies the origins of those suppression factors.Comment: 36 pages, 1 figur

An Attempt to Solve the Hierarchy Problem Based on Gravity-Gauge-Higgs Unification Scenario

We discuss a possible scenario to solve the hierarchy problem, in which 4-dimensional bosonic fields with all possible integer spins, graviton, gauge boson and Higgs are unified in a framework of a gravity theory with extra dimensions. The Higgs is identified with the extra space component of the metric tensor. One-loop quantum effect on the Higgs mass-squared is explicitly calculated in a five dimensional gravity theory compactified on $S^1$. We obtain a finite calculable Higgs mass-squared without suffering from quadratic divergence, by virtue of general coordinate transformation invariance, which is argued to be guaranteed by the summation over all Kaluza-Klein modes running in the loop diagrams.Comment: 15pages, 2figures; version accepted for publication in Phys. Lett. B, one reference adde