Nobuhiro Uekusa

H parity and the stable Higgs boson in the SO(5) X U(1) gauge-Higgs unification

In the SO(5) × U(1) gauge-Higgs unification model in the Randall-Sundrum warped space, there results the conservation of the H parity. The H parity is assigned to all 4D fields including excited modes in Kaluza-Klein towers. The neutral Higgs boson is the lightest particle of odd H parity, consequently becoming absolutely stable. Its mass is found to be 70-135 GeV for the warp factor z L = 10 5 -10 15 .

Two-loop corrections and predictability on orbifold

Abstract We study quantum loop corrections to two-point functions and extraction of physical quantities in a five-dimensional ϕ 4 theory on an orbifold. At two-loop level, we find that divergence for quartic derivative terms of ( p 2 ) 2 appear as Lagrangian terms in the bulk. The counterterms are needed and these terms make propagators have two poles. With this effect taken into account, corrections to masses are derived. We show that for extraction of physical quantities for two-point functions an ultraviolet cutoff must be orders of magnitude larger compared to a compactification scale. Even higher derivative corrections at higher loop levels are also discussed.

Simple mass relations for bulk fermions

Relations between bulk mass parameters for fermions propagating in higher dimensions are studied in analogy with the empirical mass relation for charged leptons. Masses of three generation of four-dimensional charged leptons are achieved from the bulk mass parameters of the same-order values. We find that the observed pattern of charged-lepton mass spectrum is accommodated approximately in a set of simple relations for bulk and physical masses.

Operators in ultraviolet completions for collective symmetry breaking

We investigate the Lagrangian terms of scalar-gauge interactions in a weakly coupled gauge theory beyond the ultraviolet momentum cutoff of models where the collective symmetry breaking mechanism protects the Higgs mass squared against having quadratic divergence. We also propose a five-dimensional model in which the gauge symmetry breaking is achieved by boundary conditions consistent with local gauge transformations. It is shown that the scalar-gauge operators in the two models differ in the absence of quadratic divergence.

Total-derivative supersymmetry breaking

On an interval compactification in supersymmetric theory, boundary conditions for bulk fields must be treated carefully. If they are taken arbitrarily following the requirement that a theory is supersymmetric, the conditions could give redundant constraints on the theory. We construct a supersymmetric action integral on an interval by introducing brane interactions with which total-derivative terms under the supersymmetry transformation become zero due to a cancellation. The variational principle leads equations of motion and also boundary conditions for bulk fields, which determine boundary values of bulk fields. By estimating mass spectrum, spontaneous supersymmetry breaking in this simple setup can be realized in a new framework. This supersymmetry breaking does not induce a massless R axion, which is favorable for phenomenology. It is worth noting that fermions in hyper-multiplet, gauge bosons, and the fifth-dimensional component of gauge bosons can have zero-modes (while the other components are all massive as Kaluza-Klein modes), which fits the gauge-Higgs unification scenarios.

MOST ATTRACTIVE CHANNEL FOR SELF-BREAKING OF GRAND UNIFICATION GROUP SYMMETRY

Most attractive channel is studied for SU(5) grand unified theory in five dimensions where 5* and 10 fermions and a 24 gauge boson propagate in the bulk. If there are bulk fermions with zero mode for the chirality opposite to quark and lepton multiplets, they can contribute to forming 5, 24, 50 and 75 scalar bound states. We find that the inclusion of a simple anomaly-free set for zero mode yields scalar bound states whose binding strengths are the largest for 24 and the second largest for 5. This corresponds to the breaking pattern of the SU(5) to color and electromagnetism via the standard model gauge group.

Operators in ultraviolet completions for Electroweak collective symmetry breaking

In a gauge theory with SU(5) broken to SU(2)×U(1), the Higgs mass squared receives only logarithmic divergence from all scalar‐gauge interactions at one loop. The same pattern of gauge symmetry breaking can be achieved without any scalar fields in a five‐dimensional model.

Mass ratio of W and Z bosons in SU(5) gauge-Higgs unification

We study the mass ratio of W and Z bosons in an SU(5) gauge-Higgs unification model with the left–right symmetry remaining locally for boundary conditions and with no scalar fields except for the extra-dimensional component of gauge bosons. We find that there are a variety of boundary conditions to yield distinct values of the mass ratio.