Takeo Inami

Effective gauge theory and the effect of heavy quarks in Higgs boson decays

A general framework is given for evaluating the contributions of as yet undiscovered heavy quarks to the gluonic decay rate of the Weinberg-Salam type Higgs boson. Since the Yukawa coupling of the Higgs boson to a quark pair is proportional to the quark mass, loop graphs involving heavy quarks have a non-vanishing effect on the gluonic decay width of the Higgs boson. This effect of heavy quarks with massesMj(j=t,...) much greater than the Higgs boson massmH is calculated in an effective gauge theory. The effects of two different kinds of large logarithms, lnMj2/μmh2/μ2 are separated and summed up by the renormalization group method. It is found that the higher order QCD corrections are large and that the gluonic contribution to the hadronic decay width is significant if there are more than three generations. The Higgs decay width can therefore be used to probe the number of generations of heavy quarks.

Renormalization group estimate of the hadronic decay width of the Higgs boson

Abstract The total hadronic decay width of the Weinberg-Salam type Higgs boson is estimated in QCD for the Higgs boson mass much larger than the ordinary hadronic mass scale, by use of the operator product expansion and renormalization group equation. We give an explicit formula for the decay width in terms of quark masses including strong interaction corrections up to the next-to-leading order. A numerical analysis of the hadronic decay width of the Higgs boson is made in the six-quark model. The next-to-leading order correction is found to be significant, e.g., 30-20% of the leading term for mH of oue interest, mH ⪅ 1 TeV. Application of our scheme to the decay rates of heavy Higgs bosons of other types is also discussed.

Natural suppression of flavour-changing neutral currents in supersymmetric gauge theories

Abstract Induced flavour-changing neutral currents (FCNC) in supersymmetric unified theories are investigated both in models with the standard SU(2)L × U(1) gauge symmetry and in models with an extra Ũ(1) gauge symmetry. Supersymmetric extension of the natural flavour conservation laws for neutral currents is obtained by adding a condition regarding the assumed type of supersymmetry breaking. This condition ensures no direct flavour-changing couplings of neutral gauge-Higgs fermions and at the same time is necessary and sufficient for the natural suppression of the induced FCNC. It is found that in the class of models satisfying the new condition the contribution of the scalar partners of quarks to the induced strangeness-changing neutral current is comparable to that of the quarks in K L → π π , while it is negligibly small in KL − KS mass difference.

Lepton-Flavour Nonconservation and the Type of Neutrino Masses

The lepton-flavour nonconservation is studied in the left-right symmetric gauge theory with both Majorana and Dirac mass terms of neutrinos. The tree graphs with physical Higgs scalar exchange and the one-loop graphs with light (left-handed) and heavy (right-handed) gauge boson exchange contributing to /1~ er and /1~ eee are evaluated. The one-loop graphs with intermediate heavy Majorana neutrinos are shown to give more important effects than those with light Majorana neutrinos. The latter contributions to the rare decay rates are negligibly small, independently of the value of 7J == M~jM~R because of the strong suppression by powers of light neutrino masses mvL. The former contributions are not directly related to mvL but depend on 7J. They can lead to relatively large values of the rare decay rates, unless 7J is inhibitingly small. The predictions for the rates of lepton-flavour changing processes /1~ er, /1~eee, Z~/1e, /1N~eN, KL~/1e and K+~J[+/1e- in the present gauge model are comxad pared with similar predictions in other types of gauge models with different types of neutrino masses.

Quantum effects in generalized Kaluza-Klein theories

Abstract Quantum effects are studied in Kaluza-Klein theories with a torus T n as the extra space. It is shown that some of the physical circumferences of T n tend to contract to sizes of the order of the Planck length due to quantum effects. This behaviour of contraction or expansion of the compact dimensions depends on their initial values.

Stability of Classical Solutions in Extended {Kaluza-Klein} Theories

Abstract The stability of classical solutions for a scalar field corresponding to the radius of S n = SO( n + 1)/SO( n ) in extended Kaluza-Klein theories is investigated. A stable solution is shown to emerge if an antisymmetric tensor field of rank n −1 or rank-three acquires a nonzero background field strength in S n or in four-dimensional spacetime, respectively.

Interference terms in the unitarity equation in the multiperipheral resonance production model

Abstract Interference terms in the dual unitarization are calculated by using the multiperipheral resonance production model. The breaking of the exchange degeneracy is obtained between vector and tensor trajectories and is shown to be related to the inclusive cross sections of vector and tensor resonance production. After analyzing recent data of resonance production, we find that α ϱ (0) - α A 2 (0) ≅ 0.1, α K ∗ (0) > α K ∗∗ (0) in agreement with experiments. Furthermore the ω pole reappears at α ω (0) > 0.

A new scheme of ηand η′ mixing and violations of the OZI rule

Abstract A possible mixing scheme for η and η′ is proposed based on the picture that 0 − mesons form an ideal nonet in the dual planar theory and deviate from it through nonplanar diagrams. Using the new mixing angles (θ η ≠θ η′ ), we calculate radiative decay widths and production ratio of η and η′ which are then compared with experiments. Extension of our scheme to SU(4) leads to rather large violations of the OZI rule in decays of new particles with η or η′ in the final states.

Cancellation of quadratic divergences and uniqueness of softly broken supersymmetry

Abstract Supersymmetric theories are known to be free from quadratic divergences. We investigate the inverse question whether the absence of quadratic divergences implies supersymmetry uniquely in theories of one Majorana field and a set of scalars and/or pseudoscalar fields. Relations among coupling constants derived from the requirement of no quadratic divergences up to two-loop order in the loop expansion lead uniquely to the softly broken supersymmetric theories in cases of two or less spin-0 fields.

A Model of Baryons Based on Duality and Unitarity

Abstract A model of “planar” baryons with (10 + 8) ↔ (1 + 8) exchange degeneracy is proposed, based on duality and unitarity. Dynamical mechanisms for deviation from the “planar” baryons are considered and the consequent pattern of broken exchange degenerate trajectories is compared with observed baryon spectra. Our model suggests a string picture of linear molecule type for baryons.