Mamoru Matsunaga

Unitarity in Gauge Symmetry Breaking on an Orbifold

We study the unitarity bounds of scattering amplitudes in extra-dimensional gauge theory, in which the gauge symmetry is broken by the boundary conditions. The evaluation of the amplitude of the diagram including four massive gauge bosons in the external lines shows that the asymptotic power behavior of the amplitude is canceled. The calculation is carried out with the 5-dimensional standard model and the SU(5) grand unified theory, whose 5th dimensional coordinate is compactified on S 1 /Z2. The gauge theories broken through the orbifolding preserve unitarity at high energies, similarly to the broken gauge theories in which the gauge bosons acquire masses through the Higgs mechanism. We show that the contributions of the Kaluza-Klein states play a crucial role in conserving the unitarity.

4D Equivalence Theorem and Gauge Symmetry on an Orbifold

We investigate high-energy behavior of scattering amplitudes in extra dimensional gauge theory where the gauge symmetry is broken by the boundary conditions. We study, in particular, the 5D SU(5) grand unified theory whose 5th-dimensional coordinate is compactified on S 1 /Z 2 . We pay attention to the gauge symmetry compatible with the boundary conditions on an orbifold and present the BRST formalism of the 4D theory that is obtained through integration of the 5D theory along the extra dimension. We derive the 4D equivalence theorem on the basis of the Slavnov-Taylor identities. We also calculate the amplitudes of the process including four massive gauge bosons in the external lines and compare them with those for the connected reactions in which the gauge fields are replaced by the corresponding would-be Nambu-Goldstone (NG) fields. We explicitly confirm that the equivalence theorem holds.

STATISTICAL QUANTUM OPERATION

An explicit form of a generic unital quantum operation, which transforms a given stationary pure state to an arbitrary statistical state with perfect decoherence, is presented. This allows one to operationally realize the thermal state as a special case. The loss of information due to randomness generated by the operation is discussed by evaluating the entropy. Realization of the thermal state of a bipartite spin-1/2 system is discussed as an illustrative example.

Non-Anomalous Flavor Symmetries and SU(6) ×SU(2)R Model

We introduce the flavor symmetry

Quantization of hypercharge in gauge groups locally isomorphic but globally nonisomorphic to SU(3)c × SU(2)L × U(1)Y

{\bf Z}_M \times {\bf Z}_N \times D_4

Maki-Nakagawa-Sakata matrix and Froggatt-Nielsen mechanism

into the

Semidirect product gauge group[SU(3)c×SU(2)L]⋊U(1)Yand quantization of hypercharge

SU(6) \times SU(2)_R

SU(3)L ⋊ (ℤ3 × ℤ3) GAUGE SYMMETRY AND TRI-BIMAXIMAL MIXING

string-inspired model. The cyclic group

On Noether's theorem for the invariant of the time-dependent harmonic oscillator

{\bf Z}_M

Flavor Symmetry on Non-Commutative Compact Space and SU(6) × SU(2)R Model

and the dihedral group