arXiv subjects

Shinya Kanemura

Publications and source records attributed to Shinya Kanemura.

225 records · Page 13Linked to original sources

arXiv1998

Sum rules for $e^+e^- \to W^+W^-$ helicity amplitudes from BRS invariance

The BRS invariance of the electroweak gauge theory leads to relationships between amplitudes with external massive gauge bosons and amplitudes where some of these gauge bosons are replaced with their corresponding Nambu-Goldstone bosons. Unlike the equivalence theorem, these identities are exact at all energies. In this paper we discuss such identities which relate the process $e^+e^- \to W^+W^-$ to $W^\pmχ^\mp$ and $χ^+χ^-$ production. By using a general form-factor decomposition for $e^+e^- \to W^+W^-$, $e^+e^- \to W^\pm χ^\mp$ and $e^+e^- \to χ^+χ^-$ amplitudes, these identities are expressed as sum rules among scalar form factors. Because these sum rules may be applied order by order in perturbation theory, they provide a powerful test of higher order calculations. By using additional Ward-Takahashi identities we find that the various contributions are divided into separately gauge-invariant subsets, the sum rules applying independently to each subset. After a general discussion of the application of the sum rules we consider the one-loop contributions of scalar-fermions in the Minimal Supersymmetric Standard Model as an illustration.

hep-ph↗

arXiv1997

Thermodynamic Gross-Neveu model under constant electromagnetic field

Analyzed is the effective potential of D-dimensional thermodynamic Gross-Neveu model (defined by large-N leading order, $2\leq D<4$) under constant electromagnetic field ($\vec{E}\cdot\vec{B}=0$). The potential is derived from a thermal analogy of the worldline formalism. In the magnetic case, the potential is expressed in terms of a discretized momentum sum instead of a continuum momentum integral, and it reproduces known critical values of $μ$ and $T$ in the continuum limit. In the electric case, chiral symmetry is restored at finite $T$ (with arbitrary $μ$) against instability of fermion vacuum. An electromagnetic duality is pointed out as well. Phase diagrams are obtained in both cases.

hep-ph↗

arXiv1997

Novel Enhancement of Loop-Induced $H^\pm W^\mp Z^0$ Vertex

We discuss the non-decoupling effects on the loop-induced $H^\pm W^\mp Z^0$ vertex in the general two Higgs-doublet model. The decay process $H^\pm \to W^\pm Z^0$ is analyzed at one-loop level and possible enhancement of the decay width is explored. We find that a novel enhancement can be realized by the Higgs non-decoupling effects with large mass difference between charged and CP-odd Higgs bosons. The branching ratio of the process can be a few % $\sim$ 10%. Therefore the decay mode may be detectable at LHC or future $e^+e^-$ linear colliders (LC's).

hep-ph↗

arXiv1997

Non-Decoupling Effects of Higgs Bosons on $e^+e^- \to W^+_LW^-_L$ in the Two-Doublet Model

The non-decoupling effects of heavy Higgs bosons on the process $e^+e^- \to W^+_LW^-_L$ are discussed in the two Higgs-doublet model. The one-loop corrections to the cross section are calculated by using the equivalence theorem and the explicit expressions of its deviation from the standard model are derived. The leading mass contributions to the deviation in expansion by $s$ are related to the $T$ parameter by the low-energy theorem. The next-to leading ones are free from the present data, which should be determined by future experiments. The deviation can amount to $\sim 3$ % at $\sqrt{s} = 1$ TeV under the constraint from the present data, so that it may give useful information on the Higgs sector in cooperation with data from future linear colliders.

hep-ph↗

arXiv1997

Enhancement of Loop Induced $H^\pm W^\mp Z^0$ Vertex in Two Higgs-doublet Model

The non-decoupling effects of heavy Higgs bosons as well as fermions on the loop-induced $H^\pm W^\mp Z^0$ vertex are discussed in the general two Higgs doublet model. The decay width of the process $H^+ \to W^+ Z^0$ is calculated at one-loop level and the possibility of its enhancement is explored both analytically and numerically. We find that the novel enhancement of the decay width can be realized by the Higgs non-decoupling effects with large mass-splitting between the charged Higgs boson and the CP-odd one. This is due to the large breakdown of the custodial $SU(2)_V$ invariance in the Higgs sector. The branching ratio can amount to $10^{-2} \sim 10^{-1}$ for $m_{H^\pm} = 300$ GeV within the constraint from the present experimental data. Hence this mode may be detectable at LHC or future $e^+e^-$ linear colliders.

hep-ph↗

arXiv1996

Thermodynamic properties of spontaneous magnetization in Chern-Simons QED_3

The spontaneous magnetization in Chern-Simons QED_3 is discussed in a finite temperature system. The thermodynamical potential is analyzed within the weak field approximation and in the fermion massless limit. We find that there is a linear term with respect to the magnetic field with a negative coefficient at any finite temperature. This implies that the spontaneous magnetic field does not vanish even at high temperature. In addition, we examine the photon spectrum in the system. We find that the bare Chern-Simons coefficient is cancelled by the radiative effects. The photons then become topologically massless according to the magnetization, though they are massive by finite temperature effects. Thus the magnetic field is a long-range force without the screening even at high temperature.

hep-th↗

arXiv1996

Screening Theorem for the Higgs Decays into the Gauge Boson Pairs

The radiative corrections to the decays of the neutral CP-even Higgs boson $H$ into a longitudinal gauge boson pair, {\it i.e.}, $H \rightarrow Z_LZ_L$ and $W^+_LW^-_L$ are analyzed in the two Higgs doublet model by making use of the equivalence theorem. The sensitivity of the decay rates to the masses of the heavier Higgs bosons, charged $G^{\pm}$ and CP-odd neutral $A$ bosons as well as CP-even neutral $h$ boson, is investigated. Though the width $Γ(H \rightarrow Z_LZ_L)$ is insensitive to the masses of heavier Higgs bosons, $Γ(H \rightarrow W^+_LW^-_L)$ is sensitive and the radiative corrections are minimized for $m_G = m_A$. These results are explained completely on the basis of a new screening theorem for the vertices, which is closely connected with the custodial $SU(2)_V$ symmetry.

hep-ph↗

arXiv1995

Thermodynamics in 2+1 Dimensional QED with Chern-Simons Term

It is known that in the 2+1 dimensional quantum electrodynamics with Chern-Simons term, spontaneous magnetic field induces Lorentz symmetry breaking. In this paper, thermodynamical characters, especially the phase structure of this model are discussed. To see the behavior of the spontaneous magnetic field at finite temperature, the effective potential in the finite temperature system is calculated within the weak field approximation and in the fermion massless limit. We found that the spontaneous magnetic field never vanishes at any finite temperature. This result doesn't change even when the chemical potential is introduced. We also investigate the consistency condition and the probability that fermion stays in a lowest Landau level at finite temperature.

hep-th↗

arXiv1994

Radiative Corrections to the Higgs Boson Decay into a Longitudinal $W$-Boson Pair in a Two-Doublet Model

The decay rate of a (neutral) Higgs boson ($H$) going into a longitudinal $W$-boson pair is calculated by including one loop radiative corrections in a two-Higgs doublet model. It is assumed that the Higgs boson $H$ is much heavier than the $W$ boson and a full use has been made of the equivalence theorem. A possibility is explored extensively that the precise measurement of the decay rate of $H$ could be useful as a probe of the other neutral as well as charged Higgs bosons through potentially important radiative corrections. It is pointed out that, for some choice of the parameters, the radiative corrections are sizable and that there exist a possibility of extracting useful information on the other Higgs boson masses.

hep-ph↗