arXiv subjects

Michio Hashimoto

Publications and source records attributed to Michio Hashimoto.

41 records · Page 3Linked to original sources

arXiv2001

Top Mode Standard Model with Extra Dimensions

We critically examine a version of the top mode standard model recently cast in extra dimensions by Arkani-Hamed, Cheng, Dobrescu, and Hall, based on the (improved) ladder Schwinger-Dyson (SD) equation for the D-(=6,8-)-dimensional gauge theories. We find that the bulk QCD cannot have larger coupling beyond the non-trivial ultraviolet (UV) fixed point, the existence of which is supported by a recent lattice analysis. The coupling strength at the fixed point is evaluated by using the one-loop renormalization group equation. It is then found that, in a version with only the third family (as well as the gauge bosons) living in the D-dimensional bulk, the critical (dimensionless) coupling for dynamical chiral symmetry breaking to occur is larger than the UV fixed point of the bulk QCD coupling for D=6, while smaller for D=8. We further find that the improved ladder SD equation in D dimensions has an approximate scale-invariance due to the running of the coupling and hence has an essential-singularity scaling of the ``conformal phase transition,'' similar to Miransky scaling in the four-dimensional ladder SD equation with a nonrunning coupling. This essential-singularity scaling can resolve the fine-tuning even when the cutoff (``string scale'') is large. Such a theory has a large anomalous dimension γ_m=D/2 - 1 and is expected to be free from the flavor-changing-neutral-current problem as in walking technicolor for D=4. Furthermore, the induced bulk Yukawa coupling becomes finite even at infinite cutoff limit (in the formal sense), similarly to the renormalizability of the gauged Nambu-Jona-Lasinio model. Comments are made on the use of the ``effective'' coupling, which includes finite renormalization effects, instead of the \bar{MS} running coupling in the improved ladder SD equation.

hep-ph↗

arXiv1998

Reconsidering Composite Higgs Loop Effects in the Top Mode Standard Model

Composite Higgs loop effects in the top mode standard model are discussed by using the Miransky-Tanabashi-Yamawaki (MTY) approach based on the Schwinger-Dyson equation. The top mass is obtained as 179 GeV for the Planck scale cutoff (Λ\simeq 10^{19} GeV). This result is different from that of the Bardeen-Hill-Lindner (BHL) approach based on the renormalization group equation (RGE), with QCD plus Higgs loop effects included (m_t \simeq 205 GeV). Detailed comparison of the MTY approach with the BHL approach is made. We derive ``RGE'' from the Pagels-Stokar formula by considering the infrared mass as the ``renormalization point''. Then, it is found that the MTY approach including the composite Higgs loop effects is only partially equivalent to the BHL approach with QCD plus Higgs loop effects. The difference essentially results from the treatment of the composite Higgs propagator, or more precisely, of Z_H^{-1}. Our results can be summarized as m_t (Ours) \simeq 1/\sqrt{2} m_t (MTY), in contrast to m_t (BHL) \simeq \sqrt{2/3} m_t (MTY), where m_t (MTY) \simeq 250 GeV is the original MTY prediction without Higgs loop effects.

hep-ph↗

arXiv1998

The Higgs Boson Mass and Ward-Takahashi Identity in Gauged Nambu-Jona-Lasinio Model

A new formula for the composite Higgs boson mass is given, based on the Ward-Takahashi identity and the Schwinger-Dyson(SD) equation. In this formula the dominant asymptotic solution of the SD equation yields a correct answer, in sharp contrast to the Partially Conserved Dilatation Current(PCDC) approach where the sub- and sub-sub-dominant solutions should be taken into account carefully. In the gauged Nambu-Jona-Lasinio model we find M_H \simeq \sqrt{2}M for the composite Higgs boson mass M_H and the dynamical mass of the fermion M in the case of the constant gauge coupling(with large cut off), which is consistent with the PCDC approach and the renormalization-group approach. As to the case of the running gauge coupling, we find M_H \simeq 2 \sqrt{(A-1)/(2A-1)}M, where A \equiv 18 C_2 /(11N_c - 2N_f) with C_2 being the quadratic Casimir of the fermion representation. We also discuss a straightforward application of our formula to QCD(without 4-Fermi coupling), which yields M_σ \sim \sqrt{2}M_{dyn}, with M_σ and M_{dyn} being the light scalar(``σ-meson'') mass and mass of the constituent quark, respectively.

hep-th↗

arXiv1996

Hidden Local Symmetry for Anomalous Processes with Isospin/SU(3) Breaking Effects

We show that isospin/SU(3) breaking terms can be introduced to the anomalous VVP coupling in the hidden local symmetry scheme without changing Wess-Zumino-Witten term in the low-energy limit. We make the analysis for anomalous processes of 2-body and 3-body decays; radiative vector meson decays(V \to Pγ), conversion decays of photon into a lepton pair(V \to P l^+ l^-) and hadronic anomalous decays(V \to PPP). The predictions successfully reproduce all experimental data of anomalous decays. In particular, we predict the decay widths of ρ^0 \to π^0 γand ϕ\to η' γas 101 \pm 9 keV and 0.508 \pm 0.035 keV, respectively, which will be tested in the DAFNE ϕ-factory. Moreover, prediction is also made for ϕ\to π^0 e^+ e^-, ρ\to 3π, K^* \to K ππand so on, for which only the experimental upper bounds are available now.

hep-ph↗

arXiv1996

Isospin Breaking Effects in the Anomalous Processes with Vector Mesons

We introduce isospin breaking terms as well as (SU(3)) breaking terms to the anomalous (VVP) coupling in the hidden local symmetry scheme without affecting the low energy theorem on the processes such as (π\to 2 γ) and (γ\to 3π). It is shown that the predictions from these terms coincide successfully with all the experimental data of anomalous decays. It is also predicted that the decay widths of (ρ^0 \to π^0 γ) and (ϕ\to η' γ) are (114\pm 7 keV) and (0.552 \pm 0.055 keV), respectively.

hep-ph↗