arXiv subjects

K. Nagai

Publications and source records attributed to K. Nagai.

61 records · Page 4Linked to original sources

arXiv1998

Full QCD light hadron spectrum from the CP-PACS

We report on an on-going two-flavor full QCD study on CP-PACS using an RG-improved gauge action and a tadpole-improved SW quark action. Runs are made for three lattice spacings $a^{-1}\approx 0.9$, 1.3, and 2.5 GeV on $12^3\times24$, $16^3\times32$, and $24^3\times48$ lattices. Four sea quark masses having $m_{\rm PS}/m_{\rm V} \approx 0.8$--0.6 are simulated, for each of which hadron masses are evaluated for valence quark masses corresponding to $m_{\rm PS}/m_{\rm V} \approx 0.8$--0.5. Results for hadron and light quark masses are presented and compared with those obtained in quenched QCD.

hep-lat↗

arXiv1997

The domain-wall model in an asymptotic-free dynamics

We investigate a possibility that the rough gauge problem, which have appeared to be a main reason for failures of lattice chiral gauge theories, is cured by an asymptotic-free dynamics. Taking the domain-wall model in 2(+1) dimensions with SU(2) gauge group, we carry out the quenched simulation of gauge fields in the extra dimension. By studying fermion spectra in several volumes, we show that the chiral zero modes exist on the wall without having the spontaneous symmetry breaking thanks to the asymptotic-free dynamics. This result suggests that the rough gauge problem is solved in some class of lattice chiral fermions as well as in 4 dimensions if an asymptotic-free dynamics is incorporated.

hep-lat↗

arXiv1997

Lattice fermions with Majorana couplings

We analyse stability of almost massless Dirac mode in gauge models with boundary (domain wall) fermions, and consider the possibility of decoupling one of its chiral component by giving it a Majorana mass of the order of the inverse lattice spacing. We argue that the chiral spectrum in such models is always uncharged, so they can be implemented for defining the Weyl fermions only in the real representation of the gauge group, for instance, in SUSY models.

hep-lat↗

arXiv1997

Domain wall fermions with Majorana couplings

We examine the lattice boundary formulation of chiral fermions with either an explicit Majorana mass or a Higgs-Majorana coupling introduced on one of the boundaries. We demonstrate that the low-lying spectrum of the models with an explicit Majorana mass of the order of an inverse lattice spacing is chiral at tree level. Within a mean-field approximation we show that the systems with a strong Higgs-Majorana coupling have a symmetric phase, in which a Majorana mass of the order of an inverse lattice spacing is generated without spontaneous breaking of the gauge symmetry. We argue, however, that the models within such a phase have a chiral spectrum only in terms of the fermions that are singlets under the gauge group. The application of such systems to nonperturbative formulations of supersymmetric and chiral gauge theories is briefly discussed.

hep-lat↗

arXiv1996

Chiral zero modes on the domain-wall model in 4+1 dimensions

We investigate an original domain-wall model in 4+1 dimensions numerically in the presence of U(1) dynamical gauge field only in an extra dimension, corresponding to a weak coupling limit of 4-dimensional physical gauge coupling. Using a quenched approximation we carry out numerical simulation for this model at $β_{s} (= 1 / g^{2}_{s}) =$ 0.29 (``symmetric'' phase) and 0.5 (``broken'' phase), where $g_s$ is the gauge coupling constant of the extra dimension. In the broken phase, we found that there exists a critical value of a domain-wall mass $m_{0}^{c}$ which separates a region with a fermionic zero mode on the domain wall from the one without it in the same case of (2+1)-dimensional model. On the other hand, in the symmetric phase, our numerical data suggest that the chiral zero modes disappear in the infinite limit of 4-dimensional volume. From these results it seems difficult to construct the U(1) lattice chiral gauge theory via an original domain-wall formulation.

hep-lat↗

arXiv1996

Domain-wall fermions with U(1) dynamical gauge fields in (4+1)-dimensions

We carry out a numerical simulation of a domain-wall model in (4+1) dimensions, in the presence of a quenched U(1) dynamical gauge field only in an extra dimension, corresponding to the weak coupling limit of a (4-dimensional) physical gauge coupling. Our numerical data suggest that the zero mode seems absent in the symmetric phase, so that it is difficult to construct a lattice chiral gauge theory in the continuum limit.

hep-lat↗

arXiv1995

Domain-wall fermions with $U(1)$ dynamical gauge fields

We have carried out a numerical simulation of a domain-wall model in $(2+1)$-dimensions, in the presence of a dynamical gauge field only in an extra dimension, corresponding to the weak coupling limit of a ( 2-dimensional ) physical gauge coupling. Using a quenched approximation we have investigated this model at $β_{s} ( = 1 / g^{2}_{s} ) =$ 0.5 ( ``symmetric'' phase), 1.0, and 5.0 (``broken'' phase), where $g_s$ is the gauge coupling constant of the extra dimension. We have found that there exists a critical value of a domain-wall mass $m_{0}^{c}$ which separates a region with a fermionic zero mode on the domain-wall from the one without it, in both symmetric and broken phases. This result suggests that the domain-wall method may work for the construction of lattice chiral gauge theories.

hep-lat↗