Spontaneous Flavor and Parity Breaking with Wilson Fermions

We discuss the phase diagram of Wilson fermions in the $m_0$--$g^2$ plane for two-flavor QCD. We argue that, as originally suggested by Aoki, there is a phase in which flavor and parity are spontaneously broken. Recent numerical results on the spectrum of the overlap Hamiltonian have been interpreted as evidence against Aoki's conjecture. We show that they are in fact consistent with the presence of a flavor-parity broken ``Aoki phase''. We also show how, as the continuum limit is approached, one can study the lattice theory using the continuum chiral Lagrangian supplemented by additional terms proportional to powers of the lattice spacing. We find that there are two possible phase structures at non-zero lattice spacing: (1) there is an Aoki phase of width $\Delta m_0 \sim a^3$ with two massless Goldstone pions; (2) there is no symmetry breaking, and all three pions have an equal non-vanishing mass of order $a$. Present numerical evidence suggests that the former option is realized for Wilson fermions. Our analysis then predicts the form of the pion masses and the flavor-parity breaking condensate within the Aoki phase. Our analysis also applies for non-perturbatively improved Wilson fermions.Comment: 22 pages, LaTeX, 5 figures (added several references and a comment

Tau polarization effects in the CNGS tau-neutrino appearance experiments

We studied tau polarization effects on the decay distributions of tau produced in the CNGS tau-neutrino appearance experiments. We show that energy and angular distributions for the decay products in the laboratory frame are significantly affected by the tau polarization. Rather strong azimuthal asymmetry about the tau momentum axis is predicted, which may have observable consequences in experiments even with small statistics.Comment: 5 pages, 6 eps figures, espcrc2.sty; Proceedings of the 4th International Workshop on Neutrino-Nucleus Interactions in the Few GeV Region (NuInt05), September 26-29, 2005, Okayama, Japa

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 $\beta_{s} (= 1 / g^{2}_{s}) =$ 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.Comment: 26 pages (13 figures), Latex (epsf style-file needed

Detection of Iron Emission in the z = 5.74 QSO SDSSp J104433.04-012502.2

We obtained near-infrared spectroscopy of the z=5.74 QSO, SDSSp J104433.04-012 502.2 with the Infrared Camera and Spectrograph of the Subaru telescope. The redshift of 5.74 corresponds to a cosmological age of 1.0 Gyr for the current Lambda-dominated cosmology. We found a similar strength of the Fe II (3000-3500 A) emission lines in SDSSp J104433.04-012502.2 as in low redshift QSOs. This is the highest redshift detection of iron. We subtracted a power-law continuum from the spectrum and fitted model Fe II emission and Balmer continuum. The rest equivalent width of Fe II (3000-3500 A) is ~30 A which is similar to those of low redshift QSOs measured by the same manner. The chemical enrichment models that assume the life time of the progenitor of SNe Ia is longer than 1 Gyr predict that weaker Fe II emission than low red shift. However, none of the observed high redshift (z > 3) QSOs show a systematic dec rease of Fe II emission compared with low redshift QSOs. This may due to a shorter lifetime of SNe Ia in QSO nuclei than in the solar neighborhood. Another reason of strong Fe II emission at z=5.74 may be longer cosmological age due to smaller Omega_M.Comment: 5 pages, 3 figure

Finite-temperature chiral transitions in QCD with the Wilson quark action

We investigate the finite-temperature phase structure and the scaling of the chiral condensate in lattice QCD with two degenerate light quarks, using a renormalization group improved gauge action and the Wilson quark action. We obtain a phase diagram which is consistent with that from the parity-flavor breaking scenario. The scaling relation for the chiral condensate assuming the critical exponents and the scaling function of the three dimensional O(4) model is remarkably satisfied for a wide range of parameters. This indicates that the chiral transition in two flavor QCD is of second order in the continuum limit.Comment: LaTeX, 3 pages, 4 EPS figures, Talk presented at LATTICE97 (finite temperature