Amplification of Quantum Meson Modes in the Late Time of Chiral Phase Transition

It is shown that there exists a possibility of amplification of amplitudes of quantum pion modes with low momenta in the late time of chiral phase transition by using the Gaussian wave functional approximation in the O(4) linear sigma model. It is also shown that the amplification occurs in the mechanism of the resonance by forced oscillation as well as the parametric resonance induced by the small oscillation of the chiral condensate. These mechanisms are investigated in both the case of spatially homogeneous system and the spatially expanded system described by the Bjorken coordinate.Comment: 17 pages, 16 figure

Filling-dependence of the zigzag Hubbard ladder for a quasi-one-dimensional superconductor Pr_2Ba_4Cu_7O_{15-delta}

We investigate filling dependence of the zigzag Hubbard ladder, using density matrix renormalization group method. We illustrate the chemical-potential vs. electron-density and spin gap vs. electron density curves, which reflect characteristic properties of the electron state.On the basis of the obtained phase diagram, we discuss the connection to a novel quasi-one-dimensional superconductor Pr$_2$Ba$_4$Cu$_7$O$_{15-\delta}$.Comment: 5 pages, 6 figures, fig.4 is adde