CP violation effect in long-baseline neutrino oscillation in the four-neutrino model

We investigate CP-violation effect in the long-baseline neutrino oscillation in the four-neutrino model with mass scheme of the two nearly degenerate pairs separated with the order of 1 eV, by using the data from the solar neutrino deficit, the atmospheric neutrino anomaly and the LSND experiments along with the other accelerator and reactor experiments. By use of the most general parametrization of the mixing matrix with six angles and six phases, we show that the genuine CP-violation effect could attain as large as 0.3 for \(\Delta P(\nu_\mu\to\nu_\tau) \equiv P(\nu_\mu\to\nu_\tau) - P(\bar{\nu_\mu}\to\bar{\nu_\tau})\) and that the matter effect is negligibly small such as at most 0.01 for \(\Delta P(\nu_\mu\to\nu_\tau)\) for \(\Delta m^2 = (1-5)\times 10^{-3} {\rm eV}^2\), which is the mass-squared difference relevant to the long-baseline oscillation.