Interplay of electron-phonon nonadiabaticity and Raman scattering in the wavepacket dynamics of electron-phonon-photon systems

Ultrafast wavepacket dynamics of electron-phonon-photon systems is studied by numerical calculations. When nonadiabaticity of electron-phonon systems is taken into account, Raman scattering process plays an important role in the dynamics of the system. We found that the interplay of the electron-phonon nonadiabaticity and the Raman scattering determines the wavepacket motion particularly in the vicinity of the conical intersection of adiabatic potential energy surfaces, which shows that we should consider this effect in order to reveal the photoexcitation/deexcitation process of materials in femtosecond time scale.Comment: 6 pages, 5 figure

Nonlinearity in the dynamics of photoinduced nucleation process

Nonlinear dynamics of photoinduced cooperative phenomena is studied by numerical calculations on a model of molecular crystals. We found that the photoinduced nucleation process is triggered only when certain amount of excitation energy is supplied in a narrow part of the system, i.e., there exists a smallest cluster of excited molecules which makes the nucleation possible. As a result, the portion of the cooperatively converted molecules is nonlinearly dependent on the photoexcitation strength, which has been observed in various materials.Comment: 10pages, 4 figure

Re-analysis of \pi\pi / K\pi Phase Shift and Existence of \sigma$(600) / \kappa(900)-Particle

Re-analyzing the old phase shift data of I=0, \pi\pi (I=1/2, K\pi) scattering, we show an evidence for existence of the \sigma-particle (\kappa-particle) with a comparatively light mass, which has been missing for a long time: In the analysis we have applied a new method of interfering Breit-Wigner amplitudes, which makes the scattering amplitude parametrized in terms of only physical quantities, mass and width of resonant particles, in conformity with unitarity. We have introduced phenomenologically a background phase shift \delta_{BG} of repulsive core type. The \chi^2-fits of the both \pi\pi- and K\pi- phase shifts are improved greatly with the \delta_{BG} over the conventional fits without it.Comment: Talk at HADRON'97, the 7th int. conf. on hadron spectroscopy, BNL, August 1997. 4 pages with 3 eps figure

Further Analysis on \sigma-particle Properties

In a previous work, we have reanalyzed the I=0 S-wave \pi\pi-scattering phase-shift through a new method of Interfering Breit-Wigner amplitudes, and have shown the existence of a light scalar, \sigma particle, accompanied by a negative "repulsive core"-type background phase-shift, whose origin may have some correspondence to a ``compensating'' \pi\pi contact interaction. In this work we make further analysis on the phase shift under KKbar threshold from the same standpoint, to determine precise values of \sigma mass and width, so far as present experimental data are concerned.Comment: Updated with recent progres

\sigma-Particle in Production Processes

A S-wave \pi\pi resonance below 1 GeV/c^2, sigma has been observed in analyses of the phase shift data of \pi\pi scatterings. It is important to observe it in production processes. A huge events of \pi^0\pi^0 below 1 GeV/c^2 is seen in the central production of the GAMS experiment. Its mass spectrum is well described by the variant mass and width method (VMW) including f_0(980), f_2(1270) and a S-wave resonance which might be assigned to be a sigma. We report here that the angular distributions of the \pi^0\pi^0 system are also described with the S-wave resonance interfering with f_0(980) and the tail of f_2(1270) by VMW. The same method is applied to the \pi^+\pi^- data of J/\psi \to \omega\pi\pi decay, and is shown that not only \pi^+\pi^- mass spectrum but also its cos\theta_\pi distributions are described well.Comment: Talk at HADRON'97, the 7th int. conf. on hadron spectroscopy, BNL, August 1997. 4 pages with 2 eps figure

pi^0 pi^0 Scattering Amplitudes and Phase Shifts Obtained by the pi^- P Charge Exchange Process

The results of the analysis of the pi^0 pi^0 scattering amplitudes obtained with pi^- P charge exchange reaction, pi^- P --> pi^0 pi^0 n, data at 9 GeV/c are presented. The pi^0 pi^0 scattering amplitudes show clear f_0(1370) and f_2(1270) signals in the S and D waves, respectively. The pi^0 pi^0 scattering phase shifts have been obtained below Kbar K threshold and been analyzed by the Interfering Amplitude method with introduction of negative background phases. The results show a S wave resonance, sigma. Its Breit-Wigner parameters are in good agreement with those of our previous analysis on the pi^+ pi^- phase shift data.Comment: 4 pages, 4 figures. Proceedings of the int. conf. Hadron'99 at Beijing, Aug. 1999. Presented for the collaboration of A.M.Ma, K.Takamatsu, M.Y.Ishida, S.Ishida, T.Ishida, T. Tsuru and H. Shimizu, and the E135 collaboration. For our activities on sigma, visit http://amaterasu.kek.jp/sigm