Stochastic particle acceleration in high-energy phenomena

I will discuss the particle acceleration by turbulence,and its application to blazars, GRBs and pulsar wind nebulae (PWNe).The magnetic fields in blazars and PWNe are subdominant component compared to the accelerated electrons. In such a weakly magnetized plasma,fast mode MHD waves can be responsible for the particle acceleration.The acceleration timescale is comparable to the dynamical timescale,so that the time-dependent treatment is indispensable to obtain theparticle energy distribution. Our models reproduce the hard spectraof blazars and PWNe. This process may be important for interferingthe electron cooling in GRBs.