  We compute Schwinger-Keldysh effective action for a relativistic heavy quark
(with constant background velocity) in strongly coupled N = 4 supersymmetric
Yang-Mills plasma. The holographic dual description involves a noisy trailing
string moving in Schwarzschild-AdS5 black brane. The noise is caused by Hawking
radiation emitted from string worldsheet horizon. Besides quadractic terms, the
effective action contains cubic interactions, which are entirely induced by the
constant background velocity. The nonlinear fluctuation-dissipation relations
for three-point functions are discussed based on holographic results.
