The geometric stochastic analysis on the Riemannian path space
developed recently gives rise to the concept of tangent processes. Roughly
speaking, it is the infinitesimal version of the Girsanov theorem. Using this
concept, we shall establish a formula of integration by parts on the path space
over a loop group. Following the martingale method developed in Capitaine, Hsu
and Ledoux, we shall prove that the logarithmic Sobolev inequality holds on the
full paths. As a particular case of our result, we obtain the
Driver–Lohrenz’s heat kernel logarithmic Sobolev inequalities
over loop groups. The stochastic parallel transport introduced by Driver will
play a crucial role.