Screening and D-brane Dynamics in Finite Temperature Superstring Theory

The thermal dynamics of D-branes and of open superstrings in background gauge fields is studied. It is shown that D-brane dynamics forbids constant velocity motion at finite temperature. T-duality is used to interpret this feature as a consequence of the absence of an equilibrium state of charged strings at finite temperature in a constant background electric field, as a result of Debye screening of electric fields. The effective action for the Polyakov loop operator is computed and the corresponding screening solutions are described. The finite temperature theory is also used to illustrate the importance of carefully incorporating Wu-Yang terms into the string path integral for compact target spaces.