Nambu-Goto string with massive ends at finite temperature
  It is shown that the critical (or deconfinement) temperature for the Nambu-Goto string connecting the point-like masses (quarks) does not depend on the value of these masses. This temperature turns out to be the same as that in the case of string with fixed ends (infinitely heavy immobile quarks). 
G. Lambiase and V.V. Nesterenko