Eta - xi spacetime and thermo fields.

Abstract

In this paper an intuitive picture of $\ensuremath{\eta}\ensuremath{-}\ensuremath{\xi}$ spacetime is given. It is shown why $\ensuremath{\eta}\ensuremath{-}\ensuremath{\xi}$ spacetime can be regarded as a geometric background of field theory at finite temperature. In particular, a new way is put forth. We can get the real-time thermal Green's function with a 2\ifmmode\times\else\texttimes\fi{}2 matrix by rotating the imaginary-time thermal Green's function from the Euclidean section to the Lorentzian section in $\ensuremath{\eta}\ensuremath{-}\ensuremath{\xi}$ spacetime.