Euclidean quantum field theory is the formulation of quantum field theory on Euclidean space, rather than on Lorentzian spacetime. It is commonly obtained from a Lorentzian theory by analytic continuation of the time coordinate. Its correlation functions, called Schwinger functions, can be represented formally by functional integrals with an exponentially decaying weight
where
is the Euclidean action and
is the corresponding partition function.
The Osterwalder-Schrader axioms give conditions under which Euclidean correlation functions reconstruct a quantum field theory on Minkowski space (Osterwalder and Schrader 1973, 1975). This makes Euclidean quantum field theory useful both as a mathematical definition and as a computational tool.