Hello. I am doing some reading on QED and am getting a bit confused on the different conventions used. In Matthew Schwartz's book we have the Lagrangian given as: LQED = -¼ FμνFμν + iψ*γμ(∂μ + ieAμ)ψ - V(ψ*ψ) And the path integral factor is exp(iS). In another text, however, I see the QED lagrangian given as: LQED = ¼ FμνFμν + ψ*γμ(∂μ + eAμ)ψ - V(ψ*ψ) And the exponential factor in the path integral is exp(-S). How can I see that these two conventions are physically the same? In particular, what is the difference between using exp(iS) and exp(-S) in the path integral? Thanks!