Seminarium KMMF "Teoria Dwoistości"

I will review the main steps of Epstein and Glaser's construction oftime-ordered products in perturbative Quantum Field Theory. The crucial oneis the extension of singular distributions, initially defined outside theorigin. In a joint work with D. Bahns, we propose a new method to recoverglobal symmetries lost in the extension process. We also obtain a newformula for the relation between off-shell and on-shell time-orderedproducts involving higher derivatives of the fields.