notation
recently I saw the notation , and just wondering how should I interpret it?
In my understanding, is, for example, a solution to Schrodinger-type equation with the initial data . In case , the solution to Schrodinger equation is known to involve the Schrodinger kernel in the integrand. In such case, does is a short-hand notation for the operator involving the Schrodinger kernel?
Or should I interpret as the Taylor series with terms involved? In this case, does the (operator) series converge once applied to the element in the domain of H?
Also, I would be very glad to get a reference to read more on this type of operators. Thank you very much!