Mean square values of standard L-functions attached to Ikeda lifts

In general it is very difficult to determine the exact order of the mean square of standard L-functions attached to Siegel modular forms of higher degree. However, if the form is an image of Ikeda lifting, the situation is quite different. In this talk I will report that, in such a case, we can almost determine the exact order. (A part of this talk is a joint work with A. Sankaranarayanan.)