文摘
Let denote the split symplectic group of rank 2 over . Fix a prime p. Let be a parahoric subgroup of . An arithmetic subgroup ¦£ is defined by , where . In this paper, we calculate Arthur?s -Lefschetz trace formula for in order to obtain an explicit formula for multiplicities of discrete series and some non-tempered unitary representations in the discrete spectrum of for each such ¦£. From them we derive explicit multiplicity formulas for large discrete series, which are our main results. The multiplicity formulas are applied to a study on numbers of cuspidal automorphic representations of .