On the symmetric square. Unit elements

Abstract

A twisted analogue of Kazhdan's decomposition of compact elements into a commuting product of topologically unipotent and absolutely semi-simple elements, is developed and used to give a direct and elementary proof of the Langlands' fundamental lemma for the symmetric square lifting from SL(2) to PGL(3) and the unit element of the Hecke algebra. Thus we give a simple proof that the stable twisted orbital integral of the unit element of the Hecke algebra of PGL(S) is suitably related to the stable orbital integral of the unit element of the Hecke algebra of SX(2), while the unstable twisted orbital integral of the unit element on FGL(3) is matched with the orbital integral of the unit element on PGL(2). An Appendix examines the implications of Waldspurger's fundamental lemma in the case of endolifting to the theory of endolifting and that of the metaplectic correspondence for GL(n). Let F be a p-adic field (p Φ 2), and F a separable closure of F. Put