Published online by Cambridge University Press: 20 November 2018
Let $G$ be the
$F$ -rational points of the symplectic group
$S{{p}_{2n}}$ , where
$F$ is a non-Archimedean local field of characteristic 0. Cogdell, Kim, Piatetski-Shapiro, and Shahidi constructed local Langlands functorial lifting from irreducible generic representations of
$G$ to irreducible representations of
$G{{L}_{2n+1}}\left( F \right)$ . Jiang and Soudry constructed the descent map from irreducible supercuspidal representations of
$G{{L}_{2n+1}}\left( F \right)$ to those of
$G$ , showing that the local Langlands functorial lifting from the irreducible supercuspidal generic representations is surjective. In this paper, based on above results, using the same descent method of studying
$S{{O}_{2n+1}}$ as Jiang and Soudry, we will show the rest of local Langlands functorial lifting is also surjective, and for any local Langlands parameter
$\phi \,\in \,\Phi \left( G \right)$ , we construct a representation
$\sigma $ such that
$\phi $ and
$\sigma $ have the same twisted local factors. As one application, we prove the
$G$ -case of a conjecture of Gross-Prasad and Rallis, that is, a local Langlands parameter
$\phi \,\in \,\Phi \left( G \right)$ is generic, i.e., the representation attached to
$\phi $ is generic, if and only if the adjoint
$L$ -function of
$\phi $ is holomorphic at
$s\,=\,1$ . As another application, we prove for each Arthur parameter
$\psi $ , and the corresponding local Langlands parameter
${{\phi }_{\psi }}$ , the representation attached to
${{\phi }_{\psi }}$ is generic if and only if
${{\phi }_{\psi }}$ is tempered.