%0 Journal Article %T La conjecture locale de Gross-Prasad pour les représentations tempérées des groupes unitaires %+ Institut de Mathématiques de Jussieu (IMJ) %A Beuzart-Plessis, Raphaël %Z 113 p. %< avec comité de lecture %@ 0249-633X %J Mémoires de la Société Mathématique de France %I SMF %S Mémoire de la SMF %V 149 %P 191p. %8 2016-09 %D 2016 %Z 1205.2987 %R 10.24033/msmf.457 %K conjecture de Gross-Prasad %K groupes unitaires %Z Mathematics [math]/Representation Theory [math.RT] %Z Mathematics [math]/Number Theory [math.NT]Journal articles %X Let $E/F$ be a quadratic extension of non-archimedean local fields of characteristic $0$ and let $G=U(n)$, $H=U(m)$ be unitary groups of hermitian spaces $V$ and $W$. Assume that $V$ contains $W$ and that the orthogonal complement of $W$ is a quasisplit hermitian space (i.e. whose unitary group is quasisplit over $F$). Let $\pi$ and $\sigma$ be smooth irreducible representations of $G(F)$ and $H(F)$ respectively. Then Gan, Gross and Prasad have defined a multiplicity $m(\pi,\sigma)$ which for $m=n-1$ is just the dimension of $Hom_{H(F)}(\pi,\sigma)$. For $\pi$ and $\sigma$ tempered, we state and prove an integral formula for this multiplicity. As a consequence, assuming some expected properties of tempered $L$-packets, we prove a part of the local Gross-Prasad conjecture for tempered representations of unitary groups. This article represents a straight continuation of recent papers of Waldspurger dealing with special orthogonal groups. %G French %2 https://hal.science/hal-00696745v2/document %2 https://hal.science/hal-00696745v2/file/articlefinal3.pdf %L hal-00696745 %U https://hal.science/hal-00696745 %~ UNIV-PARIS7 %~ UPMC %~ CNRS %~ IMJ %~ USPC %~ UPMC_POLE_1 %~ SORBONNE-UNIVERSITE %~ SU-SCIENCES %~ UNIV-PARIS %~ UP-SCIENCES %~ SU-TI %~ ALLIANCE-SU