Published online by Cambridge University Press: 20 November 2018
We determine the poles of the standard intertwining operators for a maximal parabolic subgroup of the quasi-split unitary group defined by a quadratic extension $E/F$ of $p$-adic fields of characteristic zero. We study the case where the Levi component $M\simeq \text{G}{{\text{L}}_{n}}\left( E \right)\times {{U}_{m}}\left( F \right)$, with $n\,\equiv \,m\,\left( \bmod \,2 \right)$. This, along with earlier work, determines the poles of the local Rankin-Selberg product $L$-function $L\left( s,\,{\tau }'\,\times \,\tau \right)$, with ${\tau }'$ an irreducible unitary supercuspidal representation of $\text{G}{{\text{L}}_{n}}\left( E \right)$ and $\tau $ a generic irreducible unitary supercuspidal representation of ${{U}_{m}}\left( F \right)$. The results are interpreted using the theory of twisted endoscopy.