Asymptotically cylindrical Calabi-Yau manifolds

Let $M$ be a complete Ricci-flat Kahler manifold with one end and assume that this end converges at an exponential rate to $[0,\infty) \times X$ for some compact connected Ricci-flat manifold $X$. We begin by proving general structure theorems for $M$; in particular we show that there is no loss of generality in assuming that $M$ is simply-connected and irreducible with Hol$(M)$ $=$ SU$(n)$, where $n$ is the complex dimension of $M$. If $n > 2$ we then show that there exists a projective orbifold $\bar{M}$ and a divisor $\bar{D}$ in $|{-K_{\bar{M}}}|$ with torsion normal bundle such that $M$ is biholomorphic to $\bar{M}\setminus\bar{D}$, thereby settling a long-standing question of Yau in the asymptotically cylindrical setting. We give examples where $\bar{M}$ is not smooth: the existence of such examples appears not to have been noticed previously. Conversely, for any such pair $(\bar{M}, \bar{D})$ we give a short and self-contained proof of the existence and uniqueness of exponentially asymptotically cylindrical Calabi-Yau metrics on $\bar{M}\setminus\bar{D}$.

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