Done for today.

This commit is contained in:
Stefan Kebekus 2024-06-07 14:28:04 +02:00
parent 4ed5112111
commit 8585a08779
3 changed files with 57 additions and 15 deletions

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@ -27,3 +27,6 @@ Albanese
Hirzebruch
multiplicitity
subvariety
Cremona
equivariant
bimeromorphic

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@ -36,7 +36,7 @@
\todo{define torus quotient}
\begin{defn}[The $\cC$-Albanese of a compact pair with trivial boundary]\label{def:1-2}%
\begin{defn}[\protect{The Albanese of a compact pair with trivial boundary, \cite[Def.~9.1]{orbiAlb2}}]\label{def:1-2}%
Let $X$ be a compact Kähler manifold. An Albanese of the $\cC$-pair $(X,0)$
is a torus quotient $(A, Δ_A)$ and a $\cC$-morphism
\[
@ -61,9 +61,9 @@
\]
\end{rem}
\begin{thm}[The Albanese of a $\cC$-pair]\label{thm:22-1} %
\begin{thm}[\protect{Existence of the Albanese, \cite[Thm.~9.2]{orbiAlb2}}]\label{thm:22-1} %
Let $X$ be a compact Kähler manifold. If $q^+_{\Alb}(X,0) < ∞$, then an
Albanese of $(X,0)$ exists.
Albanese of $(X,0)$ exists. \qed
\end{thm}

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@ -26,12 +26,9 @@
\bP¹ \ar[r, "n\text{, normalization}"'] \ar[rr, bend left=15, "\eta"] & C \ar[r, "\text{inclusion}"'] & X.
\end{tikzcd}
\]
Consider the points $0 \in \bP¹$ and $x' := n(0) \in X$.
Given that $X$ is smooth, recall from \cite{orbiAlb1} that $\eta$ is a
$\cC$-morphism, between $\cC$-pairs $(\bP¹, 0)$ and $(X, 0)$. Since
$\Alb(\bP¹,0)$ exists, the universal property of the Albanese yields a
diagram
Given that $X$ is smooth, recall from \cite[Ex.~8.6]{orbiAlb1} that $\eta$ is
a $\cC$-morphism, between $\cC$-pairs $(\bP¹, 0)$ and $(X, 0)$. Since
$\Alb(\bP¹,0)$ exists, the universal property of the Albanese yields a diagram
\[
\begin{tikzcd}[column sep=2cm]
\bP¹ \ar[r, "\alb(\bP¹{,}0)"] \ar[d, "n"'] & \Alb(\bP¹,0) \ar[d] \\
@ -41,15 +38,18 @@
The claim follows immediately once we observe that $\Alb(\bP¹,0)$ is a point.
\end{proof}
\todo{There is nothing special about $\bP¹$ here. This works for every space with nontrivial $\cC$-Albanese.}
\begin{cor}\label{cor:2}%
In Setting~\ref{set:1}, let $\mu : X \to Y$ be a morphism to a normal
projective variety. If all fibres of $\mu$ are rationally chain connected,
then $\alb(X,0)$ factors via $\mu$,
In Setting~\ref{set:1}, let $\mu : X \to Y$ be a morphism to a normal analytic
variety. If all fibres of $\mu$ are rationally chain connected, then
$\alb(X,0)$ factors via $\mu$,
\[
\begin{tikzcd}
X \ar[r, "\mu"'] \ar[rr, bend left=15, "\alb(X{,}0)"] & Y \ar[r, "\exists!\:\beta"'] & \Alb(X,0).
\end{tikzcd}
\]
\qed
\end{cor}
\begin{cor}\label{cor:3}%
@ -57,13 +57,52 @@
$\Alb(X,0)$ is a point.
\end{cor}
\begin{cor}\label{cor:4}%
In Setting~\ref{set:1}, let $\mu : X \to Y$ be a bimeromorphic modification of
a compact manifold $Y$. Then, $\alb(X,0)$ factors via $\mu$,
\[
\begin{tikzcd}
X \ar[r, "\mu"'] \ar[rr, bend left=15, "\alb(X{,}0)"] & Y \ar[r, "\exists!\:\beta"'] & \Alb(X,0),
\end{tikzcd}
\]
the morphism $\beta$ is a $\cC$-morphism between the pairs $(Y,0)$ and
$\Alb(X,0)$, and $\beta : (Y,0) \to \Alb(Y,0)$ is an Albanese of $(Y,0)$.
\end{cor}
\begin{proof}
\todo{PENDING}
\end{proof}
\begin{cor}\label{cor:5}%
In Setting~\ref{set:1}, let $Y$ be a compact Kähler manifold bimeromorphic to
$X$. Then, an Albanese of $(Y,0)$ exists. If $f : X \dasharrow Y$ is
bimeromorphic, then there exists a unique morphism of $\cC$-pairs rendering
the following diagram commutative,
\[
\begin{tikzcd}
X \ar[d, "\alb(X{,}0)"'] \ar[r, dashed, "f"] & Y \ar[d, "\alb(Y{,}0)"'] \\
\Alb(X,0) \ar[r, "\exists! \alb(f)"'] & \Alb(Y,0)
\end{tikzcd}
\]
\end{cor}
\begin{proof}
\todo{PENDING}
\end{proof}
\begin{cor}\label{cor:6}%
In Setting~\ref{set:1}, the automorphism group of $X$ and the Cremona group
act on $\Alb(X,0)$ in a way that makes the morphism $\alb(X,0)$ equivariant.
\end{cor}
\begin{proof}
\todo{PENDING}
\end{proof}
\todo{
\begin{itemize}
\item Need example where a rational variety has a
\item Factorization via minimal model.
\item Independence of bimeromorphic model.
\item Factorization via MRC quotient.
\item For varieties of general type, factorization via the canonical.
\end{itemize}
}
\begin{example}[Theorem~\ref{thm:1} is wrong for singular spaces]