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 Hirzebruch
multiplicitity multiplicitity
subvariety subvariety
Cremona
equivariant
bimeromorphic

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@ -36,7 +36,7 @@
\todo{define torus quotient} \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 $(X,0)$ 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 is a torus quotient $(A, Δ_A)$ and a $\cC$-morphism
\[ \[
@ -61,9 +61,9 @@
\] \]
\end{rem} \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 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} \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. \bP¹ \ar[r, "n\text{, normalization}"'] \ar[rr, bend left=15, "\eta"] & C \ar[r, "\text{inclusion}"'] & X.
\end{tikzcd} \end{tikzcd}
\] \]
Consider the points $0 \in \bP¹$ and $x' := n(0) \in X$. 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
Given that $X$ is smooth, recall from \cite{orbiAlb1} that $\eta$ is a $\Alb(\bP¹,0)$ exists, the universal property of the Albanese yields a diagram
$\cC$-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] \begin{tikzcd}[column sep=2cm]
\bP¹ \ar[r, "\alb(\bP¹{,}0)"] \ar[d, "n"'] & \Alb(\bP¹,0) \ar[d] \\ \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. The claim follows immediately once we observe that $\Alb(\bP¹,0)$ is a point.
\end{proof} \end{proof}
\todo{There is nothing special about $\bP¹$ here. This works for every space with nontrivial $\cC$-Albanese.}
\begin{cor}\label{cor:2}% \begin{cor}\label{cor:2}%
In Setting~\ref{set:1}, let $\mu : X \to Y$ be a morphism to a normal In Setting~\ref{set:1}, let $\mu : X \to Y$ be a morphism to a normal analytic
projective variety. If all fibres of $\mu$ are rationally chain connected, variety. If all fibres of $\mu$ are rationally chain connected, then
then $\alb(X,0)$ factors via $\mu$, $\alb(X,0)$ factors via $\mu$,
\[ \[
\begin{tikzcd} \begin{tikzcd}
X \ar[r, "\mu"'] \ar[rr, bend left=15, "\alb(X{,}0)"] & Y \ar[r, "\exists!\:\beta"'] & \Alb(X,0). X \ar[r, "\mu"'] \ar[rr, bend left=15, "\alb(X{,}0)"] & Y \ar[r, "\exists!\:\beta"'] & \Alb(X,0).
\end{tikzcd} \end{tikzcd}
\] \]
\qed
\end{cor} \end{cor}
\begin{cor}\label{cor:3}% \begin{cor}\label{cor:3}%
@ -57,13 +57,52 @@
$\Alb(X,0)$ is a point. $\Alb(X,0)$ is a point.
\end{cor} \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{ \todo{
\begin{itemize} \begin{itemize}
\item Need example where a rational variety has a
\item Factorization via minimal model. \item Factorization via minimal model.
\item Independence of bimeromorphic model. \item For varieties of general type, factorization via the canonical.
\item Factorization via MRC quotient.
\end{itemize} \end{itemize}
} }
\begin{example}[Theorem~\ref{thm:1} is wrong for singular spaces] \begin{example}[Theorem~\ref{thm:1} is wrong for singular spaces]