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Commit 33b1ac28 authored by Luke Naylor's avatar Luke Naylor
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Correct beta vs beta_{-} in loose bound theorem

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......@@ -248,6 +248,7 @@ the circular walls must be nested and non-intersecting.
\subsection{Characteristic curves for pseudo-semistabilizers}
\begin{lemma}[Numerical tests for left-wall pseudo-semistabilizers]
\label{lem:pseudo_wall_numerical_tests}
Let $v$ and $u$ be Chern characters with positive ranks and $\Delta(v),
\Delta(u)\geq 0$. Let $P$ be a point on $\Theta_v^-$.
......@@ -470,18 +471,18 @@ normal one. So $0 \leq \Delta(E)$ yields:
\end{equation}
\begin{theorem}[Bound on $r$ - Benjamin Schmidt]
Given a Chern character $v$ such that $\beta_{-}(v)\in\QQ$, the rank $r$ of
any semistabilizer $E$ of some $F \in \firsttilt\beta$ with $\chern(F)=v$ is
Given a Chern character $v$ such that $\beta_-:=\beta_{-}(v)\in\QQ$, the rank $r$ of
any semistabilizer $E$ of some $F \in \firsttilt{\beta_-}$ with $\chern(F)=v$ is
bounded above by:
\begin{equation*}
r \leq \frac{mn^2 \chern^\beta_1(v)^2}{\gcd(m,2n^2)}
r \leq \frac{mn^2 \chern^{\beta_-}_1(v)^2}{\gcd(m,2n^2)}
\end{equation*}
\end{theorem}
\begin{proof}
The restrictions on $\chern^\beta_0(E)$ and $\chern^\beta_2(E)$
The restrictions on $\chern^{\beta_-}_0(E)$ and $\chern^{\beta_-}_2(E)$
is best seen with the following graph:
% TODO: hyperbola restriction graph (shaded)
......@@ -489,18 +490,19 @@ is best seen with the following graph:
var("m") # Initialize symbol for variety parameter
\end{sagesilent}
This is where the rationality of $\beta_{-}$ comes in. If $\beta_{-} = \frac{*}{n}$
for some $*,n \in \ZZ$.
Then $\chern^\beta_2(E) \in \frac{1}{\lcm(m,2n^2)}\ZZ$ where $m$ is the integer
This is where the rationality of $\beta_{-}$ comes in. If
$\beta_{-} = \frac{*}{n}$ for some $*,n \in \ZZ$. Then
$\chern^{\beta_-}_2(E) \in \frac{1}{\lcm(m,2n^2)}\ZZ$ where $m$ is the integer
which guarantees $\chern_2(E) \in \frac{1}{m}\ZZ$ (determined by the variety).
In particular, since $\chern_2(E) > 0$ we must also have
$\chern^\beta_2(E) \geq \frac{1}{\lcm(m,2n^2)}$, which then in turn gives a bound
for the rank of $E$:
In particular, since $\chern_2^{\beta_-}(E) > 0$ (by using $P=(\beta_-,0)$ in
lemma \ref{lem:pseudo_wall_numerical_tests}) we must also have
$\chern^{\beta_-}_2(E) \geq \frac{1}{\lcm(m,2n^2)}$, which then in turn gives a
bound for the rank of $E$:
\begin{align}
\chern_0(E) &= \chern^\beta_0(E) \\
&\leq \frac{\lcm(m,2n^2) \chern^\beta_1(E)^2}{2} \\
&\leq \frac{mn^2 \chern^\beta_1(F)^2}{\gcd(m,2n^2)}
\chern_0(E) &= \chern^{\beta_-}_0(E) \\
&\leq \frac{\lcm(m,2n^2) \chern^{\beta_-}_1(E)^2}{2} \\
&= \frac{mn^2 \chern^{\beta_-}_1(F)^2}{\gcd(m,2n^2)}
\end{align}
\end{proof}
......
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