diff --git a/tex/setting-and-problems.tex b/tex/setting-and-problems.tex index da5240c3cb77751d4286d66809aa9382ac03beb1..03efa6117a6ccf35d83bf0e072532c52465bde37 100644 --- a/tex/setting-and-problems.tex +++ b/tex/setting-and-problems.tex @@ -1,28 +1,6 @@ -\section{Setting and Definitions: Clarifying `pseudo'} - -%\begin{definition}[Twisted Chern Character] -%\label{sec:twisted-chern} -%For a given $\beta$, define the twisted Chern character as follows. -%\[\chern^\beta(E) = \chern(E) \cdot \exp(-\beta \ell)\] -%\noindent -%Component-wise, this is: -%\begin{align*} -% \chern^\beta_0(E) &= \chern_0(E) -%\\ -% \chern^\beta_1(E) &= \chern_1(E) - \beta \chern_0(E) -%\\ -% \chern^\beta_2(E) &= \chern_2(E) - \beta \chern_1(E) + \frac{\beta^2}{2} \chern_0(E) -%\end{align*} -%where $\chern_i$ is the coefficient of $\ell^i$ in $\chern$. -% -%% TODO I think this^ needs adjusting for general Surface with $\ell$ -%\end{definition} -% -%$\chern^\beta_1(E)$ is the imaginary component of the central charge -%$\centralcharge_{\alpha,\beta}(E)$ and any element of $\firsttilt\beta$ -%satisfies $\chern^\beta_1 \geq 0$. - -Throughout this article, as noted in the introduction, we will be exclusively +\section{Definitions: Clarifying `pseudo'} + +Throughout this Part, as noted in the introduction, we will be exclusively working over surfaces $X$ with Picard rank 1, with a choice of ample line bundle $L$ such that $\ell\coloneqq c_1(L)$ generates $NS(X)$. We take $m\coloneqq \ell^2$ as this will be the main quantity which will @@ -50,13 +28,21 @@ affect the results. \item $0 \leq \chern_1^{\beta}(u) \leq \chern_1^{\beta}(v)$ \end{itemize} +\end{definition} +\begin{remark} Note $u$ does not need to be a Chern character of an actual sub-object of some object in the stability condition's heart with Chern character $v$. -\end{definition} -At this point, and in this document, we do not care about whether -pseudo-semistabilisers are even Chern characters of actual elements of -$\bddderived(X)$, some other sources may have this extra restriction too. + Other sources may also have extra conditions such as the integrality of Euler + characteristics or the non-triviality of certain extension groups. + These conditions depend on the Todd class of the variety in question and could + be considered but are left out for now as they do not have a great impact on + the finiteness of pseudo-walls. + In the case of a principally polarised abelian surface, the main example in + this Thesis, the Euler characteristic condition is vacuous and the extension + group condition eliminates possibities with lower rank, and often none at all + for small values of $\chern_0(v)$. +\end{remark} Later, Chern characters will be written $(r,c\ell,d\ell^2)$ because operations (such as multiplication) are more easily defined in terms of the coefficients of @@ -130,15 +116,17 @@ $d \in \frac{1}{\lcm(m,2)}\ZZ$. \end{proof} -\subsection{Characteristic Curves for Pseudo-semistabilisers} +\section{Characteristic Curves for Pseudo-semistabilisers} -These characteristic curves introduced are convenient tools to think about the +These characteristic curves introduced in +subsection \ref{subsec:charact-curves} +are convenient tools to think about the numerical conditions that can be used to test for pseudo-semistabilisers, and for solutions to the problems (\ref{problem:problem-statement-1},\ref{problem:problem-statement-2}) -tackled in this article (to be introduced later). -In particular, problem (\ref{problem:problem-statement-1}) will be translated to -a list of numerical inequalities on it's solutions $u$. +tackled in this Part (to be introduced later). +In particular, these problems will be translated to +a list of numerical inequalities on its solutions $u$. % ref to appropriate Lemma when it's written The next Lemma is a key to making this translation and revolves around the @@ -148,7 +136,8 @@ semistabilising sequence. \begin{lemma}[Numerical tests for left-wall pseudo-semistabilisers] \label{lem:pseudo_wall_numerical_tests} Let $v$ and $u$ be Chern characters with $\Delta(v), -\Delta(u)\geq 0$, and $v$ has non-negative rank (and $\chern_1(v)>0$ if rank 0). +\Delta(u)\geq 0$, and $v$ is positive, with one of $\chern_0(v)$ or +$\chern_1(v)$ non-zero. Let $P$ be a point on $\Theta_v^-$. \noindent @@ -257,6 +246,7 @@ Finally, consequence 4 along with $P$ being to the left of $V_u$ implies $\nu_P(u) > 0$ giving supposition b. The case with rank 0 can be handled the same way. +% TODO expand this case too \end{proof} @@ -348,9 +338,11 @@ typically more familiar chamber (the stable objects of Chern character $v$ in the outside chamber will only be Gieseker stable sheaves). -Also note that this last restriction does not remove any pseudo-walls found, -and if we do want to recover `outwards' semistabilisers, we can simply take -$v-u$ for each solution $u$ of the problem. +\begin{remark} + Also note that this last restriction does not remove any pseudo-walls found, + and if we do want to recover `outwards' semistabilisers, we can simply take + $v-u$ for each solution $u$ of the problem. +\end{remark} \begin{problem}[all `left' pseudo-walls] @@ -381,7 +373,7 @@ Note also that the condition on $\beta_-(v)$ always holds for $v$ rank 0. The problems introduced in this section are phrased in the context of stability conditions. However, these can be reduced down completely to purely numerical -problem with the help of Lemma \ref{lem:pseudo_wall_numerical_tests}. +problem using Lemma \ref{lem:pseudo_wall_numerical_tests}. \begin{lemma}[Numerical Tests for Sufficiently Large `left' Pseudo-walls] \label{lem:num_test_prob1}