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Let $f: \mathbb{A}^{2} \rightarrow \mathbb{A}^{1}$ be a map that sends $(x,y)$ to $xy$. Let $U \hookrightarrow \mathbb{A}^{2}$ be the preimage $f^{-1}(\mathbb{A}^{2} \setminus \{0\})$ and $X:=f^{−1}(0)$. Consider the shifted constant sheaf $\mathbb{C}_{U}[2]$ on $U$. Let $\Psi(\mathbb{C}_{U}[2])$ denote the nearby cycles functor applied to $\mathbb{C}_{U}[2]$. It gives us a perverse sheaf on $X$.

My question is: how to compute this perverse sheaf on $X$ and the action of monodromy on it? Also if the action is unipotent then how to calculate the action of "Lefshetz" $sl_{2}$ on $\operatorname{gr}(\Psi(\mathbb{C}_{U}[2]))$?

Thanks!

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  • $\begingroup$ I was given the answer on math.stackexchange.com . $\endgroup$
    – Din
    Commented Aug 19, 2017 at 16:22

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