Beijing Institute of Mathematical Sciences and Applications

Wei Cui , Fengjun Xu

Fengjun Xu

Wednesday, July 23, 2025 5:00 PM - 6:30 PM

A12-114

Zoom 388 528 9728 (BIMSA)

The monodromies of B-brane central charges of a CY3 $X$ on its stringy Kahler moduli space $M_K(X)$ can be understood as the auto-equivalences of the derived category of coherent sheaves, $B$, on $X$. When $X$ is realized as the target of a geometric phase of a 2d (2,2) GLSM, the grade restriction rule from hemisphere partition function, and hence the window category it defines, computes such monodromy action as window shift monodromy $M(B)$. We elaborated the application of the abelian grade restriction rule in the Herbst, Hori, Pages paper on a large class of X in the type I flop CICY configurations, and concluded that $M(B)=TP_ N(B(-P))$ with $TP_N$ a simple action of $N$ contracted curves under the flop. It’s proposed that $M(B)$ should depend on the $\pi_1(M_K(X))$ and can be given by the braided action of the spherical twists of $O_X$ and others. This is discussed on some examples. Based on a joint work with Mauricio Romo.

Fengjun Xu is currently an Assistant Professor at the Beijing Institute of Mathematical Sciences and Applications (BIMSA). His research interests lie in string theory and related problems. He obtained his Ph.D. from Heidelberg University in 2019. After that, He remained as a research fellow in ITP, Heidelberg University until 2021. Then he moved to YMSC, Tsinghua University as a postdoc Researcher.