Kawamata--Miyaoka type inequality for $\mathbb{Q}$-Fano varieties with canonical singularities

Abstract

Let $X$ be an $n$-dimensional normal $\mathbb{Q}$-factorial projective variety with canonical singularities and Picard number one such that $X$ is smooth in codimension two, $-K_X$ is ample and $n\ge 2$. We prove that $X$ satisfies the following Kawamata--Miyaoka type inequality: \[ c_1(X)^n< 4 c_2(X)\cdot c_1(X)^{n-2}. \] If additionally $X$ is a threefold with terminal singularities, then a stronger inequality is also obtained.

18 pages. Any comments are welcome.v2: the title and the abstract are slightly changed and the exposition is improved, to appear in Crelle's journal