Pome

Corollary 12.27.63CC0EFB19764

Corollary 12.27.6.3CC0EFB19764 Let $S$ be a compact Kähler surface and $D$ a smooth nonempty divisor whose line bundle is unitary flat near $D$, and let $B$ be the curvature form of proposition 12.27.5. For every smooth function $f>0$, every Hermitian form $h$ and every smooth positive probability form $\mu $, there are constants $L,U>0$ such that

\[ L\epsilon \leq \mathcal V_\mu (fB+\epsilon h) \leq U\epsilon ,\qquad 0<\epsilon \leq 1. \]

For a Kähler form $\kappa $, the closed background $B$ itself satisfies

\[ \mathcal V_\mu (B+\epsilon \kappa ) =2\epsilon \int _ D\kappa +\epsilon ^2\int _ S\kappa ^2. \]

For suitable $f$, the background $fB$ is not closed.

Proof. The inequalities $(\min f)B\leq fB\leq (\max f)B$ and proposition 12.26.1 give the two-sided bounds. The polynomial follows from the closed nef formula and $B^2=0$. At a point where $B$ has rank one, choose a smooth positive $f$ whose differential has a nonzero component along the kernel of $B$. Then $\mathrm d(fB)=\mathrm df\wedge B\ne 0$ there. $\square$

Cite this page

Comments

Corrections, questions, and mathematical discussion are welcome. Sign in with GitHub to comment. Comments are public.