Pome

Lemma 5.43.150018DC5A7DD0

Lemma 5.43.15.0018DC5A7DD0 For $h\in \mathrm{PSH}(C',\sigma )$, the function

\[ m_ h(s)=\max _{r(x)=s}h(x) \]

belongs to $\mathrm{PSH}(C,\beta )$ and satisfies $h\leq m_ h\circ r$. For every $s\in C$,

\[ \nu (m_ h,s)=\min _{r(x)=s}\frac{\nu (h,x)}{e_ x}. \]

If $v\in \mathrm{PSH}(C,\beta )$, then $h\preceq v\circ r$ implies $m_ h\preceq v$. The analogous implication holds for the all-weight ideal order.

Proof. On a base disk choose a smooth function $a$ with $\mathrm{dd}^{\mathrm{c}}a=\beta $. Off the branch values, $m_ h+a$ is the maximum of finitely many subharmonic functions obtained from $h+a\circ r$ by inverse branches. It is subharmonic there and locally bounded above. The removable-singularity theorem extends it across the branch values. This extension has the stated value: upper semicontinuity and properness give the upper bound at the fiber, while the genuine upper limits of $h+a\circ r$ at its points give the reverse bound. Thus the extensions glue. The function is not identically $-\infty $, since $h$ is finite at some point. This proves the curvature inequality and $h\leq m_ h\circ r$.

Choose coordinates in the disjoint disks over $s$ so that the map on the disk centered at $x$ is $t=z^{e_ x}$. Then

\[ \sup _{|t|<\delta }m_ h(t) =\max _{r(x)=s}\sup _{|z|<\delta ^{1/e_ x}}h(z). \]

Divide by $\log \delta ^2<0$ and use the supremum definition of Lelong number. Each quotient on the right tends to $\nu (h,x)/e_ x$, and the maximum becomes the minimum after division. Smooth local corrections do not affect these limits.

An ordinary bound $h\leq v\circ r+c$ gives $m_ h\leq v+c$ on every fiber. On a curve, the all-weight ideal order is equivalent to the pointwise Lelong inequalities, by theorem 5.37.3. The pullback formula 5.43.8 makes $h\preceq _{\mathcal I}v\circ r$ equivalent to $\nu (h,x)\geq e_ x\nu (v,r(x))$ at every $x$. The minimum formula gives the required base inequalities. $\square$

Cite this page

Comments

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