Integrating Green functions [01J2]
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Integrating Green functions
The definition of the convergence of a sequence of measures
is convergence of all integrals against a given continuous
compactly supported function. In applications, however, it can be
desirable to integrate against more general functions.
The inductive formula (1.2.1)
for the local height pairing in the complex case,
is such an example, as is the interpretation of Mahler measures
of polynomials as (the archimedean component of) heights.
However, its analogue (Equation 1.3.1)
a priori holds only when is continuous,
that is when the section has no zeroes nor poles.
The fact that it still holds in the archimedean case
is a theorem of Maillot [43]
building on the theory of Bedford–Taylor.
We proved in [19, Th. 4.1]
that this relation holds in the ultrametric case too.
The proof (valid both in the ultrametric and archimedean cases)
works by induction,
and ultimately relies on an approximation lemma according
to which any semi-positive Green function for a divisor
is an increasing limit of smooth functions
such that, for any , is a semi-positive Green function for .
In fact, it suffices to pose ;
then, is the maximum of
two semi-positive Green functions, hence is semi-positive.
(In the archimedean case, one needs to further regularize ;
see [19] for details.)
The symmetry of the local height pairing then implies the following
analogue of the Poincaré–Lelong formula.
When is the trivial line bundle, with
the metric defined by an admissible function ,
the factor will be written , by analogy
to the complex case.
Proposition 1.3.2.
Let be a smooth function on and let be admissible metrized line bundles ;
let be a -dimensional subvariety of
and let be an invertible meromorphic sections of .
Then,
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Démonstration.
Let be the trivial line bundle with global section
and metric defined by . Let and,
for , let be an invertible meromorphic section
of .
Since ,
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and
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One the other hand, the symmetry of the local height pairing implies that
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Combining these equations, we obtain the claim.
∎