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We now turn to the study of the complex Monge-Ampère equation
is a measure with
density , .
Proposition 3.1.
Assume is a probability measure with density
, for some .
Then for any , there exists such that
satisfies .
Proof.
It is enough to establish for compact subsets,
by regularity of and .
Let be a compact subset of . It follows from Hölder’s inequality
that
where .
Note that since we assume is a probability measure.
We claim that
(4)
for some constants that only depend on .
We will be done if we can prove (4) since we can then check by elementary computations
that is dominated from above by
, for all .
The set of functions
is compact in (see proposition 2.7, [GZ 1]). These functions have Lelong
numbers bounded from above by a uniform constant.
It follows therefore from Skoda’s uniform integrability theorem [Z],
that
Set and let
denote the Siciak extremal function of
(see section 5.1 in [GZ 1]).
Then
where denote the Alexander capacity
of (see section 5.2 in [GZ 2]).
It follows now from theorem 7.1 in [GZ 1] that
which yields (4).
∎
It follows therefore from theorem 2.1 that there exists a unique continuous function
such that
when , , with .
Actually we will be interested in measures
with -density with respect to a positive definite volume form ,
while the smooth measure may vanish along a divisor.
This does not make much difference, as follows from Hölder’s inequality:
Lemma 3.2.
Let be a -dimensional compact normal Kähler space
and be a smooth
Kähler form on . Let a resolution, ,
and let be a positive definite smooth
volume form on .
If , with for some ,
then there exists such that and .
Proof.
Observe that for some smooth density
which vanishes along the exceptional divisor of ,
thus
Fix local coordinates on a polydisk and a local
embedding .
Note that is comparable to
, being holomorphic on .
Therefore
and for
some .
Choose such that .
Then is the product of a function in
and a function in , hence it is in
by Hölder’s inequality.
A second application of Hölder’s inequality yields
where denotes the conjugate exponent to .
This shows that if is chosen so small
that .
∎