We now improve the metric on to make the volume form approximately CY except on a set with a small percentage of the CY measure.
Let . Since solves the real MA equation (8) on the -dimensional open faces , the regularity theory of real MA surveyed in section 2.5 applies. In particular, we can find finitely many small open balls properly contained in , such that has -norm uniformly bounded by on any , and the complement of has small -measure less than . The open sets form an exhaustion of , which is the -locus of the real MA solution . Recall the normalised CY measure from section 3.1.
Proof.
Choose a smooth nonnegative bump function on supported in , and equals one on , and construct supported on . We calculate
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so if is sufficiently small dependent on , we can ensure is psh on .
Consider the potential function on
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with from Lemma 4.1.
Since , we see that on the maximum is never achieved by , so the fact that this term is only locally defined causes no problem. By construction every term is -psh, so the maximum is also -psh. Near the boundary of the maximum is achieved by , so globalizes to define a Lipschitz continuous -psh function on , with .
Morever, on the maximum of is strictly greater than zero. Perturbing the bump function in the construction if necessary, we may assume the locus on where the maximum is achieved by at least two terms is a subset of codimension one, and it is automatically closed. So a.e on ,
the metric is smooth and equals for some . We calculate using the regularity estimates on that
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Using the real MA equation (8),
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where determines the constant . Comparing with section 3.1, the normalized CY measure satisfies
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For sufficiently small depending on and , we combine the above to deduce
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The total complex MA measure is , and the contribution from the smooth region in is greater than
for very small dependent on . Thus the measure contribution from the complement must be less than , namely -percent of the total measure. Thus the total variation of the signed measure is smaller than for small enough .
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