Intersection Homology Theory via Rectifiable Currents
My
Publication
What is
intersection homology theory?
There is a nice introduction of
intersection
homology theory from Wikipedia.
My work
In
the above article, I developed a setting for treating variational
problems on stratified pseudomanifolds with singularities, such as
complex projective varieties. Rather than using the ordinary homology
theory on the base space, I instead used a generalized
``homology
theory '' ---the intersection homology theory introduced by MacPherson
and Goresky. Such a theory turns out to be more suitable than ordinary
homology theory for pseudomanifolds with singularities.
In
variational problems, one
needs to take various limits (e.g. of minimizing sequences), but a
basic problem is that a limit of geometric intersection chains may fail
to be a geometric chain; and even if it is, it may not satisfy the
important perversity conditions of the approximating chains concerning
intersection with singular set. This motivates my use of rectifiable
currents with a suitably modified mass norm.
Here is a brief sketch of the results of mine. For a compact stratified
subanalytic pseudomanifold, I showed how to express
the
intersection homology groups in terms of integer multiplicity
rectifiable currents. These are then isomorphic to the usual
intersection homology groups defined by geometric or subanalytic chains
with the corresponding perversity conditions. The key idea involved a
technical modification of the proof of the Federer-Fleming's
Deformation Theorem to accommodate the perversity condition of
intersection homology theory. I studied properties of a
``safety
function'' that was used to quantify the perversity condition for each
simplex of the singular locus.
Then I
introduced a suitably modified mass on rectifiable currents such that
all rectifiable currents with finite modified mass and finite boundary
modified mass automatically satisfy the given perversity conditions.
Also, by using the Lojasiewicz' inequality for subanalytic sets, I
was able to show that all allowable subanalytic chains have finite
(modified) mass and finite boundary mass. This fact ensures that the
category of rectifiable currents with finite modified mass is still
rich enough to contain all the ``nice'' chains one might consider.
Moreover, this modified mass satisfies an important theorem---an
analogue of the compactness theorem of geometric measure
theory which implies that each sequence of rectifiable
currents
with bounded modified mass and boundary mass will have a convergent
subsequence and that the limit is a rectifiable current satisfying the
perversity conditions of the approximating chains. This property of
rectifiable currents overcomes the weakness of geometric chains stated
earlier in the basic problem. The support of the currents I
considered may intersect ( in a controlled fashion) the singular locus
of the pseudomanifold.
In
the last part of the article, I showed that there exists a
modified mass minimizer in every intersection homology class on a
compact stratified subanalytic pseudomanifold. Moreover, I
showed
that these mass minimizers are in fact almost minimizing currents.
Thus, by a lemma of Almgren, I achieved a partial regularity
theorem for these mass minimizers.
My
future work in this field