User mark hughes - MathOverflow most recent 30 from http://mathoverflow.net 2013-06-19T03:08:07Z http://mathoverflow.net/feeds/user/22424 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/92307/khovanov-rozansky-sl-2-homology-and-the-original-khovanov-homology Khovanov-Rozansky $sl_2$ homology and the "original" Khovanov homology. Mark Hughes 2012-03-26T20:38:27Z 2013-04-02T11:22:00Z <p>I'm trying to understand the connection between Khovanov's original link homology and the $sl_2$ version of Khovanov-Rozansky homology. They both categorify the same link polynomial, but is there a direct relationship known between the theories on the level of homology? </p> <p>Even more optimistically, is there any connection known relating the construction of the original Khovanov homology (in terms of enhanced states, for instance) and the matrix factorization construction of KR homology (when $n=2$)?</p> http://mathoverflow.net/questions/123893/differences-between-various-categories-of-surface-embeddings-in-4-space Differences between various categories of surface embeddings in 4-space Mark Hughes 2013-03-07T17:29:00Z 2013-03-07T19:18:37Z <p>This is a very naive question, but I'm trying to understand the difference between the various categories when it comes to embedding surfaces in 4-dimensional manifolds. The situation I'd really like to understand is when we have a surface neatly and properly embedded in the 4-ball $D^4$, so that its boundary lies in $\partial D^4 = S^3$ as a link. I'd like to understand some of the differences between assuming everything in the setup is just continuous, versus when we assume it is either locally-flat, PL locally-flat, or smooth. </p> <p>For example, if we have a PL-locally flat surface, after arbitrarily small PL-isotopy we can arrange so it has a movie presentation with only max, min, and saddle points. So it seems like we can treat such an embedded surface much as we would a smooth surface with Morse function. Intuitively it seems that the theories of smoothly embedded surfaces and PL locally-flat surfaces should be equivalent in some sense, though I've never seen it dealt with in the literature. In particular it seems like we should be able to smooth PL locally-flat surfaces and vice versa, so that equivalence under the different types of isotopy is preserved.</p> <p>Where I get really murky is when we drop the PL or smooth condition and consider topological locally-flat embeddings. Here things can be quite different, as there are knots which bound topologically locally-flat disks, but whose smooth slice genus is arbitrarily high. It seems like there's an awful lot more freedom once we drop smoothness, or even just the PL condition from PL locally-flat, even though we can use embedded PL locally-flat disks to $\varepsilon$-approximate any topological embedding.</p> <hr> <p>With that rambling out of the way, my main questions are he following:</p> <blockquote> <p>1) Are the smooth and PL locally-flat situation really that "close" to each other? Can surfaces in one category be approximated by surfaces in the other, so that equivalence under smooth and PL-isotopy is preserved? Or are their hidden subtleties I'm missing?</p> <p>2) Is there anyway to understand the problems we encounter when we drop to the topologically locally-flat situation? For example, whenever the locally-flat condition is explained, the example of the cone over a nontrivial knot is invoked to illustrate a situation where it fails. Is there a similar example to understand (even just a single situation) where a topologically locally-flat embedding fails to be PL locally-flat or smooth? </p> </blockquote> <p>Of course anything else which might help me understand the situation better would be greatly appreciated as well. </p>