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Manuel Bärenz's user avatar
Manuel Bärenz's user avatar
Manuel Bärenz's user avatar
Manuel Bärenz
  • Member for 13 years, 9 months
  • Last seen more than 1 year ago
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Is there a constructive proof that in four dimensions, the PL and the smooth category are equivalent?
@TomGoodwillie That's unfortunate news to me. I took this term from Wikipedia: en.wikipedia.org/wiki/PDIFF But I didn't check the definition.
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Are there 4d state sum models, extended TQFTs or chain mail invariant that detect smooth structures?
> In fact the identity functor gives a trivial example that does detect all smooth structures, but obviously we want something less tautological That's an intriguing comment. The identity functor is in a sense the strongest TQFT, while the constant functor is the weakest. But what additional constraints and properties would we expect for a typical TQFT? Should the target category have some kind of sums?
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Can one show corbordism invariance of the Crane-Yetter state-sum using simplicial methods / are there 'Pachner-like' moves for cobordisms?
> It would also be nice if there were versions of the Pachner move theorem for cobordisms. I'm a bit surprised by this. The Pachner theorem comes from looking at specific triangulations of cylinders, so restricting bordisms to those that induce PL homeomorphisms on the boundaries. If you want to remove that restriction, you don't really have Pachner's theory anymore, but simply triangulated bordisms. I don't know what else you'd expect there.
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DW, state sum models, and fully extended TQFTs
> According to Manuel Bärenz's edit on nLab, it can be realized as a generalized DW theory, based on quantum groups instead of finite groups. I should really have said "with a ribbon (= braided spherical) fusion category" rather than "quantum group" back then.
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Construction of invariants of 4-manifolds with the Kirby calculus
If you're interested in 3-handles and possibly stronger invariants, have a look at: arxiv.org/abs/1810.05833
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