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September 7, 2006

On n-Transport: 2-Vector Transport and Line Bundle Gerbes

Posted by Urs Schreiber

My first examples for the general concept of nn-transport # had been local transitions of principal 2-transport ##, taking values in some Lie 2-group.

For many applications in physics, one needs to have associated nn-transport, taking values in nn-vector spaces on which some nn-group is represented.

Here I present some notes which contain

  • a working definition of associated nn-transport;
  • an identification of a class of 2-representations of Lie 2-groups on bimodules # #;
  • a description of (torsion) U(1)U(1)-gerbes with connection as associated 2-transport with respect to the above representation of the 2-group Σ(Σ(U(1)))\Sigma(\Sigma(U(1)));
  • a demonstration that the transition data of such a 2-transport is precisely the data of a line bundle gerbe with connection and curving (and that in fact the 2-category of these transiton tetrahedra is equivalent to that of line bundle gerbes with connection).

Line Bundle Gerbes from 2-Transport

Apart from being interesting in its own right, this is supposed to be a warm-up for describing more sophisticated 2-vector transport.

In particular, one can see that by replacing the 2-group Σ(Σ(U(1)))\Sigma(\Sigma(U(1))) in the above setup with the strict 2-group String G\mathrm{String}_G #, one obtains – up to technical subteties related to the fact that String G\mathrm{String}_G is infinite-dimensional – something very similar (maybe identical) to the the notion of string-connection that Stolz&Teichner defined #.

I conjecture that

A string connection as defined by Stolz&Teichner is the 2-vector 2-transport associated to a principal String G\mathrm{String}_G-2-transport by way of the 2-representation defined in the above notes.

I think that in as far as this conjecture is false it is just due to technicalities that can be fixed – like the fact that in the above notes I use the ordinary tensor product of bimodules, while for the String G\mathrm{String}_G-application we need “Connes fusion” #.


(I was waiting with posting this entry until I had tied up some lose ends in the above notes. But since we are now discussing this already in the comment sections #, I thought I’d just ahead and post it.)

Posted at September 7, 2006 1:25 PM UTC

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