2,178 research outputs found
Classifying A-field and B-field configurations in the presence of D-branes - Part II: Stacks of D-branes
In the paper arXiv:0810.4291 we have shown, in the context of type II
superstring theory, the classification of the allowed B-field and A-field
configurations in the presence of anomaly-free D-branes, the mathematical
framework being provided by the geometry of gerbes. Here we complete the
discussion considering in detail the case of a stack of D-branes, carrying a
non-abelian gauge theory, which was just sketched in the previous paper. In
this case we have to mix the geometry of abelian gerbes, describing the
B-field, with the one of higher-rank bundles, ordinary or twisted. We describe
in detail the various cases that arise according to such a classification, as
we did for a single D-brane, showing under which hypoteses the A-field turns
out to be a connection on a canonical gauge bundle. We also generalize to the
non-abelian setting the discussion about "gauge bundles with non integral Chern
classes", relating them to twisted bundles with connection. Finally, we analyze
the geometrical nature of the Wilson loop for each kind of gauge theory on a
D-brane or stack of D-branes.Comment: 29 page
A Sampling Theorem for Rotation Numbers of Linear Processes in
We prove an ergodic theorem for the rotation number of the composition of a
sequence os stationary random homeomorphisms in . In particular, the
concept of rotation number of a matrix can be generalized
to a product of a sequence of stationary random matrices in .
In this particular case this result provides a counter-part of the Osseledec's
multiplicative ergodic theorem which guarantees the existence of Lyapunov
exponents. A random sampling theorem is then proved to show that the concept we
propose is consistent by discretization in time with the rotation number of
continuous linear processes on ${\R}^{2}.
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