Speaker
Prof.
Thacker H. B.
(University of Virginia)
Description
There is considerable evidence, based on large $N_c$ chiral dynamics, holographic QCD,
and Monte Carlo studies, that the topological structure of the QCD vacuum consists of
discrete quasivacua separated by domain walls across which the local value of
the topological $\theta$ parameter jumps by $\pm2\pi$.
Topological insulators are condensed matter systems which are bulk insulators with a mass gap
but which can transport quantized units of charge via topologically protected boundary states. This is
analogous to the QCD vacuum, where the pure glue theory has a bulk mass gap but,
when light quarks are included, has Goldstone bosons associated with topological modes
of the Dirac operator. As in topological insulators, Goldstone modes in QCD are boundary states
on codimension one membranes or domain walls. Following this analogy, the U(1) chiral field
in QCD is given by the closed loop integral of a Berry connection around the Brillouin zone
in lattice momentum space. This berry phase describes the local polarization of the topological
charge membranes.
Summary
I discuss the similarities between the topological structure of the QCD vacuum and that of topological insulators.
Primary author
Prof.
Thacker H. B.
(University of Virginia)
