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On 6d "Gauge" Theories with Irrational Theta Angle
A recent proposal for 6d "gauge" theories with rational theta angle is
discussed. These theories were constructed from n_C coinciding (p,q) 5-branes
of IIB in the limit of vanishing string constant. They have (1,1) supersymmetry
and the low energy theory is 6d Yang-Mills with gauge group SU(n_C) and a
rational theta angle theta_6/(2 pi)=f/q, where fp=1 (mod q). By changing the
point of view, considering the (p,q) 5-branes to be D5-branes, the 6d theta
angle is identified with a 10d theta angle. This point of view together with
some assumptions suggests a generalization of the previous limit to arbitrary
theta. This limit seems to define a decoupled 6d theory even though the 10d
theory does not become free in general.Comment: 8 pages, latex, 1 figur
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