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

Thermal Monopoles

Evidence is given that some particles with large charges in gauge theories, including 4d N=4 SU(3) and 5d theories with N=1 supersymmetry, have macroscopic entropy. The ground state entropy is found to be extensive in the charges. The mass gap for excitation is estimated and is of the same order as the binding energy. The question of the decay of excited states through Hawking radiation is raised. The analysis is based on the model of (p,q) string webs and on various other results. The evidence points to an explanation in terms of a string model.Comment: 12 pages. JHEP modified version, see note added to introductio