Physics – High Energy Physics – High Energy Physics - Theory
Scientific paper
2006-12-28
JHEP 0704:043,2007
Physics
High Energy Physics
High Energy Physics - Theory
18 pages, 19 figures, minor changes
Scientific paper
10.1088/1126-6708/2007/04/043
We analyze the resolution of the U(1)_A problem in the Sakai-Sugimoto holographic dual of large N_c QCD at finite temperature. It has been shown that in the confining phase the axial symmetry is broken at order 1/N_c, in agreement with the ideas of Witten and Veneziano. We show that in the deconfined phase the axial symmetry remains unbroken to all orders in 1/N_c. In this case the breaking is due to instantons which are described by spacelike D0-branes, in agreement with 'tHooft's resolution. The holographic dual of the symmetry breaking fermion condensate is a state of spacelike strings between the D0-brane and the flavor D8-branes, which result from a spacelike version of the string creation effect. In the intermediate phase of deconfinement with broken chiral symmetry the instanton gas approximation is possibly regulated in the IR, which would imply an eta' mass-squared of order exp(-N_c).
Bergman Oren
Lifschytz Gilad
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