QCD at Large $\theta$ Angle and Axion Cosmology

Abstract

We use the chiral Lagrangian to investigate the global properties of the $N$-flavor QCD vacuum as a function of the $\theta$ parameter. In the case of exact quark degeneracy we find evidence for first order phase transitions at $\theta =\pi \cdot (\mathrm{odd}\mathrm{integer})$. The first order transitions are smoothed by quark mass splittings, although interesting effects remain at realistic quark masses. We emphasize the role of the ${\eta }^{\prime }$ condensate in our analysis. Finally, we discuss the implications of our results on the internal hadronic structure of axion domain walls and axion cosmology.

12 pages, LaTeX, 5 epsf figures

References in corpus (2)

• Quark Masses and Chiral Symmetry
• Theta Vacua, Confinement and the Continuum Limit

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• Primordial Black Holes from Axion Domain Wall Collapse
• Mesoscopic QCD and the Theta Vacua
• Non-derivative Axionic Couplings to Nucleons at large and small N
• Quark Condensates in Non-Supersymmetric MQCD
• Softly Broken SQCD: in the Continuum, on the Lattice, on the Brane