A. A. Andrianov, V. A. Andrianov, D. Espriu
We investigate how large baryon densities (and possibly high temperatures) may induce spontaneous parity violation in the meson sector of QCD. The analysis at intermediate energy scales is done by using an extended $\sigma$-model lagrangian that includes two scalar and two pseudoscalar multiplets and fulfills low-energy QCD constraints. We elaborate on a novel mechanism of parity breaking previously proposed by the authors based on the interplay between lightest and heavier meson condensates, which therefore cannot be realized in the simplest $\sigma$ model. We emphasize that the mechanism proposed here differs from the old idea of pion condensation advocated originally by Migdal. The results are relevant for an idealized homogeneous and infinite nuclear (quark) matter where the influence of density can be examined with the help of a constant chemical potential. The model is able to describe satisfactorily the first-order phase transition to stable nuclear matter, and predicts a second-order phase transition to a state where parity is spontaneously broken. We argue that the parity breaking phenomenon is quite generic when a large enough chemical potential is present. Current quark masses are explicitly taken into account in this work and shown not to change the general conclusions. We expect that our approach will be adequate for dense nuclear matter of a few normal densities where quark percolation does not yet play a significant role.
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http://arxiv.org/abs/1211.6665
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