Abstract
We investigate how large baryon densities (and possibly high temperatures) may induce spontaneous parity violation in the composite meson sector of vector-like gauge theory (presumably QCD or techni-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 constraints for vector-like gauge theories. We elaborate on a novel mechanism of parity breaking based on the interplay between lightest and heavier meson condensates, which therefore cannot be realized in the simplest $$\sigma $$ model. The results are relevant for idealized homogeneous and infinite nuclear (quark or techniquark) matter where the influence of the 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 it 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.
Highlights
At finite baryon density pion condensation has been conjectured in nuclear physics long ago in [6,7,8,9,10] and it seems to be a plausible possibility which, cannot be proved in simple models describing pion–nucleon interactions
We argue that the parity breaking phenomenon is quite generic when a large enough chemical potential is present
In this paper we shall attempt to explore the interesting issue of parity breaking employing effective lagrangian techniques, useful to explore the range of nuclear densities where the hadron phase still persists and quark percolation does not occur yet
Summary
At finite baryon density pion condensation has been conjectured in nuclear physics long ago in [6,7,8,9,10] and it seems to be a plausible possibility which, cannot be proved in simple models describing pion–nucleon interactions. More recently the phenomenon of parity breaking was assumed to be present in meta-stable nuclear bubbles with non-zero axial charge generated by a non-trivial topological charge in hot nuclear matter [61,62,63,64,65] and/or in the presence of strong background magnetic fields [66,67,68,69,70,71,72,73,74] It was shown [75,76,77,78,79] that the associated axial chemical potential causes a distortion of the energy spectrum of photons and vector particles (ρ and ω mesons) due to the Chern–Simons term that is generated. Page 3 of 23 2932 ent in origin from the previous one and it will not be discussed in the present paper
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