No abstract

We study the possible signals of a pion string associated with the QCD chiral phase transition in LHC Pb - Pb collision at energy $ \sqrt{s}=5.5$ TeV. In terms of the Kibble-Zurek mechanism we discuss the production and evolution of the pion string. The pion string is not topologically stable, it decays into neutral pions and sigma mesons which in turn decay into pions. Our results show that all the neutral pions from the pion string are distributed at the low momentum and the ratio of neutral to charged pions from the pion string violates the isospin symmetry. For the momentum spectra of the total pions, the signal from the sigma particle decay which is from the pion string will be affected by the large decay width of the sigma significantly.Comment: 8 pages, 3 figures, one reference added, title changed, version accepted for publication in Phys. Rev.

In models in which some of the scalar field are charged and some uncharged, interactions with a finite temperature plasma will lead to corrections to the effective potential of the charged fields which may stabilize embedded defects made up of uncharged fields. In these models embedded defects, solutions of the field equations which are unstable at zero temperature, may thus be stable in the early Universe, and may then play an important role in cosmology. Two prototypical examples are the pion string in the theory of strong interactions, and the electroweak Z-string in the standard electroweak theory.PACS numbers: 98.80Cq