Dilepton excess from local parity breaking in baryon matter

Abstract

We propose that local parity breaking induced by a large-scale fluctuation of topological charge at large temperatures and/or condensation of pseudoscalar mesons in the isotriplet channel for large baryon densities may be responsible for the substantial dilepton excess that is found for low invariant masses and moderate values of $p_T$ in central heavy ions collisions. This insofar unexplained enhancement could be understood by a combination of two effects leading both to an excess of $e^+e^-$ and $\mu^+ \mu^-$ pairs with respect to theoretical predictions based on conventional hadronic processes: (a) a modification of the dispersion relation of photons and vector mesons propagating in such a nuclear medium due to local parity breaking; (b) the appearance of new decay channels, forbidden by parity conservation in QCD in the usual vacuum. Possible signatures of this effect and perspectives for its detection are discussed.Comment: 11 pages, refs corrected, PLB versio

Decays of Light Mesons Triggered by Chiral Chemical Potential

“…On the contrary, a gradient density of isosinglet pseudoscalar condensate can be formed as a result of large, "long-lived" topological fluctuations of gluon fields in the fireball in central collisions (see [10] for details). To describe various effects of hadron matter in a fireball with Local Parity Breaking (LPB), we must introduce the axial/ chiral chemical potential [10].…”

QCD with Chiral Imbalance: models vs. lattice

“…• For central collisions (and light quarks) they correspond to a phase with axial chemical potential μ 5 0 located in "fluctons" of few-Fermi size [11].…”

“…• In the hadron phase QCD bosonization of totalQ 5 can be realized [11] with the help of meson Lagrangian and the Vector Meson Dominance providing a good precision in coefficients.…”

“…Therefore, as one enforces a system to generate the right-left asymmetry by increasing chiral chemical potential, one would expect that quark condensates tended to become larger and thereby critical temperature T c of chiral symmetry restoration were to rise as well. It happens that chirality imbalance is a direct manifestation of QCD topological fluctuations and could become observable through the asymmetry in polarizations of dilepton pairs [11] in central HIC as a result of the manifestation of Local spatial Parity Breaking (LPB) effect.…”

“…phenomenology of chiral imbalance in non-Abelian quark-gluon phase; chiral imbalance in hadronic phase -influence on chiral symmetry breaking (on chiral condensates); observables sensitive to the local chiral imbalance -manifestation of LPB in central HIC: dilepton polarization asymmetry [11] new states in scalar, pseudoscalar, vector meson spectra in hadrom matter with ChI.…”