Hidden Local Field Theory and Dileptons in Relativistic Heavy Ion Collisions

TL;DR

This paper introduces the concept of hadronic freedom based on hidden local symmetry, arguing that dileptons in heavy-ion collisions do not directly reveal chiral symmetry breaking, and discusses implications for vector meson behavior and holographic QCD.

Contribution

It proposes that dileptons are suppressed due to vector manifestation of hidden local symmetry, challenging their use as direct probes of chiral symmetry breaking in heavy-ion collisions.

Findings

Dileptons may be strongly suppressed in the hadronic free region.

Vector mesons recover most of their mass at the flash point.

Holographic QCD describes baryons as coherent states of mesons.

Abstract

The notion of "hadronic freedom" is introduced based on the vector manifestation of hidden local symmetry and is used to suggest that the dileptons measured in relativistic heavy-ion collisions do not provide {\em direct} information on the spontaneous breaking of chiral symmetry and hence on the mechanism for mass generation of light-quark hadrons. We give arguments how the dileptons emitted from those vector mesons whose masses are shifted \`a la Brown-Rho (BR) scaling by the vacuum change in temperature -- as in heavy-ion collisions -- and/or density -- as in cold compressed matter -- could be strongly suppressed in the hadronic free region between the chiral restoration point and the "flash point" at which the vector mesons recover $\gsim 90%$ of their free-space on-shell masses and the full strong coupling strength. It may seem ironical that the very mechanism i.e., the vector manifestation in hidden local symmetry, that is to make the mass drop and modify the spectral function is in turn responsible for the dilepton suppression. A possible falsification of this drastic prediction will be indicated. We also briefly discuss the potential role played by the holographic dimension intrinsic in gravity-gauge duality that provides a unified field theory description of hadrons -- both mesons and baryons -- under extreme conditions. Baryons arise as coherent states of pions and vector mesons of holographic QCD which define the ground state or the "vacuum" on which mesonic excitations could undergo BR scaling.