Anomalous soft photon production from the induced currents in Dirac sea

Abstract

The propagation of a high energy quark disturbs the confining QCD vacuum inducing the currents in Dirac sea. Since quarks possess electric charge, these induced vacuum quark currents act as a source of soft photon radiation. This can lead to the enhancement of the soft photon production above the expectations based on the charged hadron yields and the Low theorem. We illustrate the phenomenon by using the exactly soluble 1+1 dimensional massless Abelian gauge model that shares with QCD all of the ingredients involved in this mechanism: confinement, chiral symmetry breaking, axial anomaly, and the periodic $\theta$-vacuum. We show that the propagating quark throughout the process of hadronization induces in the vacuum charged transition currents that lead to a strong resonant enhancement of the soft photon yield; the Low theorem however remains accurate in the limit of very soft momenta. We then construct on the basis of our result a simple phenomenological model and apply it to the soft photon production in the fragmentation of jets produced in $Z^0$ decays. We find a qualitative agreement with the recent result from the DELPHI Collaboration.Comment: 14 pages, 2 figure

Connecting real-time properties of the massless Schwinger model to the massive case

“…This configuration has been recently employed in Refs. [4][5][6]. Such a scenario with external sources on the light cone only approximately holds for a highly relativistic configuration.…”

“…We investigate two scenarios corresponding to opposite charges which are either placed at a fixed distance apart from each other or moving backto-back along the light cone. The latter scenario has been employed for effective descriptions of jet energy loss and photon production in the context of heavy-ion collisions [4][5][6]. Following these applications, we first consider the applied charges as external sources on the light cone.…”

“…The Schwinger model shares several key properties with quantum chromodynamics (QCD) such as spontaneous chiral symmetry breaking, charge screening and the axial anomaly. Since a long time it is used as an effective model for the description of some characteristic QCD properties [2,3], and has been recently employed to real-time questions of jet energy loss and photon production in the context of ultra-relativistic heavy-ion collisions [4][5][6].…”

Direct-photon spectrum and elliptic flow produced from Pb+Pb collisions at sNN=2.76 TeV at the CERN Large Hadron Collider within an integrated hydrokinetic model

“…Note, the different mechanisms of additional photon radiation from a confining process are also proposed in Refs. [19][20][21][22].) Trying to give more credibility to such mechanisms we speculate here adapting the phenomenological prescription for describing the photon emission from the hadronization space-time layer in the cross-over scenario at the LHC.…”

“…Additional productive sources of electromagnetic radiation when the QCD environment undergoes a confinement have been recently launched in Refs. [19][20][21][22].…”