Finite lifetime effects on the photon production from a quark-gluon plasma
aa r X i v : . [ h e p - ph ] J un Finite lifetime effects on the photonproduction from a quark-gluon plasma
F. Michler , B. Schenke and C. Greiner Institut f¨ur Theoretische PhysikJohann Wolfgang Goethe - Universit¨at FrankfurtMax-von-Laue-Straße 1, D-60438 Frankfurt am Main, Germany, Department of Physics, McGill University,Montreal, Quebec, H3A 2T8, Canada
Abstract
We use the real-time Keldysh formalism to investigate finite lifetimeeffects on the photon emission from a quark-gluon plasma (QGP). Weprovide an ansatz which eliminates the divergent contribution from thevacuum polarization and renders the photon spectrum UV-finite if thetime evolution of the QGP is described in a suitable manner.
The quark-gluon plasma (QGP) created during heavy-ion collisions canonly be accessed indirectly via experimental signatures such as hard andelectromagnetic probes. Besides the role of memory effects in time evolution(see e.g. [1, 2]) it is also of particular interest within the framework of non-equilibrium quantum field theory how these probes are affected by the finitelifetime of the QGP itself.For photons, this question has first been addressed by Boyanovsky et al. [3, 4]. The main result has been the contribution of first order processeswhich are kinematically forbidden in equilibrium. The spectra from theseprocesses were found to decay algebraically for k > . et al. [6] where it was claimed that the divergent vacuum con-tribution is unphysical and thus requires an appropriate renormalizationtechnique. It was concluded that the ansatz used in [5] is inadequate as itproduces the mentioned problems.We provide an ansatz that eliminates the divergent contribution fromthe vacuum polarization. For the scenario of a heavy-ion collision, it alsorenders the resulting photon spectrum UV-finite if the time evolution isdescribed in a suitable manner.The photon production rate from a homogeneous but non-stationaryemitting system reads [2, 7]: k d n ( t ) d xd k = 1(2 π ) Re (cid:26)Z t −∞ du i Π References [1] B. Schenke and C. Greiner , Phys. Rev. C73 , 034909 (2005).[2] F. Michler , B. Schenke , and C. Greiner , arXiv:0905.2930, 2009.[3] S.-Y. Wang and D. Boyanovsky , Phys. Rev. D63 , 051702 (2001).[4] S.-Y. Wang , D. Boyanovsky , and K.-W. Ng , Nucl. Phys. A699 ,819 (2002).[5] D. Boyanovsky and H. J. de Vega , Phys. Rev. D68 , 065018 (2003).[6] E. Fraga , F. Gelis , and D. Schiff , Phys. Rev. D71 , 085015 (2005).[7]