Thermal photon production rate from nonequilibrium quantum field theory

We investigate the hard thermal loop (HTL) resummation technique, which has been derived by Braaten and Pisarski starting from the imaginary time formalism (ITF). We use the real time formalism (RTF) and consider equilibrium as well as non-equilibrium situations. Choosing the Keldysh representation for the propagators, which simplifies significantly the calculation, we derive the HTL photon self energy and the resummed photon propagator. As an example of the application of the HTL resummation method within the RTF we discuss the damping rate of a hard electron. In particular we show that no pinch singularities appear even in non-equilibrium situations.

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“…Therefore we obtain the same results, (19), (20), and (23), where we have to replace now the thermal photon mass by (see (18))…”

Section: Non-equilibriummentioning

confidence: 61%

“…Baier et al [20] have studied the photon production rate in chemical non-equilibrium using the representation (1) and (2). Similarly Le Bellac and Mabilat [9] investigated the damping rate of an off-equilibrium muon in an equilibrated QED plasma and the damping rate of a quark in a QGP, where the quarks are not in equilibrium.…”

Section: Non-equilibriummentioning

confidence: 99%

Equilibrium and non-equilibrium hard thermal loop resummation in the real time formalism

1999

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“…In a plasma with locally anisotropic momentum distributions, these HTL self energies are anisotropic, too. In previous work [24][25][26], the HTL-resummed quark self-energy was evaluated for spheroidally deformed momentum distributions. In Ref.…”

Section: Viscous Corrections To Thermal Photon Emission Ratesmentioning

confidence: 99%

Anisotropic flow of thermal photons as a quark-gluon plasma viscometer

et al. 2015

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We present state-of-the-art calculations of viscous photon emission from nuclear collisions at RHIC and LHC. Fluctuating initial density profiles are evolved with event-by-event viscous hydrodynamics. Momentum spectra of thermal photons radiated by these explosively expanding fireballs and their pT -differential anisotropic flow coefficients vn(pT ) are computed, both with and without accounting for viscous corrections to the standard thermal emission rates. Viscous corrections to the rates are found to have a larger effect on the vn coefficients than the viscous suppression of hydrodynamic flow anisotropies. The benefits of taking the ratio of elliptic to triangular flow, v2/v3, are discussed, and the spacetime regions which contribute dominantly to the photon flow harmonics are identified. The directed flow v1 of thermal photons is predicted for RHIC and LHC energies.

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“…Our analysis can be extended to the case of direct photon production from a QGP away from chemical equilibrium by replacing the equilibrium (anti)quark distributions with the undersaturated ones [16]. We expect the main features to remain in the more general situation.…”

mentioning

confidence: 99%

Enhanced photon production from quark-gluon plasma: Finite-lifetime effect

Wang

Boyanovsky

2001

Phys. Rev. D

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Photon production from a thermalized quark-gluon plasma of finite lifetime is studied directly in real time with a nonequilibrium formulation that includes off-shell (energy nonconserving) effects. To lowest order we find that production of direct photons form a quark-gluon plasma of temperature T ∼ 200 MeV and lifetime t ∼ 10 − 20 fm/c is strongly enhanced by off-shell (anti)quark bremsstrahlung q(q) → q(q)γ. The yield from this nonequilibrium finite-lifetime effect dominates over those obtained from higher order equilibrium rate calculations in the range of energy E > 2 GeV and falls off with a power law for E ≫ T .PACS numbers: 12.38. Mh, 11.10.Wx The observation of a novel phase of matter, the quarkgluon plasma (QGP), is one of the most important goals of ultrarelativistic heavy ion experiments currently undertaken at CERN SPS and BNL RHIC [1]. The quarkgluon plasma formed in the early stage of the collision expands and cools rapidly to a mixed phase of quarks, gluons, and hadrons, and ultimately undergoes a freeze-out from a state of hadronic gas. Estimates based on energy deposited in the central collision region at RHIC energies √ s ∼ 200A GeV suggest that the lifetime of a deconfined phase of quark-gluon plasma is of order 10−20 fm/c with an overall freeze-out time of order 100 fm/c [2]. An important aspect is an assessment of nonequilibrium effects associated with the rapid expansion and finite lifetime of the plasma and their impact on experimental observables.Amongst various experimental signatures proposed to detect the quark-gluon plasma phase, photons (both real and virtual) have long been considered as the most promising direct signals [3]. This is because, unlike strongly interacting hadrons, photons have a mean free path much larger than the typical size of the plasma formed in ultrarelativistic heavy ion collisions. Once produced they escape from the system without further interaction, thus carrying clean information from the early hot quark-gluon plasma phase.The first observation of direct photon production in ultrarelativistic heavy ion collisions has been recently reported by the CERN WA98 Collaboration in Pb+Pb collisions at √ s = 158A GeV [4]. The transverse momentum distribution of direct photons is determined on a statistical basis and compared to the background photon yield predicted from a calculation of the radiative decays of hadrons. The most interesting result is that a significant excess of direct photons beyond that expected from proton-induced reaction at the same √ s is observed in the range of transverse momentum greater than about 1.5 GeV/c in central collisions. While it is not yet clear whether a QGP was formed in the central collision region at SPS energies, this result does suggest the experimental feasibility of direct photon production as a signal of the QGP phase, expected to be formed at RHIC energies. One goal of this article is to study directly in real time the effect of the finite QGP lifetime on direct photon production. We focus on the direct photon yield fr...

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Thermal photon production rate from nonequilibrium quantum field theory

Cited by 55 publications

References 37 publications

Equilibrium and non-equilibrium hard thermal loop resummation in the real time formalism

Equilibrium and non-equilibrium hard thermal loop resummation in the real time formalism

Anisotropic flow of thermal photons as a quark-gluon plasma viscometer

Enhanced photon production from quark-gluon plasma: Finite-lifetime effect

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