The errant life of a heavy quark in the quark–gluon plasma

Abstract

In the high-temperature phase of QCD, the heavy quark momentum diffusion constant determines, via a fluctuation-dissipation relation, how fast a heavy quark kinetically equilibrates. This transport coefficient can be extracted from thermal correlators via a Kubo formula. We present a lattice calculation of the relevant Euclidean correlators in the gluon plasma, based on a recent formulation of the problem in heavy-quark effective field theory (HQET). We find a ≈ 20% enhancement of the Euclidean correlator at maximal time separation as the temperature is lowered from 6T c to 2T c , pointing to stronger interactions at lower temperatures. At the same time, the correlator becomes flatter from 6T c down to 2T c , indicating a relative shift of the spectral weight to lower frequencies. A recent nextto-leading order perturbative calculation of the correlator agrees with the time dependence of the lattice data at the few-percent level. We estimate how much additional contribution from the ω T region of the perturbative spectral function would be required to bring it in agreement with the lattice data at 3.1T c .

Towards the Continuum Limit in Transport Coefficient Computations

“…The lattice sizes of our simulations, corresponding to a temperature T ∼ 1.43T c , substantially exceed those of earlier simulations [18,19,20], which had V max = 24 × 64 3 . Due to the increased number of multilevel updates we focussed on lattices with an aspect ratio N s /N τ = 4 (cf.…”

“…3. Preliminary lattice measurements of the colour-electric correlator have already been carried out [18,19,20]. The results look promising, hinting at a large and phenomenologically interesting non-perturbative effect in the diffusion coefficient.…”

Transport properties of the quark-gluon plasma

“…Recently, the force-force correlator was calculated in the SU(3) gauge theory on lattices with N t between ranging from 8 to 22 [157]. An N t = 16 simulation around 6T c cost about 2Gflop years (see Fig.…”

“…(137)) which is of order 1/M . Because of the smoothness of the kernel relating the spectral den- [157]. The absolute normalization has been determined by matching the data at tT = 1 4 and T = 3.1Tc with the NLO result of Burnier et al [65].…”

“…(139). Here we re-view a first calculation of the HQET correlator (142) in the SU(3) gauge theory [157], from which κ can be extracted from the Kubo-type formula (143). The classical interpretation of the correlator is that it measures the (Lorentz) force correlator along the worldline of a heavy quark.…”