85 research outputs found
The thermal dilepton rate at NLO at small and large invariant mass
We report on a recent next-to-leading order perturbative determination of the
dilepton rate from a hot QCD plasma for frequency and momentum of the order of
the temperature and for much smaller invariant mass . We briefly
review the calculation, which generalizes the previous one for the photon case
(). We then analyze the consequences of the new calculation for the
extraction of the photon rate from the small mass dilepton measurements. We
then review a recent NLO determination at large and we show how to match
and merge its results with the low-mass ones, resulting in a single rate which
is NLO-accurate over the phenomenologically relevant region.Comment: 4 pages, 6 figures. To appear in the Hard Probes 2015 proceeding
Parton energy loss and momentum broadening at NLO in high temperature QCD plasmas
We present an overview of a perturbative-kinetic approach to jet propagation,
energy loss, and momentum broadening in a high temperature quark-gluon plasma.
The leading-order kinetic equations describe the interactions between energetic
jet-particles and a non-abelian plasma, consisting of on-shell thermal
excitations and soft gluonic fields. These interactions include 22
scatterings, collinear bremsstrahlung, and drag and momentum diffusion. We show
how the contribution from the soft gluonic fields can be factorized into a set
of Wilson line correlators on the light cone. We review recent
field-theoretical developments, rooted in the causal properties of these
correlators, which simplify the calculation of the appropriate Wilson lines in
thermal field theory. With these simplifications lattice measurements of
transverse momentum broadening have become possible, and the kinetic equations
describing parton transport have been extended to next-to-leading order in the
coupling g.Comment: Review to appear in QGP5, 40 pages, 12 figure
Transport properties of the QCD medium
I present an overview of recent developments in the microscopic description
of the quark-gluon plasma. I will concentrate on medium-induced emission and
transverse momentum broadening. These are two key ingredients of the theory of
jet modifications in the QCD medium and of the kinetic theory used for
transport and thermalisation. The main focus is on progress towards a better
understanding of theory and of its uncertainties.Comment: Presented at Quark Matter 2022, to appear in the proceedings. 8
pages, 3 figure
QCD Shear Viscosity at (almost) NLO
We compute the shear viscosity of QCD with matter, including almost all
next-to-leading order corrections -- that is, corrections suppressed by one
power of relative to leading order. We argue that the still missing terms
are small. The next-to-leading order corrections are large and bring
down by more than a factor of 3 at physically relevant couplings. The
perturbative expansion is problematic even at GeV. The largest
next-to-leading order correction to arises from modifications to the
qhat parameter, which determines the rate of transverse momentum diffusion. We
also explore quark number diffusion, and shear viscosity in pure-glue QCD and
in QED.Comment: 36 pages plus appendices, 11 figures. The main results are summarized
in the introduction (Fig. 1
Jet-Medium Interactions at NLO in a Weakly-Coupled Quark-Gluon Plasma
We present an extension to next-to-leading order in the strong coupling
constant of the AMY effective kinetic approach to the energy loss of high
momentum particles in the quark-gluon plasma. At leading order, the transport
of jet-like particles is determined by elastic scattering with the thermal
constituents, and by inelastic collinear splittings induced by the medium. We
reorganize this description into collinear splittings, high-momentum-transfer
scatterings, drag and diffusion, and particle conversions (momentum-preserving
identity-changing processes). We show that this reorganized description remains
valid to NLO in , and compute the appropriate modifications of the drag,
diffusion, particle conversion, and inelastic splitting coefficients. In
addition, a new kinematic regime opens at NLO for wider-angle collinear
bremsstrahlung. These semi-collinear emissions smoothly interpolate between the
leading order high-momentum-transfer scatterings and collinear splittings. To
organize the calculation, we introduce a set of Wilson line operators on the
light-cone which determine the diffusion and identity changing coefficients,
and we show how to evaluate these operators at NLO.Comment: 37 pages plus appendices, 15 figures. A pedagogical review has been
presented in arXiv:1502.03730. v2: minor changes, matches journal versio
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