Jacopo Ghiglieri

Static quark-antiquark pairs at finite temperature

In a fram ework thatm akesclosecontactwith m odern eectiveeld theoriesfornon-relativistic bound states at zero tem perature,we study the real-tim e evolution ofa static quark-antiquark pairin a m edium ofgluonsand lightquarksatnitetem perature.Fortem peraturesranging from values larger to sm aller than the inverse distance ofthe quark and antiquark,1=r,and at short distances,we derive the potentialbetween the two static sources,and calculate theirenergy and therm aldecay width.Two m echanism scontributeto thetherm aldecay width:theim aginary part ofthe gluon selfenergy induced by the Landau dam ping phenom enon,and the quark-antiquark color singletto color octettherm albreak up. Param etrically,therstm echanism dom inates for tem peraturessuch thatthe Debye m assislargerthan the binding energy,while the latter,which wequantify hereforthersttim e,dom inatesfortem peraturessuch thattheDebyem assissm aller than thebindingenergy.IftheDebyem assisofthesam eorderas1=r,ourresultsarein agreem ent with a recentcalculation ofthestaticW ilson loop atnitetem perature.Fortem peraturessm aller than 1=r,wend new contributions to the potential, both realand im aginary,which m ay be relevantto understand theonsetofheavy quarkonium dissociation in a therm alm edium .

Next-to-leading order thermal photon production in a weakly coupled quark-gluon plasma

A bstractWe compute the next-to-leading order O(g) correction to the thermal photon production rate in a QCD plasma. The NLO contributions can be expressed in terms of gauge invariant condensates on the light cone, which are amenable to novel sum rules and Euclidean techniques. We expect these technologies to be generalizable to other NLO calculations. For the phenomenologically interesting value of αs = 0.3, the NLO correction represents a 20% increase and has a functional form similar to the LO result.

Thermal width and quarkonium dissociation by inelastic parton scattering

A bstractIn a weak-coupling effective field theory framework we study quarkonium dis-sociation induced by inelastic scattering with partons in the medium. This is the dominant dissociation process for temperatures such that the Debye mass is larger than the binding energy. We evaluate the dissociation cross section and the corresponding thermal decay width. At leading order we derive a convolution formula relating the two, which is consistent with the optical theorem and QCD at finite temperature. Bound state effects are systematically included. They add contributions to the cross section and width that are beyond a quasi-free approximation, whose validity is critically reviewed. For temperatures such that the Debye mass is smaller than the binding energy, the dominant dissociation mechanism is gluo-dissociation consisting in quarkonium dissociation induced by the absorbtion of a gluon from the medium. We calculate the gluo-dissociation cross section and width at next-to-leading-order accuracy.

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 2 2 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.

Low mass thermal dilepton production at NLO in a weakly coupled quark-gluon plasma

A bstractWe present a computation, within weakly-coupled thermal QCD, of the production rate of low invariant mass (M2 ~ g2T2) dileptons, at next-to-leading order (NLO) in the coupling (which is Og3e2T2

arXiv : QCD Shear Viscosity at (almost) NLO

\mathcal{O}\left({g}^3{e}^2{T}^2\right)

Review of the EFT treatment of quarkonium at finite temperature

). This involves extending the NLO calculation of the photon rate which we recently presented to the case of small nonzero photon invariant mass. Numerical results are discussed and tabulated forms and code are provided for inclusion in hydrodynamical models. We find that NLO corrections can increase the dilepton rate by up to 30–40% relative to leading order. We find that the electromagnetic response of the plasma for real photons and for small invariant mass but high energy dilepton pairs (e.g., M2< (300 MeV)2 but pT> 1 GeV) are close enough that dilepton pair measurements really can serve as ersatz photon measurements. We also present a matching a la Ghisoiu and Laine between our results and results at larger invariant masses.

Next-to-leading order thermal photon production in a weakly-coupled plasma

A bstractIn finite-temperature field theory, the cyclic Wilson loop is defined as a rectangular Wilson loop spanning the whole compactified time direction. In a generic non-abelian gauge theory, we calculate the perturbative expansion of the cyclic Wilson loop up to order g4. At this order and after charge renormalization, the cyclic Wilson loop is known to be ultraviolet divergent. We show that the divergence is not associated with cusps in the contour but is instead due to the contour intersecting itself because of the periodic boundary conditions. One consequence of this is that the cyclic Wilson loop mixes under renormalization with the correlator of two Polyakov loops. The resulting renormalization equation is tested up to order g6 and used to resum the leading logarithms associated with the intersection divergence. Implications for lattice studies of this operator, which may be relevant for the phenomenology of quarkonium at finite temperature, are discussed.