Abstract

The determination of transport coefficients plays a central role in characterizing hot and dense nuclear matter. Currently, there are significant discrepancies between various calculations of the electric conductivity of hot hadronic matter. It has been shown that dilepton emission spectra can be described by calculating the electromagnetic correlator within the vector dominance model (VDM). Transport coefficients probe the low-energy limit of the medium, thus the interactions of the low mass pion are expected to play an important role in determining the conductivity of hot hadronic matter. In the present work we calculate the electric conductivity of hot pion matter by extracting it from the electromagnetic spectral function, as its zero energy limit at vanishing 3-momentum. Within the VDM the photon couples primarily to the rho meson. Therefore, we use hadronic many-body theory to calculate the rho meson’s self-energy in hot pion matter. This requires the dressing of the pion propagators within the rho self-energy with thermal π-ρ and π- σ loops, and the inclusion of vertex corrections to maintain gauge invariance. In particular, we analyze the transport peak of the spectral function and extract its behavior with temperature.

Abstract

We present novel predictions for open and closed heavy flavor suppression in heavy ion collisions from AdS/CFT.  Including only leading order mean energy loss, AdS/CFT overpredicts the suppression of D and B mesons as measured by RHIC and LHC.  However, fluctuations in the energy loss provides the crucial bridge to data.  We derive a new result for the fluctuations in energy loss for open heavy flavor in AdS/CFT including a new, independent calculation of the transport coefficient qhat.  With this result for the fluctuations, our predictions for D and B meson suppression are in surprisingly good agreement with data.  We extend the phenomenological application of AdS/CFT to closed heavy flavor by computing the suppression of Upsilon at LHC.  Using the complex quarkonia potential derived from AdS/CFT, we compute the complex binding energies of the quarkonia.  Just like the open heavy flavor case, the suppression prediction based on this leading order, non-fluctuating complex binding energy leads to an oversuppression of Upsilon compared to data.  We conclude with a discussion future avenues of research in strongly-coupled heavy flavor physics in heavy ion collisions.

Abstract: Relativistic heavy-ion experiments at Brookhaven National Laboratory have successfully reproduced the Quark Gluon Plasma in the laboratory, which is the smallest fluid known to humankind.  The QGP acts as a nearly perfect fluid whose flow fluctuations are extremely well described by event-by-event relativistic viscous hydrodynamics.   Additionally, the QGP can be scanned by particles produced in the early stages after the collision such as high pT particles. There is an enhancement of the flow fluctuations at high pT, which indicates the importance of energy loss fluctuations in a strongly interacting medium.  Recently, dilepton studies have gained attention since these particles allow one to scan different parts of the QGP evolution.  Here we use the state of the art IP-Glasma+MUSIC model to analyze their dilepton flow fluctuations where we find there is a suppression in the fluctuations, in contrast to both the soft and hard sectors associated with light hadrons.