R. W. Moerman | Searcharxiv

arXiv2021

Strongly Coupled Heavy and Light Quark Thermal Motion from AdS/CFT

We give a pedagogical presentation of heavy and light probe quarks in a thermal plasma using the AdS/CFT correspondence. Three cases are considered: external heavy and light quarks undergoing Brownian motion in the plasma, and an external heavy quark moving through the plasma with a constant velocity. For the first two cases we compute the mean-squared transverse displacement of the string's boundary endpoint. At early times the behaviour is ballistic, while the late time dynamics are diffusive. We extract the diffusion coefficient for both heavy and light quarks in an arbitrary number of dimensions and comment on the relevance for relativistic heavy ion phenomenology.

hep-th↗

arXiv2016

A semi-classical recipe for wobbly limp noodles in partonic soup

We compute the average squared distance, $s^2(t)$, travelled by a light-flavour off-mass-shell coloured parton in a strongly-coupled $\mathcal{N}=4$ $SU(N_c)$ super-symmetric Yang Mills plasma using the gauge/string duality. In fact, we derive a closed integral expression for $s^2(t;a)$ in $AdS_3$-Schwarzschild, which interpolates between a heavy quark when $a = 0$ and a light quark when $a = 1$, that we evaluate analytically for small virtualities - labelled $s_\text{small}^2(t;a)$. For arbitrary virtualities, we show that for asymptotically early times the motion is ballistic, $\left.s^2(t;a)\right|_{t\llβ}\sim t^2$, while at asymptotically late times the motion is diffusive, $\left. s^2(t;a) \right|_{t\ggβ} = s_\text{small}^2(t;a) \sim 2D(a) t$, from which we are able to extract the diffusion coefficient $D(a)$. Motivated by the apparent universality of the late time behaviour, we compute $s_{\text{small}}^2(t;a,d)$ and $D(a,d)$ for an arbitrary $AdS_d$-Schwarzschild geometry. From $D(a,d)$ we then compute for the first time the dynamic, time-dependent transverse momentum squared per unit path length picked up by a high momentum light quark in a strongly-coupled plasma, the transport coefficient $\hat{q}(t)$, which is critically important for phenomenology in heavy ion collisions.

hep-th↗