Speaker
Description
The ``Sphaleron Rate'' (imaginary linear-in-frequency part of the topological density retarded Green's function) determines the real-time relaxation rate of axial quark number for light quarks in a hot medium, and is relevant in heavy-ion collisions and electroweak baryogenesis. We recently showed how it can be determined in pure-glue QCD via standard Euclidean simulations, via a novel saddlepoint method. We extend this work to find the sphaleron rate for (2+1)-flavor QCD with $N_\tau=8 - 16$ and HISQ action at almost physical pion masses in the temperature range $0.2 - 3$ GeV or $1.2 - 18$ times the crossover temperature $T_{pc}$.
Similar to the pure gauge case, the QCD result is well described across the range of $1.6 - 8$ times $T_{pc}$ as $\Gamma_s \simeq 20 (\alpha_s T)^4$, where $\alpha_s$ is the MSbar coupling at $\overline{\mu}=2\pi T$, determined using the gradient-flow technique.
