Date : 8th of September 2020, 16:00 CET
Danny Brattan (University of Genova)
Title: Diffusion in a magnetic field
Even with the simplifying assumption of non-dynamical (external) electromagnetic fields, magnetohydrodynamics is a technically subtle framework for understanding the long wavelength and low frequency regime of interacting theories. One of these technicalities is that for many models of interdisciplinary relevance the magnetic field is a constant in equilibrium. Intuitively however, for momentum to be approximately conserved and enter the hydrodynamic description, the magnetic field must vanish at leading order.
In this talk I will review recent work that sheds light on some of the unique features of magnetohydrodynamics in (2+1)-dimensions, with a particular emphasis on diffusion. I will show that there is a qualitative and quantitative improvement in matching holographic and hydrodynamic correlators if one correctly accounts for the magnetic field being non-zero in the background. Consequently, I will give conclusive evidence that there is a non-zero incoherent Hall conductivity in the absence of parity violation that was missed in previous approaches. Finally, I will discuss some ways in which this new approach can be applied to non-stringy systems.