MHD Turbulence: An Unbiased Review*

The last few years have seen significant, and intellectually exciting, progress in the theory of MHD turbulence. The refrain of this progress is the definitive intertwining of turbulence and reconnection physics in all interesting contexts: tearing-mediated inertial-range cascade in MHD with a guide field [1 and references therein], reconnection-controlled decay of MHD turbulence [2], tearing-limited dynamo saturation [3], etc. I tried to give a long, detailed account of the subject in [1] --- an account that could be useful as a tutorial and was, therefore, deliberately biased towards a particular logical (and chronological) narrative. In this talk, I will attempt a different (and perhaps more difficult) task, viz., to explain how several distinct (and distinctive) intellectual threads of MHD turbulence theory pursued by different groups of researchers over the last few decades are coming together in the emerging overall narrative: the critical-balance phenomenology (Goldreich & Sridhar, Boldyrev, Beresnyak, Loureiro, Chandran, Mallet...), the focus on selective decay and coherent structures (Matthaeus, Pouquet...), the school of stochastic reconnection (Lazarian, Vishniac, Eyink...). What are sometimes perceived as mutually exclusive approaches seem to me to be different viewing angles of the same picture --- rather a beautiful one, and one we can all be quite proud of.

[1] A. A. Schekochihin, "MHD Turbulence: A Biased Review", submitted to JPP (2020); arXiv:2010.00699

[2] D. N. Hosking and A. A. Schekochihin, "Reconnection-controlled decay of magnetohydrodynamic turbulence and the role of invariants,'' submitted to PRX (2020); arXiv:2012.01393

[3] A. Galishnikova, M. W. Kunz and A. A. Schekochihin, "Tearing-limited saturated MHD dynamo", in preparation (2021).