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The transport of angular momentum (AM) and chemical elements within evolvingstars remains poorly understood. Recent observations showed that the radiativecores of low mass main sequence stars and red giants rotate orders of magnitudeslower than classical stellar evolution models predictions and that theirsurface light elements abundances are too small. Magnetohydrodynamic (MHD)turbulence can enhance the transport in radiative stellar interiors but itsefficiency is still largely uncertain. Here we explore the transport of AM andchemical elements due to azimuthal magnetorotational instability (AMRI) using3D MHD direct numerical simulations in a spherical shell. First, we provideevidence of AMRI in the parameter regime expected from local and global linearstability studies and then we analyze its nonlinear evolution. For unstratifiedflow, we observe AMRI-driven dynamo action at values of the magnetic Prandtlnumber Pm in the range $0.6-1$, the smallest ever reported in a global setup.When considering stable stratification (under the Boussinesq approximation) at$\text{Pm}=1$, the turbulence is instead transitional and becomes lesshomogeneous and isotropic upon increasing buoyancy effects. We find that thetransport of AM occurs radially outwards and is dominated by the Maxwellstresses when stratification is large enough. The associated turbulentviscosity decreases when buoyancy effects strengthen and scales with the squareroot of the ratio of the rotation rate to the Brunt-V\"ais\"al\"a frequency,predicting that, for example, red giant cores may reach a state of uniformrotation in a few thousand years. A passive scalar allows us to study thetransport of chemical elements. The chemical turbulent diffusion coefficientscales with stratification similarly to the turbulent viscosity but is lower inamplitude as suggested by recent stellar evolution models of low mass stars.

Angular momentum and chemical transport by azimuthal magnetorotational instability in radiative stellar interiors