Nonflat bands and chiral symmetry in magic-angle twisted bilayer graphene

In this work, we study an interacting tight-binding model of magic-angle twisted bilayer graphene (MATBG) with a twist angle of $1.{05}^{\ensuremath{\circ}}$. We derive effective theories based on a mean-field normal state at charge neutrality, thereby including the renormalizations coming from integrating out high-energy modes. In these theories, the flat bands display a sizable increase of the bandwidth, suggesting the renormalization of the magic angle. Additionally, the corresponding wave functions flow towards the limit of perfect particle-hole symmetry and sublattice polarization (the ``chiral'' limit). We further represent the flat bands in the ``vortex Chern'' basis and discuss the implications on the dynamics, regarding the ``flat'' and chiral symmetries of MATBG, as manifested in the symmetry-broken states at neutrality.