The functional renormalization group (FRG) approach for spin models relying on a pseudofermionic description has proven to be a powerful technique in simulating ground-state properties of strongly frustrated magnetic lattices. A drawback of the FRG framework is that it is formulated in the imaginary-time Matsubara formalism and thus only able to access static correlations, a limitation shared with most other many-body approaches. A description of the dynamical properties of magnetic systems is the key to bridging the gap between theory and neutron-scattering spectra. We take the decisive step of expanding the scope of pseudofermion FRG to the Keldysh formalism, which, while originally developed to address nonequilibrium phenomena, enables a direct calculation of the equilibrium dynamical spin structure factors on generic lattices in arbitrary dimensions. We identify the principal features characterizing the low-energy spectra of exemplary zero-, one- and two-dimensional spin-$1/2$ Heisenberg models as well as the Kitaev honeycomb model while identifying current limitations of the method that have to be improved upon.

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• Frustrated magnetism
• Magnetism
• Spin dynamics
• Functional renormalization group
• Heisenberg model
• Kitaev model
• Numerical techniques
• Spin lattice models