From carriers and virtual excitons to exciton populations: Insights into time-resolved ARPES spectra from an exactly solvable model

We calculate the {\em exact} time-resolved ARPES spectrum of a two-band model semiconductor driven out equilibrium by resonant and nonresonant laser pulses, highlighting effects phonon-induced decoherence relaxation. Resonant} excitations initially yield replica valence} band shifted upward energy exciton peak in photoabsorption. This phase is eventually destroyed decoherence: valence-band lowers Stokes shift, locating at photoluminescence, its width grows due to phonon dressing. Nonresonant} map conduction band. Then electrons transfer their excess lattice bind with holes left behind form excitons. In this relaxed regime conduction} appears inside gap. At fixed momentum lineshape conduction-band versus photoelectron proportional wavefunction "energy space" it highly asymmetric. Although represents an oversimplified description real materials highlighted features are qualitative nature; hence they provide useful insights into spectra physical interpretation.