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We present a theory for Raman scattering on 2D quantum antiferromagnets. Themicroscopic Fleury-Loudon Hamiltonian is expressed in terms of an effective$O(3)$ - model. Well within the N\'eel ordered phase, the Raman spectrumcontains a two-magnon and a two-Higgs contribution, which are calculateddiagramatically. The vertex functions for both the Higgs and magnoncontributions are determined from a numerical solution of the correspondingBethe-Salpeter equation. Due to the momentum dependence of the Raman vertex inthe relevant $B_{1g}+E_{2g}$ symmetry, the contribution from the Higgs mode isstrongly suppressed. Except for intermediate values of the Higgs mass, it doesnot show up as separate peak in the spectrum but gives rise to a broadcontinuum above the dominant contribution from two-magnon excitations. Thelatter give rise to a broad, asymmetric peak at $\omega\simeq 2.44\, J$, whichis a result of magnon-magnon interactions mediated by the Higgs mode. The fullRaman spectrum is determined completely by the antiferromagnetic exchangecoupling $J$ and a dimensionless Higgs mass. Experimental Raman spectra ofundoped cuprates turn out to be in very good agreement with the theory onlywith inclusion of the Higgs contribution. They thus provide a clear signatureof the presence of a Higgs mode in spin one-half 2D quantum antiferromagnets.

Higgs Mode and Magnon Interactions in 2D Quantum Antiferromagnets from Raman Scattering