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The Kβ emission and K-absorption spectra of sulfur in Ag2S are carefully measured and compared with the sulfur Kβ emission and K-absorption spectra of Cu1.8S reported previously. The spectra of Ag2S clearly show the existence of the energy gap in semiconducting Ag2S in contrast to the metallic phase Cu1.8S where the Kβ band edge overlaps with the K absorption edge. The sulfur-Kβ emission spectrum of Ag2S consists of two prominent peaks. The intensity of the high-energy peak is much greater than that of the low-energy peak, contrary to the sulfur-Kβ emission spectrum of Cu1.8S. It is suggested that the bottom of the conduction band of Ag2S arises mainly from the sulfur 4p states.

The light-front Hamiltonian, path integral and BRST formulations of the Chern-Simons-Higgs theory in (2 + 1) dimensions are investigated under appropriate gauge fixing.

The sulfur-Kβ emission spectra in fluorescence from alkaline-earth sulfides MgS, CaS, SrS and BaS are measured with a high-resolution two-crystal vacuum spectrometer. The spectra consist of a prominent peak accompanied by a low-energy shoulder or high-energy satellite. In going from MgS to BaS, the width of the main peak is gradually narrowed and the presence of the shoulder gradually becomes unclear in contrast to the appearence of the satellite.

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