Squark contributions to Higgs boson masses in the next-to-minimal supersymmetric standard model

Abstract Within the context of an effective potential formalism we calculate the contribution to Higgs boson masses in the next-to-minimal supersymmetric standard model from squark loops. We then supplement a previously performed renormalisation group analysis of the Higgs sector of this model with these results in order to determine the shift in the bound on the lightest CP -even Higgs boson mass as a result of squark effects. The improved bound on the lightest neutral CP -even Higgs boson mass, including squark contributions, is m h ⩽ 146 (139, 149) GeV for m t = 90 (140, 190) GeV. For m t = 190 GeV squark effects contribute 23 GeV to the bound, with smaller contributions for small m t values.