Impact of an extra gauge interaction on naturalness of supersymmetry

Abstract: It is pointed out that in supersymmetric models with a new gauge symmetry under which the Higgs is charged, the fine-tuning of the electroweak symmetry breaking is relaxed due to suppression of the top Yukawa coupling at higher scales by a new large gauge coupling. We calculate the fine-tuning in an explicit model and find that the lower bounds on stops and gluino masses from the naturalness criterion are increased by several hundred GeV in comparison to the Minimal Supersymmetric Standard Model (MSSM). The fine-tuning is improved by one to two orders of magnitude as compared to the MSSM, as a consequence of both the suppression of the top Yukawa coupling and the additional tree-level contribution to the Higgs mass allowing for much lighter stops.