Two-loop renormalisation and Higgs phenomenology in the five-dimensional MSSM

Abstract: The five-dimensional Minimal Supersymmetric Standard Model (5D MSSM) provides an attractive framework in which power-law renormalisation group evolution naturally generates a sizeable trilinear stop coupling, allowing the observed Higgs boson mass to be reproduced without requiring too heavy a supersymmetric spectra. In this work we present a comprehensive two-loop analysis of the 5D MSSM, deriving the complete renormalisation group equations governing the gauge, Yukawa and soft supersymmetry-breaking sectors and examining the perturbative consistency of the theory. Particular attention is given to the ultraviolet behaviour of the model, where we demonstrate that the potentially dangerous leading two-loop contributions cancel as a consequence of the underlying $\mathcal{N}=2$ supersymmetry, leaving a well-behaved perturbative expansion. Building upon this framework, we compute the radiatively corrected Higgs effective potential including the complete Kaluza-Klein (KK) contributions through KK resummation, and investigate the resulting implications for the Higgs sector. The phenomenological viability of the model is subsequently explored through detailed numerical studies of the Higgs boson mass, electroweak precision observables, Higgs coupling modifiers and signal strengths, allowing constraints on the compactification scale and supersymmetric parameter space to be established. We find that the inclusion of the two-loop corrections preserves the characteristic power-law behaviour of the five-dimensional theory while yielding a phenomenologically viable parameter space consistent with current collider and precision measurements.