Partially flavour non-universal $U(1)$ and radiative fermion masses

Abstract: We investigate an extension of the Standard Model with a partially flavour non-universal abelian gauge symmetry that enables radiative mass generation for lighter fermions. With flavour-universal charges for the first two generations, gauge-induced loop corrections generate second-generation masses while keeping the first generation massless. Small first-generation masses can arise from subdominant scalar loops within this framework. A single anomaly-free $U(1)$ is sufficient for a realistic model, and the partial universality relaxes the gauge boson mass bound from several thousand TeV to about 200 TeV compared with previous frameworks of this type. We also identify an alignment limit matching the lightest scalar to the observed Higgs and compute its couplings with the fermions, which largely agree with Standard Model values but show testable deviations.