Radiative symmetry breaking from the on-shell perspective

Abstract

Models with classical scale symmetry, which feature radiative symmetry breaking, generically lead to a supercooled first-order phase transition in the early Universe resulting in a strong gravitational-wave signal, potentially observable by LISA. This is thanks to the absence of mass terms in the potential and the resulting logarithmic structure of the zero-temperature effective potential. It is known that imposing a symmetry at classical level does not prohibit breaking it by quantum corrections. In the case of scale symmetry, a mass term can in principle appear through renormalisation. This is not the case in the commonly used $\overline{\mathrm{MS}}$ or Coleman-Weinberg schemes. In this work, we renormalise a scale-invariant model in the on-shell scheme to check whether parameterising it with the physical masses will introduce mass terms to the potential. We find that indeed mass terms appear for an arbitrary choice of the physical masses. However, we formulate an on-shell condition for radiative symmetry breaking, sufficient and necessary for the cancellation of mass terms in the renormalised potential, yielding a logarithmic potential needed for supercooled phase transitions.