Natural and model-independent conditions for evading the limits on the scale of new physics

TL;DR

The paper addresses how model-independent bounds on the scale of new physics, $\Lambda$, can be invalidated if the heavy sector respects a symmetry that prevents leading virtual effects. It adopts an effective field theory approach to show that, in decoupling, weakly coupled scenarios, the leading beyond-Standard-Model contributions come from dimension-5 and dimension-6 operators, with tree-level generated operators dominating unless forbidden by symmetry. It identifies concrete mechanisms—such as MSSM-like R-parity and universal extra dimensions—and gauge symmetry constraints that eliminate tree-level operators, causing heavy physics to be loop-suppressed and potentially much harder to detect indirectly. The practical implication is that a class of heavy-physics models could evade precision constraints while remaining accessible to direct production at colliders, significantly impacting how current and future data are interpreted. These insights underscore the need to consider symmetry-protected, non-tree-level scenarios when inferring limits on new physics scales from precision measurements.

Abstract

I argue that the limits on this quantity obtained using model-independent parameterizations contain an tacit assumption that could be invalidated under a variety of situations. As a specific example, existing limits on $Λ$ would be decreased by at least an order of magnitude if the underlying physics has a symmetry under which all \sm particles are singlets but none of the heavy excitations are. In this case current experiments would see no clear indications of new physics using precision measurements while future colliders capable of directly producing the heavy particles would only occur in pairs.