Implications for New Physics from Fine-Tuning Arguments: II. Little Higgs Models

We examine the fine-tuning associated to electroweak breaking in Little Higgsscenarios and find it to be always substantial and, generically, much higherthan suggested by the rough estimates usually made. This is due to implicittunings between parameters that can be overlooked at first glance but show upin a more systematic analysis. Focusing on four popular and representativeLittle Higgs scenarios, we find that the fine-tuning is essentially comparableto that of the Little Hierarchy problem of the Standard Model (which thesescenarios attempt to solve) and higher than in supersymmetric models. This doesnot demonstrate that all Little Higgs models are fine-tuned, but stresses theneed of a careful analysis of this issue in model-building before claiming thata particular model is not fine-tuned. In this respect we identify the mainsources of potential fine-tuning that should be watched out for, in order toconstruct a successful Little Higgs model, which seems to be a non-trivialgoal.Comment: 39 pages, 26 ps figures, JHEP forma