Recent work shows not only the necessity of a 1/N c expansion to explain the observed mass spectrum of the lightest baryons, but also that at least two distinct large N c expansions, in which quarks transform under either the color fundamental or the two-index antisymmetric representation of SU(N c ), work comparably well. Here we show that the baryon magnetic moments do not support this ambivalence; they strongly prefer the color-fundamental 1/N c expansion, providing experimental evidence that nature decisively distinguishes among 1/N c expansions for this observable.

The Lee-Wick (LW) formulation of higher-derivative theories can be extended from one in which the extra degrees of freedom are represented as a single heavy, negative-norm partner for each known particle (N = 2), to one in which a second, positive-norm partner appears (N = 3). We explore the extent to which the presence of these additional states in a LW Standard Model affect precision electroweak observables, and find that they tend either to have a marginal effect (e.g., quark partners on T ), or a substantial beneficial effect (e.g., Higgs partners on the Zbb couplings).We find that precision constraints allow LW partners to exist in broad regions of mass parameter space accessible at the LHC, making LW theories a viable beyond-Standard Model candidate.

The Lee-Wick Standard Model at temperatures near the electroweak scale is considered, with the aim of studying the electroweak phase transition. While Lee-Wick theories possess states of negative norm, they are not pathological but instead are treated by imposing particular boundary conditions and using particular integration contours in the calculation of S-matrix elements. It is not immediately clear how to extend this prescription to formulate the theory at finite temperature; we explore two different pictures of finite-temperature LW theories, and calculate the thermodynamic variables and the (one-loop) thermal effective potential. We apply these results to study the LeeWick Standard Model and find that the electroweak phase transition is a continuous crossover, much like in the Standard Model. However, the high-temperature behavior is modified due to cancellations between thermal corrections arising from the negative-and positive-norm states.

We consider a recently-proposed model which posits the existence of composite dark matter, wherein dark "quarks" transforming as fundamentals under an SU (3) d gauge group undergo a confining phase and form dark baryons. The model attempts to explain both the O(1) relic density ratio, Ω dark /Ω baryon ∼ 5.4, as well as the asymmetric production of both dark and baryonic matter via leptogenesis. Though the solution of β functions for SU (3)c and SU (3) d constitutes the main drive of the model, no threshold corrections were taken into account as the renormalization scale crosses the mass threshold of the heavy new fields in the model. We extend this work by explicitly calculating the threshold-corrected renormalization-group flow for the theory using an effective-field matching technique. We find that the theory has a much wider range of applicability than previously thought, and that a significant fraction of models (defined by the number of fields contained therein) is able to account for the observed relic density.

Inspired by the Lee-Wick higher-derivative approach to quantum field theory, Grinstein, O'Connell, and Wise have illustrated the utility of introducing into the Standard Model negativenorm states that cancel quadratic divergences in loop diagrams, thus posing a potential resolution of the hierarchy problem. Subsequent work has shown that consistency with electroweak precision parameters requires many of the partner states to be too massive to be detected at the LHC. We consider the phenomenology of a yet-higher derivative theory that exhibits three poles in its bare propagators (hence N = 3), whose states alternate in norm. We examine the interference effects of W boson partners on LHC scattering cross sections, and find that the N = 3 LWSM already makes verifiable predictions at 10 fb −1 of integrated luminosity.