UKQCD Beyond Standard Model

UKQCD Beyond Standard Model

Novel strong interactions might provide an explanation for the mechanism of electroweak symmetry breaking. In order for a strong dynamics to be able to explain the electroweak breaking, the theory must be near the onset of the conformal window and possess an anomalous dimension of the chiral condensate of order one. Furthermore, after the experimental observation of a light Higgs and no unexpected particle, a crucial requirement for a Beyond the Standard Model (BSM) theory is the existence of a light scalar in the spectrum.

The a priori interesting theories can be divided into two classes: infrared conformal theories, which are inside the conformal window and are scale-invariant in the limit of infinite distance, and walking theories, showing confinement at large distance, but behaving as infrared conformal theories for a wide range of intermediate scales. Theories in both categories can be used to construct BSM models without violating the existing constraints from precision measurements.

 Figure 1. Selected spectral states of the theory in lattice units.

Our investigations of the SU(2) with one adjoint fermion model show that this theory displays crucial dynamical features attributed to phenomenologically viable models of electroweak symmetry breaking (see figure 1 of the spectrum from arXiv:1311.4155).

Indeed simulations performed for values of the couplings in the region connected with the continuum indicate that the system is close to the edge of the conformal window, with an anomalous dimension close to one and a scalar particle much lighter than the other particles in the spectrum.

At the present stage this is the only system showing such intriguing features. Moreover, our calculation provides the first evidence that concrete models with the non-perturbative features mandated by experimental constraints do exist.