Figure 1: The topological charge distribution of one of the new two-flavour configurations. This image was selected as the winner in the Particle and Nuclear Physics category of the DiRAC 2022 Research Image Competition.

Nearly-conformal gauge theories have been singled out as potential avenues for new physicics that can explain electroweak symmetry breaking in the standard model. Among them, SU(2) gauge theory with one or two adjoint fermions have shown good indications of being nearly conformal. Project dp208 has set out to probe closer to the continuum limit of these gauge theories than had been done in previous work, to observe whether previous tentative observations of near-conformality continue to hold.

We approach the continuum by increasing the value of the lattice inverse coupling β.

Figure 2: Fits of the Dirac mode number spectrum of the one-flavour theory, showing the mass anomalous dimension of the theory decreasing as the lattice coupling β is increased.

As we do this in the theory with Nf=1 fermion flavour, we see that the curcial quantity indicating near-conformality, the anomalous dimension, which has been measured both via the Dirac mode number (Figure 2) and via hyperscaling fits of spectral quantities, continues to decrease with increasing β. We also see that the previously observed trend—that the scalar is the lightest state in the spectrum, lighter than the pion that would be predicted to be the lightest state in chiral perturbation theory—persists (Figure 3), and is indeed enhanced at larger values of β.  Our results confirm the interesting properties of the model and at the same time highlight the need to perform further calculations in order to gain a clearer understanding of its large-distance behaviour. 

Figure 3: Mass spectrum of the one-flavour theory, showing the scalar remaining the lightest state observed at the new finer lattice spacings studied.

In the two-flavour theory, our early results were contaminated by finite-volume effects and poor plateaux, which are more severe than they were in our previous runs used for calibration. While computations on the largest volume are still ongoing, they have already produced a high-resolution view of topological charge density of one field configuration from this theory (Figure 1).

Categories: 2022 Highlights