Conformal vs confining scenario in SU(2) with adjoint fermions

TL;DR

This study investigates the mass spectrum and confinement properties of an SU(2) gauge theory with adjoint fermions, providing insights into whether the theory is conformal or confining in the massless limit.

Contribution

It offers lattice measurements of low-lying states across different fermion masses and discusses a strategy to distinguish conformal from confining phases.

Findings

Lightest glueballs are lighter than the lightest mesons even for light fermions.

String tension varies significantly with fermion mass and diminishes near the chiral limit.

Implications for the phase of the theory in the massless limit are discussed.

Abstract

The masses of the lowest-lying states in the meson and in the gluonic sector of an SU(2) gauge theory with two Dirac flavors in the adjoint representation are measured on the lattice at a fixed value of the lattice coupling $\beta = 4/g_0^2 = 2.25$ for values of the bare fermion mass $m_0$ that span a range between the quenched regime and the massless limit, and for various lattice volumes. Even for light constituent fermions the lightest glueballs are found to be lighter than the lightest mesons. Moreover, the string tension between two static fundamental sources strongly depends on the mass of the dynamical fermions and becomes of the order of the inverse squared lattice linear size before the chiral limit is reached. The implications of these findings for the phase of the theory in the massless limit are discussed and a strategy for discriminating between the (near--)conformal and the confining scenario is outlined.