On the QCD Axion Potential in Fried's QCD Functional Formalism

Abstract

We examine the QCD axion potential in Fried's nonperturbative QCD functional formalism. The axion is introduced in the standard way through (\Theta=\theta_{\rm QCD}+a/f_a). The question addressed is how the resulting (\Theta)-dependence of the QCD vacuum energy is represented after the effective-locality reduction of the gluonic degrees of freedom. The construction is organized around two nonperturbative quantities: the Fried chiral condensate (\Sigma_{\rm F}=-\langle\bar q q\rangle_{\rm F}), generated by the scalar/pseudoscalar projection of the effective-locality kernel, and the pure-glue topological stiffness (A_{\rm F}=\chi_{\rm YM}^{\rm F}), represented in the Halpern formulation by a CP-odd self-dual/anti-self-dual curvature. Under these assumptions, [ \chi_{\rm top}^{\rm F} ====================== \left[ A_{\rm F}^{-1} + \sum_f (m_f\Sigma_{\rm F})^{-1} \right]^{-1}, \qquad m_a^2f_a^2=\chi_{\rm top}^{\rm F}. ] This expression has the expected heavy-quark, light-quark, and massless-quark limits. In a separable scalar/pseudoscalar approximation, (\Sigma_{\rm F}=N_cr\Lambda_{\rm EL}^3 I(r)/(4\pi^2)), with (r=M_0/\Lambda_{\rm EL}) fixed by (1=\alpha_\chi^{\rm F}J(r)). The result is conditional: a complete first-principles derivation requires computing (\Sigma_{\rm F}) and (A_{\rm F}) from the full Fried--Gabellini--Grandou--Tsang--Sheu measure. We also note that the Fried-QCD contribution to a multi-axion mass matrix is rank one; additional massive axion-like species require additional independent topological sectors.