# The derivative of the topological susceptibility at zero momentum and an estimate of $\eta^1$ mass in the chiral limit

Pasupathy, J and Singh, JP and Singh, RK and Upadhyay, A (2005) The derivative of the topological susceptibility at zero momentum and an estimate of $\eta^1$ mass in the chiral limit. [Preprint]

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The anomaly-anomaly correlator is studied using QCD sum rules. Using the matrix elements of anomaly between vacuum and pseudoscalars \pi, \eta and $\eta^1$, the derivative of correlator $Xâ�²^1(0)$ is evaluated and found to be $\approx 1.82 \times 10^-^3 GeV^2$. Assuming that $Xâ�²^1(0)$ has no significant dependence on quark masses, the mass of Î·â�² in the chiral limit is found to be \approx723 MeV. The same calculation also yields for the singlet pseudoscalar decay constant in the chiral limit a value of \approx 178 MeV.