Axial coupling constant in a magnetic background

The nucleon axial coupling constant $g_A$ is calculated in the presence of an external uniform magnetic field using finite energy sum rules. correlation function proton, neutron and axial-vector currents both hadronic QCD sector. Once contribution form factor isolated, a double rule considered, i.e., usual contour integration for moments proton current. effects come mainly through in-medium current-nucleon constants $\lambda_N(B)$ thresholds $s_0(B)$ provided by nucleon-nucleon correlators. As result, decreases field.