Tracing remnants of the baryon vector current anomaly in neutron radiative β-decay

We show that a triple-product correlation in the neutron radiative β-decay rate, characterized by the kinematical variable η ≡ (l_e × l_ν) ·k, where n(p) → p(p′) + ē(l_e) + ν̄_e(l_ν) + γ(k), isolates the pseudo-Chern-Simons term found by Harvey, Hill, and Hill as a consequence of the baryon vector current anomaly and SU(2)L×U(1)Y gauge invariance at low energies. The correlation appears if the imaginary part of the coupling constant is nonzero, so that its observation at anticipated levels of sensitivity would reflect the presence of sources of CP violation beyond the Standard Model. We compute the size of the asymmetry in n → pe^- ν̄_eγ decay as a function of the coupling, estimate the effect of Standard-Model final-state interactions, and discuss the role nuclear processes can play in discovering the effect.