Quest for CMB spectral distortions to probe the scalar-induced gravitational wave background interpretation of pulsar timing array data

One of the favored explanations for the recently observed stochastic gravitational wave background by NANOGrav's Pulsar Timing Array (PTA) measurements are primordial fluctuations sourcing gravitational waves. These fluctuations also cause small-scale spectral distortions in the CMB. The authors show how these can be measured in future experiments like PIXIE and constrain the scalar-induced interpretation of the PTA data. It will also distinguish it from alternative explanations of the NANOGrav signal like black holes, etc., that do not predict any significant spectral distortion.