Extra-tensor-induced origin for the PTA signal: No primordial black hole production

Understand

Recently, pulsar timing array (PTA) collaborations announced evidence for an isotropic stochastic gravitational wave (GW) background.

• The origin of the PTA signal can be astrophysical or cosmological.
• In the latter case, the so-called secondary scalar-induced GW scenario is one of the viable explanations, but it has a potentially serious issue of the overproduction of primordial black holes (PBHs) due to the enhanced curvature perturbation.
• In this letter, we present a new interpretation of the PTA signal.