Novel echoes from black holes in conformal Weyl gravity

We reveal a novel class of echoes from black holes in conformal Weyl gravity and show that they are generated due to the large-scale structure of the cosmos, rather than near-horizon modifications of black holes as well as wormhole spacetimes. To this end, we take into account the evolution of a massive scalar perturbation on the background geometry of conformal Weyl black holes and show that the corresponding effective potential enjoys a double-peak barrier against the incident scalar waves. We perform the calculations for the time evolution profiles of scalar perturbations to understand how the linear term in the metric function and the cosmological constant produce echoes. The Prony method is also employed to calculate the quasinormal frequencies of the early-stage quasinormal ringing phase.