Echoes in multi-ALP scenarios

Abstract

We present a theoretical study of axion echoes in the context of multiple ALP models. We begin by reviewing the single ALP case, deriving the conditions for resonance and echo formation. Starting from a set of N ALPs coupled to the photon, we then derive the relevant echo equations for both coherent and incoherent configurations. In the former case, we show that the echo power scales with N leading to sharper amplification and potentially improving sensitivity estimates discussed earlier in literature. Small mass splittings between the ALPs further increase this amplification, even for a N = 2 case. In the incoherent scenario, we show that the random phases lead to a suppression of the echo power, eventually resulting in observable signals akin to or even weaker than the single ALP case. We also outline the potential experimental implications of our results and discuss prospects for detecting these echoes in a wide range of ALP masses.