Multiple ALPs and enhanced echoes

TL;DR

This paper investigates how multiple axion-like particles (ALPs) influence echo signals, revealing that coherent ALP ensembles can significantly amplify echoes, while incoherent phases suppress them, impacting detection strategies.

Contribution

It extends the single ALP echo model to multiple ALPs, deriving new equations and showing how coherence affects echo amplification and experimental detection prospects.

Findings

Echo power scales with the number of ALPs in coherent configurations.

Small mass splittings between ALPs enhance echo amplification.

Incoherent phases suppress echo signals, making detection more challenging.

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 coupling 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 projected bounds discussed earlier in literature. Small mass splittings between the ALPs further increase this amplification, even for a N = 2 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. 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.