# Black hole superradiance of self-interacting scalar fields

**Authors:** Masha Baryakhtar, Marios Galanis, Robert Lasenby, Olivier Simon  
**arXiv:** [2011.11646](https://arxiv.org/abs/2011.11646)  
**Date:** 2020-11-23  
**Summary page:** https://www.summarizepaper.com/en/paper/2011.11646v1/

## Key points

- Black hole superradiance is a powerful probe of light, weakly-coupled hidden sector particles
- Self-interactions of candidate particles like axions play a crucial role in shaping the evolution of the superradiant instability
- High self-couplings can lead to a saturation point with reduced level occupation numbers
- Quartic self-interactions dominate the evolutionary trajectory for most relevant models
- Researchers suggest that "bosenova" collapse may not manifest across a significant portion of astrophysical parameter space
- Gravitational wave signals related to black hole spin-down experience parametric suppression with increasing interactions, but new signals can emerge under moderate interaction conditions
- Scalar wave emission exhibits less suppression at elevated couplings and could be detectable through proposed axion dark matter experiments.

## Summary

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Black hole superradiance is a fascinating phenomenon that serves as a powerful probe of light, weakly-coupled hidden sector particles. In particular, candidate particles like axions often possess self-interactions that play a crucial role in shaping the evolution of the superradiant instability. Previous studies have pointed out that many analyses of spin-0 superradiance overlook significant self-interaction-induced processes. These processes result in energy exchange between quasi-bound levels and the emission of particles to infinity. Notably, for high self-couplings, the growth of superradiance reaches a saturation point characterized by a quasi-equilibrium configuration with reduced level occupation numbers. In their recent paper titled "Black hole superradiance of self-interacting scalar fields," authors Masha Baryakhtar, Marios Galanis, Robert Lasenby, and Olivier Simon delve into an intricate analysis of the dynamic interplay between spin-0 superradiance and self-interactions. The focus lies on quartic self-interactions, which dominate the evolutionary trajectory for most relevant models. The study explores various distinct parameter space regimes introduced by non-zero self-interactions, including scenarios where two or more bound levels are simultaneously populated. At higher couplings, the researchers confirm the fundamental concept of quasi-equilibrium saturation and provide compelling evidence suggesting that the anticipated "bosenova" collapse may not manifest across a significant portion of astrophysical parameter space. In comparison to gravitational superradiance, the team observes that signals related to gravitational wave "annihilation" and black hole spin-down experience parametric suppression with increasing interactions. However, they also identify new gravitational wave "transition" signals that can emerge under moderate interaction conditions. Additionally, they highlight a novel phenomenon involving scalar wave emission which exhibits less suppression at elevated couplings. Furthermore, if these particles exhibit Standard Model interactions, coherent and monochromatic axion wave signals stemming from black hole superradiance could potentially be detectable through proposed axion dark matter experiments. This comprehensive analysis sheds light on the intricate dynamics at play in spin-0 superradiance with self-interactions and underscores its significance as a valuable tool for exploring hidden sector particles within black hole environments.