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Lectures on Light Particles and Compact Objects

Alessandro Lella, Jamie McDonald

Abstract

This document is based on lectures delivered at a recent COSMIC WISPers COST Action training school in Annecy in September 2025. They examine detection of weakly interacting slim particles (WISPs), specifically axions and high-frequency gravitational waves, with compact objects. These slightly expanded notes focus on searches for axion dark matter and axion-like particles with neutron stars, superradiance, white dwarfs and astrophysical searches for high-frequency gravitational waves. They are accompanied by a set of practical exercises. Comments on these notes are gratefully received.

Lectures on Light Particles and Compact Objects

Abstract

This document is based on lectures delivered at a recent COSMIC WISPers COST Action training school in Annecy in September 2025. They examine detection of weakly interacting slim particles (WISPs), specifically axions and high-frequency gravitational waves, with compact objects. These slightly expanded notes focus on searches for axion dark matter and axion-like particles with neutron stars, superradiance, white dwarfs and astrophysical searches for high-frequency gravitational waves. They are accompanied by a set of practical exercises. Comments on these notes are gratefully received.

Paper Structure

This paper contains 18 sections, 100 equations, 4 figures.

Table of Contents

  1. Introduction
  2. WISP Theory
  3. Black Hole and Stellar Superradiance
  4. WISP searches with Neutron Stars
  5. WISP impact on Neutron Star cooling
  6. Axion Detection in Neutron Star Magnetospheres
  7. WISP searches with White Dwarfs
  8. WISP signatures on the secular drift of the pulsation period
  9. WISP signatures on the luminosity function
  10. WISP signatures in photon spectra
  11. HFGWs and Compact Objects
  12. Hands-on tutorials
  13. Solution.
  14. $r<R.$
  15. $r > R$.
  16. ...and 3 more sections

Figures (4)

  • Figure 1: Diagrams contributing to the neutron electric dipole moment dark and hatched circles denote the CP odd and CP even interactions in eq. \ref{['eq:ChPTCPOdd']}, respectively.
  • Figure 2: Photon, neutrino and scalar cooling light-curves computed in the best fit model for the isolated NS J1605 derived in Ref. Fiorillo:2025zzx. The scalar emissivity is obtained by assuming a scalar-nucleon coupling $g_N=2\times10^{-13}$.
  • Figure 3: Schematic representation of the WD cooling process including photon (solid), neutrino (dotted) and axion (dashed) luminosities as well. Vertical dashed lines identify regions dominated by different kinds of energy sink. The figure also shows the position of the variable white dwarfs. Figure taken from Ref. Carenza:2024ehj with permission.
  • Figure 4: Panel A: Early luminosity functions based on data from Ref. 1988ApJ...332..891L (full circles), Ref. 1992MNRAS.255..521E (full squares), Ref. 1996Natur.382..692O (open triangles), Ref. 1998ApJ...497..294L (open diamonds) and Ref. 1999MNRAS.306..736K (open circles). Panel B: WDLFs obtained with the SCSS catalogue 2011MNRAS.417...93R (black crosses), the SDSS catalogue 2006AJ....131..571H (red squares), and from UV-excesses 2009AA...508..339K (blue crosses) normalized at $M_{\rm bol}\approx12$. Panel C: Luminosity function of WDs located within a 100 pc horizon based on the Gaia Early Data Release 3 2021AA...649A...6G. Figure taken from Ref. Carenza:2024ehj with permission.