Searching for Cold Dark Matter Axions with the SKA

1. Searching for Cold Dark Matter Axionswith the SKA Katharine Kelley 3 June 2019 Supervisor Prof. Peter Quinn

2. Agenda • Introduction • Where were we two years ago – what’s changed? • The challenge with astrophysical observation • Non-resonant conversion • Astrophysical magnetic fields • Approach • Results: Unique Spectral Features • Results: Central Molecular Zone • Pulsars: Key Considerations and Results • Summary A Radio Astronomy Search for Axion Dark Matter

3. Introduction A Radio Astronomy Search for Axion Dark Matter

4. Introduction • Compton Frequency • 10-6 – 10-3eV0.2 – 200GHz A Radio Astronomy Search for Axion Dark Matter

5. Axion-two photon coupling • Non-resonant conversion of a cold axion: • momentum required from the virtual photon to satisfy E=pc- direction of propagation therefore perpendicular to the field • Dependency on the spatial profile of the field • Non-static fields may contribute energy to the interaction • Changes in environment may impact rate • Resonant conversion: • Axion and real photon have the same properties • Field transverse to propagation of axion contributes to conversion • Astrophysically the real photon requires an ‘effective mass’ to balance energy - momentum • Direction of propagation of real photon the same as the axion A Radio Astronomy Search for Axion Dark Matter

6. New Radio Telescopes 0.7 – 1.8GHz 0.4 – 2.5 GHz 2.5 – 13.8 GHz 0.4 – 13.8 GHz Axion Mass: ~ 1.7 – 57 μ eV A Radio Astronomy Search for Axion Dark Matter

7. New Radio Telescopes SKA1-low: 130,000 dipoles 70 – 350 MHz MWA 70 – 300 MHz A Radio Astronomy Search for Axion Dark Matter

8. Why the SKA? A Radio Astronomy Search for Axion Dark Matter

9. 20172019 A Radio Astronomy Search for Axion Dark Matter

10. Radio Telescopes • Observations of the Central Molecular Zone • Turbulent magnetic fields • Non-resonant axion conversion • Magnetic energy over millimetre to metre length scales A Radio Astronomy Search for Axion Dark Matter

11. Photon Production Rate Static Field Non-Static Field Very Challenging Static Field 1 – 1,000 m-1 Presentation Title (Edit in File > 'Page Setup’ > ‘Header/footer’)

12. Approach A Radio Astronomy Search for Axion Dark Matter

13. Astrophysical Magnetic Fields Central Molecular Zone: 130 micro G ISM (MW and M31): 50 micro G decaying r-1 Galaxy cluster: Core ~ 4 micro G Pulsars: B < 109 T A Radio Astronomy Search for Axion Dark Matter

14. Astrophysical Magnetic Fields Galactic Centre: R ~ 1 kpc B ~ 10-3 G ISM: R ~ 10s kpc B ~ 10-6G Galaxy clusters: R ~ 1000s kpc B ~ 10-6 G Pulsars: R ~ 1 km B ~ 109 - 1012G A Radio Astronomy Search for Axion Dark Matter

15. Dark Matter Density A Radio Astronomy Search for Axion Dark Matter

16. Results:Unique Spectral Features A Radio Astronomy Search for Axion Dark Matter

17. Natural Spectral Features • Unique spectral features • Strength proportional to: • - dark matter density • - square of the magnetic field • - volume observed • - integration time • - distance to source • Polarisation given by the B field – perpendicular to synchrotron radiation • Central frequency: • - 0.2 – 200 GHz for conversion in a static field • Maxwellian profile: axion velocity distribution in the frame of conversion • The frame of the B field sets the frame of conversion Frames of Reference A Radio Astronomy Search for Axion Dark Matter

18. Unique Spectral Profiles Central Molecular Zone Galaxy Cluster Andromeda Interstellar Medium A Radio Astronomy Search for Axion Dark Matter

19. Results: Central Molecular Zone A Radio Astronomy Search for Axion Dark Matter

20. CMZ: Low Density Plasma A Radio Astronomy Search for Axion Dark Matter

21. Axion Coupling - CMZ A Radio Astronomy Search for Axion Dark Matter

22. Pulsars: Key considerations and Results A Radio Astronomy Search for Axion Dark Matter

23. Pulsars • Density: 1015 – 1016 m-3 • Conversion frame is rotating • Non-resonant vs resonant conversion • Solar dark matter density • Vacuum polarisation effect • Non-static components of the field • ~ 1,000 ATNF vs 107 • Same frame as the Earth Presentation Title (Edit in File > 'Page Setup’ > ‘Header/footer’)

24. Flux and Spectral Profiles Presentation Title (Edit in File > 'Page Setup’ > ‘Header/footer’)

25. Pulsars Presentation Title (Edit in File > 'Page Setup’ > ‘Header/footer’)

26. Summary • Non-resonant conversion very challenging due to scale of magnetic field • Best opportunity may be nearby pulsars, modelling shows 107 within 5kpc • Unique spectral profile for each observation could support identification • Very difficult to exclude regions of parameter space due to uncertainty over field structure • Could support identification if a detection is made in the laboratory • Investigation of unidentified spectral lines should continue • Neutron star mergers, binary stars, AGN A Radio Astronomy Search for Axion Dark Matter

27. Coma Cluster A Radio Astronomy Search for Axion Dark Matter

28. ISM: Milky Way A Radio Astronomy Search for Axion Dark Matter

29. ISM: Andromeda A Radio Astronomy Search for Axion Dark Matter