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Searching for Axion-Like Particles using Black Holes and Pulsars

This study explores the search for axion-like particles (ALPs) using black holes and pulsars. It discusses the theory motivations, search strategies, and scenarios that can help identify these particles. The study also examines the impact of axion clouds on the position angle change and the expected sensitivity of the Event Horizon Telescope. Additionally, it investigates the potential role of pulsars in measuring linearly polarized photons for the detection of axion dark matter.

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Searching for Axion-Like Particles using Black Holes and Pulsars

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  1. Searching for axion-like particles using black holes and pulsars Yue Zhao University of Utah Yifan Chen, Jing Shu, Xiao Xue, Qiang Yuan, and Y.Z. arXiv:1905.02213 [hep-ph] Tao Liu, George Smoot, Y.Z. arXiv:1901.10981 [astro-ph.CO]

  2. Current Status of Particle Physics:

  3. Left-over problems: • The identity of dark matter • Gauge hierarchy problem • Strong CP problem QCD axion • The identity of inflaton field • Baryogenesis • Cosmological constant • • •

  4. Left-over problems: • The identity of dark matter misalignment mechanism • Gauge hierarchy problem relaxion • Strong CP problem QCD axion • The identity of inflaton field • Baryogenesis can be related to axion • Cosmological constant • • •

  5. Theory motivations: Strong CP-problem: Introduce axion field: Couplings: axion-gluon-gluon axion-photon-photon axion-fermion-fermion < 10^-11

  6. Theory motivations: Axion like particles (ALPs) generically appear in compactification models (6D) (5D) (4D) Gauge symmetry in higher dim becomes shift symmetry in 4D. One particular linear combination is QCD axion axion-gluon-gluon coupling mass is directly related to axion coupling Axion-like particle does not obey mass-coupling relation. Axion are excellent ultralight DM candidates.

  7. Search strategies: • axion-gluon-gluon coupling: CASPEr QCD phase transition inside neutron stars • axion-photon-photon coupling: ADMX CAST ALPS • axion-fermion-fermion coupling: stellar cooling absorption in superconductor

  8. Search strategies: • axion induced birefringent effect The condensation of a CP-odd particle distinguishes helicities of a photon

  9. Search strategies: • axion induced birefringent effect different phase velocities for +/- helicities A linearly polarized photon can be decomposed into the super-position of photons with +/- helicities. change of position angle

  10. Search strategies: A region with: a concentration of axion field axion field is an oscillating background field + source for linearly polarized photon the position angle, at emission, should be stable Search for: • position angle oscillates with time • study the axion induced position angle change as a function of spatial distribution. (extended light source) Scenarios: EHT-SMBH & pulsars measurements

  11. Event Horizon Telescope: telescope array at radio frequency around the Earth

  12. Event Horizon Telescope: Image of the supermassive black hole at the center of the elliptical galaxy M87, for four different days.

  13. Event Horizon Telescope: Black holes measured: M87*: 16 Mpc, 10^9 solar mass 10^13 m, 10^-20 eV 10^5 s, a=0.99 Sgr A*: 8 kpc, 10^6 solar mass 10^10 m, 10^-17 eV 100 s, a=? Excellent angular resolution: ~ 20 micro-as! resolve features ~ BH size

  14. Event Horizon Telescope: Accretion disk around SMBH gives linearly polarized radiation. Millimeter wavelength: optimal for the position angle measurement! measure Sgr A* A subset of EHT has achieved a precision at 3 degrees!

  15. Black hole superradiance: Superradiance condition When λa ∼ GM: a rapidly rotating black hole loses: energy + angular momentum axion cloud will be produced around BH energy in axion cloud can be comparable to BH mass!

  16. Black hole superradiance: A gravitational bound state between BH and axion cloud. Very similar to the hydrogen solution: reduce to in spherical/non-relativistic limit Axion cloud populates more efficiently at lower l-mode. m=l mode is more efficient than other m-levels.

  17. Black hole superradiance: similar to Hydrogen atom energy spectrum non-relativistic ~ 10^-7 – 10^-10 sizable axion cloud has been built during the age of galaxies

  18. Black hole superradiance: The ring from EHT has a radius comparable to the peaking radius of the axion cloud

  19. Axion cloud in non-linear region: axion Lagrangian including self-interaction: take slowly varying function gravitational potential non-relativistic limit: leading self-potential term

  20. Axion cloud in non-linear region: axion self-interaction becomes important when gravitational potential ~ self-interaction potential two possible consequences: bosenova: a drastic process which explodes away axion cloud steady axion outflow to infinity numerical simulation has been performed: H. Yoshino and H. Kodama, Prog. Theor. Phys. 128, 153 (2012), etc

  21. Axion cloud in non-linear region: In either scenario, the amplitude of the axion cloud remains O(1) of its maximal value for most of the time ~ O(1)

  22. Axion cloud induced position angle change: additional loop suppression to translate fa to axion-photon coupling

  23. Axion cloud induced position angle change: • temporal dependence for a fixed position • spatial dependence for a fixed time

  24. EHT expected sensitivity:

  25. Axion dark matter: Axion is an excellent DM candidate! Can be produced by misalignment mechanism. Ultralight axion DM is expected to have a soliton core. Pulsars are commonly producing stable linearly polarized photons. (Milli)-second pulsars may be largely populated near the galactic center. Measurements on pulsar radiation provides an excellent tool to study axion DM.

  26. Axion dark matter: soliton solution NFW profile

  27. Pulsar measurements: Most measurements are in radio-wave band. Excellent on polarization measurements. The properties of each pulse are not completely the same. After averaging O(100) pulses, properties become stable. Only a few pulsars are found near our galactic center. VLA is expected to find many more. Position angle accuracy ~ O(1) degree.

  28. Sensitivity by pulsar measurements: Significant enhancement is expected by correlating many pulsars.

  29. Conclusion Astrophysics provides excellent probes to search for axion! Supermassive Black holes: A dense axion cloud can build up near by SMBHs. Accretion disk emits linearly polarized photons. EHT resolves the fine features near SMBHs. EHT can provide measurements on position angles. Probe the existence of axion clouds by EHT. Pulsars: Axion DM is concentrated near galactic center. Pulsars emits linearly polarized photons. Probe axion DM by pulsar measurements.

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