Axion dark matter and 21cm line signal
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- The document discusses using 21cm forest observations to constrain properties of ultra-light dark matter particles like axions. - 21cm forest observations can probe particle masses up to 10^-19 eV, 3 orders of magnitude higher than Lyman-alpha forest observations. - Fisher forecast analysis suggests 21cm forest observations could probe ultra-light particle masses around 10^-20 eV and particle fraction values around 0.3. - Ongoing work is studying effects of isocurvature fluctuations from breaking the Peccei-Quinn symmetry on 21cm forest observations.
Axion dark matter and 21cm line signal
- 1. Constraining the nature of ultra-light dark matter particles with 21cm forest Hayato Shimabukuro (Yunnan university,SWIFAR) Collaborate with K.Ichiki and K.Kadota References: Shimabukuro et al. PRD 101,Iss.4,043516 (2020) (astro-ph/1910.06010) Kadota et al. JCAP 1406 (2014) 011 (astro-ph/1312.1898) Shimabukuro et al. PRD 90 Iss.8, 083003 (2014) (astro-ph/1403.1605 )
- 2. Introduction •ultra-light particle (e.g. axion) In QCD, it is known that there exists the term that violates CP symmetry in Lagrangian. However, experiments show that QCD conservers the CP symmetry. In order to conserve CP symmetry, Peccei-Quinn(PQ) symmetry was introduced (Peccei &Quinn, 1977). As the result of breaking PQ symmetry, axion like ultra-light particles (ULPs) are generated. The ULP is one of the candidates of dark matter.
- 3. Introduction What is the property of ULP?? In our work, we focus on mass and ratio of ULP. mu, fu What is current constraint on ULP from cosmological observations? Lyman-alpha forest Shaded regions are excluded Lyman-alpha observation can explore mu ⇠ 10 22 eV (k ⇠ 10Mpc 1 ) (Iršič et al 2017)
- 4. The effect of ULPs on P(k) P(k) starts to be suppressed at higher k as the mass of ULPs becomes larger. If we can explore higher k, we can study larger mass of ULPs. P(k) is suppressed inside Jeans scale because the pressure of ULPs prevents matter fluctuations from growing.
- 5. wavenumber .vs. mass Bullock et al (2017)
- 6. Minihalo Minihalo Minihalos are collapsed objects with Tvir 104 K If virial temperature is less than 10ˆ4K, atomic hydrogen cooling is inefficient. Instead of atomic cooling, gas cools by hydrogen molecular cooling. Insufficient cooling, insufficient star formation. Mvir . 108 M
- 7. 21cm forest Background source HI cloud in minihalo Carilli et al 2002 21cm forest is 21cm absorption lines appeared in continuum spectrum due to intervened HI gas (e.g. IGM, minihalo). The depth of 21cm absorption lines is characterised by optical depth ⌧
- 8. The abundance of 21cm absorption lines The abundance of 21cm absorption lines per line of sight. Smaller mass and larger fraction of ULPs suppress the number of 21cm absorption lines much more. @z=10
- 9. The largest mass 21cm forest can probe We can probe up to mu ⇠ 10 19 eV for fu 0.5 If fu = 1 ,we also can probe up to mu ⇠ 10 19 eV 3 order of magnitude higher than Lya forest
- 10. Fisher forecast log10(mu/H0) = 12, 13, 13.5 fu = 0.2@ fu = 0.2, 0.3, 0.4 @ log10(mu/H0) = 13
- 11. Fisher forecast The pivot scales of the ULP parameters that 21cm forest can probe is around (log10(mu/H0), fu) = (13, 0.3) (mu ⇠ 10 20 eV)
- 12. Summary&On-going work • The effect of axion like ultra-light particle is remarkable at smaller scales of matter power spectrum • We suggest the 21cm forest to probe the nature of such ULPs • The 21cm forest can probe much smaller scales than Lyman alpha forest • We found that we can probe m_u sim 10ˆ{-20}eV by 21cm forest. • Currently, we have been studying the effect of isocurvature fluctuations generated by breaking PQ symmetry after inflation via 21cm forest (Shimabukuro, Ichiki,Kadota in prep). • Any good idea?
- 13. Backup
- 14. Minihalo properties ⌧⌫ = 3hpc3 A10 32⇡kB⌫2 21 Z Rmax Rmax dR nHI(r) TS(r) p ⇡b(r) exp ✓ v2 (⌫) b2 ◆ Optical depth The number of absorption lines
- 15. Fisher forecast For more quantitatively estimation, we perform Fisher forecast. Fisher matrix Likelihood function The number of 21cm absorption lines
- 16. Minimum optical depth The minimum optical depth depends on the brightness of back ground sources.