DM overproduction Excluded by X-ray observations. Dark matter mass MDM [kev]

Light Dark Matter Kenji Kadota IBS Center for Theoretical Physics of the Universe (CTPU) Institute for Basic Science, Korea Ø Two concrete examples ü Sterile neutrino DM Production mechanism ü Axion(-like) Particle Radio (SKA-like) survey Ø Conclusion

scales: 0.5/h-50/h com. Mpc 1.00 MIKE&HIRES Age of the Universe: 1-3 Gyr F 2 (k) z=5.4 0.10 z=5 z=4.6 z=4.2 A concrete example for the warm dark matter: Sterile Neutrinos z=4.0 z=3.8 z=3.6 z=3.4 z=3.2 best fit z=3 SDSS z=2.8 Dodelson-Widrow mechanism: Thermal active neutrinos conversion to sterile neutrinos 0.01 WDM thermal relic 2keV z=2.6 z=2.4 z=2.2 0.001 0.100 1 MNN 2 0.010 L = ynlhk (s/km) y H M θ = 10-7 10-8 10-9 10-10 10-11 Tremaine-Gunn / Lyman-α Interaction strength Sin2(2θ) Figure 17. Best fit model for the data sets used in the analysis (SDSS+HIRES+MIKE) shown as green curves. We also show a WDM model that has the best fit values of the green model except for the WDM (thermal relic) mass of 2 kev (red dashed curves). These data span about two orders of magnitude in scale and the period 1.1-3.1 Gyrs after the Big Bang. From this plot is is apparent how the WDM model does not fit the data at small scales and high redshift. DM overproduction Excluded by X-ray observations e N Ue e W± Figure 18. Decay channels of the sterile neutrino N with the mass below twicep the electron mass. P Left panel: dominant decay channel to three (anti)neutrinos. Right panel shows radiative decay channel that allows to look for the signal of sterile neutrino DM in the spectra of DM dominated objects. 10-12 panel). The decay width of this process is about 128 times smaller that the main into active neutrinos a and photon with energy E = ms /2, with the width [485, 766] 10-13= 256 4 N! a 10-14 9 G2F 4 sin2 2 m5s = 5.5 10 22 2 h m i5 s s 1 kev 1 (4.13). X X Figure 16. Evolution of the phase space density in time: initially occupying the compact region (left panel) particles spread over the phase space (right panel). The volume remains intact, but the coarse grained 70phase space density decreases in the dense regions. 1 2 5 10 Drewes et al (2016)50 Dark matter mass MDM [kev] which are provided by observations of the stellar dynamics in the smallest structures, dwarf spheroidal galaxies, [378] M /pc3 Q = (0.005 0.02). (4.4) (km/s) The galaxies are compact and dim with mass strongly dominated even in the central part by the DM component. Hence, one has 0 = MX nx with nx standing for the number density of the DM particles in the galaxy center. For the spheroidal dwarfs one can substitute hvk2 i = hv2 i/3, where hv2 i is the average squared velocity. For the DM particles with average 2 hv2 i. squared momentum hp2 i = MX Collecting all terms together we arrive at n 2 (p, X, t ), Q = 3 Mangle' 3sin M f (2 ) Figure 19. Limits on the mixing as a function of sterile neutrino DM mass. The hp i in the last equality we used the phase spaceworkshop, distribution of DM particles in the galaxy Kenji Kadota (IBS) 2018 bounds are based onwhere the works [270,YKIS 449, 466, 469,Feb 480, 499, 500, 500, 501, 503, 504, 776, 780 center, x ' 0 at present, t = t. Then from eq. (4.3) we obtain the lower limit on the DM particle mass known as the Tremaine Gunn-type bound [74], 784, 787 789, 791, 792, 794, 795, 854]. All bounds are smoothed and additionally divided by a factor 3/2 4 X 3/2 4 X 2 3/2 0 MX & 1/4 Q 3/2 0

Production from (active-sterile) neutrino oscillation Ω N > Ω DM X-ray Ω N < Ω DM Cherry,Horiuch(2017)

DM constraints heavily depend on the production mechanism! 1) Active-Sterile neutrino oscillation (e.g. Dodelson-Widrow) 2) Active-Sterile neutrino oscillation with the resonance (e.g. Shi-Fuller) 3) Decay of a heavier particle, Thermal freeze-out, variable mixing angle,... ( e.g. Kusenko, Petraki, Asaka, Shaposhnikov, Merle, Schneider,Berlin, Hooper,.. ) 4) Sterile-sterile oscillation! (KK and Kaneta (2017)) Also the left-handed neutrino masses via the seesaw mechanism! L = L SM + L N, L N = R i/@ R apple R c T y LH 1 2 c R T M N R c + h.c. Ω N1 h 2 sin 2 2θ N M 1 (y ν y ν + ) 22

! "## $ aff '= g *++ ae - B Axion Coupling G Aγγ (GeV -1 ) 10-6 10-8 10-10 10-12 10-14 10-16 LSW (OSQAR) Helioscopes (CAST) SN 1987A Haloscopes (ADMX and others) Previous work: Relativistic axion converted into photon in presence of B. Non-relativistic axion decay into two photons for CDM axion. Fermi HESS KSVZ DFSZ Horizontal Branch Stars 10-10 10-8 10-6 10-4 10-2 10 0 Axion Mass m A (ev) VMB (PVLAS) Figure 61.1: Exclusion plot for axion-like particles as described in the text. Sun Telescopes PDG (2017) f~ 1 " 23 ~240 1 " 789 MHz SKA Line-like radio signal for non-relativistic axion conversion: Non-resonant conversion: Kelley and Quinn (2017), Sigl (2017) Resonant conversion: Huang, KK, Sekiguchi and Tashiro to appear 50MHz-14 GHz, S~μJy, Axion mass: 0.2~60 μev

Square Kilometer Array South Africa- Karoo Australia- Western Outback dio Technology The Square Kilometre Array Construction 2019-2025, Early Science 2022-, Full Science 2025-2030 Cost: ~650 M Euros, Operation ~ 50 M Euros per year. Project Description for Astro2010 Response to Program Prioritization Panels 1 April 2009 Contact Author: James Cordes Chair, US SKA Consortium 607 255 0608 Cornell University cordes@astro.cornell.edu CERN-SKA Big data co-operation agreement Kenji Kadota (IBS) YKIS workshop, Feb 2018 Authors and Participants:

61. Axions and other similar particles -1 Axion Coupling GAγγ (GeV ) 10-6 LSW (OSQAR) VMB (PVLAS) 10-8 Figure 3. Telescopes 4 Kelley, Quinn [ApJ Letter (2017)] The sensitivity of SKA-mid shows considerable improvement on the Sunpre-cursor telescopes, the Australian Helioscopes (CAST) SKA Pathfinder (ASKAP) and the Karoo Array Telescope 10-10 Horizontal Branch Stars (MEERKAT). In this Figure we show the coupling strength HESS that could be probed by observing the Interstellar Medium Fermi SN 1987A across the frequency range accessible to ASKAP, MEERKAT 10-12 and SKA-mid. The system temperature of the SKA is minimised Haloscopes between 2 7GHz, corresponding to an axion mass of (ADMX 8.26and others) 28.91µeVc 2 and providing a good opportunity for detection of both the KSVZ and DFSZ axion. Z 10-14 SV K Z S DF The higher CDM density and magnetic field 10-16 -10-8 -2 10 10Galactic 10-6 10-4 10make 100this an obvious Kenji Kadota (IBS) YKIS workshop, Feb 2018 at the Centre Axion Mass ma (ev) strengths choice of observations within the Milky Way, and with the denfigure 61.1: Exclusion plot for axion-like particles as described in the text.

Model: ALP (Axion-like particles) i.e. Ultra-light scalars Ultra-light mass : m u ~ H 0 ~ 10 33 ev m u ~ 10 22 ev m u ~ 10 22 ev 10 10 ev DE (Barbieri et al (2005), ) Fuzzy DM (Hu (2000), ) String axiverse (Arvanitaki et al (2009),...) m u, f u = Ω u / Ω m ~ O(0.01) m u H(t) : ρ u = const m u > H(t) : ρ u 1/ a 3 KK, Mao, Ichiki, Silk (2014) 10000 P(k)[(Mpc/h) 3 ] 1000 Linear: f u =0 f u =0.05 Nonlinear: f u =0 f u =0.05 100 0.001 0.01 0.1 1 k [h/mpc] Kenji Kadota Figure (IBS) 2: Left: The YKIS workshop, (linear Feb 2018and nonlinear) powe

21 cm signals 1420 MHz

Years since the Big Bang ~300000 (z~1000) Brief History of Universe ß Big Bang: the Universe is filled with ionized gas ß Recombination:The gas cools and becomes neutral Dark Ages ~100 million (z~20-40) ß The first structures begin to form. Reionization starts (z ~12) Reionization ~1 billion (z~6) ß Reionization is complete ~13 billion (z=0) ß Today s structures

What can we do with 21cm? High precision on small-scale power spectrum ΔP / P ~ 1/ N Kleban+(2007) 0.024 0.022 0.02 m u =1e3 m u =1e5 m u =1e7 0.018 0.016 fν 0.014 Oyama+(2013) 0.012 0.01 0.008 0.006 0.004 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 f u KK, Mao, Ichiki, Silk (2014)