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Axion as a Cold Dark Matter Candidate J. Hwang, H. Noh & C-G Park
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Convention: no tensor-pert. Spatial gauge condition: anisotropic stress
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Axion as a CDM
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Scalar field: Axion: PLB 126, 179 (1991) Axenides et al
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Axion: PRD 44, 352 (1991) Ratra Strictly ignore: Ansatz: EOM: Fluid quantities: ⇒ ∴ Pressureless fluid!
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Axion: PLB 680, 1 (2009) JH, Noh Axion-comoving gauge: Ansatz: Fluids: EOM:
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Jeans scale: (Khlopov, Malomed, Zeldovich, MN 1985; Nambu, Sasaki PRD 1990) Sound speed: Axion (K = 0): PRD 86, 083535 (2012) Park, JH, Noh; PRL 103, 111301 (2009) Sikivie, Yang in zero-shear gauge ∴ CDM in ALL cosmological scales
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Axion (K = 0): Exact solution in mde with K=0=Lambda: Large-scale asymptotic solution in mde with K=0=Lambda: PLB 680, 1 (2009) JH, Noh
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To second order
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Axion (K = 0): PLB 726, 559 (2013) JH, Noh ⇒ with perturbed trace of extrinsic curvature
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Low-mass Axion
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Axion: } ⇒ Boltzmann eq. Tight coupling PRD 86, 083535 (2012) Park, JH, Noh G i j - … T (a)c 0;c T (b)c i;c T (b)c 0;c T (r)c 0;c T (r)c i;c EOM
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Axion: PRD 86, 083535 (2012) Park, JH, Noh
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Axion: Constant mass: Evolving mass: PRD 86, 083535 (2012) Park, JH, Noh
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Low-mass axion as a CDM with SS cut: PRD 86, 083535 (2012) Park, JH, Noh
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Neutrino as a HDM: PRD 86, 083535 (2012) Park, JH, Noh
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Summary - Axion as a CDM, shown to second order pert. -Roles of low-mass axion as a CDM with small-scale cut off in the power spectrum -Axion mass smaller than 10 24 eV induces a significant damping in the baryonic density power spectrum in cosmologically relevant scales Future -Third order perturbation and NL power spectra -Axion as a Bose-Einstein condensate -Axion generated as isocurvature perturbation
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The 6th KIAS Workshop on Cosmology and Structure Formation Nov. 3 - 7, 2014 KIAS, Seoul
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