TY - JOUR

T1 - Constraints on small-scale primordial density fluctuation from cosmic microwave background through dark matter annihilation

AU - Kawasaki, Masahiro

AU - Nakatsuka, Hiromasa

AU - Nakayama, Kazunori

N1 - Publisher Copyright:
© 2022 IOP Publishing Ltd and Sissa Medialab.

PY - 2022/3/1

Y1 - 2022/3/1

N2 - The cosmic microwave background (CMB) observation by the Planck satellite precisely determines primordial curvature fluctuations on larger scales than o(1) Mpc, while the small-scale curvature fluctuation is still less constrained. The constraint on small-scale fluctuations is highly improved if we assume the standard thermal relic dark matter scenario. When small-scale fluctuations are large enough, dense regions collapse to form small halos even in a redshift z ≥ 103, which is called "ultracompact minihalos". These minihalos enhance the annihilation of the dark matter and it is constrained by observations such as extragalactic gamma rays and the CMB. We revisit the effect of minihalos formed by the small-scale density fluctuations and calculate the ionization history modified by the dark matter annihilation assuming the thermally produced WIMP accounting for all dark matter with e + e -channel annihilation. We perform the Markov Chain Monte Carlo method to constrain the size of small-scale curvature fluctuations by the CMB power spectrum. It is found that the constraint from the CMB power spectrum is comparable to that from the extragalactic gamma rays. Assuming a pair-annihilation cross section σ ν = 3 × 10-26cm3/s and a mass of dark matter 1 TeV, we constrain the curvature power spectrum PR(k) < o(10-6) over 1 Mpc-1 < k < 106 Mpc-1. We confirm that our constraint mainly comes from the energy injection in early time (z ≥ 100) and hence it is independent of the uncertainty of minihalo properties in the late time.

AB - The cosmic microwave background (CMB) observation by the Planck satellite precisely determines primordial curvature fluctuations on larger scales than o(1) Mpc, while the small-scale curvature fluctuation is still less constrained. The constraint on small-scale fluctuations is highly improved if we assume the standard thermal relic dark matter scenario. When small-scale fluctuations are large enough, dense regions collapse to form small halos even in a redshift z ≥ 103, which is called "ultracompact minihalos". These minihalos enhance the annihilation of the dark matter and it is constrained by observations such as extragalactic gamma rays and the CMB. We revisit the effect of minihalos formed by the small-scale density fluctuations and calculate the ionization history modified by the dark matter annihilation assuming the thermally produced WIMP accounting for all dark matter with e + e -channel annihilation. We perform the Markov Chain Monte Carlo method to constrain the size of small-scale curvature fluctuations by the CMB power spectrum. It is found that the constraint from the CMB power spectrum is comparable to that from the extragalactic gamma rays. Assuming a pair-annihilation cross section σ ν = 3 × 10-26cm3/s and a mass of dark matter 1 TeV, we constrain the curvature power spectrum PR(k) < o(10-6) over 1 Mpc-1 < k < 106 Mpc-1. We confirm that our constraint mainly comes from the energy injection in early time (z ≥ 100) and hence it is independent of the uncertainty of minihalo properties in the late time.

KW - dark matter theory

KW - particle physics-cosmology connection

KW - physics of the early universe

KW - recombination

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U2 - 10.1088/1475-7516/2022/03/061

DO - 10.1088/1475-7516/2022/03/061

M3 - Article

AN - SCOPUS:85128363023

VL - 2022

JO - Journal of Cosmology and Astroparticle Physics

JF - Journal of Cosmology and Astroparticle Physics

SN - 1475-7516

IS - 3

M1 - 061

ER -