TY - JOUR
T1 - Isocurvature constraints and anharmonic effects on QCD axion dark matter
AU - Kobayashi, Takeshi
AU - Kurematsu, Ryosuke
AU - Takahashi, Fuminobu
PY - 2013/9
Y1 - 2013/9
N2 - We revisit the isocurvature density perturbations induced by quantum fluctuations of the axion field by extending a recently developed analytic method and approximations to a time-dependent scalar potential, which enables us to follow the evolution of the axion until it starts to oscillate. We find that, as the initial misalignment angle approaches the hilltop of the potential, the isocurvature perturbations become significantly enhanced, while the non-Gaussianity parameter increases slowly but surely. As a result, the isocurvature constraint on the inflation scale is tightened as H∼(100) GeV for the axion decay constant f∼1010 GeV, near the smaller end of the axion dark matter window. We also derive useful formulae for the power spectrum and non-Gaussianity of the isocurvature perturbations.
AB - We revisit the isocurvature density perturbations induced by quantum fluctuations of the axion field by extending a recently developed analytic method and approximations to a time-dependent scalar potential, which enables us to follow the evolution of the axion until it starts to oscillate. We find that, as the initial misalignment angle approaches the hilltop of the potential, the isocurvature perturbations become significantly enhanced, while the non-Gaussianity parameter increases slowly but surely. As a result, the isocurvature constraint on the inflation scale is tightened as H∼(100) GeV for the axion decay constant f∼1010 GeV, near the smaller end of the axion dark matter window. We also derive useful formulae for the power spectrum and non-Gaussianity of the isocurvature perturbations.
KW - axions
KW - cosmological perturbation theory
KW - non-gaussianity
UR - http://www.scopus.com/inward/record.url?scp=84884888415&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84884888415&partnerID=8YFLogxK
U2 - 10.1088/1475-7516/2013/09/032
DO - 10.1088/1475-7516/2013/09/032
M3 - Article
AN - SCOPUS:84884888415
VL - 2013
JO - Journal of Cosmology and Astroparticle Physics
JF - Journal of Cosmology and Astroparticle Physics
SN - 1475-7516
IS - 9
M1 - 032
ER -