Isocurvature and Curvaton Perturbations with Red Power Spectrum and Large Hemispherical Asymmetry

Understand

We calculate the power spectrum and hemispherical asymmetry of isocurvature and curvaton perturbations due to a complex field \Phi which is evolving along the tachyonic part of its potential.

• Using a semi-classical evolution of initially sub-horizon quantum fluctuations, we compute the power spectrum, mean field and hemispherical asymmetry as a function of the number of e-foldings of tachyonic growth \Delta N and the tachyonic mass term cH^2.
• We find that a large hemispherical asymmetry due to the modulation of |\Phi| can easily be generated via the spatial modulation of |\Phi| across the horizon, with Delta |\Phi|/|\Phi| > 0.5 when the observed Universe exits the horizon within 10-40 e-foldings of the beginning of tachyonic evolution and c is in the range 0.1-1.
• The spectral index of the isocurvature and curvaton perturbations is generally negative, corresponding to a red power spectrum.