Figure 1

Adiabatic matter power spectra, with varying axion mass $m_a={10}^{-28}$, ${10}^{-26}$, ${10}^{-25}$, ${10}^{-23}\mathrm{eV}$ at fixed density fraction ${\Omega }_a/{\Omega }_d=0.5$ (dashed) and varying ${\Omega }_a/{\Omega }_d=0.1$, 0.5, 1 at fixed $m_a={10}^{-25}\mathrm{eV}$ (solid). Spectra are calculated using the methods of Ref. 23.Reuse & Permissions

Figure 2

Phenomenology in the $\{m_a,{\Omega }_a/{\Omega }_d\}$ plane. The shaded regions lie between the dashed contours and satisfy $\{0.01<r<0.1,0.01<{\alpha }_{\mathrm{CDM}}<0.047\}$, evading current constraints, while being potentially observable with future data. These are not exclusions; outside of the contours, either parameter can be large while the other is unobservably small, thereby jointly evading constraints to tensors and isocurvature. The region above the black solid lines, labeled “Ruled out 95% C.L. LSS (2005),” uses the $2\sigma$ adiabatic constraints on ${\Omega }_a/{\Omega }_d$ of Ref. 14 and is excluded. The dark shaded regions evade these density constraints yet still have $\{\alpha ,r\}$ observable so that it may be possible to unambiguously infer $H_I$ from a combination of tensor and isocurvature measurements in the CMB, combined with a LSS measurement of ${\Omega }_a$. The dashed black line (“CMB”) estimates the modified $\{\alpha ,r\}$ contours taking into account isocurvature power suppression for low masses (see Fig. 3).Reuse & Permissions

Figure 3

CMB axion isocurvature power spectrum, with adiabatic $\Lambda \mathrm{CDM}$ for scale (black dashed). We demonstrate the normalization difference between ${\alpha }_{\mathrm{CDM}}$ (grey dotted-dashed line) and ${\alpha }_a$ (solid line), with ${\Omega }_a/{\Omega }_d=0.01$ implying a normalization difference of $(0.01{)}^2={10}^{-4}$. We also show small-scale power suppression by the lightest axions. The axion masses are $m_a={10}^{-32}$, ${10}^{-29}$, ${10}^{-28}$, ${10}^{-20}\mathrm{eV}$.Reuse & Permissions