
We investigate the axion dark matter scenario (ADM), in which axions account for all of the dark matter in the Universe, in light of the most recent cosmological data. In particular, we use the Planck temperature data, complemented by WMAP Epolarization measurements, as well as the recent BICEP2 observations of Bmodes. Baryon acoustic oscillation data, including those from the baryon oscillation spectroscopic survey, are also considered in the numerical analyses. We find that, in the minimal ADM scenario and for Delta(QCD) = 200 MeV, the full data set implies that the axion mass m(a) = 82.2 +/ 1.1 μeV [corresponding to the PecceiQuinn symmetry being broken at a scale f(a) = (7.54 +/ 0.10) x 10(10) GeV], or m(a) = 76.6 +/ 2.6 μeV [f(a) = (8.08 +/ 0.27) x 10(10) GeV] when we allow for a nonstandard effective number of relativistic species Neff. We also find a 2 sigma preference for Neff > 3.046. The limit on the sum of neutrino masses is Sigma m(v) < 0.25 eV at 95% C.L. for Neff = 3.046, or Sigma m(v) < 0.47 eV when Neff is a free parameter. Considering extended scenarios where either the dark energy equationofstate parameter w, the tensor spectral index n(t), or the running of the scalar index dn(s)/d ln k is allowed to vary does not change significantly the axion massenergy density constraints. However, in the case of the full data set exploited here, there is a preference for a nonzero tensor index or scalar running, driven by the different tensor amplitudes implied by the Planck and BICEP2 observations. We also study the effect on our estimates of theoretical uncertainties, in particular the imprecise knowledge of the QCD scale Delta(QCD), in the calculation of the temperaturedependent axion mass. We find that in the simplest ADM scenario the Planck + WP data set implies that the axion mass m(a) = 63.7 +/ 1.2 μeV for Delta(QCD) = 400 MeV. We also comment on the possibility that axions do not make up for all the dark matter, or that the contribution of stringproduced axions has been grossly underestimated; in that case, the values that we find for the mass can conservatively be considered as lower limits. Dark matter axions with mass in the 6080 μeV (corresponding to an axionphoton coupling G(a gamma gamma) similar to 10(14) GeV1) range can, in principle, be detected by looking for axiontophoton conversion occurring inside a tunable microwave cavity permeated by a highintensity magnetic field, and operating at a frequency nu similar or equal to 1520 GHz. This is out of the reach of current experiments like the axion dark matter experiment (limited to a maximum frequency of a few GHzs), but is, on the other hand, within the reach of the upcoming axion dark matter experimenthigh frequency experiment that will explore the 440 GHz frequency range and then be sensitive to axion masses up to similar to 160 μeV.
