Claudia Antolini, Matteo Martinelli, Yabebal Fantaye, Carlo Baccigalupi
We evaluate our capability to constrain the abundance of primordial gravitational waves (PGWs), in cosmologies with generalized expansion history in the epoch of cosmic acceleration. Forthcoming satellite and sub-orbital experiments probing polarization in the CMB are expected to measure the B-mode power in CMB polarization, coming from PGWs on the degree scale, as well as gravitational lensing on arcminutes; the latter is the main contaminant for PGWs measurement, and is directly affected by the underlying expansion history, determined by the presence of a Dark Energy (DE) component. In particular, we consider early DE scenarios, in which the expansion history is substantially modified at the epoch in which the CMB lensing is most relevant. We show that the relaxation of these degrees of freedom may induce a variation as large as 30% in the ratio of the power of lensing and primordial GWs on the degree scale. We find that adopting the nominal specifications of upcoming satellite measurements, the constraining power on primordial GWs is weakened by the inclusion of the extra degrees of freedom, resulting in a reduction of about 10% of the upper limits on r in fiducial models with no GWs, as well as a comparable increase in the error bars in models with non-zero tensor power. Moreover, we find that the inclusion of sub-orbital CMB experiments, capable of mapping the B-mode power up to the angular scales which are affected by lensing, has the effect of restoring the forecasted performances with a fixed cosmological expansion history corresponding to a cosmological constant. Finally, we show how the combination of CMB data with Type Ia SNe, BAO and Hubble constant allows to constrain simultaneously the primordial tensor power and the DE quantities in the parametrization we consider, consisting of present abundance and first redshift derivative of the energy density.
View original:
http://arxiv.org/abs/1208.3960
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