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Detecting inflationary gravity waves

Present precision measurements of cosmic microwave background (CMB) temperature anisotropies lend considerable support to simple models of inflation; however, the most spectacular prediction of inflation—the generation of gravitational waves with wavelengths as large as our present horizon—remains unconfirmed. Several initiatives from the ground and from stratospheric balloons are currently underway to attempt to detect these gravitational waves through the B-mode spectrum of the CMB polarization. However they suffer from severe handicaps such as limited frequency coverage due to atmospheric opacity, unstable seeing conditions, and far sidelobes from the ground. It is only from space that one may hope to detect B-modes due to the re-ionization bump. Because of its broad frequency coverage and extreme stability, PRISM will be able to detect the very low-l B-modes at 5σ for r = 5 × 10−4, even under pessimistic assumptions concerning the complexity of the astrophysical foreground emissions which must be removed reliably. Moreover, PRISM will be able to de-lens the majority of the parasitic signal due to gravitational lensing deflections.

Fig 3a
Constraints on inflationary potentials from Planck and the predicted constraints from PRISM (not assuming de-lensing) for a fiducial value of r = 5 × 10−2 (adapted from Planck Collaboration XXII [86]).

Fig 3b
Distribution of inflationary model parameters generated using a model independent approach that Monte-Carlo samples the inflationary flow equations. While these simulations cannot be interpreted in a statistical way (e.g., Kinney [65], Peiris et al. [81], Chongchitnan and Efstathiou [29]), they show that models cluster around attractor regions.