Lensing of 21-cm Fluctuations by Primordial Gravitational Waves
Weak-gravitational-lensing distortions to the intensity pattern of 21-cm radiation from the dark ages can be decomposed geometrically into curl and curl-free components. Lensing by primordial gravitational waves induces a curl component, while the contribution from lensing by density fluctuations is strongly suppressed. Angular fluctuations in the 21-cm background extend to very small angular scales, and measurements at different frequencies probe different shells in redshift space. There is thus a huge trove of information with which to reconstruct the curl component of the lensing field, allowing tensor-to-scalar ratios conceivably as small as r∼10^(-9)—far smaller than those currently accessible—to be probed.
Additional Information© 2012 American Physical Society. Received 8 December 2011; published 22 May 2012. This work was supported by DoE DE-FG03-92-ER40701, NASA NNX10AD04G, and the Betty and Gordon Moore Foundation.
Published - Book2012p18505Phys_Rev_Lett.pdf