OK 2002-02-02T14:10:02Z astro-ph/0702600 http://arxiv.org/pdf/astro-ph/0702600 http://arxiv.org/ps/astro-ph/0702600 http://arxiv.org/abs/astro-ph/0702600 2007-02-22T14:10:02Z At redshifts $z \agt 30$ neutral hydrogen... Antony Lewis IoA, Cambridge http://cosmologist.info/ http://arxiv.org/find/astro-ph/1/au:+Lewis_A/0/1/0/all/0/1 Anthony Challinor IoA, Cambridge DAMTP, Cambridge http://arxiv.org/find/astro-ph/1/au:+Challinor_A/0/1/0/all/0/1 29 pages..emphasise that if text it can contain formatting http://arxiv.org/pdf/astro-ph/0702600v1 http://arxiv.org/ps/astro-ph/0702600v1 http://arxiv.org/abs/astro-ph/0702600v1 21cm dark ages CMB power spectrum astro-ph