2005/02/02 by Naoki Seto, Asantha Cooray
Physics and Astronomy · #Cosmology and Gravitation Theories #Pulsars and Gravitational Waves Research #Radio Astronomy Observations and Technology #astro-ph
paper · pdf · doi:10.1103/physrevd.73.023005
published as Phys.Rev. D73 (2006) 023005 · 8 pages 2 figures
arxiv created 2005/02/02 · openalex publication_date 2006/01/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/30
The curl modes of cosmic microwave background polarization allow one to indirectly constrain the primordial background of gravitational waves with frequencies around 10^\ensuremath-18 to 10^\ensuremath-16 Hz. The proposed high precision timing observations of a large sample of millisecond pulsars with the pulsar timing array or with the square kilometer array can either detect or constrain the stochastic gravitational-wave background at frequencies greater than roughly 0.1 yr^\ensuremath-1. While existing techniques are limited to either observe or constrain the gravitational-wave background across six or more orders of magnitude between 10^\ensuremath-16 and 10^\ensuremath-10 Hz, we suggest that the anisotropy pattern of time variation of the redshift related to a sample of high-redshift objects can be used to study the background around a frequency of 10^\ensuremath-12 Hz. Useful observations to detect an anisotropy signal in the global redshift change include spectroscopic observations of the Ly\mathrm\text\ensuremath-\ensuremathα forest in absorption towards a sample of quasars, redshifted 21 cm line observations either in absorption or emission towards a sample of neutral HI regions before or during reionization, and high-frequency (0.1 to 1 Hz) gravitational-wave analysis of a sample of neutron star--neutron star binaries detected with gravitational-wave instruments such as the Decihertz Interferometer Gravitational Wave Observatory (DECIGO). For reasonable observations expected in the future involving extragalactic sources, we find limits at the level of \ensuremathΩGW<10^\ensuremath-6 at a frequency around 10^\ensuremath-12 Hz while the ultimate limit is likely to be around \ensuremathΩGW<10^\ensuremath-11. On the other hand, if there is a background of gravitational waves at 10^\ensuremath-12 Hz with an amplitude larger than this limit, its presence will be visible as a measurable anisotropy in the time-evolving redshift of extragalactic sources.