Particle decays during the cosmic dark ages
We consider particle decays during the cosmic dark ages with two aims: (1) to explain the high optical depth reported by the Wilkinson Microwave Anisotropy Probe (WMAP), and (2) to provide new constraints to the parameter space for decaying particles. We delineate the decay channels in which most of the decay energy ionizes and heats the intergalactic medium gas [and thus affects the cosmic microwave background (CMB)], and those in which most of the energy is carried away—e.g. photons with energies 100 keV<~E<~1 TeV—and thus appears as a contribution to diffuse x-ray and gamma-ray backgrounds. The new constraints to the decay-particle parameters from the CMB power spectrum thus complement those from the cosmic x-ray and gamma-ray backgrounds. Although decaying particles can indeed produce an optical depth consistent with that reported by WMAP, in so doing they produce new fluctuations in the CMB temperature and polarization power spectra. For decay lifetimes less than the age of the Universe, the induced power spectra generally violate current constraints, while the power spectra are usually consistent if the lifetime is longer than the age of the Universe.
Additional Information© 2004 The American Physical Society. Received 19 October 2003; revised 14 April 2004; published 4 August 2004. We thank R. Sunyaev, E. Scannapieco, S.-P. Oh, and M. Kaplinghat for helpful comments and discussions. The CAMB code we used in this research was developed by A. Lewis and A. Challinor. X.C. is supported by NSF grant PHY99-07949, and M.K. is supported by NASA grant NAG 5-9821 and DOE grant DE-FG 03-92-ER40701.
Published - CHEprd04.pdf