2007/01/31 by Lotty Ackerman, Sean M. Carroll, Mark B. Wise
Physics and Astronomy · #astro-ph #gr-qc #hep-ph #hep-th
paper · pdf · doi:10.1103/physrevd.75.083502
published as Phys.Rev.D75:083502,2007; Erratum-ibid.D80:069901,2009 · 7 pages, no figures; v5: Corrections, as well as use of more standard convention, in section II
arxiv created 2009/08/10 · arxiv updated 2014/10/13
Rotational invariance is a well-established feature of low-energy physics. Violations of this symmetry must be extremely small today, but could have been larger in earlier epochs. In this paper we examine the consequences of a small breaking of rotational invariance during the inflationary era when the primordial density fluctuations were generated. Assuming that a fixed-norm vector picked out a preferred direction during the inflationary era, we explore the imprint it would leave on the cosmic microwave background anisotropy, and provide explicit formulas for the expected amplitudes <almal'm'^*> of the spherical-harmonic coefficients. We suggest that it is natural to expect that the imprint on the primordial power spectrum of a preferred spatial direction is approximately scale-invariant, and examine a simple model in which this is true.