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Phys. Rev. D 82, 063524 (2010) [15 pages]


Peter W. Graham1, Roni Harnik2,1, and Surjeet Rajendran3
1Department of Physics, Stanford University, Stanford, California 94305, USA
2Theoretical Physics Department, Fermilab, Batavia, Illinois 60510, USA
3Center for Theoretical Physics, Laboratory for Nuclear Science and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
Received 19 March 2010; published 20 September 2010
It seems generic to have vacua with lower dimensionality than ours. We consider the possibility that the observable universe originated in a transition from one of these vacua. Such a universe has anisotropic spatial curvature. This may be directly observable through its late-time effects on the CMB if the last period of slow-roll inflation was not too long. These affect the entire sky, leading to correlations which persist up to the highest CMB multipoles, thus allowing a conclusive detection above cosmic variance. Further, this anisotropic curvature causes different dimensions to expand at different rates. This leads to other potentially observable signals including a quadrupolar anisotropy in the CMB which limits the size of the curvature. Conversely, if isotropic curvature is observed it may be evidence that our parent vacuum was at least 3+1 dimensional. Such signals could reveal our history of decompactification, providing evidence for the existence of vastly different vacua.
© 2010 The American Physical Society