Joint Seminars on Cosmology and Gravitation

Speaker: Ghazal Geshnizjani (Perimeter Institute)
Title: Observational Evidence for Cosmological-Scale Extra Dimensions
Date (JST): Fri, Feb 27, 2009, 15:30 - 17:00
Place: Seminar Room at IPMU Prefab. B
Related File: 10.pdf
Abstract: I present a case that current observations may already indicate new
gravitational physics on cosmological scales. The excess of power seen
in the Lyman-alpha forest and small-scale CMB experiments, the
anomalously large bulk flows seen both in peculiar velocity surveys and
in kinetic SZ, and the higher ISW cross-correlation all indicate that
structure may be more evolved than expected from LCDM. I argue that
these observations find a natural explanation in models with
infinite-volume (or, at least, cosmological-size) extra dimensions,
where the graviton is a resonance with a tiny width. The longitudinal
mode of the graviton mediates an extra scalar force which speeds up
structure formation at late times, thereby accounting for the above
anomalies. The required graviton Compton wavelength is relatively small
compared to the present Hubble radius, of order 300-600 Mpc. Moreover,
with certain assumptions about the behavior of the longitudinal mode on
super-Hubble scales, our modified gravity framework can also alleviate
the tension with the low quadrupole and the peculiar vanishing of the
CMB correlation function on large angular scales, seen both in COBE and
WMAP. This relies on a novel mechanism that cancels a late-time ISW
contribution against the primordial Sachs-Wolfe amplitude.
Remarks: Joint Seminars on Cosmology and Gravitation