5 research outputs found
Effects of Scale-Dependent Non-Gaussianity on Cosmological Structures
The detection of primordial non-Gaussianity could provide a powerful means to
test various inflationary scenarios. Although scale-invariant non-Gaussianity
(often described by the formalism) is currently best constrained by
the CMB, single-field models with changing sound speed can have strongly
scale-dependent non-Gaussianity. Such models could evade the CMB constraints
but still have important effects at scales responsible for the formation of
cosmological objects such as clusters and galaxies. We compute the effect of
scale-dependent primordial non-Gaussianity on cluster number counts as a
function of redshift, using a simple ansatz to model scale-dependent features.
We forecast constraints on these models achievable with forthcoming data sets.
We also examine consequences for the galaxy bispectrum. Our results are
relevant for the Dirac-Born-Infeld model of brane inflation, where the
scale-dependence of the non-Gaussianity is directly related to the geometry of
the extra dimensions.Comment: 43 pages, 9 figures; references added, submitted to JCAP; typo
corrected in Table 1, minor changes to the tex
Predictions for Nongaussianity from Nonlocal Inflation
In our previous work the nonlinearity parameter f_NL, which characterizes
nongaussianity in the cosmic microwave background, was estimated for a class of
inflationary models based on nonlocal field theory. These models include p-adic
inflation and generically have the remarkable property that slow roll inflation
can proceed even with an extremely steep potential. Previous calculations found
that large nongaussianity is possible; however, the technical complications
associated with studying perturbations in theories with infinitely many
derivatives forced us to provide only an order of magnitude estimate for f_NL.
We reconsider the problem of computing f_NL in nonlocal inflation models,
showing that a particular choice of field basis and recent progress in
cosmological perturbation theory makes an exact computation possible. We
provide the first quantitatively accurate computation of the bispectrum in
nonlocal inflation, confirming our previous claim that it can be observably
large. We show that the shape of the bispectrum in this class of models makes
it observationally distinguishable from Dirac-Born-Infeld inflation models.Comment: 26 pages, 5 figures; references added, sign convention for f_NL
clarified, minor correction
Observing the Evolution of the Universe
How did the universe evolve? The fine angular scale (l>1000) temperature and polarization anisotropies in the CMB are a Rosetta stone for understanding the evolution of the universe. Through detailed measurements one may address everything from the physics of the birth of the universe to the history of star formation and the process by which galaxies formed. One may in addition track the evolution of the dark energy and discover the net neutrino mass. We are at the dawn of a new era in which hundreds of square degrees of sky can be mapped with arcminute resolution and sensitivities measured in microKelvin. Acquiring these data requires the use of special purpose telescopes such as the Atacama Cosmology Telescope (ACT), located in Chile, and the South Pole Telescope (SPT). These new telescopes are outfitted with a new generation of custom mm-wave kilo-pixel arrays. Additional instruments are in the planning stages
Recommended from our members
The Origin of the Universe as Revealed Through the Polarization of the Cosmic Microwave Background
Modern cosmology has sharpened questions posed for millennia about the origin of our cosmic habitat. The age-old questions have been transformed into two pressing issues primed for attack in the coming decade:
• How did the Universe begin?
The current cosmological paradigm successfully explains how the majestic structure observed in the Universe today grew out of small ripples in the density of matter. What is the physical origin of the primordial seeds which are ultimately responsible for the existence of galaxies, stars, planets, and people in the Universe? It is natural to expect (and many theories predict) that whatever produced the density ripples also produced gravity waves – undulations in the fabric of space-time which travel at the speed of light. Does the Universe contain a spectrum of primordial gravity waves produced by the same mechanism which produced the ripples in the density?
• What physical laws govern the Universe at the highest energies?
All explanations for the seeds of structure rely on physics at energies far beyond those probed by, e.g., CERN’s Large Hadron Collider. Experiments probing these seeds therefore may provide information about new particles, forces, or perhaps even extra dimensions of space that are visible only at the highest energies.
The clearest window onto these questions is the pattern of polarization in the Cosmic Microwave Background (CMB), which is uniquely sensitive to primordial gravity waves. A detection of the special pattern produced by gravity waves would be not only an unprecedented discovery, but also a direct probe of physics at the earliest observable instants of our Universe. Experiments which map CMB polarization over the coming decade will lead us on our first steps towards answering these age-old questions.Astronom