4 research outputs found
Trans-Planckian wimpzillas
Two previously proposed conjectures--gravitational trans-Planckian particle
creation in the expanding universe, and the existence of ultra-heavy stable
particles with masses up to the Planck scale (wimpzillas)--are combined in a
proposal for trans-Planckian particle creation of wimpzillas. This new scenario
leads to a huge enhancement in their production compared to mechanisms put
forward earlier. As a result, it requires the trans-Planckian particle creation
parameter to be rather small to avoid overproduction of such particles, much
less than that is required for observable effects in the primordial
perturbation spectrum. This ensures also that wimpzillas are mainly created at
the end of primordial inflation. Conditions under which trans-Planckian
wimpzillas can constitute the present dark matter are determined.Comment: Replaced with the version to be published in JCAP. Division into
sections introduced, discussion expanded, references added, conclusions
unchange
Slow Roll Reconstruction: Constraints on Inflation from the 3 Year WMAP Dataset
We study the constraints on the inflationary parameter space derived from the
3 year WMAP dataset using ``slow roll reconstruction'', using the SDSS galaxy
power spectrum to gain further leverage where appropriate. This approach
inserts the inflationary slow roll parameters directly into a Monte Carlo
Markov chain estimate of the cosmological parameters, and uses the inflationary
flow hierarchy to compute the parameters' scale-dependence. We work with the
first three parameters (epsilon, eta and xi) and pay close attention to the
possibility that the 3 year WMAP dataset contains evidence for a ``running''
spectral index, which is dominated by the xi term. Mirroring the WMAP team's
analysis we find that the permitted distribution of xi is broad, and centered
away from zero. However, when we require that inflationary parameters yield at
least 30 additional e-folds of inflation after the largest observable scales
leave the horizon, the bounds on xi tighten dramatically. We make use of the
absence of an explicit pivot scale in the slow roll reconstruction formalism to
determine the dependence of the computed parameter distributions on the pivot.
We show that the choice of pivot has a significant effect on the inferred
constraints on the inflationary variables, and the spectral index and running
derived from them. Finally, we argue that the next round of cosmological data
can be expected to place very stringent constraints on the region of parameter
space open to single field models of slow roll inflation.Comment: 26 pages, 11 figures, JHEP format. v2: version accepted by JCAP:
minor clarifications and references added, 1 figure added, v3: 1 reference
adde
Duality Cascade in Brane Inflation
We show that brane inflation is very sensitive to tiny sharp features in
extra dimensions, including those in the potential and in the warp factor. This
can show up as observational signatures in the power spectrum and/or
non-Gaussianities of the cosmic microwave background radiation (CMBR). One
general example of such sharp features is a succession of small steps in a
warped throat, caused by Seiberg duality cascade using gauge/gravity duality.
We study the cosmological observational consequences of these steps in brane
inflation. Since the steps come in a series, the prediction of other steps and
their properties can be tested by future data and analysis. It is also possible
that the steps are too close to be resolved in the power spectrum, in which
case they may show up only in the non-Gaussianity of the CMB temperature
fluctuations and/or EE polarization. We study two cases. In the slow-roll
scenario where steps appear in the inflaton potential, the sensitivity of brane
inflation to the height and width of the steps is increased by several orders
of magnitude comparing to that in previously studied large field models. In the
IR DBI scenario where steps appear in the warp factor, we find that the
glitches in the power spectrum caused by these sharp features are generally
small or even unobservable, but associated distinctive non-Gaussianity can be
large. Together with its large negative running of the power spectrum index,
this scenario clearly illustrates how rich and different a brane inflationary
scenario can be when compared to generic slow-roll inflation. Such distinctive
stringy features may provide a powerful probe of superstring theory.Comment: Corrections in Eq.(5.47), Eq (5.48), Eq(5.49) and Fig
Large Non-Gaussianities in Single Field Inflation
We compute the 3-point correlation function for a general model of inflation
driven by a single, minimally coupled scalar field. Our approach is based on
the numerical evaluation of both the perturbation equations and the integrals
which contribute to the 3-point function. Consequently, we can analyze models
where the potential has a "feature", in the vicinity of which the slow roll
parameters may take on large, transient values. This introduces both scale and
shape dependent non-Gaussianities into the primordial perturbations. As an
example of our methodology, we examine the ``step'' potentials which have been
invoked to improve the fit to the glitch in the for ,
present in both the one and three year WMAP data sets. We show that for the
typical parameter values, the non-Gaussianities associated with the step are
far larger than those in standard slow roll inflation, and may even be within
reach of a next generation CMB experiment such as Planck. More generally, we
use this example to explain that while adding features to potential can improve
the fit to the 2-point function, these are generically associated with a
greatly enhanced signal at the 3-point level. Moreover, this 3-point signal
will have a very nontrivial shape and scale dependence, which is correlated
with the form of the 2-point function, and may thus lead to a consistency check
on the models of inflation with non-smooth potentials.Comment: 23 pages JHEP-style, 7 Figures. Updated with improved results.
Accepted for publication by JCA