47 research outputs found
Tensors, BICEP2 results, prior dependence, and dust
We investigate the prior dependence on the inferred spectrum of primordial
tensor perturbations, in light of recent results from BICEP2 and taking into
account a possible dust contribution to polarized anisotropies. We highlight an
optimized parameterization of the tensor power spectrum, and adoption of a
logarithmic prior on its amplitude , leading to results that transform
more evenly under change of pivot scale. In the absence of foregrounds the
tension between the results of BICEP2 and Planck drives the tensor spectral
index to be blue-tilted in a joint analysis, which would be in
contradiction to the standard inflation prediction (). When foregrounds
are accounted for, the BICEP2 results no longer require non-standard
inflationary parameter regions. We present limits on primordial and
, adopting foreground scenarios put forward by Mortonson & Seljak and
motivated by Planck 353 GHz observations, and assess what dust contribution
leaves a detectable cosmological signal. We find that if there is sufficient
dust for the signal to be compatible with standard inflation, then the
primordial signal is too weak to be robustly detected by BICEP2 if Planck+WMAP
upper limits from temperature and E-mode polarization are correct.Comment: 10 pages, 9 figures. v3, minor update to match journal accepted
versio
Dynamical Dark Energy or Simply Cosmic Curvature?
We show that the assumption of a flat universe induces critically large
errors in reconstructing the dark energy equation of state at z>~0.9 even if
the true cosmic curvature is very small, O(1%) or less. The spuriously
reconstructed w(z) shows a range of unusual behaviour, including crossing of
the phantom divide and mimicking of standard tracking quintessence models. For
1% curvature and LCDM, the error in w grows rapidly above z~0.9 reaching
(50%,100%) by redshifts of (2.5,2.9) respectively, due to the long cosmological
lever arm. Interestingly, the w(z) reconstructed from distance data and Hubble
rate measurements have opposite trends due to the asymmetric influence of the
curved geodesics. These results show that including curvature as a free
parameter is imperative in any future analyses attempting to pin down the
dynamics of dark energy, especially at moderate or high redshifts.Comment: 5 pages, 2 figures. To appear in JCA
Inflationary scalar spectrum in loop quantum cosmology
In the context of loop quantum cosmology, we consider an inflationary era
driven by a canonical scalar field and occurring in the semiclassical regime,
where spacetime is a continuum but quantum gravitational effects are important.
The spectral amplitude and index of scalar perturbations on an unperturbed de
Sitter background are computed at lowest order in the slow-roll parameters. The
scalar spectrum can be blue-tilted and far from scale invariance, and tuning of
the quantization ambiguities is necessary for agreement with observations. The
results are extended to a generalized quantization scheme including those
proposed in the literature. Quantization of the matter field at sub-horizon
scales can provide a consistency check of such schemes.Comment: 29 pages, 2 figures. v2: typos corrected, discussion improved and
extended, new section added. Conclusions are unchange
Non-parametric Dark Energy Degeneracies
We study the degeneracies between dark energy dynamics, dark matter and
curvature using a non-parametric and non-perturbative approach. This allows us
to examine the knock-on bias induced in the reconstructed dark energy equation
of state, w(z), when there is a bias in the cosmic curvature or dark matter
content, without relying on any specific parameterisation of w. Even assuming
perfect Hubble, distance and volume measurements, we show that for z > 1, the
bias in w(z) is up to two orders of magnitude larger than the corresponding
errors in Omega_k or Omega_m. This highlights the importance of obtaining
unbiased estimators of all cosmic parameters in the hunt for dark energy
dynamics.Comment: 10 pages, 8 figures. Invited Review for special issue of General
Relativity and Gravitation issue on Dark Energy, eds. G. F.R Ellis et a
Planck 2013 results. XXII. Constraints on inflation
We analyse the implications of the Planck data for cosmic inflation. The Planck nominal mission temperature anisotropy measurements, combined with the WMAP large-angle polarization, constrain the scalar spectral index to be ns = 0:9603 _ 0:0073, ruling out exact scale invariance at over 5_: Planck establishes an upper bound on the tensor-to-scalar ratio of r < 0:11 (95% CL). The Planck data thus shrink the space of allowed standard inflationary models, preferring potentials with V00 < 0. Exponential potential models, the simplest hybrid inflationary models, and monomial potential models of degree n _ 2 do not provide a good fit to the data. Planck does not find statistically significant running of the scalar spectral index, obtaining dns=dln k = 0:0134 _ 0:0090. We verify these conclusions through a numerical analysis, which makes no slowroll approximation, and carry out a Bayesian parameter estimation and model-selection analysis for a number of inflationary models including monomial, natural, and hilltop potentials. For each model, we present the Planck constraints on the parameters of the potential and explore several possibilities for the post-inflationary entropy generation epoch, thus obtaining nontrivial data-driven constraints. We also present a direct reconstruction of the observable range of the inflaton potential. Unless a quartic term is allowed in the potential, we find results consistent with second-order slow-roll predictions. We also investigate whether the primordial power spectrum contains any features. We find that models with a parameterized oscillatory feature improve the fit by __2 e_ _ 10; however, Bayesian evidence does not prefer these models. We constrain several single-field inflation models with generalized Lagrangians by combining power spectrum data with Planck bounds on fNL. Planck constrains with unprecedented accuracy the amplitude and possible correlation (with the adiabatic mode) of non-decaying isocurvature fluctuations. The fractional primordial contributions of cold dark matter (CDM) isocurvature modes of the types expected in the curvaton and axion scenarios have upper bounds of 0.25% and 3.9% (95% CL), respectively. In models with arbitrarily correlated CDM or neutrino isocurvature modes, an anticorrelated isocurvature component can improve the _2 e_ by approximately 4 as a result of slightly lowering the theoretical prediction for the ` <_ 40 multipoles relative to the higher multipoles. Nonetheless, the data are consistent with adiabatic initial conditions