11 research outputs found
The Full Second-Order Radiation Transfer Function for Large-Scale CMB Anisotropies
We calculate the full second-order radiation transfer function for Cosmic
Microwave Background anisotropies on large angular scales in a flat universe
filled with matter and cosmological constant. It includes (i) the second-order
generalization of the Sachs-Wolfe effect, and of (ii) both the early and late
Integrated Sachs-Wolfe effects, (iii) the contribution of the second-order
tensor modes, and is valid for a generic set of initial conditions specifying
the level of primordial non-Gaussianity.Comment: 30 pages, LaTeX fil
Gravitational instability on the brane: the role of boundary conditions
An outstanding issue in braneworld theory concerns the setting up of proper
boundary conditions for the brane-bulk system. Boundary conditions (BC's)
employing regulatory branes or demanding that the bulk metric be nonsingular
have yet to be implemented in full generality. In this paper, we take a
different route and specify boundary conditions directly on the brane thereby
arriving at a local and closed system of equations (on the brane). We consider
a one-parameter family of boundary conditions involving the anisotropic stress
of the projection of the bulk Weyl tensor on the brane and derive an exact
system of equations describing scalar cosmological perturbations on a generic
braneworld with induced gravity. Depending upon our choice of boundary
conditions, perturbations on the brane either grow moderately (region of
stability) or rapidly (instability). In the instability region, the evolution
of perturbations usually depends upon the scale: small scale perturbations grow
much more rapidly than those on larger scales. This instability is caused by a
peculiar gravitational interaction between dark radiation and matter on the
brane. Generalizing the boundary conditions obtained by Koyama and Maartens, we
find for the Dvali-Gabadadze-Porrati model an instability, which leads to a
dramatic scale-dependence of the evolution of density perturbations in matter
and dark radiation. A different set of BC's, however, leads to a more moderate
and scale-independent growth of perturbations. For the mimicry braneworld,
which expands like LCDM, this class of BC's can lead to an earlier epoch of
structure formation.Comment: 35 pages, 9 figures, an appendix and references added, version to be
published in Classical and Quantum Gravit
Radiative Corrections to the Inflaton Potential as an Explanation of Suppressed Large Scale Power in Density Perturbations and the Cosmic Microwave Background
The Wilkinson Microwave Anisotropy Probe microwave background data suggest
that the primordial spectrum of scalar curvature fluctuations is suppressed at
small wavenumbers. We propose a UV/IR mixing effect in small-field inflationary
models that can explain the observable deviation in WMAP data from the
concordance model. Specifically, in inflationary models where the inflaton
couples to an asymptotically free gauge theory, the radiative corrections to
the effective inflaton potential can be anomalously large. This occurs for
small values of the inflaton field which are of the order of the gauge theory
strong coupling scale. Radiative corrections cause the inflaton potential to
blow up at small values of the inflaton field. As a result, these corrections
can violate the slow-roll condition at the initial stage of the inflation and
suppress the production of scalar density perturbations.Comment: 20 pages, 2 figures, v2: refs added, v3: JCAP versio
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
Planck 2015 results. XIII. Cosmological parameters
We present results based on full-mission Planck observations of temperature and polarization anisotropies of the CMB. These data are consistent with the six-parameter inflationary LCDM cosmology. From the Planck temperature and lensing data, for this cosmology we find a Hubble constant, H0= (67.8 +/- 0.9) km/s/Mpc, a matter density parameter Omega_m = 0.308 +/- 0.012 and a scalar spectral index with n_s = 0.968 +/- 0.006. (We quote 68% errors on measured parameters and 95% limits on other parameters.) Combined with Planck temperature and lensing data, Planck LFI polarization measurements lead to a reionization optical depth of tau = 0.066 +/- 0.016. Combining Planck with other astrophysical data we find N_ eff = 3.15 +/- 0.23 for the effective number of relativistic degrees of freedom and the sum of neutrino masses is constrained to < 0.23 eV. Spatial curvature is found to be |Omega_K| < 0.005. For LCDM we find a limit on the tensor-to-scalar ratio of r <0.11 consistent with the B-mode constraints from an analysis of BICEP2, Keck Array, and Planck (BKP) data. Adding the BKP data leads to a tighter constraint of r < 0.09. We find no evidence for isocurvature perturbations or cosmic defects. The equation of state of dark energy is constrained to w = -1.006 +/- 0.045. Standard big bang nucleosynthesis predictions for the Planck LCDM cosmology are in excellent agreement with observations. We investigate annihilating dark matter and deviations from standard recombination, finding no evidence for new physics. The Planck results for base LCDM are in agreement with BAO data and with the JLA SNe sample. However the amplitude of the fluctuations is found to be higher than inferred from rich cluster counts and weak gravitational lensing. Apart from these tensions, the base LCDM cosmology provides an excellent description of the Planck CMB observations and many other astrophysical data sets
Probing Inflation with CMB Polarization
International audienceWe summarize the utility of precise cosmic microwave background (CMB)polarization measurements as probes of the physics of inflation. We focus onthe prospects for using CMB measurements to differentiate various inflationarymechanisms. In particular, a detection of primordial B-mode polarization woulddemonstrate that inflation occurred at a very high energy scale, and that theinflaton traversed a super-Planckian distance in field space. We explain howsuch a detection or constraint would illuminate aspects of physics at thePlanck scale. Moreover, CMB measurements can constrain the scale-dependence andnon-Gaussianity of the primordial fluctuations and limit the possibility of asignificant isocurvature contribution. Each such limit provides crucialinformation on the underlying inflationary dynamics. Finally, we quantify theseconsiderations by presenting forecasts for the sensitivities of a futuresatellite experiment to the inflationary parameters
Recommended from our members
Dark Matter Science in the Era of LSST
Astrophysical observations currently provide the only robust, empirical
measurements of dark matter. In the coming decade, astrophysical observations
will guide other experimental efforts, while simultaneously probing unique
regions of dark matter parameter space. This white paper summarizes
astrophysical observations that can constrain the fundamental physics of dark
matter in the era of LSST. We describe how astrophysical observations will
inform our understanding of the fundamental properties of dark matter, such as
particle mass, self-interaction strength, non-gravitational interactions with
the Standard Model, and compact object abundances. Additionally, we highlight
theoretical work and experimental/observational facilities that will complement
LSST to strengthen our understanding of the fundamental characteristics of dark
matter