All publications

Phenomenology of dark energy: exploring the space of theories with future redshift surveys

Date of publication: 

2013-12-20 15:15:00

Author: 

Federico Piazza, Heinrich Steigerwald, Christian Marinoni

Abstract: We use the effective field theory of dark energy to explore the space of modified gravitymodels which are capable of driving the present cosmic acceleration. We identify five universal functions of cosmic time, which are enough to describe a wide range of theories containing a single scalar degree of freedom in addition to the metric. The first function (the effective equation of state) uniquely controls the expansion history of the universe. The remaining four functions appear in the linear cosmological perturbation equations, but only three of them regulate the growth history of large scale structures. We propose a specific parameterization of such functions in terms of characteristic coefficients that serve as coordinates in the space of modified gravity theories and can be effectively constrained by the next generation of cosmological experiments. We address in full generality the problem of the soundness of the theory against ghost-like and gradient instabilities and show how the space of non-pathological models shrinkswhen a more negative equation of state parameter is considered. This analysis allows us to locate a large class of stable theories that violate the null energy condition (i.e. super-acceleration models) and to recover, as particular subsets, various models considered so far. Finally, under the assumption that the true underlying cosmological model is the Lambda Cold Dark Matter scenario, and relying on the figure of merit with which relevant observables of the model will be constrained by future experiments, we demonstrate that the space spanned by stable gravitational theories that will not be statistically rejected by data is actually much smaller than the space enclosed by the likelihood contours.

Reconstruction of broad features in the primordial spectrum and inflaton potential from Planck

Date of publication: 

2013-10-11 12:45:00

Author: 

Dhiraj Kumar Hazra, Arman Shafieloo, George F. Smoot

Absract :

With the recently published Cosmic Microwave Background data from Planck we address the optimized binning of the primordial power spectrum. As an important modification to the usual binning of the primordial spectrum, along with the spectral amplitude of the bins, we allow the position of the bins also to vary. This technique enables us to address the location of the possible broad physical features in the primordial spectrum with relatively smaller number of bins compared to the analysis performed earlier. This approach is in fact a reconstruction method looking for broad features in the primordial spectrum and avoiding fitting noise in the data. Performing Markov Chain Monte Carlo analysis we present samples of the allowed primordial spectra with broad features consistent with Planck data. To test how realistic it is to have step-like features in primordial spectrum we revisit an inflationary model, proposed by A. A. Starobinsky which can address the similar features obtained from the binning of the spectrum. Using the publicly available code BINGO, we numerically calculate the local f_{NL} for this model in equilateral and arbitrary triangular configurations of wavevectors and show that the obtained non-Gaussianity for this model is consistent with Planck results. In this paper we have also considered different spectral tilts at different bins to identify the cosmological scale that the spectral index needs to have a red tilt and it is interesting to report that spectral index cannot be well constrained up to k ~ 0.01 Mpc^{-1}.

Effective Field Theory of Cosmological Perturbations

Date of publication: 

2013-07-16 09:45:00

Author: 

Federico Piazza (APC, Paris & Paris Cent. Cosmol. Phys.) , Filippo Vernizzi (Saclay, SPhT & Saclay, SPhT)

Abstract:

The effective field theory of cosmological perturbations stems from considering a cosmological background solution as a state displaying spontaneous breaking of time translations and (adiabatic) perturbations as the related Nambu–Goldstone modes. With this insight, one can systematically develop a theory for the cosmological perturbations during inflation and, with minor modifications, also describe in full generality the gravitational interactions of dark energy, which are relevant for late-time cosmology. The formalism displays a unique set of Lagrangian operators containing an increasing number of cosmological perturbations and derivatives. We give an introductory description of the unitary gauge formalism for theories with broken gauge symmetry—that allows us to write down the most general Lagrangian—and of the Stückelberg ‘trick’—that allows to recover gauge invariance and to make the scalar field explicit. We show how to apply this formalism to gravity and cosmology and we reproduce the detailed analysis of the action in the ADM variables. We also review some basic applications to inflation and dark energy.
The effective field theory of cosmological perturbations stems from considering a cosmological background solution as a state displaying spontaneous breaking of time translations and (adiabatic) perturbations as the related Nambu-Goldstone modes. With this insight, one can systematically develop a theory for the cosmological perturbations during inflation and, with minor modifications, also describe in full generality the gravitational interactions of dark energy, which are relevant for late-time cosmology. The formalism displays a unique set of Lagrangian operators containing an increasing number of cosmological perturbations and derivatives. We give an introductory description of the unitary gauge formalism for theories with broken gauge symmetry---that allows to write down the most general Lagrangian---and of the Stueckelberg "trick"---that allows to recover gauge invariance and to make the scalar field explicit. We show how to apply this formalism to gravity and cosmology and we reproduce the detailed analysis of the action in the ADM variables. We also review some basic applications to inflation and dark energy.

A Consistency Relation for Single-Field Inflation with Power Spectrum Oscillations

Date of publication: 

2013-03-20 14:30:00

Author: 

Mark G. Jackson, Gary Shiu

We derive a theoretical upper bound on the oscillation frequency in the scalar perturbation power spectrum of single-field inflation. Oscillations are most naturally produced by modified vacua with varying phase. When this phase changes rapidly, it induces strong interactions between the scalar fluctuations. If the interactions are sufficiently strong the theory cannot be evaluated using perturbation theory, hence imposing a limit on the oscillation frequency. This complements the bound found by Weinberg governing the validity of effective field theory. The generalized consistency relation also allows one to use squeezed configurations of higher-point correlations to place constraints on the power spectrum oscillations.

Planck 2013 results. I. Overview of products and scientific results

Date of publication: 

2013-03-20 14:00:00

Author: 

Planck Collaboration: P. A. R. Ade, N. Aghanim, C. Armitage-Caplan, M. Arnaud, M. Ashdown, F. Atrio-Barandela, J. Aumont, C. Baccigalupi, A. J. Banday, R. B. Barreiro, M. Bartelmann, J. G. Bartlett, E. Battaner, K. Benabed, A. Benoît, A. Benoit-Lévy, J.-P. Bernard, M. Bersanelli, P. Bielewicz, J. Bobin, J. J. Bock, A. Bonaldi, J. R. Bond, J. Borrill, F. R. Bouchet, F. Boulanger, J. W. Bowyer, M. Bridges, M. Bucher, C. Burigana, R. C. Butler, B. Cappellini, J.-F. Cardoso, R. Carr, M. Casale, A. Catalano, A. Challinor, A. Chamballu, R.-R. Chary, X. Chen, L.-Y Chiang, H. C. Chiang, P. R. Christensen, S. Church, D. L. Clements, S. Colombi, L. P. L. Colombo, F. Couchot, A. Coulais, B. P. Crill, A. Curto, F. Cuttaia, L. Danese, R. D. Davies, R. J. Davis, P. de Bernardis, A. de Rosa, G. de Zotti, et al. (218 additional authors not shown)

Abstract:

The ESA's Planck satellite, dedicated to studying the early universe, was launched on May 2009 and has been surveying the microwave and submillimetre sky since August 2009. In March 2013, ESA and the Planck Collaboration publicly released the initial cosmology products based on the first 15.5 months of Planck operations, along with a set of scientific and technical papers and a web-based explanatory supplement. This paper describes the mission and its performance, and gives an overview of the processing and analysis of the data, the characteristics of the data, the main scientific results, and the science data products and papers in the release. Scientific results include robust support for the standard, six parameter LCDM model of cosmology and improved measurements for the parameters that define this model, including a highly significant deviation from scale invariance of the primordial power spectrum. The Planck values for some of these parameters and others derived from them are significantly different from those previously determined. Several large scale anomalies in the CMB temperature distribution detected earlier by WMAP are confirmed with higher confidence. Planck sets new limits on the number and mass of neutrinos, and has measured gravitational lensing of CMB anisotropies at 25 sigma. Planck finds no evidence for non-Gaussian statistics of the CMB anisotropies. There is some tension between Planck and WMAP results; this is evident in the power spectrum and results for some of the cosmology parameters. In general, Planck results agree well with results from the measurements of baryon acoustic oscillations. Because the analysis of Planck polarization data is not yet as mature as the analysis of temperature data, polarization results are not released. We do, however, illustrate the robust detection of the E-mode polarization signal around CMB hot- and cold-spots.

Planck 2013 results. XIV. Zodiacal emission

Date of publication: 

2013-03-20 14:00:00

Author: 

Planck Collaboration: P. A. R. Ade, N. Aghanim, C. Armitage-Caplan, M. Arnaud, M. Ashdown, F. Atrio-Barandela, J. Aumont, C. Baccigalupi, A. J. Banday, R. B. Barreiro, J. G. Bartlett, E. Battaner, K. Benabed, A. Benoît, A. Benoit-Lévy, J.-P. Bernard, M. Bersanelli, P. Bielewicz, J. Bobin, J. J. Bock, A. Bonaldi, J. R. Bond, J. Borrill, F. R. Bouchet, F. Boulanger, M. Bridges, M. Bucher, C. Burigana, R. C. Butler, J.-F. Cardoso, A. Catalano, A. Chamballu, R.-R. Chary, X. Chen, L.-Y Chiang, H. C. Chiang, P. R. Christensen, S. Church, D. L. Clements, J.-M. Colley, S. Colombi, L. P. L. Colombo, F. Couchot, A. Coulais, B. P. Crill, A. Curto, F. Cuttaia, L. Danese, R. D. Davies, P. de Bernardis, A. de Rosa, G. de Zotti, J. Delabrouille, J.-M. Delouis, F.-X. Désert, C. Dickinson, et al. (174 additional authors not shown)

Abstract:

The Planck satellite provides a set of all-sky maps spanning nine frequencies from 30 GHz to 857 GHz, with an unprecedented combination of sensitivity and angular resolution. Planets, minor bodies, and diffuse interplanetary dust (IPD) contribute to the submillimetre and millimetre sky emission it observed. The diffuse emission can be effectively separated from Galactic and other emissions, because Planck views a given point on the distant celestial sphere multiple times, through different columns of IPD. We use the Planck data to investigate the behaviour of Zodiacal emission over the whole sky in the sub-millimetre and millimetre. We fit the COBE Zodiacal model to the Planck data to find the emissivities of the various components of this model -- a diffuse cloud, three asteroidal dust bands, a circumsolar ring, and an Earth-trailing feature. The emissivity of the diffuse Zodiacal cloud decreases with increasing wavelength, as expected from earlier analyses. The emissivities of the dust bands, however, decrease less rapidly, indicating that the properties of the grains in the bands are different than those in the diffuse cloud. As part of the analysis, we fit the small amount of Galactic emission seen through the instrument's far sidelobes and place limits on possible contamination of the CMB results from both Zodiacal emission and Galactic emission seen through these far sidelobes. When necessary, these results are used in the Planck pipeline to make maps with Zodiacal emission and far sidelobes removed. We show that the spectrum of the Zodiacal correction to the CMB maps is small compared to the Planck CMB temperature power spectrum.

Integrating out Heavy Fields in Inflation

Date of publication: 

2013-03-17 07:45:00

Author: 

Mark G. Jackson

I present the procedure for integrating out quantum fields whose mass M is well above the Hubble scale H in de Sitter space. The effective interaction and density matrix are explicitly computed for a simple example and are found to be of order H/M, are nonlocally distributed in time and contain a highly oscillatory phase. This radical departure from the static space-time result demonstrates that these new tools are necessary for constructing effective inflationary potentials. The effective coupling naturally forms a perturbative series in the relative energy transferred \Delta E/M, whose coefficients can then be compared to observation.

Model-Independent Signatures of New Physics in non-Gaussianity

Date of publication: 

2012-02-03 00:45:00

Author: 

Mark G. Jackson, Koenraad Schalm

We compute the model-independent contributions to the primordial bispectrum and trispectrum in de Sitter space due to high-energy physics. We do this by coupling a light inflaton to an auxiliary heavy field, and then evaluating correlation functions in the Schwinger-Keldysh "in-in" formalism. The high-energy physics produces corrections parametrized by $H/M$ where $H$ is the scale of inflation and $M$ is the mass of the heavy field. The bispectrum peaks near the elongated shape, but otherwise contains no features. The trispectrum receives no corrections at order $H/M$.

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