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Title: Constraints on single-field inflation

Abstract

Many alternatives to canonical slow-roll inflation have been proposed over the years, one of the main motivations being to have a model, capable of generating observable values of non-Gaussianity. In this work, we (re-)explore the physical implications of a great majority of such models within a single, effective field theory framework (including novel models with large non-Gaussianity discussed for the first time below). The constraints we apply — both theoretical and experimental — are found to be rather robust, determined to a great extent by just three parameters: the coefficients of the quadratic EFT operators (δN){sup 2} and δNδE, and the slow-roll parameter ε. This allows to significantly limit the majority of single-field alternatives to canonical slow-roll inflation. While the existing data still leaves some room for most of the considered models, the situation would change dramatically if the current upper limit on the tensor-to-scalar ratio decreased down to r<10{sup −2}. Apart from inflationary models driven by plateau-like potentials, the single-field model that would have a chance of surviving this bound is the recently proposed slow-roll inflation with weakly-broken galileon symmetry. In contrast to canonical slow-roll inflation, the latter model can support r<10{sup −2} even if driven by a convexmore » potential, as well as generate observable values for the amplitude of non-Gaussianity.« less

Authors:
 [1]; ;  [2];  [3]
  1. Institut de Théorie des Phénoménes Physiques,EPFL Lausanne (Switzerland)
  2. Scuola Normale Superiore,Piazza dei Cavalieri 7, 56126, Pisa (Italy)
  3. (Italy)
Publication Date:
Sponsoring Org.:
SCOAP3, CERN, Geneva (Switzerland)
OSTI Identifier:
22572107
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2016; Journal Issue: 06; Other Information: PUBLISHER-ID: JCAP06(2016)051; OAI: oai:repo.scoap3.org:16189; cc-by Article funded by SCOAP3. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 License. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COSMOLOGICAL INFLATION; FIELD OPERATORS; INFLATIONARY UNIVERSE; POTENTIALS; QUANTUM FIELD THEORY; SCALAR FIELDS; SYMMETRY BREAKING; TENSOR FIELDS

Citation Formats

Pirtskhalava, David, Santoni, Luca, Trincherini, Enrico, and INFN - Sezione di Pisa,56200, Pisa. Constraints on single-field inflation. United States: N. p., 2016. Web. doi:10.1088/1475-7516/2016/06/051.
Pirtskhalava, David, Santoni, Luca, Trincherini, Enrico, & INFN - Sezione di Pisa,56200, Pisa. Constraints on single-field inflation. United States. doi:10.1088/1475-7516/2016/06/051.
Pirtskhalava, David, Santoni, Luca, Trincherini, Enrico, and INFN - Sezione di Pisa,56200, Pisa. 2016. "Constraints on single-field inflation". United States. doi:10.1088/1475-7516/2016/06/051.
@article{osti_22572107,
title = {Constraints on single-field inflation},
author = {Pirtskhalava, David and Santoni, Luca and Trincherini, Enrico and INFN - Sezione di Pisa,56200, Pisa},
abstractNote = {Many alternatives to canonical slow-roll inflation have been proposed over the years, one of the main motivations being to have a model, capable of generating observable values of non-Gaussianity. In this work, we (re-)explore the physical implications of a great majority of such models within a single, effective field theory framework (including novel models with large non-Gaussianity discussed for the first time below). The constraints we apply — both theoretical and experimental — are found to be rather robust, determined to a great extent by just three parameters: the coefficients of the quadratic EFT operators (δN){sup 2} and δNδE, and the slow-roll parameter ε. This allows to significantly limit the majority of single-field alternatives to canonical slow-roll inflation. While the existing data still leaves some room for most of the considered models, the situation would change dramatically if the current upper limit on the tensor-to-scalar ratio decreased down to r<10{sup −2}. Apart from inflationary models driven by plateau-like potentials, the single-field model that would have a chance of surviving this bound is the recently proposed slow-roll inflation with weakly-broken galileon symmetry. In contrast to canonical slow-roll inflation, the latter model can support r<10{sup −2} even if driven by a convex potential, as well as generate observable values for the amplitude of non-Gaussianity.},
doi = {10.1088/1475-7516/2016/06/051},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 06,
volume = 2016,
place = {United States},
year = 2016,
month = 6
}
  • Inflation is now an accepted paradigm in standard cosmology, with its predictions consistent with observations of the cosmic microwave background. It lacks, however, a firm physical theory, with many possible theoretical origins beyond the simplest, canonical, slow-roll inflation, including Dirac-Born-Infeld inflation and k-inflation. We discuss how a hierarchy of Hubble flow parameters, extended to include the evolution of the inflationary sound speed, can be applied to compare a general, single field inflationary action with cosmological observational data. We show that it is important to calculate the precise scalar and tensor primordial power spectra by integrating the full flow and perturbationmore » equations, since values of observables can deviate appreciably from those obtained using typical second-order Taylor expanded approximations in flow parameters. As part of this, we find that a commonly applied approximation for the tensor-to-scalar ratio, r{approx_equal}16c{sub s}{epsilon}, becomes poor (deviating by as much as 50%) as c{sub s} deviates from 1 and hence the Taylor expansion including next-to-leading order contribution terms involving c{sub s} is required. By integrating the full flow equations, we use a Monte-Carlo-Markov-Chain approach to impose constraints on the parameter space of general single field inflation, and reconstruct the properties of such an underlying theory in light of recent cosmic microwave background and large-scale structure observations.« less
  • We present constraints on canonical single-field inflation derived from WMAP five year, ACBAR, QUAD, BICEP data combined with the halo power spectrum from SDSS LRG7. Models with a non-scale-invariant spectrum and a red tilt n{sub S} < 1 are now preferred over the Harrison-Zel'dovich model (n{sub S} = 1, tensor-to-scalar ratio r = 0) at high significance. Assuming no running of the spectral indices, we derive constraints on the parameters (n{sub S}, r) and compare our results with the predictions of simple inflationary models. The marginalised credible intervals read n{sub S} = 0.962{sup +0.028}{sub −0.026} and r < 0.17 (95%more » confidence level). With respect to previous analyses, the portion of the 68% c.l. contours compatible with potentials which are concave in the observable region becomes even smaller, but the quadratic potential model remains inside the 95% c.l. contours. We demonstrate that these results are robust to changes in the datasets considered and in the theoretical assumptions made. We then consider a non-vanishing running of the spectral indices by employing different methods, non-parametric but approximate, or parametric but exact. With our combination of CMB and LSS data, running models are preferred over power-law models only by a Δχ{sup 2} ≅ 5.8, allowing inflationary stages producing a sizable negative running −0.063{sup +0.061}{sub −0.049} and larger tensor-scalar ratio r < 0.33 at the 95% c.l. This requires large values of the third derivative of the inflaton potential within the observable range. We derive bounds on this derivative under the assumption that the inflaton potential can be approximated as a third order polynomial within the observable range.« less
  • We constrain models of single field inflation with the pre-Planck CMB data. The data used here is the 9-year Wilkinson Microwave Anisotropy Probe (WMAP) data, South Pole Telescope (SPT) data and Atacama Cosmology Telescope (ACT) data. By adding in running of spectral index parameter, we find that the χ{sup 2} is improved by a factor of Δχ{sup 2} = 8.44, which strongly indicates the preference of this parameter from current data. In addition, we find that the running of spectral index α{sub s} does not change very much even if we switch to different pivot scales, which suggests that themore » power law expansion of power spectrum is accurate enough till the 1st order term. Furthermore, we find that the joint constraints on r−n{sub s} give very tight constraints on single-field inflation models, and the models with power law potential φ{sup p} can only survive if 0.9∼« less
  • We use WMAP 9-year bispectrum data to constrain the free parameters of an 'effective field theory' describing fluctuations in single-field inflation. The Lagrangian of the theory contains a finite number of operators associated with unknown mass scales. Each operator produces a fixed bispectrum shape, which we decompose into partial waves in order to construct a likelihood function. Based on this likelihood we are able to constrain four linearly independent combinations of the mass scales. As an example of our framework we specialize our results to the case of 'Dirac-Born-Infeld' and 'ghost' inflation and obtain the posterior probability for each model,more » which in Bayesian schemes is a useful tool for model comparison. Our results suggest that DBI-like models with two or more free parameters are disfavoured by the data by comparison with single-parameter models in the same class.« less