Can self-ordering scalar fields explain the BICEP2 B-mode signal?

Durrer, Ruth; Figueroa, Daniel G.; Kunz, M.

doi:10.1088/1475-7516/2014/08/029

Cited by 15 publications

(20 citation statements)

References 66 publications

(104 reference statements)

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“…Defects produce scalar, vector and tensor perturbations in proportions which are fixed for a given defect model, while in inflationary models vector modes are absent and the tensor contribution can vary almost independently of the scalar, apart from the inflationary consistency relation [71]. In addition, defect-induced polarization is suppressed on large angular scales, as causality requires their fluctuations to be uncorrelated beyond the horizon distance at decoupling [6].…”

Section: Cmb Spectra From Defectsmentioning

confidence: 99%

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Constraining topological defects with temperature and polarization anisotropies

et al. 2014

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We analyse the possible contribution of topological defects to cosmic microwave anisotropies, both temperature and polarisation. We allow for the presence of both inflationary scalars and tensors, and of polarised dust foregrounds that may contribute to or dominate the B-mode polarisation signal. We confirm and quantify our previous statements that topological defects on their own are a poor fit to the B-mode signal. However, adding topological defects to a models with a tensor component or a dust component improves the fit around ℓ = 200. Fitting simultaneously to both temperature and polarisation data, we find that textures fit almost as well as tensors (∆χ 2 = 2.0), while Abelian Higgs strings are ruled out as the sole source of the B-mode signal at low ℓ. The 95% confidence upper limits on models combining defects and dust are Gµ < 2.7 × 10 −7 (Abelian Higgs strings), Gµ < 9.8 × 10 −7 (semilocal strings) and Gµ < 7.3 × 10 −7 (textures), a small reduction on the Planck bounds. The most economical fit overall is obtained by the standard ΛCDM model with a polarised dust component.

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Section: Cmb Spectra From Defectsmentioning

confidence: 99%

“…We will also see that textures can combine with primordial gravitational waves to improve the fit to the BICEP2 data, as they help with the points at ℓ 200 which are above the lensing signal [4][5][6].…”

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confidence: 93%

Constraining topological defects with temperature and polarization anisotropies

et al. 2014

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“…The recent observation by the BICEP2 experiment [1] of B-mode polarisation of the cosmic microwave background in excess of the signal due to lensing [2], at first credited to gravitational waves generated during inflation, turned out to be due to Galactic foregrounds [3,4]. (There are also other possible cosmological sources of B-modes, such as magnetic fields [5], topological defects [6] and self-ordering scalar fields [7], though these could not have explained the signal. )…”

Section: Introductionmentioning

confidence: 99%

Inflation without quantum gravity

2015

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It is sometimes argued that observation of tensor modes from inflation would provide the first evidence for quantum gravity. However, in the usual inflationary formalism, also the scalar modes involve quantised metric perturbations. We consider the issue in a semiclassical setup in which only matter is quantised, and spacetime is classical. We assume that the state collapses on a spacelike hypersurface, and find that the spectrum of scalar perturbations depends on the hypersurface. For reasonable choices, we can recover the usual inflationary predictions for scalar perturbations in minimally coupled single-field models. In models where non-minimal coupling to gravity is important and the field value is sub-Planckian, we do not get a nearly scale-invariant spectrum of scalar perturbations. As gravitational waves are only produced at second order, the tensor-to-scalar ratio is negligible. We conclude that detection of inflationary gravitational waves would indeed be needed to have observational evidence of quantisation of gravity.Comment: 18 pages, 1 figure. v2: Published version. Clarified text, fixed typos, added references, updated discussion of BICEP2 result

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“…Vectors do not propagate in a FriedmannLemaître universe (see, however, Ref. [4]) and can be a potential explanation of the BICEP2 data only if they are incessantly generated by active sources such as cosmic strings [5][6][7] or magnetic fields [8]. These, however, are severely constrained by other measurements [9,10].…”

Section: Introductionmentioning

confidence: 99%

Compatibility of Planck and BICEP2 results in light of inflation

et al. 2014

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We investigate the implications for inflation of the detection of B-modes polarization in the Cosmic Microwave Background (CMB) by BICEP2. We show that the hypothesis of primordial origin of the measurement is favored only by the first four bandpowers, while the others would prefer unreasonably large values of the tensor-to-scalar ratio. Using only those four bandpowers, we carry out a complete analysis in the cosmological and inflationary slow-roll parameter space using the BICEP2 polarization measurements alone and extract the Bayesian evidences and complexities for all the Encyclopaedia Inflationaris models. This allows us to determine the most probable and simplest BICEP2 inflationary scenarios. Although this list contains the simplest monomial potentials, it also includes many other scenarios, suggesting that focusing model building efforts on large field models only is unjustified at this stage. We demonstrate that the sets of inflationary models preferred by Planck alone and BICEP2 alone are almost disjoint, indicating a clear tension between the two data sets. We address this tension with a Bayesian measure of compatibility between BICEP2 and Planck. We find that for models favored by Planck the two data sets tend to be incompatible, whereas there is a moderate evidence of compatibility for the BICEP2 preferred models. As a result, it would be premature to draw any conclusion on the best Planck models, such as Starobinsky and/or Kähler moduli inflation. For the subset of scenarios not exhibiting data sets incompatibility, we update the evidences and complexities using both data sets together.

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Can self-ordering scalar fields explain the BICEP2 B-mode signal?

Cited by 15 publications

References 66 publications

Constraining topological defects with temperature and polarization anisotropies

Constraining topological defects with temperature and polarization anisotropies

Inflation without quantum gravity

Compatibility of Planck and BICEP2 results in light of inflation

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