Blue tensor spectrum from particle production during inflation

Mukohyama, Shinji; Namba, Ryo; Peloso, Marco; Shiu, Gary

doi:10.1088/1475-7516/2014/08/036

Cited by 108 publications

(105 citation statements)

References 133 publications

(225 reference statements)

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“…As stated above, for our model to give interesting results inflation should occur below ∼ 10 11 GeV. As a consequence, the contribution to r by the standard amplification of the vacuum fluctuations of the metric is completely negligible: this model violates the Lyth bound [25] in a way that is analogous to the one discussed first in [26] and subsequently in [21,27,28], since it displays a large tensor-to-scalar ratio without Planckian excursions of the inflaton.…”

Section: Introductionmentioning

confidence: 57%

Adding helicity to inflationary magnetogenesis

Caprini

Sorbo

2014

J. Cosmol. Astropart. Phys.

155

271

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Abstract. The most studied mechanism of inflationary magnetogenesis relies on the timedependence of the coefficient of the gauge kinetic term F µν F µν . Unfortunately, only extremely finely tuned versions of the model can consistently generate the cosmological magnetic fields required by observations. We propose a generalization of this model, where also the pseudoscalar invariant F µνF µν is multiplied by a time dependent function. The new parity violating term allows more freedom in tuning the amplitude of the field at the end of inflation. Moreover, it leads to a helical magnetic field that is amplified at large scales by magnetohydrodynamical processes during the radiation dominated epoch. As a consequence, our model can satisfy the observational lower bounds on fields in the intergalactic medium, while providing a seed for the galactic dynamo, if inflation occurs at an energy scale ranging from 10 5 to 10 10 GeV. Such energy scale is well below that suggested by the recent BICEP2 result, if the latter is due to primordial tensor modes. However, the gauge field is a source of tensors during inflation and generates a spectrum of gravitational waves that can give a sizable tensor to scalar ratio r = O(0.2) even if inflation occurs at low energies. This system therefore evades the Lyth bound. For smaller values of r, lower values of the inflationary energy scale are required. The model predicts fully helical cosmological magnetic fields and a chiral spectrum of primordial gravitational waves.

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Section: Introductionmentioning

confidence: 57%

Adding helicity to inflationary magnetogenesis

Caprini

Sorbo

2014

J. Cosmol. Astropart. Phys.

155

271

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“…In [8] we have discussed canonical inflationary models, Whipped Inflation, that can generate the large scale scalar suppression. Afterwards, different inflationary models have been discussed in the context of reconciling Planck and BICEP2 [15][16][17][18][19][20][21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Wiggly whipped inflation

Hazra

Shafieloo

Smoot

et al. 2014

J. Cosmol. Astropart. Phys.

122

159

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Abstract. Motivated by BICEP2 results on the CMB polarization B-mode which imply primordial gravitational waves are produced when the Universe has the expansion rate of about H ≈ 10 14 GeV, and by deviations from a smooth power-law behavior for multipoles ℓ < 50 in the CMB temperature anisotropy power spectrum found in the WMAP and Planck experiments, we have expanded our class of large field inflationary models that fit both the BICEP2 and Planck CMB observations consistently. These best-fitted large field models are found to have a transition from a faster roll to the slow roll V (φ) = m 2 φ 2 /2 inflation at a field value around 14.6 M Pl and thus a potential energy of V (φ) ∼ (10 16 GeV) 4 . In general this transition with sharp features in the inflaton potential produces not only suppression of scalars relative to tensor modes at small k but also introduces wiggles in the primordial perturbation spectrum. These wiggles are shown to be useful to explain some localized features in the CMB angular power spectrum and can also have other observational consequences. Thus, primordial GW can be used now to make a tomography of inflation determining its fine structure. The resulting Wiggly Whipped Inflation scenario is described in details and the anticipated perturbation power spectra, CMB power spectra, non-Gaussianity and other observational consequences are calculated and compared to existing and forthcoming observations.

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“…There were various attempts at addressing the discrepancy by invoking a cosmological origin. These branched mainly into investigating modifications of the scalar sector of the perturbations as well as parameters which are degenerate with it [8][9][10][11][12][13][14], and into analyses considering a positive value for the tilt of the tensor perturbations n T [11,[15][16][17][18][19][20][21] which would be in contradiction to normal models of inflation. However, these analyses make prior assumptions in the modeling of the tensor perturbations which we shall show may be inappropriate.…”

Section: Introductionmentioning

confidence: 99%

Tensors, BICEP2 results, prior dependence, and dust

2015

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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 parametrization of the tensor power spectrum, and adoption of a logarithmic prior on its amplitude A T , 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 n T to be blue tilted in a joint analysis, which would be in contradiction to the standard inflation prediction (n T < 0). When foregrounds are accounted for, the BICEP2 results no longer require nonstandard inflationary parameter regions. We present limits on primordial A T and n T , adopting foreground scenarios put forward by Mortonson and 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 þ WMAP upper limits from temperature and E-mode polarization are correct.

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Blue tensor spectrum from particle production during inflation

Cited by 108 publications

References 133 publications

Adding helicity to inflationary magnetogenesis

Adding helicity to inflationary magnetogenesis

Wiggly whipped inflation

Tensors, BICEP2 results, prior dependence, and dust

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