Observational constraints on theories with a blue spectrum of tensor modes

Stewart, Andrew F.; Brandenberger, Robert H.

doi:10.1088/1475-7516/2008/08/012

Cited by 56 publications

(64 citation statements)

References 22 publications

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“…On the other hand, in the same context, if we change the cutoff value to k UV ¼ 10 54 Mpc −1 we obtain n t < 0.2, which is a very restrictive limit. Higher values of r imply more restrictive constraints on n t , in agreement with the results obtained in [31]. In Fig.…”

Section: Resultssupporting

confidence: 90%

“…We analyze three scenarios that take into account the contribution of N GW eff using recent data of cosmic microwave background, baryon acoustic oscillation, the latest measurement of the local expansion rate, along with the LIGO constraints on the tensor to scalar ratio, r, and the tensor index. For the models explored, we show that an additional contribution from the primordial GW's background to N eff does not solve but alleviates the current H 0 -tension problem.The contribution of N GW eff to the radiation content of the universe also affects the predictions of the primordial nucleosynthesis (BBN) [31,32].…”

mentioning

confidence: 99%

“…The contribution of N GW eff to the radiation content of the universe also affects the predictions of the primordial nucleosynthesis (BBN) [31,32].…”

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confidence: 99%

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Primordial gravitational waves and the H0 -tension problem

2019

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We analyze the H 0 -tension problem in the context of models of the early universe that predict a blue tilted spectrum of primordial gravitational waves (GWs), which is a positive value of the tensor tilt n T . By considering the GW's contribution, N GW eff , to the effective number of relativistic degrees of freedom, N eff , and assuming standard particle physics, we discuss the effects of N GW eff on the background expansion, especially the constraints on the Hubble parameter H 0 . We analyze three scenarios that take into account the contribution of N GW eff using recent data of cosmic microwave background, baryon acoustic oscillation, the latest measurement of the local expansion rate, along with the LIGO constraints on the tensor to scalar ratio, r, and the tensor index. For the models explored, we show that an additional contribution from the primordial GW's background to N eff does not solve but alleviates the current H 0 -tension problem.The contribution of N GW eff to the radiation content of the universe also affects the predictions of the primordial nucleosynthesis (BBN) [31,32].

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Section: Resultssupporting

confidence: 90%

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confidence: 99%

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Primordial gravitational waves and the H0 -tension problem

2019

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“…Complementary probes such as pulsar timing, direct detection of gravitational waves, and nucleosynthesis bounds could be used to constrain blue values for the tensor spectral index (Stewart & Brandenberger 2008), but here we are primarily interested in what CMB data can tell us. We caution the reader that in the absence of a clear detection of a tensor component, joint constraints on r and n t depend strongly on priors, or equivalently on the choice of parameterization.…”

Section: Relaxing the Standard Single-field Consistency Conditionmentioning

confidence: 99%

Planck2015 results

Ade¹,

Aghanim²,

Arnaud³

et al. 2016

A&A

1,368

964

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We present the implications for cosmic inflation of the Planck measurements of the cosmic microwave background (CMB) anisotropies in both temperature and polarization based on the full Planck survey, which includes more than twice the integration time of the nominal survey used for the 2013 release papers. The Planck full mission temperature data and a first release of polarization data on large angular scales measure the spectral index of curvature perturbations to be n s = 0.968 ± 0.006 and tightly constrain its scale dependence to dn s /dln k = −0.003 ± 0.007 when combined with the Planck lensing likelihood. When the Planck high-polarization data are included, the results are consistent and uncertainties are further reduced. The upper bound on the tensor-to-scalar ratio is r 0.002 < 0.11 (95% CL). This upper limit is consistent with the B-mode polarization constraint r < 0.12 (95% CL) obtained from a joint analysis of the BICEP2/Keck Array and Planck data. These results imply that V(φ) ∝ φ 2 and natural inflation are now disfavoured compared to models predicting a smaller tensor-to-scalar ratio, such as R 2 inflation. We search for several physically motivated deviations from a simple power-law spectrum of curvature perturbations, including those motivated by a reconstruction of the inflaton potential not relying on the slow-roll approximation. We find that such models are not preferred, either according to a Bayesian model comparison or according to a frequentist simulation-based analysis. Three independent methods reconstructing the primordial power spectrum consistently recover a featureless and smooth P R (k) over the range of scales 0.008 Mpc −1 < ∼ k < ∼ 0.1 Mpc −1 . At large scales, each method finds deviations from a power law, connected to a deficit at multipoles ≈ 20−40 in the temperature power spectrum, but at an uncompelling statistical significance owing to the large cosmic variance present at these multipoles. By combining power spectrum and non-Gaussianity bounds, we constrain models with generalized Lagrangians, including Galileon models and axion monodromy models. The Planck data are consistent with adiabatic primordial perturbations, and the estimated values for the parameters of the base Λ cold dark matter (ΛCDM) model are not significantly altered when more general initial conditions are admitted. In correlated mixed adiabatic and isocurvature models, the 95% CL upper bound for the non-adiabatic contribution to the observed CMB temperature variance is |α non-adi | < 1.9%, 4.0%, and 2.9% for CDM, neutrino density, and neutrino velocity isocurvature modes, respectively. We have tested inflationary models producing an anisotropic modulation of the primordial curvature power spectrum finding that the dipolar modulation in the CMB temperature field induced by a CDM isocurvature perturbation is not preferred at a statistically significant level. We also establish tight constraints on a possible quadrupolar modulation of the curvature perturbation. These results are consistent with the Pl...

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“…Although these limits are far above the prediction of the standard inflationary models, a strongly blue-tilted tensor spectrum can easily be excluded by these constraints, which has been investigated in [40,41].…”

Section: Introductionmentioning

confidence: 99%

Blue-tilted tensor spectrum and thermal history of the Universe

Kuroyanagi

Takahashi

Yokoyama

2015

J. Cosmol. Astropart. Phys.

110

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We investigate constraints on the spectral index of primordial gravitational waves (GWs), paying particular attention to a blue-tilted spectrum. Such constraints can be used to test a certain class of models of the early Universe. We investigate observational bounds from LIGO+Virgo, pulsar timing and big bang nucleosynthesis, taking into account the suppression of the amplitude at high frequencies due to reheating after inflation and also late-time entropy production. Constraints on the spectral index are presented by changing values of parameters such as reheating temperatures and the amount of entropy produced at late time. We also consider constraints under the general modeling approach which can approximately describe various scenarios of the early Universe. We show that the constraints on the blue spectral tilt strongly depend on the underlying assumption and, in some cases, a highly blue-tilted spectrum can still be allowed.

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Observational constraints on theories with a blue spectrum of tensor modes

Cited by 56 publications

References 22 publications

Primordial gravitational waves and the H0 -tension problem

Primordial gravitational waves and the H0 -tension problem

Planck2015 results

Blue-tilted tensor spectrum and thermal history of the Universe

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