Inflation and Alternatives with Blue Tensor Spectra

Abstract

We study the tilt of the primordial gravitational waves spectrum. A hint of blue tilt is shown from analyzing the BICEP2 and POLARBEAR data. Motivated by this, we explore the possibilities of blue tensor spectra from the very early universe cosmology models, including null energy condition violating inflation, inflation with general initial conditions, and string gas cosmology, etc. For the simplest G-inflation, blue tensor spectrum also implies blue scalar spectrum. In general, the inflation models with blue tensor spectra indicate large non-Gaussianities. On the other hand, string gas cosmology predicts blue tensor spectrum with highly Gaussian fluctuations. If further experiments do confirm the blue tensor spectrum, non-Gaussianity becomes a distinguishing test between inflation and alternatives.

13 pages, 10 figures. v2: references and minor improvements added. v3: version to appear on JCAP

References in corpus (16)

• Observational Signatures and Non-Gaussianities of General Single Field Inflation
• Generalized Galileons: All scalar models whose curved background extensions maintain second-order field equations and stress tensors
• G-inflation: inflation driven by the Galileon field
• Toward an Understanding of Foreground Emission in the BICEP2 Region
• Tensor Modes from a Primordial Hagedorn Phase of String Cosmology
• A joint analysis of Planck and BICEP2 B modes including dust polarization uncertainty
• String Gas Cosmology and Structure Formation
• Closed String Thermodynamics and a Blue Tensor Spectrum
• Gravitational wave signal from massive gravity
• $\alpha$-vacuum and inflationary bispectrum
• Testing quantum gravity effects with latest CMB observations
• Blue Gravity Waves from BICEP2 ?
• Statistical Anisotropies in Gravitational Waves in Solid Inflation
• Blue running of the primordial tensor spectrum
• Atick-Witten Hagedorn Conjecture, near scale-invariant matter and blue-tilted gravity power spectrum
• The Tilt of Primordial Gravitational Waves Spectra from BICEP2

Cited by in corpus (4)

• Science with the space-based interferometer LISA. IV: Probing inflation with gravitational waves
• Blue-tilted Tensor Spectrum and Thermal History of the Universe
• Non-Minimal Two-Loop Inflation
• Dynamical Fractional Chaotic Inflation -- Dynamical Generation of a Fractional Power-Law Potential for Chaotic Inflation