Constraints on standard and non-standard early universe models from CMB B-mode polarization

Abstract

We investigate the observational signatures of three models of theearly Universe in the B-mode polarization of the CosmicMicrowave Background (CMB) radiation. In addition to the standardsingle field inflationary model, we also consider the constraintsobtainable on the loop quantum cosmology model (from Loop QuantumGravity) and on cosmic strings, expected to be copiously producedduring the latter stages of Brane inflation. We first examine theobservational features of the three models, and then use currentB-mode polarization data from the BICEP and QUaD experiments toconstrain their parameters. We also examine the detectability ofthe primordial B-mode signal predicted by these models andforecast the parameter constraints achievable with future CMBpolarization experiments. We find that: (a) since B-modepolarization measurements are mostly unaffected by parameterdegeneracies, they provide the cleanest probe of these earlyUniverse models; (b) using the BICEP and QUaD data we obtain thefollowing parameter constraints: r = 0.02+0.31−0.26(1σ for the tensor-to-scalar ratio in the single fieldinflationary model); m < 1.36 × 10−8Mpland k* < 2.43 × 10−4 Mpc−1 (1σ forthe mass and scale parameters in the loop quantum cosmologymodel); and Gμ < 5.77 × 10−7 (1σ for the cosmicstring tension); (c) future CMB observations (both satellitemissions and forthcoming sub-orbital experiments) will providemuch more rigorous tests of these early Universe models.