Abstract
The field of Cosmology is currently undergoing a positive and constructive crisis. Controversies concerning inflation are not really new. But after the 2013-2014 Planck and BICEP2 announcements, and the more recent joint analysis by Planck, BICEP2 and the Keck Array (PBKA), the basic issues can involve more direct links between the Mathematical Physics aspects of cosmological patterns and the interpretation of experimental results. Open questions and new ideas on the foundations of Cosmology can emerge, while future experimental and observational programs look very promising. The BICEP2 result reporting an excess of B-mode polarization signal of the cosmic microwave background (CMB) radiation was initially presented as a signature of primordial gravitational waves from cosmic inflation. But polarized dust emission can be at the origin of such a signal, and the evidence claimed by BICEP2 is no longer secure after the PBKA analysis. Furthermore, even assuming that significant CMB B-mode polarization has indeed been generated by the early Universe, its theoretical and cosmological interpretation would be far from obvious. Inflationary gravitational waves are not the only possible source of primordial CMB B-modes. Alternative cosmologies such as pre-Big Bang patterns and the spinorial space-time (SST) we introduced in 1996-97 can naturally produce this polarization. Furthermore, the SST automatically generates for each comoving observer a local privileged space direction (PSD) whose existence may have been confirmed by Planck data. If such a PSD exists, vector perturbations have most likely been strong in the early Universe and may have produced CMB B-modes. Pre-Big Bang cosmologies can also generate gravitational waves in the early Universe without inflation. After briefly describing detectors devoted to the study of the CMB polarization, we discuss the situation emerging from BICEP2 results, Planck results and the PBKA analysis. In particular, we further analyze possible alternatives to the inflationary interpretation of a primordial B-mode polarization of cosmic microwave background radiation.
Highlights
After briefly describing detectors devoted to the study of the cosmic microwave background (CMB) polarization, we discuss the situation emerging from BICEP2 results, Planck results and the PBKA analysis
Contrary to the standard isotropic description of the early Universe, where only E-modes associated to gradients are assumed to be present in the primordial CMB polarization except for the B-modes due to inflationary gravitational waves, a cosmology based on the spinorial space-time naturally leads to primordial CMB B-modes generated by rotations around the local privileged space direction and vector products by this direction [17, 18]
The possible existence of CMB B-modes of primordial origin, initially claimed on the grounds of BICEP2 data but not confirmed by more recent analyses, would in any case not be a compelling evidence for the standard Big Bang model with cosmic inflation
Summary
The standard cosmological model (Big Bang + inflation + ΛCDM) is far from being well-defined and well-established. It cannot completely account for recent cosmological observations and analyses [20,21,22]. It can be challenged from a more fundamental point of view including space-time structure and the formation of the Universe[18, 23]. Alternative cosmologies [24, 25] must be seriously taken into account and can be more performing to explain data than the standard pattern based on the conventional Big Bang with inflation
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