Two months after the controversial BICEP2 announcement, The Washington Post writes « Big Bang backlash: BICEP2 discovery of gravity waves questioned by cosmologists » and National Geographic emphasizes « Big Bang Discovery Comes Under Fire. Rumors ripple about flaws in the discovery of gravitational waves in the big bang's aftermath ». Both articles refer to the blog post « Is BICEP wrong? » by Adam Falkowski in Résonaances. Science did the same in « Blockbuster Big Bang Result May Fizzle, Rumor Suggests », and also Nature in « Gravitational wave discovery faces scrutiny » reporting « Cosmologist casts doubts on BICEP2's analysis of cosmic microwaves, but the team stands by its conclusions » on a recent lecture by Raphael Flauger at Princeton. By now, there is no new revised version of the BICEP2 article and its authors seem to confirm their experimental claim. The Planck collaboration is expected to provide in a few months its own E and B spectra of the cosmic microwave background (CMB) polarization. But what about the possible theoretical interpretations of the BICEP2 result, if the observed CMB B-modes really correspond to a signal from the early Universe? Alternatives to cosmic inflation exist, as I already pointed out in my posts « BICEP2, CMB B-modes And Spinorial Space-time » and « BICEP2, cosmic inflation, pre-Big Bang, SST, galactic effects... ».

Another paper that has not been revised by its authors is « Fingerprints of Galactic Loop I on the Cosmic Microwave Background », arXiv:1404.1899, by Hao Liu, Philipp Mertsch and Subir Sarkar on the possible role of galactic dust in BICEP2 data. See also the statements by Philipp Mertsch in « Star dust casts doubt on recent big bang wave result » (New Scientist, 15 April 2014). The last results made public by the Planck collaboration (arXiv:1405.0871, arXiv:1405.0872, arXiv:1405.0873 and arXiv:1405.0874) do not yet clarify this situation. Again, the concerns are purely experimental and phenomenological, with nothing new about theoretical cosmology and possible alternatives to the inflationary scenario like those discussed in my March 28 article « CMB B-modes, spinorial space-time and Pre-Big Bang (I) ».

The spinorial space-time

The spinorial space-time (SST) with to complex cosmic coordinates corresponds to space and time such as they are seen by fermions (particles with half-integer spin). Il must therefore be considered as more fundamental than the standard relativistic space-time with four real coordinates. A specific property of the SST is that it automatically generates a privileged space direction (PSD) for each comoving observer. Then, local rotation modes around the privileged space direction in the early Universe may have produced CMB B-modes naturally providing an alternative to the inflationary scenario.

The standard argument to interpret BICEP2 data as an evidence for inflation is that scalar (density) perturbations cannot produce B-modes in the polarization of the CMB, and that the only possibility to generate them is through tensor perturbations (gravitational waves). Vector perturbations (local rotational modes) are not really considered in such an approach. But if a local privileged space direction exists due to space-time geometry, local rotation around the PSD can be present in the early Universe and generate CMB B-modes.

Recent Planck results (see arXiv:1303.5083) may have confirmed the existence of such a local privileged space direction.

I discussed the SST properties and potentialities in two talks given at ICNFP 2012 and ICNFP 2013 :
Pre-Big Bang, fundamental Physics and noncyclic cosmologies
Pre-Big Bang, space-time structure, asymptotic Universe

as well as in other recent papers :
Cosmic rays and tests of fundamental principles (see the Post Scriptum)
Planck data, spinorial space-time and asymptotic Universe
Spinorial space-time and privileged space direction (I)
Spinorial space-time and Friedmann-like equations (I)

My last article :
CMB B-modes, spinorial space-time and Pre-Big Bang (I)

specifically discusses the issue of the interpretation of BICEP2 data. A second paper on the subject is in preparation.

Pre-Big Bang patterns

The spinorial space-time is just an example of how alternative cosmologies can naturally explain the BICEP2 data, assuming they really correspond to a signature from the early Universe.

SST-based pre-Big Bang models can be at the origin of a new cosmology successfully replacing the standard approach. But other pre-Big Bang models can also account for the BICEP2 result.

Even assuming that the BICEP2 signal corresponds to primordial gravitational waves, cosmic inflation is not the only way to generate them. The work by Grichka and Igor Bogdanoff, based on the evolution of a singular gravitational instanton from the zero space-time scale, provides an obvious illustration of this potentiality of pre-Big Bang models. It can be found at the adresses : (Grichka thesis, 1999, in French) (Igor thesis, 2002, in French with four published papers in English)

Other pre-Big Bang models can be based on new ultimate constituents of matter, such as the superbradyons (superluminal preons) that I suggested in 1995. Then, as I pointed out the same year, primordial superluminal propagation naturally solves the horizon problem and inflation is no longer required. 

In particular, superbradyons can be naturally incorporated in a pre-Big Bang cosmology using the spinorial space-time. More details can be found in my papers already mentioned, as well as in two other ICNFP 2012 and 2013 contributions :
High-energy cosmic rays and tests of basic principles of Physics
Ultra-high energy physics and standard basic principles

Clearly, much further work is required before the cosmological origin of the primordial CMB B-modes possibly seen by BICEP2 can really be elucidated.

                                                                             Luis Gonzalez-Mestres