Following a draft published on arXiv a couple of weeks ago, the BICEP2's observations could be explained not only with the cosmic inflation, but also with another mechanism:
The recent claimed observation of primordial gravitational waves provides a dramatic new empirical window on the early universe. In particular, it provides the opportunity, in principle, to de nitively test the inflationary paradigm, and to explore the speci c physics of inflationary models. However, while there is little doubt that inflation at the Grand Unfi ed Scale is the best motivated source of such primordial waves, it is important to demonstrate that other possible sources cannot account for the current BICEP2 data before definitely claiming Inflation has been proved.A possible contribution to BICEP2's signal could be given by a self ordering scalar field:
Finally we note that while current data cannot de nifitively rule out a SOSF transition as the source of gravitational waves, it nevertheless does imply that the source for such waves is at, or near the Grand Uni ed Scale. Thus, it allows an exploration of physics at a scale far larger than we can currently constrain at terrestrial experiments. This will be very important for constraining physics beyond the standard model, whether or not inflation is responsible for the entire BICEP2 signal, even though existing data from cosmology is strongly suggestive that it does.About the SOSF I found some interesting paper on arXiv:
A Nearly Scale Invariant Spectrum of Gravitational Radiation from Global Phase Transitions, Probing the Gravitational Wave Signature from Cosmic Phase Transitions at Different Scales, and Gravitational waves from self-ordering scalar fields.
via AstronomicaMens, The Physics arXiv Blog