Actually, pre-Big Bang patterns beyond conventional cosmology do not require inflation and can generate CMB B-modes.
Two papers by the BICEP2 Collaboration :
BICEP2 I: Detection Of B-mode Polarization at Degree Angular Scales, arXiv:1403.3985
BICEP2 II: Experiment and Three-Year Data Set, arXiv:1403.4302
announced the possible finding of a B-mode polarization signature of the cosmic microwave background. This was immediately interpreted, assuming it would be confirmed, as an observational proof of cosmic inflation through gravitational wave effects. The claim being that a gravitational potential can only generate E-modes (basically, a gradient) whereas gravitational waves can also generate (rotational) B-modes.
However, this argument does no longer hold if a privileged space direction exists for each point of space-time, as automatically generated by the spinorial space-time (SST) I introduced in 1996-97 (see my previous articles in this blog) and possibly found by the Planck collaboration :
Planck 2013 results. XXIII. Isotropy and statistics of the CMB, arXiv:1303.5083
In the SST pattern, the privileged space direction is an intrinsic property of space-time and was already present in the very early Universe. Then, a simple rotation around the privileged space direction generates a B-mode and the vector product of any E-like vector by this direction naturally leads to a B-like pseudovector. Such a scenario appears much less ad hoc than inflation.
The spinorial space-time describes and automatically expanding universe where the spinor modulus corresponds to the cosmic time (age of the Universe). Standard matter is then generated in an already expanding space, and can dynamically react (in particular, through gravitation) to this pre-existing expansion of purely geometric origin. This can be at the origin of a nonstandard contribution of gravitation to the generation of CMB B-modes.
See also my recent papers on the subject :
Pre-Big Bang, fundamental Physics and noncyclic cosmologies, http://hal.archives-ouvertes.fr/hal-00795588
Planck data, spinorial space-time and asymptotic Universe, https://archive.org/details/PlanckSST
Spinorial space-time and privileged space direction (I), https://archive.org/details/PrivSpDir
Spinorial space-time and Friedmann-like equations (I), https://archive.org/details/SSTFriedmannbis
My two contributions to the ICNFP 2013 Proceedings will also be soon available.