Eva guest blog

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Let us assume that the BICEP2 result is confirmed as cosmological, and indicates primordial gravitational waves generated during inflation. Within the context of inflationary theory, this groundbreaking discovery has important implications for quantum gravity, for which string theory is our leading candidate.

String theory contains a rather simple mathematical structure -- monodromy -- which can generate a significant tensor signal. Here I'll explain that mechanism, and discuss its range of applicability as we currently understand it. String theory also contains a plethora of scalar fields, which in itself gives a realization of assisted inflation, N-flation, covered in and earlier blog post. (More generally, one has multiple directions along which monodromy operates, a combination of these two mechanisms.)

In two lines one can relate the number of e-foldings of inflation to the field range, assuming no strong variations in the slow roll parameters during the process. This relation, the so-called Lyth ``bound", implies a super-Planckian field range for the inflaton field $\varphi$ during the process. Inflation requires a slowly decreasing source of potential energy $V(\varphi )$ over this range $\mathrm{\Delta }\varphi >M_{Planck}$.

From a low energy point of view, we may parameterize our ignorance of