Abstract
We develop new scenarios of large field inflation in type IIA string compactifications in which the key ingredient is a D6-brane that creates a potential for a B-field axion. The potential has the multi-branched structure typical of F-term axion monodromy models and, near its supersymmetric minima, it is described by a 4d supergravity model of chaotic inflation with a stabiliser field. The same statement applies to the D6-brane Wilson line, which can also be considered as an inflaton candidate. We analyse both cases in the context of type IIA moduli stabilisation, finding an effective potential for the inflaton system and a simple mechanism to lower the inflaton mass with respect to closed string moduli stabilised by fluxes. Finally, we compute the B-field potential for trans-Planckian field values by means of the DBI action. The effect of Planck suppressed corrections is a flattened potential which, in terms of the compactification parameters, interpolates between linear and quadratic inflation. This renders the cosmological parameters of these models compatible with current experimental bounds, with the tensor-to-scalar ratio ranging as 0.08 < r < 0.12
Highlights
Its periodicity by means of creating a non-periodic, multi-branched potential for it
We develop new scenarios of large field inflation in type IIA string compactifications in which the key ingredient is a D6-brane that creates a potential for a B-field axion
It has been realised that one may create such multi-branched potential by means of compactifications whose low energy superpotential depends on the axion. These models, dubbed F-term axion monodromy in [11], have the advantage that they directly connect with the 4d framework in [12, 13] and that at small inflaton vevs they are described by 4d supergravity models of F-term inflation
Summary
Let us consider type IIA string theory compactified in a six-dimensional manifold X6, in the presence O6-planes wrapping three-cycles of X6 and filling the remaining four spacetime dimensions. From the general arguments of [61] one expects the D6-brane Wilson line A to only appear through its derivatives in the 4d effective action, and to exhibit a shift symmetry in the Kahler potential. These terms are suppressed by a factor exp(−A/α ), with A the string frame volume of a holomorphic two-cycle of M6, so in the supergravity large volume regime they will be subleading compared to the superpotential terms discussed previously They will contribute to the scalar potential for Kahler moduli and in particular one expects that they generate a periodic sinusoidal-like potential for a B-field axion. This will allow to develop a bilinear superpotential in which two of the above axions (namely B-field and Wilson line axions) are involved, and to build chaotic inflation scenarios for both of them
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