Abstract
Pseudo-Goldstone bosons (pGBs) can provide technically natural inflatons, as has been comparatively well-explored in the simplest axion examples. Although inflationary success requires trans-Planckian decay constants, f ≳ Mp, several mechanisms have been proposed to obtain this, relying on (mis-)alignments between potential and kinetic energies in multiple-field models. We extend these mechanisms to a broader class of inflationary models, including in particular the exponential potentials that arise for pGB potentials based on noncompact groups (and so which might apply to moduli in an extra-dimensional setting). The resulting potentials provide natural large-field inflationary models and can predict a larger primordial tensor signal than is true for simpler single-field versions of these models. In so doing we provide a unified treatment of several alignment mechanisms, showing how each emerges as a limit of the more general setup.
Highlights
Inflationary models continue to provide a good description of the primordial fluctuations whose imprint is seen in precision measurements [1] of the Cosmic Microwave Background (CMB)
Because slow-roll inflation requires the existence of very light scalar fields, pseudo-Goldstone Bosons [2, 3] provide among the best-motivated inflationary models, at least from an ultraviolet (UV) perspective
In the case of a pseudo-Goldstone Bosons (pGBs) corresponding to a compact symmetry, slow-roll occurs when the relevant field φ takes generic values and so slow-roll relies on achieving f ∼> Mp [4]
Summary
Inflationary models continue to provide a good description of the primordial fluctuations whose imprint is seen in precision measurements [1] of the Cosmic Microwave Background (CMB). For a large number of fields N based on a randommatrix-theory approach, Bachlechner et al [14] point out that the eigenvectors of the kinetic matrix are overwhelming likely to align with the diagonals in moduli space. In the case of two fields, Kim, Nilles and Peloso [15] point out that super-Planckian decay constants can arise when the directions defined by the scalar potential in (3) are sufficiently aligned. When this happens the ‘other’ direction becomes sufficiently flat to allow inflation to proceed. Note added: upon completetion of this manuscript, we became aware of the preprint [16] discussing related isses
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