Abstract

We analyse the prospects for constructing hybrid models of inflation that provide a dynamical realisation of the apparent closeness between the supersymmetric GUT scale and the possible scale of cosmological inflation. In the first place, we consider models based on the flipped SU(5)×U(1) gauge group, which has no magnetic monopoles. In one model, the inflaton is identified with a sneutrino field, and in the other model it is a gauge singlet. In both cases we find regions of the model parameter spaces that are compatible with the experimental magnitudes of the scalar perturbations, As, and the tilt in the scalar perturbation spectrum, ns, as well as with an indicative upper limit on the tensor-to-scalar perturbation ratio, r. We also discuss embeddings of these models into SO(10), which is broken at a higher scale so that its monopoles are inflated away.

Highlights

  • It has long been recognised that the naive extrapolation of the gauge coupling strengths measured at accessible energies is consistent with simple supersymmetric models of grand unification at an energy scale MGUT ∼ 2 × 1016 GeV. [1,2,3,4] In parallel, it has long been apparent that successful cosmological inflation probably requires new physics at some energy scale far beyond that of the Standard Model

  • Perhaps inflation was generated along some direction in the space of grand unified Higgs fields? In this case, the requirement of successful inflation might impose some interesting restrictions on the possible structure of a supersymmetric grand unified theory (GUT)

  • How does one ensure the absence of GUT monopoles, or the suppression of their relic density? the requirement of consistency with grand unification might provide some interesting constraint on inflationary model-building, perhaps leading to some interesting predictions for inflationary observables such as As, r and the tilt of the scalar perturbation spectrum, ns

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Summary

Introduction

It has long been recognised that the naive extrapolation of the gauge coupling strengths measured at accessible energies is consistent with simple supersymmetric models of grand unification at an energy scale MGUT ∼ 2 × 1016 GeV. [1,2,3,4] In parallel, it has long been apparent that successful cosmological inflation probably requires new physics at some energy scale far beyond that of the Standard Model. Interest in the possible connection between supersymmetric GUTs and inflation was greatly stimulated by the observation in the BICEP2 experiment of substantial B-mode polarisation in the CMB [7] If this were mainly due to primordial tensor perturbations generated during inflation, it would point to a value of r close to the Planck upper limit, and confirm the remarkable coincidence between the energy scales of inflation and grand unification. We seek realisations of this scenario within the frameworks of specific (relatively) simple GUT models based on minimal gauge groups, namely flipped SU(5)×U(1) and SO(10) ¶ In the former case, there are no GUT monopoles and the model can be derived in a natural way from weakly-coupled string theory.

Minimal GUT Inflation
Flipped Sneutrino Inflation
Singlet Inflation
Discussion and Outlook
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