Abstract
We implement inflation in a non-supersymmetric SU(5) model based on a non-minimal coupling of the axion field to gravity. The isocurvature fluctuations are adequately suppressed, axions comprise the dark matter, proton lifetime estimates are of order 8e34-3e35 years, and the observed baryon asymmetry arises via non-thermal leptogenesis. The presence of low scale colored scalars ensures unification of the Standard Model gauge couplings and also helps in stabilizing the electroweak vacuum.
Highlights
Successful inflation models based on SUð5Þ grand unified theory (GUT) and employing a ColemanWeinberg potential with minimal coupling to gravity were constructed some time ago [1] and, for values of the scalar spectral index ns ∼ 0.96–0.97, the tensor-to-scalar ratio r is ≳10−2 [2]
An axion decay constant fa ∼1011−12 GeV is the desired value for axion dark matter (DM). It has been known for a while that primordial inflation driven by a scalar quartic potential and based on nonminimal coupling to gravity is fully consistent with the Planck observations [6] for plausible values, say ξ ≲ 10, of the dimensionless nonminimal coupling parameter ξ
The realistic GUT model we propose successfully addresses several problems of the standard model (SM) at once, namely the existence and nature of dark matter, the strong CP problem, baryogenesis, the stability of the electroweak vacuum, the origin of the inflationary phase, and the physics behind neutrino masses
Summary
Successful inflation models based on SUð5Þ grand unified theory (GUT) and employing a ColemanWeinberg potential with minimal coupling to gravity were constructed some time ago [1] and, for values of the scalar spectral index ns ∼ 0.96–0.97, the tensor-to-scalar ratio r is ≳10−2 [2] In these models the inflaton field, an SUð5Þ gauge singlet, evolves from the origin to its nonzero vacuum expectation value, reaching trans-Planckian values near its minimum during the last 60 or so e-foldings. We outline the main features of inflation based on a quartic potential with nonminimal coupling of the inflaton field to gravity in Sec. V, and derive the predictions for the spectral index ns, the scalar-to-tensor ratio r, and the running of the spectral index α. VII we show how the inflaton coupling to the adjoint 24-plet ensures SUð5Þ breaking during inflation so that the superheavy monopoles are inflated away
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