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A double hybrid inflationary scenario in non-minimal supergravity which can predict values of the tensor-to-scalar ratio up to about 0.05 is presented. Larger values of this ratio would require unacceptably large running of the scalar spectral index. The underlying supersymmetric particle physics model possesses, for the chosen values of the parameters, practically two inflationary paths, the trivial and the semi-shifted one. The trivial path is stabilized by supergravity and supports a first stage of inflation with a limited number of e-foldings. The tensor-to-scalar ratio can become appreciable with the scalar spectral index remaining acceptable, as a result of the competition between the relatively mild supergravity and the strong radiative corrections to the inflationary potential. The additional number of e-foldings required for solving the puzzles of hot big bang cosmology are generated by a second stage of inflation along the semi-shifted path. This is possible only because the semi-shifted path is almost orthogonal to the trivial one and, thus, not affected by the strong radiative corrections on the trivial path and also because the supergravity effects remain mild. The model predicts the formation of an unstable network of open cosmic strings connecting monopoles to antimonopoles. This network decays to gravity waves well before recombination leading to possibly detectable signatures in future space-based laser interferometer gravitational-wave detectors.
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We present a two stage hybrid inflationary scenario in non-minimal supergravity which can predict values of the tensor-to-scalar ratio of the order of few times 0.01. For the parameters considered, the underlying supersymmetric particle physics model possesses two inflationary paths, the trivial and the semi-shifted one. The trivial path is stabilized by supergravity corrections and supports a first stage of inflation with a limited number of e-foldings. The tensor-to-scalar ratio can become appreciable while the value of the scalar spectral index remains acceptable as a result of the competition between the relatively mild supergravity corrections and the strong radiative corrections to the inflationary potential. The additional number of e-foldings required for solving the puzzles of hot big bang cosmology are generated by a second stage of inflation taking place along the semi-shifted path. This is possible only because the semi-shifted path is almost perpendicular to the trivial one and, thus, not affected by the strong radiative corrections along the trivial path and also because the supergravity effects remain mild. The requirement that the running of the scalar spectral index remains acceptable limits the possible values of the tensor-to-scalar ratio not to exceed about 0.05. Our model predicts the formation of an unstable string-monopole network, which may lead to detectable gravity wave signatures in future space-based laser interferometer observations.
We investigate supersymmetric hybrid inflation in a realistic model based on the gauge symmetry $SU(4)_c times SU(2)_L times SU(2)_R$. The minimal supersymmetric standard model (MSSM) $mu$ term arises, following Dvali, Lazarides, and Shafi, from the coupling of the MSSM electroweak doublets to a gauge singlet superfield which plays an essential role in inflation. The primordial monopoles are inflated away by arranging that the $SU(4)_c times SU(2)_L times SU(2)_R$ symmetry is broken along the inflationary trajectory. The interplay between the (above) $mu$ coupling, the gravitino mass, and the reheating following inflation is discussed in detail. We explore regions of the parameter space that yield gravitino dark matter and observable gravity waves with the tensor-to-scalar ratio $r sim 10^{-4}-10^{-3}$.
BICEP2 has observed a primordial gravitational wave corresponding to the tensor-to-scalar ratio of 0.16. It seems to require a super-Planckian inflationary model. In this paper, we propose a double hybrid inflation model, where the inflaton potential dynamically changes with the evolution of the inflaton fields. During the first phase of inflation over 7 e-folds, the power spectrum can be almost constant by a large linear term in the hybrid potential, which is responsible also for the large tensor-to-scalar ratio. In the second phase of 50 e-folds, the dominant potential becomes dynamically changed to the logarithmic form as in the ordinary supersymmetric hybrid inflation, which is performed by the second inflaton field. In this model, the sub-Planckian field values (~0.9 M_P) can still yield the correct cosmic observations with the sufficient e-folds.
We demonstrate how to realize within supergravity a novel chaotic-type inflationary scenario driven by the radial parts of a conjugate pair of Higgs superfields causing the spontaneous breaking of a grand unified gauge symmetry at a scale assuming the value of the supersymmetric grand unification scale. The superpotential is uniquely determined at the renormalizable level by the gauge symmetry and a continuous R symmetry. We select two types of Kahler potentials, which respect these symmetries as well as an approximate shift symmetry. In particular, they include in a logarithm a dominant shift-symmetric term proportional to a parameter c- together with a small term violating this symmetry and characterized by a parameter c+. In both cases, imposing a lower bound on c-, inflation can be attained with subplanckian values of the original inflaton, while the corresponding effective theory respects perturbative unitarity for r+-=c+/c-<1. These inflationary models do not lead to overproduction of cosmic defects, are largely independent of the one-loop radiative corrections and accommodate, for natural values of r+-, observable gravitational waves consistently with all the current observational data. The inflaton mass is mostly confined in the range (3.7-8.1)x10^10 GeV.
We show how successful supersymmetric hybrid inflation is realized in realistic models where the resolution of the minimal supersymmetric standard model mu problem is intimately linked with axion physics. The scalar fields that accompany the axion, such as the saxion, are closely monitored during and after inflation to ensure that the axion isocurvature perturbations lie below the observational limits. The scalar spectral index n_s is about 0.96 - 0.97, while the tensor-to-scalar ratio r, a canonical measure of gravity waves, lies well below the observable range in our example. The axion domain walls are inflated away, and depending on the axion decay constant f_a and the magnitude of the mu parameter, the axions and/or the lightest supersymmetric particle compose the dark matter in the universe. Non-thermal leptogenesis is naturally implemented in this class of models.
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