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Register a new user$mu$-Hybrid Inflation with Low Reheat Temperature and Observable Gravity Waves
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In $mu$-hybrid inflation a nonzero inflaton vacuum expectation value induced by supersymmetry breaking is proportional to the gravitino mass $m_{3/2}$, which can be exploited to resolve the minimal supersymmetric standard model $mu$ problem. We show how this scenario can be successfully implemented with $m_{3/2} sim 1-100$ TeV and reheat temperature as low as $10^6$ GeV by employing a minimal renormalizable superpotential coupled with a well defined non-minimal Kahler potential. The tensor-to-scalar ratio $r$, a canonical measure of primordial gravity waves in most cases is less than or of the order of $10^{-6}-10^{-3}$.
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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 $r sim 10^{-4}-10^{-3}$.
Motivated by recent cosmological observations of a possibly unsuppressed primordial tensor component $r$ of inflationary perturbations, we reanalyse in detail the 5D conformal SUGRA originated natural inflation model of Ref. [1]. The model is a supersymmetric variant of 5D extra natural inflation, also based on a shift symmetry, and leads to the potential of natural inflation. Coupling the bulk fields generating the inflaton potential via a gauge coupling to the inflaton with brane SM states we necessarily obtain a very slow gauge inflaton decay rate and a very low reheating temperature $T_rstackrel{<}{_sim }{cal O}(100)$~GeV. Analysis of the required number of e-foldings (from the CMB observations) leads to values of $n_s$ in the lower range of present Planck 2015 results. Some related theoretical issues of the construction, along with phenomenological and cosmological implications, are also discussed.
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.
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 revisit supersymmetric hybrid inflation in the context of flipped $SU(5)$ model. With minimal superpotential and minimal Kahler potential, and soft SUSY masses of order $(1 - 100)$ TeV, compatibility with the Planck data yields a symmetry breaking scale $M$ of flipped $SU(5)$ close to $(2 - 4) times 10^{15}$ GeV. This disagrees with the lower limit $M gtrsim 7 times 10^{15}$ GeV set from proton decay searches by the Super-Kamiokande collaboration. We show how $M$ close to the unification scale $2times 10^{16}$ GeV can be reconciled with SUSY hybrid inflation by employing a non-minimal Kahler potential. Proton decays into $e^+ pi^0$ with an estimated lifetime of order $10^{36}$ years. The tensor to scalar ratio $r$ in this case can approach observable values $sim 10^{-4} - 10^{-3}$.
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