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Thomas C. Bachlechner
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We argue that moduli stabilization generically restricts the evolution following transitions between weakly coupled de Sitter vacua and can induce a strong selection bias towards inflationary cosmologies. The energy density of domain walls between vacua typically destabilizes Kahler moduli and triggers a runaway towards large volume. This decompactification phase can collapse the new de Sitter region unless a minimum amount of inflation occurs after the transition. A stable vacuum transition is guaranteed only if the inflationary expansion generates overlapping past light cones for all observable modes originating from the reheating surface, which leads to an approximately flat and isotropic universe. High scale inflation is vastly favored. Our results point towards a framework for studying parameter fine-tuning and inflationary initial conditions in flux compactifications.
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Hyperbolic inflation is an extension of the slow-roll inflation in multi-field models. We extend hyperbolic inflation by adding a gauge field and find four-type attractor solutions: slow-roll inflation, hyperbolic inflation, anisotropic slow roll inflation, and anisotropic hyperbolic inflation. We perform the stability analysis with the dynamical system method. We also study the transition behaviors of solutions between anisotropic slow roll inflation and anisotropic hyperbolic inflation. Our result indicates that destabilization of the standard slow-roll inflation ubiquitously occurs in multi-scalar-gauge field inflationary scenarios.
We comment on Weinbergs interesting analysis of asymptotically safe inflation (arXiv:0911.3165). We find that even if the gravity theory exhibits an ultraviolet fixed point, the energy scale during inflation is way too low to drive the theory close to the fixed point value. We choose the specific renormalization groupflow away from the fixed point towards the infrared region that reproduces the Newtons constant and todays cosmological constant. We follow this RG flow path to scales below the Planck scale to study the stability of the inflationary scenario. Again, we find that some fine tuning is necessary to get enough efolds of infflation in the asymptotically safe inflationary scenario.
We discuss supergravity inflation in braneworld cosmology for the class of potentials $V(phi)=alpha phi^nrm{exp}(-beta^m phi^m)$ with $m=1,~2$. These minimal SUGRA models evade the $eta$ problem due to a broken shift symmetry and can easily accommodate the observational constraints. Models with smaller $n$ are preferred while models with larger $n$ are out of the $2sigma$ region. Remarkably, the field excursions required for $60$ $e$-foldings stay sub-planckian $Deltaphi <1$.
In this paper, we analyze the inflationary cosmology using string field theory. This is done by using the zero level contribution from string field theory, which is a non-local tachyonic action. We will use the non-local Friedmann equations for this model based on string field theory, and calculate the slow-roll parameters for this model. We will then explicitly obtain the scalar and tensorial power spectrum, their related indices, and the tensor-to-scalar ratio for this model. Finally, we use cosmological data from Planck 2013 to 2018 to constrain the free parameters in this model and find that string field theory is compatible with them.
We develop analytic and numerical techniques for studying the statistics of slow-roll inflation in random Gaussian landscapes. As an illustration of these techniques, we analyze small-field inflation in a one-dimensional landscape. We calculate the probability distributions for the maximal number of e-folds and for the spectral index of density fluctuations $n_s$ and its running $alpha_s$. These distributions have a universal form, insensitive to the correlation function of the Gaussian ensemble. We outline possible extensions of our methods to a large number of fields and to models of large-field inflation. These methods do not suffer from potential inconsistencies inherent in the Brownian motion technique, which has been used in most of the earlier treatments.
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