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We review the recently proposed Trans-Planckian Censorship Conjecture that stems from the Trans-Planckian problem of cosmological perturbations. We analyze the implications and constraints that TCC introduces in different frameworks of…
The Weak Gravity Conjecture holds that in a theory of quantum gravity, any gauge force must mediate interactions stronger than gravity for some particles. This statement has surprisingly deep and extensive connections to many different…
We discuss quantum gravitational effects in Einstein theory coupled to periodic axion scalars to analyze the viability of several proposals to achieve superplanckian axion periods (aka decay constants) and their possible application to…
We study the possibility that inflation is driven by a scalar field together with a vector field minimally coupled to gravity. By assuming an effective potential that incorporates both fields into the action, we explore two distinct…
We construct effective supergravity theories from customized constrained superfields which provide a setup consistent both for the description of inflation and the subsequent reheating processes. These theories contain the minimum degrees…
A specific theoretical framework is important for designing and conducting an experiment, and for interpretation of its results. The field of gravitational physics is expanding, and more clarity is needed. It appears that some popular…
We explore the observational implications of models of intermediate inflation driven by modified dispersion relations, specifically those representing the phenomenon of dimensional reduction in the ultraviolet limit. These models are…
We identify a new mechanism in supergravity theories which leads to successful inflation without any need for fine tuning. The simplest model yields a spectrum of density fluctuations tilted away from scale-invariance and negligible…
Inflation is the currently accepted paradigm for the beginnings of the Universe. To explain the observed almost scale invariant spectrum of density perturbations with only a slight spectral tilt, inflation must have been "slow roll", that…
A field kinetic coupling with the Einstein tensor leads to a gravitationally enhanced friction during inflation, by which even steep potentials with theoretically natural model parameters can drive cosmic acceleration. In the presence of…
We examine implications of the weak gravity conjecture for the mechanisms for discharging cosmological constant via membrane nucleations. Once screening fluxes and membranes which source them enter, and weak gravity bounds are enforced, a…
In models of natural inflation, the inflaton is an axion-like particle. Unfortunately, axion potentials in UV-complete theories appear to be too steep to drive inflation. We show that, even for a steep potential, natural inflation can occur…
Supergravity models of natural inflation and its generalizations are presented. These models are special examples of the class of supergravity models proposed in arXiv:1008.3375 and arXiv:1011.5945, which have a shift symmetric K\"ahler…
Although natural inflation is a theoretically well-motivated model for cosmic inflation, it is in tension with recent Planck cosmic microwave background anisotropy measurements. We present a way to alleviate this tension by considering a…
Motivated by the gauge theory of gravity with local scaling symmetry proposed recently in 1712.04537 and 1506.01807, we investigate whether the scalar field therein can be responsible for the inflation. We show that the classical theory…
We provide a compact review on recent developments on axion $F(R)$ gravity. The axion field is a string theory originating theoretical particle that is a perfect candidate for low-mass particle dark matter. In this review we present how a…
Slow-roll inflation generically makes several predictions: a flat Universe, primordial adiabatic density perturbations, and a stochastic gravity-wave background. Each inflation model will further predict specific relations between the…
It is conjectured that inflation, taking account of quantum gravity, leads to a discrete spectrum of cosmological perturbations, instead of the continuous Gaussian spectrum predicted by standard field theory in an unquantized background.…
By considering the Friedmann equations emerging from the entropy-area law of black hole thermodynamics in the context of the generalized uncertainty principle, we study tachyon inflation in the early universe. The presence of a minimal…
Natural (axionic) inflation provides a well-motivated and predictive scheme for the description of the early universe. It leads to sizeable primordial tensor modes and thus a high mass scale of the inflationary potential. Naively this seems…