I examine one-loop corrections from small-scale curvature perturbations to the superhorizon-limit ones in single-field inflation models, which have recently caused controversy. I consider the case where the Universe experiences transitions of slow-roll (SR) → intermediate period → SR. The intermediate period can be an ultra-slow-roll period or a resonant amplification period, either of which...

At high energies, such as during inflation, the quartic coupling of the Standard Model (SM) Higgs potential runs negative, according to current measurements. This can lead the potential into a tachyonic regime, where the square of the mass of the SM Higgs becomes negative. This tachyonic instability can exponentially enhance Higgs particle production via Hubble-induced effects and via the...

We propose a new classes of inflation models based on the modular symmetry, where modulus field $\tau$ serves as the inflaton. We make a connection between modular inflation and modular stabilization, and the modulus field rolls towards fixed point after inflation. We find the modular symmetry strongly constraints the possible shape of the potential and find some parameter space where the...

In this study, we explore the evolution of a system composed of an unstable scalar field ($\phi$), and radiation in the context of non-standard cosmology where initially the Universe is dominated by the energy density of $\phi$. Later, the unstable $\phi$ with decay width $\Gamma_\phi$ decays into radiation and we focus on two relevant quantities: the maximum radiation temperature $T_{max}$...

We make use of Borel resummation to extract the exact time dependence from the divergent series found in the context of stochastic inflation. Correlation functions of self-interacting scalar fields in de Sitter spacetime are known to develop secular IR divergences via loops, and the first terms of the divergent series have been consistently computed both with standard techniques for curved...

Cosmological first order phase transitions are typically associated with physics beyond the Standard Model, and thus of great theoretical and observational interest. Models of phase transitions where the energy is mostly converted to dark radiation can be constrained through limits on the dark radiation energy density (parameterized by $\Delta N_{\rm eff}$). However, the current constraint...

A new theory is presented to estimate the mass, size, lifetime, and other properties of cold dark matter particles (CDM) within the ΛCDM cosmology. Using Illustris simulations, we demonstrate the existence of mass and energy cascade that facilitates the formation of hierarchical structures. A scale-independent rate of cascade $\varepsilon_u\approx 10^{-7}m^2/s^3$ can be identified. The energy...

The main limitation for pre-inflationary breaking of Peccei-Quinn (PQ) symmetry is the upper bound on the Hubble rate during inflation from axion isocurvature fluctuations. This leads to a tension between high scale inflation and QCD axions with Grand Unified Theory (GUT) scale decay constants, which reduces the potential for a detection of tensor modes at next generation CMB experiments. We...

When the inflaton is coupled to the gluon Chern-Simons term for successful reheating, mixing between the inflaton and the QCD axion is generally expected given the solution of the strong CP problem by the QCD axion. This is particularly natural if the inflaton is a different, heavier axion. We propose a scenario in which the QCD axion plays the role of the inflaton by mixing with heavy axions....