We construct a hybrid-inflation model where the inflaton potential is generated radiatively, as gauge symmetries guarantee it to be accidentally flat at tree level. The model can be regarded as a small-field version of Natural Inflation, with inflation ending when the mass of a second scalar, the waterfall field, turns tachyonic. This provides a minimal, robust realisation of hybrid inflation,...
In this work we extend the Standard Model with a Peccei-Quinn (PQ) scalar, whose radial component drives inflation near the pole of its kinetic term, and identify the angular component with the axion field. During inflation, the PQ violating terms give a non-zero velocity to the axion, which evolves with an approximately conserved Noether PQ charge. We investigate the reheating dynamics and...
Axion inflation is a well-motivated inflationary model with many fascinating phenomenological consequences, for example, the production of large scalar perturbations, which could seed primordial black holes and source scalar-induced gravitational waves. Furthermore, the parity-violating nature of axion inflation implies the production of circularly polarized gravitational waves. The production...
Einstein–Cartan $f(R)$ theory is known not to induce an additional scalar degree of freedom, the scalaron, contrary to the case in the metric formalism. In this research, we show that by including other geometric quantities in the Einstein-Cartan gravity such as the Nieh-Yan and the Holst term, it is possible to have a propagating scalaron and realize alpha-attractor inflation and its...
While adiabatic perturbations explain CMB and large-scale structure data very well, isocurvature fluctuations could still play a subdominant role. The observation of such a perturbation could hint at more complex cosmic histories such as multi field inflation scenarios. Interactions between the primordial fluids would determine the isocurvature amplitudes in the present epoch.
We revisit the...
For the first time, we investigate the non-perturbative dynamics of single field inflation with a departure from slow-roll. Using simulations, we find that oscillatory features in the potential can drastically alter the course of inflation, with major phenomenological implications. In certain cases, the entire Universe gets trapped in a forever inflating de Sitter state. In others, only some...
The tail of the PDF of primordial scalar perturbations is a key element to determine the abundance of primordial black holes. These primordial non-Gaussianities arise, at least partly, from the non-linear, super-horizon dynamics of inflationary perturbations. Such non-linear evolution is usually addressed through the stochastic $\delta N$ formalism. This formalism is based on the deterministic...
A possible way to generate primordial black holes as candidates for the entirety of dark matter is a large power spectrum of inflationary curvature fluctuations. Recently, questions have been raised regarding the validity of perturbation theory in this context. We compute the one-loop power spectrum in ultra-slow roll inflation, including all relevant interactions for such analysis, along with...
We examine one-loop corrections from small-scale curvature perturbations to the superhorizon-limit ones in single-field inflation models, which have recently caused controversy. We 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...
A non-minimal interaction between the Standard-Model Higgs and spacetime curvature offers a fascinating connection between the physics of post-inflationary reheating and the parameters of the Standard Model. Such an interaction helps stabilising the Higgs at high energies, avoiding the problem of vacuum stability during inflation. It also leads to the explosive tachyonic production of Higgs...
We compute the non-Gaussian corrections to the energy density and anisotropies of gravitational waves induced after an ultra-slow-roll phase of inflation by using a diagrammatic approach, and present the corresponding Feynman rules. Our two-loop calculation includes both the intrinsic non-Gaussianity of the inflaton perturbation $\delta\phi$ and the non-Gaussianity arising from the nonlinear...
Although there is substantial observational evidence for an early period of exponential expansion of the Universe, known as inflation, followed by a subsequent era of radiation domination, the intermediate period connecting these two epochs, referred to as reheating, remains challenging to constrain.
In this talk, I will present the primordial black hole (PBH) reheating scenario, where tiny...
Gravitational waves (GWs) provide a powerful probe to test gravity in the very early Universe. This presentation will explore the effects of a Horndeski scalar field on secondary scalar-induced GWs. The higher-derivative interactions easily dominate the source term on subhorizon scales, significantly enhancing the amplitude of induced GWs. The main effects of these modifications of gravity are...
In this talk, I will discuss how pulsar timing arrays (PTA) can probe primordial black holes (PBH) through gravitational waves. If PBHs exist, they can form in the early universe from the collapse of large density perturbations, necessarily triggering a background of secondary-order scalar-induced gravitational waves. In the late universe, these PBHs will form clusters, leading to enhanced PBH...
Primordial black holes (PBHs) could have played a significant role in our cosmological history and are potential candidates for dark matter composition. Ultra slow-roll (USR) inflation has garnered significant interest (arXiv: 1707.05644, arXiv: 1811.11158) for its ability to amplify the primordial power spectrum, leading to additional PBH production. Recent studies have explored spherically...
