In the context of inflation, we show how to account for quantum modes in general and numerical relativity on scales bigger than the Hubble radius, from where they behave classically and can grow non-perturbatively.
We provide a formulation of Stochastic Inflation in full general relativity that goes beyond the slow-roll and separate universe approximations. Starting from the initial...
A key prediction of consistent theories of classical gravity coupled to quantum matter is that the metric has to evolve stochastically. Motivated by these considerations,
we study a stochastic Einstein-de Sitter Universe, in order to explore whether a random source in Einstein’s equations can reproduce the phenomenology of Λ. We find two interesting effects. At early times, we argue that...
Cosmic shear, the weak gravitational lensing effect on distant galaxies due to matter in the foreground, is a powerful tool to study the distribution of matter, to probe its large-scale structure, and infer the cosmological model of the Universe. Standard analyses are typically based on the assumption of a Gaussian likelihood with a parameter-independent covariance, but these assumptions may...
Forthcoming stage-IV cosmological surveys will perform measurements with unprecedented accuracies up to non-linear scales. At this level of accuracy, limitations of our theoretical prescriptions lead to biased predictions for cosmological models. We have developed a novel machine learning approach to detect beyond-standard-model physics in the data using a Bayesian Neural Network and...
Extremal black holes are black holes of which the asymptotic charges saturate certain inequalities that ensure weak cosmic censorship. As theoretical playgrounds, they have proven to be instrumental in our understanding of quantum gravity through e.g. microstate counting and swampland conjectures.
Recently, it was noted that extremal black holes generically suffer from singularities on...
In this talk, I will present a novel method for obtaining bounds on the Wilson coefficients of EFTs living in cosmological backgrounds by requiring that their physical modes do not propagate further than a minimally coupled photon by a resolvable amount. In analogy with causality bounds for flat spacetimes which are based on the time delay, I will explain how the cosmological version arises...
The idea that the strength of gravity may have evolved over cosmic history has attracted considerable attention for several decades. This possibility is often thought of in terms of modified theories of gravity, where, for example, the gravitational coupling is controlled by some new fundamental field. The best constraints to date on the present-day time variation of Newton’s constant are...
The cosmic web, or Large-Scale Structure (LSS) is the massive spiderweb- like arrangement of galaxy clusters and the dark matter holding them together under gravity. The lumpy, spindly universe we see today evolved from a much smoother, infant universe. How this structure formed and the information embedded within is considered one of the “Holy Grails”of modern cosmology, and might hold the...
It has been suggested that the effects of renormalization significantly reduce the amplitude of the inflationary spectra at scales measurable in the cosmic microwave background. Via a gauge-invariant analysis, we compute the renormalized scalar and tensor power spectra and follow their evolution in an inflating universe that undergoes a transition to an FRW phase with a growing horizon. For...
Quantum fluctuations from cosmic inflation give rise to the macroscopic structures of the universe. The strongest fluctuations collapse into primordial black holes, a dark matter candidate. Stochastic inflation is a tool to compute the fluctuation statistics non-perturbatively, needed for accurate black hole predictions. I discuss recent progress in these computations, their numerical...
Gravitational waves provide a new observational tool to study the universe. Second-order cosmological perturbation theory allows to study gravitational waves sourced by terms quadratic in first order quantities. For example, so-called scalar induced gravitational waves are sourced by first order scalar fluctuations and have been studied extensively. In this presentation I discuss the...
The recent observation of a gravitational wave background by the NANOGrav collaboration has generated excitement about the possible future detection of primordial gravitational waves. Gravitational waves can be generated by a number of processes during inflation, and their correlation functions can be used to tightly constrain the vast space of inflationary models. But in order to calculate...
We propose a new model of scalar field dark matter interacting with dark energy. Adopting a fluid description of the dark matter field in the regime of rapid oscillations, we find that the equation of state for dark matter is non-zero and even becomes increasingly negative at late times during dark energy domination. Furthermore, the speed of sound of dark matter is non-vanishing at all length...
21cm intensity surveys in interferometer mode can directly measure the small-scale post-reionisation temperature fluctuations in Fourier space. In single-dish mode, these surveys can measure the modes on larger scales.
We show that this complementarity provides a new way to measure the squeezed bispectrum. The interferometer/ single-dish combination can deliver a high signal-to-noise...
We present a general formalism to calculate the non-Gaussianity arising from vacuum decay during inflation in the presence of a light spectator field. This is shown to generate large, potentially detectable non-Gaussianity when applied to an observationally-viable model of inflaton non-minimally coupled to gravity.
The aim of this talk is to give a motivation of why one should consider inhomogeneous initial condition for inflation and an account for our relevant recent work. We consider single scalar field inflation and we use Numerical Relativity simultationso study inflation with generic fast-roll, inhomogeneous initial conditions for different inflationary models. Specifically, we investigate the...
