David Wands
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View article: Stochastic inflation beyond slow roll: noise modelling and importance sampling
Stochastic inflation beyond slow roll: noise modelling and importance sampling Open
We simulate the distribution of very rare, large excursions in the primordial density field produced in models of inflation in the very early universe which include a strong enhancement of the power spectrum. The stochastic δ𝒩 formalism is…
View article: Fast Radio Bursts and Artificial Neural Networks: a cosmological-model-independent estimation of the Hubble constant
Fast Radio Bursts and Artificial Neural Networks: a cosmological-model-independent estimation of the Hubble constant Open
Fast Radio Bursts (FRBs) have emerged as powerful cosmological probes in recent years offering valuable insights into cosmic expansion. These predominantly extragalactic transients encode information on the expansion of the Universe throug…
View article: Steepest Growth in the Primordial Power Spectrum from Excited States at a Sudden Transition
Steepest Growth in the Primordial Power Spectrum from Excited States at a Sudden Transition Open
Sudden phase transitions during inflation can give rise to strongly enhanced primordial density perturbations on scales much smaller than those directly probed by cosmic microwave background anisotropies. In this paper, we study the effect…
View article: Fast Radio Bursts and Artificial Neural Networks: a cosmological-model-independent estimation of the Hubble Constant
Fast Radio Bursts and Artificial Neural Networks: a cosmological-model-independent estimation of the Hubble Constant Open
Fast Radio Bursts (FRBs) have emerged as powerful cosmological probes in recent years offering valuable insights into cosmic expansion. These predominantly extragalactic transients encode information on the expansion of the Universe throug…
View article: The separate-universe approach and sudden transitions during inflation
The separate-universe approach and sudden transitions during inflation Open
The separate-universe approach gives an intuitive way to understand the evolution of cosmological perturbations in the long-wavelength limit. It uses solutions of the spatially-homogeneous equations of motion to model the evolution of the …
View article: Inflation (2023)
Inflation (2023) Open
This is a review of the current status of studies of cosmological inflation, extracted from Chapter 23 of the 2023 edition of the `Review of Particle Physics': R.L. Workman et al. (Particle Data Group), Prog. Theor. Exp. Phys., 2022, 083C0…
View article: The separate-universe approach and sudden transitions during inflation
The separate-universe approach and sudden transitions during inflation Open
The separate-universe approach gives an intuitive way to understand the evolution of cosmological perturbations in the long-wavelength limit. It uses solutions of the spatially-homogeneous equations of motion to model the evolution of the …
View article: Primordial black holes and their gravitational-wave signatures
Primordial black holes and their gravitational-wave signatures Open
In the recent years, primordial black holes (PBHs) have emerged as one of the most interesting and hotly debated topics in cosmology. Among other possibilities, PBHs could explain both some of the signals from binary black hole mergers obs…
View article: Novel CMB constraints on the α parameter in alpha-attractor models
Novel CMB constraints on the α parameter in alpha-attractor models Open
Cosmological α -attractors are a compelling class of inflationary models. They lead to universal predictions for large-scale observables, broadly independent from the functional form of the inflaton potential. In this work we derive improv…
View article: Non-perturbative non-Gaussianity and primordial black holes
Non-perturbative non-Gaussianity and primordial black holes Open
We present a non-perturbative method for calculating the abundance of primordial black holes given an arbitrary one-point probability distribution function for the primordial curvature perturbation, . A non-perturbative method is essential…
View article: Observational constraints on interacting vacuum energy with linear interactions
Observational constraints on interacting vacuum energy with linear interactions Open
We explore the bounds that can be placed on interactions between cold dark matter and vacuum energy, with equation of state w = -1, using state-of-the-art cosmological observations. We consider linear perturbations about a simple backgroun…
View article: Non-perturbative non-Gaussianity and primordial black holes
Non-perturbative non-Gaussianity and primordial black holes Open
We present a non-perturbative method for calculating the abundance of primordial black holes given an arbitrary one-point probability distribution function for the primordial curvature perturbation, $P(ζ)$. A non-perturbative method is ess…
View article: Observational constraints on interacting vacuum energy with linear interactions
Observational constraints on interacting vacuum energy with linear interactions Open
We explore the bounds that can be placed on interactions between cold dark matter and vacuum energy, with equation of state $w=-1$, using state-of-the-art cosmological observations. We consider linear perturbations about a simple backgroun…
View article: Numerical simulations of stochastic inflation using importance sampling
Numerical simulations of stochastic inflation using importance sampling Open
We show how importance sampling can be used to reconstruct the statistics of rare cosmological fluctuations in stochastic inflation. We have developed a publicly available package, PyFPT ,[ https://github.com/Jacks0nJ/PyFPT .] that solves …
View article: Revisiting small-scale fluctuations in α-attractor models of inflation
Revisiting small-scale fluctuations in α-attractor models of inflation Open
Cosmological α -attractors stand out as particularly compelling models to describe inflation in the very early universe, naturally meeting tight observational bounds from cosmic microwave background (CMB) experiments. We investigate α -att…
View article: Nonsingular cosmology from an interacting vacuum
Nonsingular cosmology from an interacting vacuum Open
We examine the dynamics of FLRW cosmologies in which the vacuum interacts\nwith a perfect fluid through an energy exchange, focusing on the exploration of\nnonsingular configurations, including cyclic and bouncing models. We consider\ntwo …
View article: Revisiting small-scale fluctuations in $\\alpha$-attractor models of\n inflation
Revisiting small-scale fluctuations in $\\alpha$-attractor models of\n inflation Open
Cosmological $\\alpha$-attractors stand out as particularly compelling models\nto describe inflation in the very early universe, naturally meeting tight\nobservational bounds from cosmic microwave background (CMB) experiments. We\ninvestig…
View article: Fully relativistic predictions in Horndeski gravity from standard Newtonian N-body simulations
Fully relativistic predictions in Horndeski gravity from standard Newtonian N-body simulations Open
The N-body gauge allows the introduction of relativistic effects in Newtonian cosmological simulations. Here we extend this framework to general Horndeski gravity theories, and investigate the relativistic effects that the scalar field int…
View article: John David Barrow
John David Barrow Open
John David Barrow was a distinguished cosmologist, an original and creative thinker, and a brilliant communicator. His work addressed fundamental questions about why our universe is the way it is and whether it could have been otherwise. A…
View article: Qualitative dynamics of interacting vacuum cosmologies
Qualitative dynamics of interacting vacuum cosmologies Open
We present a phase-space analysis of the qualitative dynamics cosmologies\nwhere dark matter exchanges energy with the vacuum component. We find fixed\npoints corresponding to power-law solutions where the different components\nremain a co…
View article: Growth of structure in interacting vacuum cosmologies
Growth of structure in interacting vacuum cosmologies Open
We examine the growth of structure in three different cosmological models with interacting dark matter and vacuum energy. We consider the case of geodesic dark matter with zero sound speed, where the relativistic growing mode in comoving-s…
View article: Interferometer constraints on the inflationary field content
Interferometer constraints on the inflationary field content Open
With an energy scale that can be as high as $10^{14}\\,{\\rm GeV}$, inflation\nmay provide a unique probe of high-energy physics. Both scalar and tensor\nfluctuations generated during this early accelerated expansion contain crucial\ninfor…
View article: Stochastic collapse
Stochastic collapse Open
We investigate cosmological models described by a scalar field with an exponential potential, and apply the stochastic formalism, which allows us to study how quantum field fluctuations give rise to stochastic noise. This modifies the clas…
View article: Constraints on the interacting vacuum–geodesic CDM scenario
Constraints on the interacting vacuum–geodesic CDM scenario Open
We investigate an interacting dark sector scenario in which the vacuum energy is free to interact with cold dark matter (CDM), which itself is assumed to cluster under the sole action of gravity, i.e. it is in freefall (geodesic), as in ΛC…
View article: Measuring the duration of inflation with the curvaton
Measuring the duration of inflation with the curvaton Open
Simple models of single-field inflation in the very early universe can\ngenerate the observed amplitude and scale dependence of the primordial density\nperturbation, but models with multiple fields can provide an equally good fit\nto curre…
View article: The attractive behaviour of ultra-slow-roll inflation
The attractive behaviour of ultra-slow-roll inflation Open
International audience
View article: The decisive future of inflation
The decisive future of inflation Open
International audience
View article: The stochastic spectator
The stochastic spectator Open
We study the stochastic distribution of spectator fields predicted in\ndifferent slow-roll inflation backgrounds. Spectator fields have a negligible\nenergy density during inflation but may play an important dynamical role later,\neven giv…
View article: A quantum window onto early inflation
A quantum window onto early inflation Open
Inflation in the early universe is one of the most promising probes of gravity in the high-energy regime. However, observable scales give access to a limited window in the inflationary dynamics. In this paper, we argue that quantum correct…