829 citations · 2.8k across the 42 of their papers we have counts for
18 papers · 1 filter
On tachyonic stability priors for dark energy
Rafaela Gsponer, Johannes Noller
A number of stability criteria exist for dark energy theories, associated with requiring the absence of ghost, gradient and tachyonic instabilities. Tachyonic instabilities are the…
Theoretical priors in scalar-tensor cosmologies: Shift-symmetric Horndeski models
Dina Traykova, Emilio Bellini, Pedro G. Ferreira +3
Attempts at constraining theories of late time accelerated expansion often assume broad priors for the parameters in their phenomenological description. Focusing on shift-symmetric…
Positivity Bounds on Dark Energy: When Matter Matters
Claudia de Rham, Scott Melville, Johannes Noller
Positivity bounds - constraints on any low-energy effective field theory imposed by the fundamental axioms of unitarity, causality and locality in the UV - have recently been used…
Scalar-tensor cosmologies without screening
Johannes Noller, Luca Santoni, Enrico Trincherini +1
Scalar-tensor theories are frequently only consistent with fifth force constraints in the presence of a screening mechanism, namely in order to suppress an otherwise unacceptably l…
Cosmological constraints on dark energy in light of gravitational wave bounds
Johannes Noller
Gravitational wave (GW) constraints have recently been used to significantly restrict models of dark energy and modified gravity. New bounds arising from GW decay and GW-induced da…
Positivity in the sky
Scott Melville, Johannes Noller
Positivity bounds - the consequences of requiring a unitary, causal, local UV completion - place strong restrictions on theories of dark energy and/or modified gravity. We derive a…
Cosmological parameter constraints for Horndeski scalar-tensor gravity
Johannes Noller, Andrina Nicola
We present new cosmological parameter constraints for general Horndeski scalar-tensor theories, using CMB, redshift space distortion, matter power spectrum and BAO measurements fro…
Radiative stability and observational constraints on dark energy and modified gravity
Johannes Noller, Andrina Nicola
We investigate the radiative stability of Horndeski scalar-tensor theories with luminally propagating gravitational waves (as extensively discussed in the wake of GW170817) and sho…
Inflation in a scale invariant universe
Pedro G. Ferreira, Christopher T. Hill, Johannes Noller +1
A scale-invariant universe can have a period of accelerated expansion at early times: inflation. We use a frame-invariant approach to calculate inflationary observables in a scale…
Strong constraints on cosmological gravity from GW170817 and GRB 170817A
Tessa Baker, Emilio Bellini, Pedro G. Ferreira +3
The detection of an electromagnetic counterpart (GRB 170817A) to the gravitational wave signal (GW170817) from the merger of two neutron stars opens a completely new arena for test…
Beyond CDM: Problems, solutions, and the road ahead
Philip Bull, Yashar Akrami, Julian Adamek +37
Despite its continued observational successes, there is a persistent (and growing) interest in extending cosmology beyond the standard model, CDM. This is motivated by a range o…
Relativistic scalar fields and the quasi-static approximation in theories of modified gravity
Johannes Noller, Francesca von Braun-Bates, Pedro G. Ferreira
Relativistic scalar fields are ubiquitous in modified theories of gravity. An important tool in understanding their impact on structure formation, especially in the context of N-bo…
Three-form inflation and non-Gaussianity
David J. Mulryne, Johannes Noller, Nelson J. Nunes
We calculate the perturbed action, at second and third order, for a massive three-form field minimally coupled to gravity, and use it to explore the observational predictions of th…
Constraining fast-roll inflation
Johannes Noller
We present constraints on how far single field inflation may depart from the familiar slow-roll paradigm. Considering a fast-roll regime while requiring a (near)-scale-invariant po…
Non-Gaussianity in single field models without slow-roll
Johannes Noller, Joao Magueijo
We investigate non-Gaussianity in general single field models without assuming slow-roll conditions or the exact scale-invariance of the scalar power spectrum. The models considere…
Bimetric structure formation: non-Gaussian predictions
Joao Magueijo, Johannes Noller, Federico Piazza
The minimal bimetric theory employing a disformal transformation between matter and gravity metrics is known to produce exactly scale-invariant fluctuations. It has a purely equila…
Non-adiabatic primordial fluctuations
J. Noller, J. Magueijo
We consider general mixtures of isocurvature and adiabatic cosmological perturbations. With a minimal assumption set consisting of the linearized Einstein equations and a primordia…
Primordial fluctuations without scalar fields
J. Magueijo, J. Noller
We revisit the question of whether fluctuations in hydrodynamical, adiabatical matter could explain the observed structures in our Universe. We consider matter with variable equati…