# Publications by Pedro Ferreira

## Galaxy morphology rules out astrophysically relevant Hu-Sawicki f (R) gravity

PHYSICAL REVIEW D American Physical Society (APS) **102** (2020) ARTN 104060

## Detecting the anisotropic astrophysical gravitational wave background in the presence of shot noise through cross-correlations

Physical Review D American Physical Society **102** (2020) 23002

The spatial and temporal discreteness of gravitational wave sources leads to shot noise that may, in some regimes, swamp any attempts at measuring the anisotropy of the gravitational wave background. Cross-correlating a gravitational wave background map with a sufficiently dense galaxy survey can alleviate this issue, and potentially recover some of the underlying properties of the gravitational wave background. We quantify the shot noise level and we explicitly show that cross-correlating the gravitational wave background and a galaxy catalog improves the chances of a first detection of the background anisotropy with a gravitational wave observatory operating in the frequency range (10 Hz, 100 Hz), given sufficient sensitivity.

## Noise angular power spectrum of gravitational wave background experiments

Physical Review D American Physical Society **101** (2020) 124048

We construct a model for the angular power spectrum of the instrumental noise in interferometer networks mapping gravitational wave backgrounds (GWBs) as a function of detector noise properties, network configuration, and scan strategy. We use the model to calculate the noise power spectrum for current and future ground-based experiments, as well as for planned space missions. We present our results in a language similar to that used in cosmic microwave background and intensity mapping experiments, and connect the formalism with the sensitivity curves that are common lore in GWB analyses.

## Scale invariant gravity and black hole ringdown

Physical Review D American Physical Society **101** (2020) 024011

## Testing self-interacting dark matter with galaxy warps

PHYSICAL REVIEW D **100** (2019) ARTN 123006

## Growth of massive scalar hair around a Schwarzschild black hole

Physical Review D American Physical Society **100** (2019) 063014-

## The phenomenology of beyond Horndeski gravity

Journal of Cosmology and Astroparticle Physics IOP Publishing **2019** (2019) 035

We study the phenomenology of the beyond Horndeski class of scalar-tensor theories of gravity, which on cosmological scales can be characterised in terms of one extra function of time, βH, as well as the usual four Horndeski set of free functions. We show that βH can be directly related to the damping of the matter power spectrum on both large and small scales. We also find that the temperature power spectrum of the cosmic microwave background (CMB) is enhanced at low multipoles and the lensing potential is decreased, as a function of βH. For a particular choice of time dependence we find constraints on βH of order (1) using measurements of the temperature and polarisation of the CMB, as well as the lensing potential derived from it, combined with large scale structure data. We find that redshift space distortion measurements can play a significant role in constraining these theories. Finally, we comment on the recent constraints from the observation of an electromagnetic counterpart to a gravitational wave signal; we find that these constraints reduce the number of free parameters of the model but do not significantly change the constraints on the remaining parameters.

## Forecasts for low spin black hole spectroscopy in Horndeski gravity

Physical Review D American Physical Society **99** (2019) 104082

## The fifth force in the local cosmic web

Monthly Notices of the Royal Astronomical Society: Letters Oxford University Press **483** (2018) L64-L68

Extensions of the standard models of particle physics and cosmology often lead to long-range fifth forces with properties dependent on gravitational environment. Fifth forces on astrophysical scales are best studied in the cosmic web where perturbation theory breaks down. We present constraints on chameleon- and symmetron-screened fifth forces with Yukawa coupling and megaparsec range – as well as unscreened fifth forces with differential coupling to galactic mass components – by searching for the displacements they predict between galaxies’ stars and gas. Taking data from the AlfalfaH I survey, identifying galaxies’ gravitational environments with the maps of Desmond et al. and forward modelling with a Bayesian likelihood framework, we set upper bounds on fifth-force strength relative to Newtonian gravity from ∼few × 10−4 (1σ) for range λC = 50 Mpc, to ∼0.1 for λC = 500 kpc. In f(R) gravity this requires fR0 ≲ few × 10−8. The analogous bounds without screening are ∼few × 10−4 and few × 10−3. These are the tightest and among the only fifth-force constraints on galaxy scales. We show how our results may be strengthened with future survey data and identify the key features of an observational programme for furthering fifth-force tests beyond the Solar system.

## Cosmological Tests of Gravity

in *ANNUAL REVIEW OF ASTRONOMY AND ASTROPHYSICS, VOL 57, 2019*, **57** (2019) 335-374

## Fifth force constraints from galaxy warps

Physical Review D American Physical Society **98** (2018) 083010

Intragalaxy signals contain a wealth of information on fundamental physics, both the dark sector and the nature of gravity. While so far largely unexplored, such probes are set to rise dramatically in importance as upcoming surveys provide data of unprecedented quantity and quality on galaxy structure and dynamics. In this paper, we use warping of stellar disks to test the chameleon- or symmetron-screened fifth forces which generically arise when new fields couple to matter. We take r -band images of mostly late-type galaxies from the Nasa Sloan Atlas and develop an automated algorithm to quantify the degree of U-shaped warping they exhibit. We then forward model the warp signal as a function of fifth-force strength, ΔG/GN, and range, λC, and the gravitational environments and internal properties of the galaxies, including full propagation of the non-Gaussian uncertainties. Convolving this fifth-force likelihood function with a Gaussian describing astrophysical and observational noise and then constraining ΔG/GN and λC by Markov chain Monte Carlo, we find the overall likelihood to be significantly increased (Δlog(L)≃20) by adding a screened fifth force with λC≃2 Mpc and ΔG/GN≃0.01. The variation of Δlog(L) with λC is quantitatively as expected from the correlation of the magnitude of the fifth-force field with the force’s range, and a similar model without screening achieves no increase in likelihood over the General Relativistic case ΔG=0. Although these results are in good agreement with a previous analysis of the same model using offsets between galaxies’ stellar and gas mass centroids [H. Desmond et al., Phys. Rev. D 98, 064015 (2018).], we caution that the effects of confounding baryonic and dark matter physics must be thoroughly investigated for the results of the inference to be unambiguous.

## Fifth force constraints from the separation of galaxy mass components

Physical Review D American Physical Society **98** (2018)

One of the most common consequences of extensions to the standard models of particle physics or cosmology is the emergence of a fifth force. While generic fifth forces are tightly constrained at Solar System scales and below, they may escape detection by means of a screening mechanism which effectively removes them in dense environments. We constrain the strength ΔG/GN and range λC of a fifth force with Yukawa coupling arising from a chameleon- or symmetron-screened scalar field—as well as an unscreened fifth force with differential coupling to galactic mass components—by searching for the displacement it predicts between galaxies’ stellar and gas mass centroids. Taking data from the Alfalfa survey of neutral atomic hydrogen (HI), identifying galaxies’ gravitational environments with the maps of [H. Desmond, P. G. Ferreira, G. Lavaux, and J. Jasche, Mon. Not. R. Astron. Soc. 474, 3152 (2018)] and forward modeling with a Bayesian likelihood framework, we find, with screening included, 6.6σ evidence for ΔG>0 at λC≃2Mpc. The maximum-likelihood ΔG/GN is 0.025. A similar fifth force model without screening gives no increase in likelihood over the case ΔG=0 for any λC. Although we validate this result by several methods, we do not claim screened modified gravity to provide the only possible explanation for the data: this conclusion would require knowing that the signal could not be produced by “galaxy formation” physics. We show also the results of a more conservative—though less well-motivated—noise model which yields only upper limits on ΔG/GN, ranging from ∼10−1 for λC ≃ 0.5 Mpc to ∼ few ×10−4 at λC ≃ 50 Mpc. Corresponding models without screening receive the somewhat stronger bounds ∼ few ×10−3 and ∼ few ×104 respectively. We show how these constraints may be improved by future galaxy surveys and identify the key features of an observational program for directly constraining fifth forces on scales beyond the Solar System. This paper provides a complete description of the analysis summarized in [H. Desmond, P. G. Ferreira, G. Lavaux, and J. Jasche, arXiv:1802.07206].

## Emergent dark energy from dark matter

PHYSICAL REVIEW D **97** (2018) ARTN 121301

## Inflation in a scale-invariant universe

PHYSICAL REVIEW D **97** (2018) ARTN 123516

## Quasinormal modes of black holes in Horndeski gravity

PHYSICAL REVIEW D **97** (2018) ARTN 104047

## A general theory of linear cosmological perturbations: stability conditions, the quasistatic limit and dynamics

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS (2018) ARTN 021

## General theories of linear gravitational perturbations to a Schwarzschild black hole

PHYSICAL REVIEW D **97** (2018) ARTN 044021

## The impact of relativistic effects on cosmological parameter estimation

Physical Review D American Physical Society **97** (2018) 1-14

Future surveys will access large volumes of space and hence very long wavelength fluctuations of the matter density and gravitational field. It has been argued that the set of secondary effects that affect the galaxy distribution, relativistic in nature, will bring new, complementary cosmological constraints. We study this claim in detail by focusing on a subset of wide-area future surveys: Stage-4 cosmic microwave background experiments and photometric redshift surveys. In particular, we look at the magnification lensing contribution to galaxy clustering and general relativistic corrections to all observables. We quantify the amount of information encoded in these effects in terms of the tightening of the final cosmological constraints as well as the potential bias in inferred parameters associated with neglecting them. We do so for a wide range of cosmological parameters, covering neutrino masses, standard dark-energy parametrizations and scalar-tensor gravity theories. Our results show that, while the effect of lensing magnification to number counts does not contain a significant amount of information when galaxy clustering is combined with cosmic shear measurements, this contribution does play a significant role in biasing estimates on a host of parameter families if unaccounted for. Since the amplitude of the magnification term is controlled by the slope of the source number counts with apparent magnitude, $s(z)$, we also estimate the accuracy to which this quantity must be known to avoid systematic parameter biases, finding that future surveys will need to determine $s(z)$ to the $\sim$5-10\% level. On the contrary, large-scale general-relativistic corrections are irrelevant both in terms of information content and parameter bias for most cosmological parameters, but significant for the level of primordial non-Gaussianity.

## Comparison of Einstein-Boltzmann solvers for testing general relativity

PHYSICAL REVIEW D **97** (2018) ARTN 023520

## Strong Constraints on Cosmological Gravity from GW170817 and GRB 170817A.

Physical review letters **119** (2017) 251301-251301

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 testing theories of gravity. We show that this measurement allows us to place stringent constraints on general scalar-tensor and vector-tensor theories, while allowing us to place an independent bound on the graviton mass in bimetric theories of gravity. These constraints severely reduce the viable range of cosmological models that have been proposed as alternatives to general relativistic cosmology.