## About

62

Publications

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Introduction

My goal is to use astronomical observations to test the laws of nature and basic assumptions about our universe. More specifically, I am interested in the problems of dark matter, dark energy and testing gravity. I am interested in the search of new tests using gravitational waves, gravitational lensing, large-scale structure and the development of computational codes to make predictions and test the models. I am also very interested in theoretical aspects of standard and modified gravity.

Additional affiliations

January 2020 - May 2021

November 2017 - November 2020

May 2016 - October 2017

## Publications

Publications (62)

Black hole merger events detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) have revived dark matter models based on primordial black holes (PBH) or other massive compact halo objects (MACHO). This macroscopic dark matter paradigm can be distinguished from particle physics models through their gravitational lensing predictio...

Multimessenger gravitational-wave (GW) astronomy has commenced with the detection of the binary neutron star merger GW170817 and its associated electromagnetic counterparts. The almost coincident observation of both signals places an exquisite bound on the GW speed |cg/c−1|≤5×10−16. We use this result to probe the nature of dark energy (DE), showin...

Testing fundamental physics has become a major aim of modern cosmology, with the nature of gravity under very close scrutiny due to its plausible connection to cosmic acceleration. This program requires flexible tools to obtain accurate numerical predictions in a variety of models, which should also be fast to allow for an efficient exploration of...

The next generation of surveys will greatly improve our knowledge of cosmological gravity. In this paper we focus on how Stage IV photometric redshift surveys, including weak lensing and multiple tracers of the matter distribution and radio experiments combined with measurements of the cosmic microwave background will lead to precision constraints...

We study the structure of scalar-tensor theories of gravity based on
derivative couplings between the scalar and the matter degrees of freedom
introduced through an effective metric. Such interactions are classified by
their tensor structure into conformal (scalar), disformal (vector) and extended
disformal (traceless tensor), as well as by the der...

The Laser Interferometer Space Antenna (LISA) has the potential to reveal wonders about the fundamental theory of nature at play in the extreme gravity regime, where the gravitational interaction is both strong and dynamical. In this white paper, the Fundamental Physics Working Group of the LISA Consortium summarizes the current topics in fundament...

The Laser Interferometer Space Antenna (LISA) has the potential to reveal wonders about the fundamental theory of nature at play in the extreme gravity regime, where the gravitational interaction is both strong and dynamical. In this white paper, the Fundamental Physics Working Group of the LISA Consortium summarizes the current topics in fundament...

The Laser Interferometer Space Antenna (LISA) has two scientific objectives of cosmological focus: to probe the expansion rate of the universe, and to understand stochastic gravitational-wave backgrounds and their implications for early universe and particle physics, from the MeV to the Planck scale. However, the range of potential cosmological app...

The standard Λ Cold Dark Matter (ΛCDM) cosmological model provides a good description of a wide range of astrophysical and cosmological data. However, there are a few big open questions that make the standard model look like an approximation to a more realistic scenario yet to be found. In this paper, we list a few important goals that need to be a...

In this paper we will list a few important goals that need to be addressed in the next decade, also taking into account the current discordances between the different cosmological probes, such as the disagreement in the value of the Hubble constant $H_0$, the $\sigma_8$--$S_8$ tension, and other less statistically significant anomalies. While these...

The next generation of ground-based gravitational-wave detectors will observe coalescences of black holes and neutron stars throughout the cosmos, thousands of them with exceptional fidelity. The Science Book is the result of a 3-year effort to study the science capabilities of networks of next generation detectors. Such networks would make it poss...

The next generation of ground-based gravitational-wave detectors will observe coalescences of black holes and neutron stars throughout the cosmos, thousands of them with exceptional fidelity. The Science Book is the result of a 3-year effort to study the science capabilities of networks of next generation detectors. Such networks would make it poss...

Attempts at constraining theories of late time accelerated expansion often assume broad priors for the parameters in their phenomenological description. Focusing on shift-symmetric scalar-tensor theories with standard gravitational wave speed, we show how a more careful analysis of their dynamical evolution leads to much narrower priors. In doing s...

Since the very beginning of astronomy the location of objects on the sky has been a fundamental observational quantity that has been taken for granted. While precise two dimensional positional information is easy to obtain for observations in the electromagnetic spectrum, the positional accuracy of current and near future gravitational wave detecto...

We propose a space-based interferometer surveying the gravitational wave (GW) sky in the milli-Hz to μ-Hz frequency range. By the 2040s, the μ-Hz frequency band, bracketed in between the Laser Interferometer Space Antenna (LISA) and pulsar timing arrays, will constitute the largest gap in the coverage of the astrophysically relevant GW spectrum. Ye...

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 introduces in the matter power spectrum at intermediate and large scales. In particular, we show that the kinetici...

Attempts at constraining theories of late time accelerated expansion often assume broad priors for the parameters in their phenomenological description. Focusing on shift-symmetric scalar-tensor theories with standard gravitational wave speed, we show how a more careful analysis of their dynamical evolution leads to much narrower priors. In doing s...

Gravitational waves (GW), as light, are gravitationally lensed by intervening matter, deflecting their trajectories, delaying their arrival and occasionally producing multiple images. In theories beyond general relativity, new gravitational degrees of freedom add an extra layer of complexity and richness to GW lensing. We develop a formalism to com...

Gravitational waves (GW), as light, are gravitationally lensed by intervening matter, deflecting their trajectories, delaying their arrival and occasionally producing multiple images. In theories beyond general relativity (GR), new gravitational degrees of freedom add an extra layer of complexity and richness to GW lensing. We develop a formalism t...

In this paper, which is of programmatic rather than quantitative nature, we aim to further delineate and sharpen the future potential of the LISA mission in the area of fundamental physics. Given the very broad range of topics that might be relevant to LISA, we present here a sample of what we view as particularly promising directions, based in par...

Discrepant measurements of the Universe’s expansion rate (H0) may signal physics beyond the standard cosmological model. Here I describe two early modified gravity mechanisms that reconcile H0 value by increasing the expansion rate in the era of matter-radiation equality. These mechanisms, based on viable Horndeski theories, require significantly l...

Discrepant measurements of the Universe's expansion rate ($H_0$) may signal physics beyond the standard cosmological model. Here I describe two early modified gravity mechanisms that reconcile the value of $H_0$ by increasing the expansion rate in the era of matter-radiation equality. These mechanisms, based on viable Horndeski theories, require si...

The late time acceleration of the Universe can be characterized in terms of an extra, time-dependent, component of the Universe—dark energy. The simplest proposal for dark energy is a scalar-tensor theory—quintessence—which consists of a scalar field, ϕ, whose dynamics is solely dictated by its potential, V(ϕ). Such a theory can be uniquely charact...

We provide an updated assessment of the fundamental physics potential of LISA. Given the very broad range of topics that might be relevant to LISA, we present here a sample of what we view as particularly promising directions, based in part on the current research interests of the LISA scientific community in the area of fundamental physics. We org...

The late time acceleration of the Universe can be characterized in terms of an extra, time dependent, component of the universe -- dark energy. The simplest proposal for dark energy is a scalar-tensor theory -- quintessence -- which consists of a scalar field, $\phi$, whose dynamics is solely dictated by its potential, $V(\phi)$. Such a theory can...

Cosmological datasets have great potential to elucidate the nature of dark energy and test gravity on the largest scales available to observation. Theoretical predictions can be computed with hi_class (www.hiclass-code.net), an accurate, fast and flexible code for linear cosmology, incorporating a wide range of dark energy theories and modification...

We propose a space-based interferometer surveying the gravitational wave (GW) sky in the milli-Hz to $\mu$-Hz frequency range. By the 2040s', the $\mu$-Hz frequency band, bracketed in between the Laser Interferometer Space Antenna (LISA) and pulsar timing arrays, will constitute the largest gap in the coverage of the astrophysically relevant GW spe...

Since the very beginning of astronomy the location of objects on the sky has been a fundamental observational quantity that has been taken for granted. While precise two dimensional positional information is easy to obtain for observations in the electromagnetic spectrum, the positional accuracy of current and near future gravitational wave detecto...

Modifications of General Relativity leave their imprint both on the cosmic expansion history through a non-trivial dark energy equation of state, and on the evolution of cosmological perturbations in the scalar and in the tensor sectors. In particular, the modification in the tensor sector gives rise to a notion of gravitational-wave (GW) luminosit...

Modifications of General Relativity leave their imprint both on the cosmic expansion history through a non-trivial dark energy equation of state, and on the evolution of cosmological perturbations in the scalar and in the tensor sectors. In particular, the modification in the tensor sector gives rise to a notion of gravitational-wave (GW) luminosit...

The $\alpha$-attractor inflationary models are nowadays favored by CMB Planck observations. Their similarity with canonical quintessence models motivates the exploration of a common framework that explains both inflation and dark energy. We study the expected constraints that next-generation cosmological experiments will be able to impose for the d...

Future gravitational-wave observations will enable unprecedented and unique science in extreme gravity and fundamental physics answering questions about the nature of dynamical spacetimes, the nature of dark matter and the nature of compact objects.

No Slip Gravity is a simple modified gravity theory with only one free function and the interesting characteristic that - unlike many modified gravity theories - it suppresses growth. This allows it to fit current redshift space distortion and σ 8 mass fluctuation amplitude data better than ΛCDM in general relativity, while retaining a ΛCDM backgro...

Gravitational waves (GWs) provide a new tool to probe the nature of dark energy (DE) and the fundamental properties of gravity. We review the different ways in which GWs can be used to test gravity and models for late-time cosmic acceleration. Lagrangian-based gravitational theories beyond general relativity (GR) are classified into those breaking...

No Slip Gravity is a simple modified gravity theory with only one free function and the interesting characteristic that -- unlike many modified gravity theories -- it suppresses growth. This allows it to fit current redshift space distortion and $\sigma_8$ mass fluctuation amplitude data better than $\Lambda$CDM in general relativity, while retaini...

The nature of dark matter (DM) remains unknown despite very precise knowledge of its abundance in the Universe. An alternative to new elementary particles postulates DM as made of macroscopic compact halo objects (MACHO) such as black holes formed in the very early Universe. Stellar-mass primordial black holes (PBHs) are subject to less robust cons...

Gravitational waves (GWs) provide a new tool to probe the nature of dark energy (DE) and the fundamental properties of gravity. We review the different ways in which GWs can be used to test gravity and models for late-time cosmic acceleration. Lagrangian-based gravitational theories beyond general relativity (GR) are classified into those breaking...

The possibility of linking inflation and late cosmic accelerated expansion using the $\alpha$-attractor models has received increasing attention due to their physical motivation. In the early universe, $\alpha$-attractors provide an inflationary mechanism compatible with Planck satellite CMB observations and predictive for future gravitational wave...

Cosmic shear, the weak gravitational lensing caused by the large-scale structure, is one of the primary probes to test gravity with current and future surveys. There are two main techniques to analyse a cosmic shear survey; a tomographic method, where correlations between the lensing signal in different redshift bins are used to recover redshift in...

Multi-messenger gravitational wave (GW) astronomy has commenced with the detection of the binary neutron star merger GW170817 and its associated electromagnetic counterparts. The almost coincident observation of the GW and the gamma ray burst GRB170817A constrain the speed of GWs at the level of $|c_g/c-1|\leq4.5\cdot10^{-16}$. We use this result t...

We compare Einstein-Boltzmann solvers that include modifications to General Relativity and find that, for a wide range of models and parameters, they agree to a high level of precision. We look at three general purpose codes that primarily model general scalar-tensor theories, three codes that model Jordan-Brans-Dicke (JBD) gravity, a code that mod...

Cosmological models with Galileon gravity are an alternative to the standard $\Lambda {\rm CDM}$ paradigm with testable predictions at the level of its self-accelerating solutions for the expansion history, as well as large-scale structure formation. Here, we place constraints on the full parameter space of these models using data from the cosmic m...

We study the role of field redefinitions in general scalar-tensor theories. In particular, we first focus on the class of field redefinitions linear in the spin-2 field and involving derivatives of the spin-0 mode, generically known as disformal transformations. We start by defining the action of a disformal transformation in the tangent space. The...

We investigate the propagation speed of gravitational waves (GWs) in generic scalar-tensor gravity. A difference in the speed of gravity relative to the speed of light can be caused by the emergence of a disformal geometry in the gravitational sector. This requires the background scalar configuration to both spontaneously break Lorentz symmetry and...

Many theories of modified gravity with higher order derivatives are usually ignored because of serious problems that appear due to an additional ghost degree of freedom. Most dangerously, it causes an immediate decay of the vacuum. However, breaking Lorentz invariance can cure such abominable behavior. By analyzing a model that describes a massive...

Observations of cosmological large scale structures (LSS) offer a unique opportunity to test the nature of gravity. We address the impact of consistent modifications of gravity on the largest observable scales, focusing on relativistic effects in galaxy number counts and the cross-correlation between the matter distribution and the cosmic microwave...

We use a description based on differential forms to systematically explore the space of scalar-tensor theories of gravity. Within this formalism, we propose a basis for the scalar sector at the lowest order in derivatives of the field and in any number of dimensions. This minimal basis is used to construct a finite and closed set of Lagrangians des...

The scale of Baryon Acoustic Oscillations (BAO) imprinted in the matter power spectrum provides an almost-perfect standard ruler: it only suffers sub-percent deviations from fixed comoving length due to non-linear effects. We study the BAO shift in the large Horndeski class of gravitational theories and compute its magnitude in momentum space using...

Kinetic mixing between the metric and scalar degrees of freedom is an
essential ingredient in contemporary scalar-tensor theories. This often makes
hard to understand their physical content, especially when derivative mixing is
present, as it is the case for Horndeski action. In this work we develop a
method that allows to write a Ricci curvature-f...

The theory of bigravity offers one of the simplest possibilities to describe
a massive graviton while having self-accelerating cosmological solutions
without a cosmological constant. However, it has been shown recently that
bigravity is affected by early-time fast growing modes on the tensor sector.
Here we argue that we can only trust the linear a...

It is shown that a disformally coupled theory in which the gravitational
sector has the Einstein-Hilbert form is equivalent to a quartic DBI Galileon
Lagrangian, possessing non-linear higher derivative interactions, and hence
allowing for the Vainshtein effect. This Einstein Frame description
considerably simplifies the dynamical equations and high...

The current wealth of cosmological data has produced a Standard Cosmological Model that, although very successful, relies on three elements of new physics with no conventional explanation. As science can not prove a model right, but rather disprove its alternatives, it is necessary to consider models that challenge the standard assumptions and comp...

It is shown that extensions to General Relativity, which introduce a strongly
coupled scalar field, can be viable if the interaction has a non-conformal
form. Such disformal coupling depends upon the gradients of the scalar field.
Thus, if the field is locally static and smooth, the coupling becomes invisible
in the solar system: this is the disfor...

It has been recently proposed that gravity might be an entropic force.
Although a well defined fundamental description for such a mechanism is still
lacking, it is still possible to address the viability of phenomenological
models of entropic-inspired modified gravities. I will summarize some recent
work directed to using cosmology as a tool to con...

New constraints on inhomogeneous Lema\^itre-Tolman-Bondi (LTB) models alternative to Dark Energy are presented, focusing on adiabatic profiles with space-independent Big Bang and baryon fraction. The Baryon Acoustic Oscillation (BAO) scale at early times is computed in terms of the asymptotic value and then projected to different redshifts by follo...

It has been recently proposed that the interpretation of gravity as an emergent, entropic force might have nontrivial implications to cosmology. Here two approaches are investigated: in one, the Friedman equation receives entropic contributions from the usually neglected surface terms, and in another, the extra terms are derived from quantum correc...

Disformal transformations have proven to be very useful to devise models of the dark sector. In the present paper we apply such transformation to a single scalar field theory as a way to drive the field into a slow roll phase. The canonical scalar field Lagrangian, when coupled to a disformal metric, turns out to have relations to bimetric dark mat...

## Projects

Projects (3)

Explore the possibilities offered by gravitational wave astronomy to test the fundamental properties of gravity and constrain possible explanations to cosmic acceleration.

Observations of unprecedented quality reveal a Universe that is at tension with the standard, and very successful description of matter and energy in Physics. Around 95% of the substratum of the Universe is of unknown nature, split into an accreting component (dark matter) and a repelling component (dubbed dark energy). There are auspicious prospects that the combination of state-of-the-art experiments, and theoretical advances will provide us with tools to elucidate this fundamental issue. This Action explores the viewpoint that cosmological observations reveal a degree of incongruous with theory not because of mysterious elements, but because of a need to review and extend Einstein Relativity to scales where it has not been properly tested. So this Action “CANTATA” gathers a team of European leading experts in gravitational physics and cosmology around the timely goal of investigating the extension of Einstein’s theory of General Relativity. A program including complementary aspects of theoretical physics, cosmology and astrophysics is put forward which is set to consider, in a coordinated and multidisciplinary way, the build up self-consistent models at the various scales and, in principle, to find out some “crucial feature” capable of confirming or ruling out Extended Theories of Gravity with respect to General Relativity. This Action will enhance already existing collaborations and establish an European network with the goal of developing a synergy between expertise and competences, leverage female gender representation, and foster participation of young researchers.