Research

Einstein Telescope GW cosmology LGWA EFT of Dark Energy

Einstein Telescope

The Einstein Telescope is the European project for a ground-based detector of gravitational waves of next generation. I contribute to the activities of the Observational Science Board. In particular, I am one of the coordinators of the division "Common Tools" (Div. 9). Here are some of my main contributions:

  • I developed GWFAST (available on GitHub), a python code conceived in 2022 at the University of Geneva to compute signal-to-noise ratios and parameter estimation capabilities for networks of GW detectors, using the Fisher information matrix formalism. The code is presented in F. Iacovelli, M. Mancarella, S. Foffa and M. Maggiore, GWFAST: A Fisher Information Matrix Python Code for Third-generation Gravitational-wave Detectors, Astrophys.J.Supp. 263 (2022) 1, 2 , arXiv:2207.06910
  • In F. Iacovelli, M. Mancarella, S. Foffa and M. Maggiore, Forecasting the detection capabilities of third-generation gravitational-wave detectors using GWFAST, Astrophys. J. 941 (2022) 208, arXiv:2207.02771 we provided a thorough study of the capabilities of ET as a single detector and in a network with other detectors in detecting and reconstructing the parameters of different classes of coalescing compact objects.
  • I contributed to the study M. Branchesi, M. Maggiore et al., Science with the Einstein Telescope: a comparison of different designs, arXiv:2303.15923, a work performed by the Observational Science Board of the ET collaboration to study the impact on the science outcome of the experiment of variations of its design, location, arm-length, and sensitivity. The work will contribute to the final decision on the design. It is also the most complete study of ET science, covering a broad range of science cases (multimessenger astronomy, cosmology, tests of GR, population studies...). Two more papers expanding part of my contribution, covering in detail nuclear physics constraints and Primordial Black Holes observations, can be found here

Gravitational-wave cosmology

Coalescing binaries at cosmological distance are probes of the cosmological evolution of the Universe. This follows from the fact that the luminosity distance is among the parameters that determines the strength of the signal, and can therefore be reconstructed from gravitational-wave data without any additional calibration. For this reason, we refer to gravitational waves as "standard sirens". Combining the determination of distance and redshift gives a measurement of the cosmological parameters and in particular of the ''Hubble constant'' \( H_0\). Unfortunately, most of the time the gravitational-wave measurements cannot determine the redshift, due to its perfect degeneracy with the mass of the source. One possibility to break this degeneracy is the detection of a counterpart, as in the case of GW170817 and its counterpart GRB 170817A. In this case the source is called a ''bright siren''. This however happens only for a small fraction of sources. In absence of a counterpart, the GW source is called a ''dark siren''. In this case, we use statistical methods that combine an ensemble of sources with some prior knowledge on the population. I study the application of standard siren techniques to LIGO/Virgo data and to future gravitational-wave observatories. In particular, from 2023 I am a member of the Virgo collaboration where I contribute to the cosmology working group. I am particularly interested in using bright and dark sirens to answer two questions:

  • Do gravitational waves propagate as predicted by General Relativity? A very generic phenomenon predicted by theories modifying GR at cosmological scales is the presence of extra friction in the propagation of gravitational waves through an expanding Universe. This modifies the value of the distance inferred from GW data. The modification is usually quantified with a parameter \( \Xi_0\) that can be measured with bright and dark sirens. General Relativity is defined by \( \Xi_0=1\). I am interested in determining if data are consistent with the GR prediction.
  • What is the value of the Hubble constant? The value of the Hubble constant, the very first parameter describing the local expansion rate of the Universe, is a hot topic in modern cosmology. Measurements from the local Universe and from the CMB disagree with each other at the 4-5 \( \sigma\) level. Testing the distance-redshift relation with gravitational waves provides a third, independent probe

State-of-the-art pipelines and perspectives for dark sirens

Recently, in a project led by N. Borghi at the University of Bologna (Italy), we developed CHIMERA (Combined Hierarchical Inference Model for Electromagnetic and gRavitational-wave Analysis), a new, state-of-the-art pipeline for the analysis of gravitational-wave and galaxy catalogues, available on GitHub . The associated paper Cosmology and Astrophysics with Standard Sirens and Galaxy Catalogs in View of Future Gravitational Wave Observations recently appeared on APJ and can be found here.

Applications of dark siren techniques to LIGO/Virgo data

I applied dark sirens techniques to the latest data releases of LIGO/Virgo. Here is a selection of works:
  • Gravitational waves + models of the population of Binary Black Holes: using the presence of scales in the mass distribution of Binary Black Holes, we can break the distance-redshift degeneracy and measure cosmological parameters. In the paper M. Mancarella, E. Genoud-Prachex and M. Maggiore Cosmology and modified gravitational wave propagation from binary black hole population models, Phys.Rev.D 105 (2022) 6, 06403, arXiv:2112.05728, we applied this technique to the GWTC-3 data, obtaining in particular the most stringent constraint on modified gravitational-wave propagation, \( \Xi_0=1.2\pm 0.7 \) (compatible with GR). For this analysis I developed the code MGCosmoPop, publicly available on GitHub
  • Gravitational waves + galaxy catalogues: a galaxy catalogue can be used to construct a prior on the unknown redshift of GW sources. We studied this technique in detail and applied it to the GWTC-2 catalogue and the GLADE galaxy catalogue in Finke et al., Cosmology with LIGO/Virgo dark sirens: Hubble parameter and modified gravitational wave propagation, JCAP 08 (2021) 026, arXiv:2101.12660. An updated application to the GWTC-3 catalogue with the GLADE+ catalogue can be found in Mancarella et al. arXiv:2203.09238. We developed and open-sourced the code DarkSirensStat, available on GitHub

The Lunar Gravitational-Wave Antenna

Building gravitational-wave detectors on the surface of the Earth (like Virgo, LIGO, and Kagra) or in space (like LISA) is not the unique possibility for detecting them. For example, gravitational waves make the Moon vibrate, and those vibrations can be captured by inertial sensors placed on its surface, providing a planetary-scale gravitational-wave antenna. This would allow to measure gravitational waves in the decihertz band, filling a gap between ground and space based detectors with important consequences for astrophysics and cosmology. Recently, I contributed to a first comprehensive analysis of the Lunar Gravitational Wave Antenna science case. The preprint is available at arXiv:2404.09181.

The effective theory of dark energy

The Effective Theory of Dark Energy amounts to the description of linear cosmological perturbations in scalar-tensor theories of gravity through all the possible operators compatible with symmetries. It provides a simple yet general way to bridge theory and observations, and allows to test General Relativity with observations of the Large Scale Structures of the Universe and of the Cosmic Microwave Background radiation. This approach fully takes into account the respect of basic principles of physics (locality, causality) when analysing data, and allows a direct link of the observables to physically meaningful parameters of the action, at the same time. This was the subject of my PhD thesis.

My main contributions were the study of the coupling of gravity to matter fields to test the Equivalence Principle at cosmological scales, the first comprehensive treatment of the most general class of modified gravity theories of the "scalar-tensor" type, known as "DHOST", and the first forecasts for Large Scale Structures observables. My papers on the subject can be found at this link.

Recently, with the group of C. Bonvin at the University of Geneva, we studied extensively a way of constraning the breaking of the Equivalence Principle and deviations from General relativity with the distortion of time that induces a dipole in the two-point correlation of galaxies. The paper is in press on JCAP and the preprint is available at arXiv:2311.14425.