CP3 - Research directions and experiments

Virgo is a laser interferometer designed to detect gravitational waves. Virgo is operated and improved in Cascina, a small town near Pisa on the site of the European Gravitational Observatory (EGO), by an international collaboration of about 300 scientists from France, Italy, the Netherlands, Hungary, Poland, Spain, and Belgium (since July 2018).


Academic staff

Physicists, engineers and computer scientists


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  • The existing UCLouvain/CP3 computing cluster has been augmented with GW-dedicated computing and storage resources. The cluster is integrated into the International Gravitational-Wave Observatory Network (IGWN) Computing Grid, leveraging on the infrastructure CP3 has in place for serving the cluster to the World LHC GRID (WLCG). The UCLouvain GW group has also taken up the responsibility of maintaining at the UCLouvain cluster a service that hosts and serves Virgo data to GW analysis codes submitted over the GRID by the entire LIGO/Virgo/KAGRA international Collaborations.

  • The stochastic gravitational wave background (SGWB) originates from the superposition of GWs emitted by a large number of
    unresolved and uncorrelated sources. Its detection is considered to be one of the ”holy grails” of
    GW astronomy, because of its possible cosmological origin and consequently its impact on our
    comprehension of the Universe.

    The Louvain GW group has been contributing a major effort to the search
    for an anisotropic SGWB and the publication of its results. The group is esponsible for one
    of the three data analysis algorithms of the LIGO/Virgo/KAGRA (LVK) Collaboration, called broadband radiometer analysis.
    Dr J. Suresh has been acting as the anisotropic sub-group chair for the LVK SGWB
    group. Not having found any evidence for an SGWB signal, upper limits have been set as a
    function of the sky direction.

    Millisecond pulsars are one of the potential candidates contributing to the anisotropic stochastic
    gravitational-wave background observable in the ground-based gravitational-wave detectors.
    We have been contributing to a project aiming to estimate and detect the
    stochastic gravitational-wave background produced by millisecond pulsars in the Milky Way.

    We have contributed significantly to the published results of a search that looks for
    persistent stochastic gravitational-wave sources in all directions of the sky at all frequencies at
    which the detectors are sensitive.

    Our group has also published a search that is capable of setting constraints on the
    ensemble properties of neutron stars, like their average ellipticity, from cross-correlation-based
    stochastic gravitational-wave background measurements.

  • Asymmetrically rotating neutron stars (NS) are the canonical sources of continuous gravitational
    waves, which is the name given to long-duration, almost monochromatic GW signals. There has
    been a growing number of other sources of similar signals, which are in general very weak, but
    because they are almost monochromatic and of very long duration, they can be integrated over
    observation periods lasting up to years and become observable. Sophisticated corrections need to be devised
    in order to capture these long and weak signals. These corrections
    take into account the deviation from perfect mono-chromaticity of the signal frequency spectrum, which are caused either
    by the source dynamics of by the relative movement of the source and the detector.

    Our group has been setting up a search for new ultra-light bosons, which could be dark matter (DM) candidates and could accumulate around spinning black holes (BH) via superradiance. In particular, we have been
    focusing on the search for vector boson accumulating in known X-ray binaries in our galaxy.
    In addition to the movement of the earth, the signal will be modulated by the Doppler effect due to the motion of the source black hole (BH)
    around its barycenter.

    Our group is also active on studies aiming to detect planetary-mass (10^-7 to 10^-2 M⊙) primordial BHs (PBH) with continuous-wave
    methods. The method applies to binary
    systems that are still far from the merger and has allowed to constrain the rates and abundance of PBHs in the universe. Limits on the
    fraction of DM made of such PBHs (in the galactic halo, in the galactic centre, and in the solar
    system vicinity) have also been calculated, for LIGO/Virgo as well as ET.

    Ultra-light (10^-13 - 10^-11 eV) bosons could interact with the baryons and leptons in the LIGO/Virgo
    mirrors, causing a constant, narrowband signal in the instruments, very similar to a quasi-monochromatic GW.
    This project displays synergy between particle physics and GW physics and shows that we can
    now directly look for DM candidates with GW instruments. Both short-author list and Collaboration-wide publications have resulted from this project.

  • A gravitational wave detector consists of many coupled optical cavities, the shortest being centimeter scale with sub-millimeter beams and the longest being several kilometers long with several centimeter size beams. When an input beam’s shape is not matched to the cavity eigenmode (the preferred beam shape of the cavity), we speak of mode mismatch (MM). MM is a source of optical loss from the fundamental mode, shown in the top figure, into cylindrical higher order modes (HOMs) of which an example is shown in the bottom figure. Minimising optical losses in a gravitational wave detector is important if techniques such as squeezed light injection are to be more fruitful. At the moment, no gravitational wave detector has an automated way to control MM. We investigate error signal generation by detection of the cylindrical HOMs. These signals then serve as input for control of MM a coupled cavity set-up.