Cosmology and General Relativity
Our data analysis activities have been focused on the Planck satellite measurements and are now turning to the next generation of CMB polarization experiments, such as the CORE satellite. We are also part of the EUCLID and LISA missions, with measurements of the large scale structure of the Universe and gravitational waves, respectively.
Our works on late-time cosmology concern the reionization era and the development of numerical codes to solve for the cosmological perturbations at second order. For this we have developed the SONG code. In particular, our results are used to implement General Relativity effects within the numerical simulations of the formation of the large scale structures.
With respect to early universe cosmology, we explore the observable consequences of Cosmic Inflation and the existence of topological defects, and maintain the public numerical libraries ASPIC and FieldInf allowing to solve any slow-roll and multifield inflationary models.
Another part of our theoretical activities is concerned with modified gravity theories as well as supersymmetric model building for dark matter candidates.
Research project coordinators
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We study supersymmetric models in which modifications of the neutrino sector, to include a mass term, are connected to the dark matter sector. We analyse if the dark matter particles can be good dark matter candidates by considering cosmological and astrophysical constraints, as well as if the new neutrino sector can accommodate neutrino data.
On Feb 1, 2020 the R&D EU Interreg project E-TEST officially started. It involves 11 institutes from Belgium, Germany and Netherlands and will carry on crucial detector developments for the Einstein Telescope (ET) - a 3rd generation antenna of gravitational waves, related mostly to cryogenic operations of large mass mirrors and their suspensions, ultra-precise metrology and sensing, as well as to advanced geological studies in the region (the ET is a deep-underground detector). The CP3 group is a partner in this project and is working on work package 1 : "Ultra-cold vibration control" and in particular on a cryogenic superconducting inertial sensor.
Gravitational wave signals below a frequency of about 10 Hz are obscured by thermal noise in current detectors. Because temperature is the vibration of atoms in some respect, making the distance measurement between the mirror surfaces more challenging, the mirrors of future detectors will need to be cooled down to temperatures around 10 K. We need to control the motion of some of the cold objects, for which we develop inertial sensors that can survive this harsh environment. The interferometric readout of the inertial sensor also serves as to monitor a ringdown or the E-TEST mirror. After it is excited by a tiny hammer strike, the interferometer follows the ringdown and can determine the quality factor. Additionally, we are investigating an alternative suspension technique, where instead of long fibres under tension, we use short flexures under compression in combination with long, fat rods so we obtain good thermal conductivity and low stiffness suspension.
CP3 members collaborate mostly with KU Leuven (we are collaborating to develop cryogenic readout electronics for the sensor) and ULiège (we align our sensor efforts), RWTH Aachen (they are preparing a cryostat where we will test the inertial sensor).
The ETpathfinder is an R&D infrastructure for testing and prototyping innovative concepts and enabling technologies for the Einstein Telescope, the European concept for a new class of future gravitational wave observatories. ETpathfinder is funded by the interreg program of the EU. The ETpathfinder project broadly consists of six vacuum towers. Four towers are cryogenic and hold suspensions for the mirrors (or test masses) of the experiment. Two towers are operated at room temperature. They hold suspensions for optical tables which hold smaller optics that prepare the beams to be shot into both arms (mode cleaning, frequency stabilisation etc.) and hold the beamsplitters and detection optics.
Many of these optics are suspended individually with small bench top suspensions so they can be steered and additionally seismically isolated. This project concerns the design, prototyping and partial fabrication of >10 suspensions of order 75cm high.
The strong equivalence principle (SEP) does not hold anymore in various extensions of General Relativity. Its violations can be revealed by the non-universality of free-falling for compact objects and we have developed a generic and effective way to test the SEP in the Cosmic Microwave Background (CMB). A violation of the SEP indeed alters the amplitude of the acoustic oscillations in the primeval plasma. Using the WMAP data, we have contrained a possible SEP violation for the baryons.
Our interests are also focused on the scalar-tensor theories of gravitation and their cosmologies. In a more specific way, we are currently studying a model where the scalar sector is conformally invariant. The effective fluid related to the non-minimally coupled scalar field differs from the other cosmological fluids of radiation by its very particular anisotropic pressure and we are studying its impact on the CMB anisotropies by modifying the CAMB code.
We study the perspectives to probe the origin of baryonic matter in the observable universe with laboratory experiments. Currently the focus lies on low scale leptogenesis scenarios. A key element of our approach lies in the description of CP violating nonequilibrium processes in the early universe from first principles of nonequilibrium quantum field theory.