PhD thesis (M/F) : Tests of gravity with next generation of gravitational wave detectors

Job Description

Thesis Subject

The advent of gravitational-wave (GW) astronomy offers an unprecedented opportunity to test gravity and astrophysics under extreme conditions. Since the first detection of a binary black hole merger by the LIGO-Virgo collaboration, GW observations have enabled the precise testing of general relativity (GR) in the non-linear regime, constrained the properties of the black hole population (BHs) and provided new insights into the formation and evolution of compact objects. These achievements rely critically on precise waveform models describing the complete evolution of the coalescence of compact binaries—BHs and neutron stars—through the three phases of inspiral, merger and ringdown. The coming decades will mark a qualitative leap in this field. The advent of third-generation ground-based gravitational wave (GW) detectors, notably the Einstein Telescope (ET), will significantly increase detection rates and signal-to-noise ratios for binary BHs of stellar to intermediate masses (from 1 to 1000 solar masses). At the same time, space-based interferometers such as the Laser Interferometer Space Antenna (LISA) will open the milli-Hz window, providing access to massive black hole binaries and asymmetric systems such as extreme and intermediate mass ratio (EMRI) spirals.

To enable this science with future GR detectors such as LISA and ET, it is essential: (i) to understand all the implications and observables of GR and (ii) to investigate how potential discrepancies might manifest themselves and possibly be confused with other phenomena. The first point is essential to avoid misinterpreting a poorly understood aspect of GR theory as a violation, whilst the second point helps to guide data analysis efforts and to correctly understand and address systematic effects. Despite these recent developments, the data analysis carried out by the LIGO-Virgo-KAGRA (LVK) collaboration still relies solely on a database of waveforms developed within the framework of GR, with phenomenological modifications. The aim of this project is to implement the alternative waveforms obtained at LUX into the data analysis algorithms developed at L2IT. This will enable credible tests of gravity to be carried out for the first time with future LGO detectors (LISA, ET), including a hierarchical analysis that optimally combines the constraints obtained from observations of a population of sources.

The aim of the thesis is to carry out reliable tests of gravity with future gravitational wave detectors (LISA, Einstein Telescope). For this, a first part, carried out at LUX (INSU) will consist of developing realistic waveforms in certain theories of gravity, using perturbative methods such as the post-Newtonian formalism. Among the theories considered, we could consider scalar-tensor theories, motivated as an alternative to the standard model of cosmology, and/or theories with higher order curvature terms considered as an effective model of gravity to improve behavior at high energies of gravity. The second part, carried out at L2IT (IN2P3), will consist of applying these alternative waveforms to a data analysis algorithm to obtain credible predictions, using and adapting the codes developed at L2IT, such as for example LISAbeta. This will prepare the science of future detectors, by developing advanced gravity tests. To do this, the project will be included in the scientific activities underway in the two major international collaborations (LISA and ET). This thesis project in co-supervision between LUX and L2IT will train a student in both theoretical methods and numerical methods (data analysis).

Your Work Environment

The PhD will be a co-supervision between Laura Bernard at LUX (Meudon, INSU) and Nicola Tamanini at L2IT (Toulouse, IN2P3). The PhD student will also be co-supervised by Sylvain Marsat at L2IT (Toulouse, IN2P3).
The PhD student will equally share his/her time between the LUX and L2IT laboratories. It will allow him/her to work in different environments among different teams. Collaboration meetings will be reagularly organized online and two in-person workshops per year will be scheduled (one in Meudon, the other one in Toulouse).

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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