Research Topics and Main Results
In brief: My research is focused on the nature of dark matter, at the interface of particle physics, cosmology, astrophysics, and, more recently, gravitational-wave astronomy. A recurring theme of my work has been to connect fundamental particle-physics questions to realistic astrophysical observables, and to develop robust strategies for identifying dark matter in the presence of substantial theoretical and experimental uncertainties. My work is currently supported by the Dutch national funding agency NWO, and by the European Research Council. In particular the ERC Advanced Grant de Tenebris supports a new programme that focuses on the interplay between dark matter and black holes, and the use of gravitational waves as probes of fundamental physics.
Black holes, dark matter, and gravitational waves
Gravitational wave probes of dark matter: A major current direction of my research is the development of a new field at the interface of dark matter physics, black-hole astrophysics, and gravitational-wave science. Building on earlier work on dark matter overdensities around black holes, I have helped push this problem into the gravitational-wave era, especially in view of the forthcoming LISA mission of the European Space Agency, schedule for launch in 2035. The aim is to establish gravitational waves as a genuinely new way of probing dark matter in extreme astrophysical environments.
White paper: This research has combined conceptual, methodological, and phenomenological work. On the community side, I helped define the scope and scientific agenda of the field through papers such as the white paper I led with Djuna Croon, Gravitational Wave Probes of Dark Matter: Challenges and Opportunities.
New search strategies: In parallel, my collaborators and I developed some of the first concrete waveform predictions and observational strategies for this programme, in papers including Detecting Dark Matter Around Black Holes with Gravitational Waves, Measuring the Dark Matter Environments of Black Hole Binaries with Gravitational Waves, and Distinguishing Environmental Effects on Binary Black Hole Gravitational Waveforms. This line of work has helped establish gravitational waves as a realistic probe of dark matter environments and, more broadly, as a new tool for fundamental physics beyond the Standard Model.
Shaping the Conceptual Framework of Dark Matter
Book and review articles: I contributed to shape the modern discourse on dark matter through reviews, books, and perspective articles that organized a rapidly expanding field and gave it a common conceptual language. My review with Dan Hooper and Joe Silk, Particle Dark Matter: Evidence, Candidates and Constraints, became one of the standard reference works of the subject, bringing together the observational evidence for dark matter, the main particle candidates, and the full range of search strategies in a single framework. My book Particle Dark Matter: Observations, Models and Searches extended this effort by providing a broad reference volume for researchers and students entering the field.
History: This work was followed by review and perspective articles that helped frame successive phases of dark matter research. In History of Dark Matter, written with Dan Hooper, I placed the subject in its broader scientific context and clarified how the dark matter problem acquired its present form. In How Dark Matter Came to Matter, with Jaco de Swart and Jeroen van Dongen, I examined how separate missing-mass problems were brought together into a single anomaly, thereby helping to explain why dark matter became central to modern cosmology. Two Nature articles then addressed the strategic evolution of the field: The Moment of Truth for WIMP Dark Matter argued that WIMPs had become a sharply testable hypothesis, while A New Era in the Search for Dark Matter, with Tim Tait, assessed the implications of the absence of evidence for WIMPS and other popular candidates and argued for a broader and more diversified programme. Taken together, these works helped define both the language and the strategic orientation of modern dark matter research.
Dark matter in the Milky Way and in galactic centres
Another sustained line of research concerns the astrophysical distribution of dark matter and its consequences for detection. In early work with David Merritt, including Time-Dependent Models for Dark Matter at the Galactic Center and Dark Matter Dynamics and Indirect Detection, I studied how dark matter distributions evolve in the presence of stars, self-annihilation, and supermassive black holes. These papers helped replace oversimplified static pictures with dynamical models and clarified when large signal enhancements near black holes are plausible and when they are not.
I have also contributed to the empirical determination of the dark matter distribution in our own Galaxy. Papers such as Evidence for Dark Matter in the Inner Milky Way, Dark Matter Distribution in the Milky Way: Microlensing and Dynamical Constraints, and Dynamical Constraints on the Dark Matter Distribution in the Milky Way helped establish a more data-driven basis for Milky Way dark matter studies, with direct implications for both direct and indirect searches.
Indirect detection and the problem of robust identification
One of my main long-term research themes has been indirect detection, especially through gamma rays, neutrinos, and cosmic rays. My work in this area has emphasized not simply the existence of possible signals, but the conditions under which an astrophysical observation could be interpreted as convincing evidence for dark matter. Representative papers include Dark Matter: the Connection with Gamma-Ray Astrophysics, Gamma-rays from Decaying Dark Matter, and Investigating Gamma-Ray Lines from Dark Matter with Future Observatories.
A related contribution has been to stress that dark matter identification requires complementarity between indirect searches, direct searches, and collider data, rather than reliance on any single anomaly or experimental hint. This perspective is reflected, for example, in Identification of Dark Matter Particles. The broader significance of this body of work lies in helping move the field from suggestive signal-spotting to more rigorous, multi-channel inference.
Broader significance
My work has contributed to the maturation of dark matter research as a field, across its conceptual, methodological, and observational aspects. It has included influential review and historical articles, the development of robust standards for identifying dark matter, the integration of particle models with realistic astrophysical environments, and the opening of new detection strategies at the intersection with black holes and gravitational waves. These contributions have helped shape how the field formulates its central questions and sets its long-term agenda.