Research
Flavour physics
 The exploration of flavour physics and CP violation, with a focus on the decays of Bmesons, is the main research topic of Robert Fleischer and Keri Vos. Here the goal is to perform precision tests of the flavour structure of the Standard Model by means of rare, strongly suppressed processes that are caused by virtual quantum effects and are sensitive probes for contributions from physics beyond the Standard Model. There is a strong interaction with Nikhef’s experimental Bphysics group working on the LHCb experiment at CERN.
Perturbative QCD and collider phenomenology
 The perturbative description of Quantum Chromodynamics continues to pose fascinating puzzles. The research interests of Eric Laenen, Wouter Waalewijn, and Jos Vermaseren here range from fixed order calculations to allorder resummations, jets production and substructure, the transverse and spin structure of the proton, and powerful computer algebra programs such as FORM to carry out for very highorder perturbative calculations. Other research topics in this category include higherorder perturbative calculations for Higgs and top quark production, where there is a strong collaboration with members of the local ATLAS group. One important aim of this research line is to improve the theoretical accuracy of predictions in phenomenologicallyrelevant kinematic limits, through the resummation of large logarithms in the cross section, that arise due to the multiscale nature of collisions.
Nonperturbative QCD and proton structure
 The research interests of Piet Mulders and Juan Rojo include the quark and gluon structure of protons and nuclei, applications of machine learning to particle physics, the intrinsic transverse momenta structure in polarized and unpolarized quark and gluon distribution and fragmentation functions, as well as general interest in the symmetries of the Standard Model. Jordy de Vries applies chiral effective field theory for precision calculations for lowenergy hadronic and nuclear observables related to experiments looking for BeyondtheStandard Model physics. Examples include neutrinoless double beta decay, beta decays, and electric dipole moments.
Cosmology and particle physics
 The early universe provides a unique test bed for our theories of physics beyond the Standard Model, as the energy scales involved are many orders of magnitude larger than what can ever be reached in terrestrial particle accelerators. The research of Marieke Postma is motivated by the question what particle physics can tell us about the evolution of the universe and, in turn, what cosmology can teach us about the fundamental laws of nature from dark matter to topological defects, Higgs inflation and electroweak baryogenesis.
Beyond the Standard Model physics
 The search for physics beyond the Standard Model is one of the main goals of particle physics, explored by several Nikhef staff members by means of different techniques. The research of Kallia Petraki focuses on particle models of dark matter and the interplay between particle and astroparticle physics. Susanne Westhoff pursues a similar approach, searching for longlived particles as mediators to feebly interacting dark matter candidates. Juan Rojo, Jordy de Vries and Susanne Westhoff adopt a model independent strategy based on effective field theories, in particular the SMEFT, where the general effects of new particles and interactions are encoded in terms of higher dimensional operators. Finding indirect evidence for new physics in the flavour sector is also one of the goals of the research led by Robert Fleischer and Keri Vos.
Gravitational waves

Gravitational waves have, since their initial discovery in 2015, opened a whole new window on the Universe that leads to new insights on black holes, cosmology, the nuclear equation of state at high energies, and general relativity itself. The comparison of measurement to theory is expected to become unfeasibly difficult as gravitational wave measurements become more abundant and more precise and theoretical models more refined. The main research topic of Gideon Koekoek is to use developments in quantum computing to tackle such challenges.
 Béatrice Bonga focuses on foundational questions in general relativity and predictions for future gravitationalwave observatories such as the Einstein Telescope and LISA. Her research aims to reveal new physics one can learn from gravitational wave detections such as the influence of third bodies, testing the nonlinear structure of Einstein’s equations, and distinguishing black holes from other (exotic) objects.
Manybody QCD and heavy ion collisions
 In the collisions of ultrarelativistic lead ions at the LHC thousands of particles are produced that behave collectively. During the collision a thermal state is reached, called the quarkgluon plasma or QGP, that explores the phase diagram of QCD. The research interests of Wilke van der Schee studies its formation and properties, such as its shear viscosity or how the QGP affects the jets produced by the perturbative QCD processes as described above.
Quantum field theory and gravity
 The research of Jan Willem van Holten involves the question how to construct quantum fieldtheoretical models incorporating new symmetries (such as supersymmetry) one the one hand, and gravity in a consistent manner on the other. He also investigates the physics of black holes, and gravitational waves.
 Quantum fields on curved spacetimes are studied by Béatrice Bonga to determine if a quantum signature in the cosmic microwave background can be detected and linked back to the early universe. Related to this goal, she and her group study entanglement entropy between finite regions on flat and curved spacetimes using techniques from quantum information theory.
String theory
 String theory is the subject of Bert Schellekens’ research, in particular its relation to conformal field theory. There have been exciting recent developments in string theory, involving surprising connections (dualities) between apparently unrelated theories. His recent research focusses in particular on the open string sector.