The proven capability of LIGO in discovering gravitational waves (GWs) from presumed binary black hole mergers has opened up unprecedented opportunities to probe the nature of relativistic compact objects, and offers real possibilities to put current thinking in quantum gravity and cosmology to the test. In quantum gravity, Hawking’s information paradox suggests Planck-scale modifications of black hole horizons (firewalls) or other alterations of their structure (fuzzballs). In cosmology, dark matter particles have been proposed that may congregate into compact star-like objects. Yet another possibility concerns stars whose cores consist of self-repulsive spacetime, the existence of which may provide direct insight into the nature of dark energy. When such objects enter into binary systems that undergo merger, their GW signals can be accessed. I want to use upcoming GW detections to search for evidence of black hole mimickers: relativistic compact objects that are modifications to classical black holes, or different kinds of objects altogether. I will do this through three complementary avenues: (1) by looking for evidence of tidal deformability in inspiralling binary objects that would be inconsistent with a ‘standard’ black hole nature; (2) by using the ‘ringing’ of the remnant object resulting from merger to look for violations of the black hole no-hair theorem; and (3) by searching for gravitational-wave ‘echoes’ that would be tell-tale signs of a horizon modification, e.g. as a result of quantum effects. The comprehensive and timely investigation proposed here will turn relativistic compact objects into laboratories for fundamental physics and cosmology, with the potential to radically alter our views on both.

During the second half of 2008, the Large Hadron Collider (LHC) at CERN is foreseen to deliver its first proton-proton collisions at a centre-of-mass energy of 10-14 TeV. This unprecedented energy, and the very high luminosity, will push elementary particle physics into a new age, recreating conditions as they were just after the Big Bang. The potential of this machine to search for new phenomena surpassing our current understanding, as described by the Standard Model of particle physics, are excellent and exciting. The ATLAS detector, designed to measure the LHC collisions, is ready to enter this new domain. I believe that the theory of supersymmetry provides the best motivated framework for a search for new physics. If supersymmetry is realized in nature, it may solve urgent problems in particle physics and cosmology, such as the nature of dark matter, or the origin of the asymmetry between matter and anti-matter in the universe. I propose to build a strong group that will first pursue the discovery of supersymmetry with the ATLAS detector in an inclusive way, and subsequently unravel the behaviour of individual supersymmetric particles by focussing on heavy flavour quarks and leptons: the top and bottom quarks, and the tau lepton. I believe that such a study of supersymmetric heavy-flavour physics is innovative and urgent, and also challenging. The team will make use of our investments in ATLAS as well as the Dutch Grid computing facilities, and will have strong links to astroparticle physics and advanced data analysis groups.

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In 2012, a particle with mass of 125 GeV was observed by the Atlas and CMS collaborations at the Large Hadron Collider, consistent with the Higgs boson predicted by the Brout-Englert-Higgs mechanism of electroweak-symmetry breaking. However, various fundamental questions in the standard model of particle physics (SM) remain unanswered. With the existence of the Higgs boson confirmed, the SM now faces a theoretical challenge: large known quantum corrections to the Higgs mass turn out to nearly perfectly cancel each other in practice, without explanation. Various proposed extensions of the SM that introduce new fundamental physics at the TeV energy scale provide such an explanation and stabilize the theory up to the energy scale of the Big Bang. One of the proposed solutions results in five types of Higgs bosons, which may strongly couple to b-quarks. I propose to search for the H->ZA decay, a signature that is still largely unexplored. Secondly, evidence for the existence of dark matter from cosmological observations is abundant, yet the SM provides no particle that has the properties of dark matter. I propose to search for its production in scalar-boson decays; would dark matter couple only to the scalar sector, decays of the Higgs boson could probe for the first time directly its interactions. Thirdly, extensions of the SM do not only predict the existence of new particles, but will also subtly modify the properties of the observed 125 GeV particle. New precision studies of the decay of this boson into quarks will provide a complementary strategy to search for new physics. I propose to address several of these questions by exploring a single LHC collision topology: the rare production of Z bosons in association with b jets. Using my expertise in this topology, while simultaneously targeting three research topics, I will address fundamental questions.

The discovery of a process where leptons are created (leptons are particles such as electrons) would violate the known laws of physics. It would be clear evidence for new particle physics and shed light on the most elusive elementary particle: the neutrino. This research investigates novel ways of testing conservation of lepton number, while providing theoretical predictions for precise laboratory experiments as well as astrophysical and cosmological observations.