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The existence of dark matter and the hierarchy problem motivates the search for new physics. The formulation of new search strategies and models is crucial in the hunt for physics beyond the Standard Model, and in this work we present three studies of new physics relevant for current and upcoming experiments. First, we study models that contain a singlet dark matter particle with cubic renormalizable couplings between standard model particles and `partner' particles with the same gauge quantum numbers as the standard model quark. The dark matter has spin 0, 1/2, or 1, and may or may not be its own antiparticle. Each model has 3 parameters: the masses of the dark matter and standard model partners, and the cubic coupling. Requiring the correct relic abundance gives a 2-dimensional parameter space where collider and direct detection constraints can be directly compared. We find that collider and direct detection searches are remarkably complementary for these models. Direct detection limits for the cases where the dark matter is not its own antiparticle require dark matter masses to be in the multi-TeV range, where they are extremely difficult to probe in collider experiments. The models where dark matter is its own antiparticle are strongly constrained by collider searches for monojet and jets + MET signals. These models are constrained by direct detection mainly near the limit where the dark matter and partner masses are nearly degenerate, where collider searches become more difficult. Second, we study the case where the singlet dark matter has trilinear couplings to leptons and a new ``lepton partner'' particle. The most sensitive collider probe is the search for leptons + MET, while the most sensitive direct detection channel is scattering from nuclei arising from loop diagrams. Collider and direct detection searches are highly complementary: colliders give the only meaningful constraint when dark matter is its own antiparticle, while direct detection is generally more sensitive if the dark matter is not its own antiparticle. Third, we study the constraints on new physics from Higgs production through vector boson fusion in the context of an effective field theory that preserves Standard Model gauge symmetries. We find that constraints on dimension-6 operators are significantly improved over those from the VBF signal strength by studying the Higgs transverse momentum distribution. Focusing on the O[subscript]HW operator, we find that boosted VBF decaying to photons yields constraints competitive with boosted WW production in the fully leptonic final state, and calculate projected limits for both at the 14 TeV LHC. The PT cuts required to maximize the reach of VBF searches are substantially softer, making the use of the effective field theory more robust than in the case of WW production which requires very high PT cuts to obtain similar limits.
This thesis studies collider phenomenology of physics beyond the Standard Model at the Large Hadron Collider (LHC). It also explores in detail advanced topics related to Higgs boson and supersymmetry – one of the most exciting and well-motivated streams in particle physics. In particular, it finds a very large enhancement of multiple Higgs boson production in vector-boson scattering when Higgs couplings to gauge bosons differ from those predicted by the Standard Model. The thesis demonstrates that due to the loss of unitarity, the very large enhancement for triple Higgs boson production takes place. This is a truly novel finding. The thesis also studies the effects of supersymmetric partners of top and bottom quarks on the Higgs production and decay at the LHC, pointing for the first time to non-universal alterations for two main production processes of the Higgs boson at the LHC–vector boson fusion and gluon–gluon fusion. Continuing the exploration of Higgs boson and supersymmetry at the LHC, the thesis extends existing experimental analysis and shows that for a single decay channel the mass of the top quark superpartner below 175 GeV can be completely excluded, which in turn excludes electroweak baryogenesis in the Minimal Supersymmetric Model. This is a major new finding for the HEP community. This thesis is very clearly written and the introduction and conclusions are accessible to a wide spectrum of readers.
In the field of particle and astrophysics, one of the major unresolved problems is to understand the nature and properties of dark matter, which constitutes almost 80% of the matter content of the universe. This book gives a pedagogical introduction to the field of dark matter in general, and in particular to the model building perspective. Starting from the evidence and need for dark matter, it goes into the deeper understanding of how to accommodate a dark matter candidate in a particle physics model. This book focuses on teaching the basic tools for model building of dark matter, starting from the easiest to gradually the difficult one. Although there are plenty of dark matter models available in the literature, this book concentrates on the important ones. This book aims to motivate the reader to propose a new dark matter model complying with all observational constraints.
TheFifthHEIDELBERGInternationalConferenceonDarkMatterinAst- and Particle Physics, DARK 2004, took place at Texas A&M University, College Station Texas, USA, October 3–9, 2004. It was, after Cape Town 2002, the second conference of this series held outside Germany. The earlier meetings, starting in 1996, were held in Heidelberg. Dark Matter is still one of the most exciting and central ?elds of ast- physics, particle physics and cosmology. The conference covered, as usual for this series, a large range of topics, theoretical and experimental. Theoretical talks covered SUSY/SUGRA phenomenology, which provides at present a preferred theoretical framework for the existence of cold dark matter. Also included were other possible explanations of dark matter such as SUSY Q balls, exciting New Symmetries, etc. The most important experiments in the underground search for cold and hot dark matter were presented. Talks describing the current experimental dark matter bounds, what might be obtained in the near future, and the reach of future large (i.e. one ton) detectors were given. The potential of future colliders to correlate accelerator physics with dark matter searches was also outlined. Thus the reader will be able to see the present status and future prospects in the search for dark matter. The exciting astronomical evidence for dark matter and corresponding observations concerning the Milky Way’s black hole, high-redshift clusters, wakes in dark matter halos were other important topics at the conference.
An extraordinary discovery has recently shaken the foundations of Cosmology and Particle Physics, sparking a scientific revolution that has profoundly modified our understanding of our Universe and that is still far from over. Pioneering astronomers in the 1920s and 1930s had already noticed suspicious anomalies in the motion of celestial bodies in distant galaxies and clusters of galaxies, but it wasn't until the late 20th century that the scientific community was confronted with an astonishing conclusion: the Universe is filled with an unknown, elusive substance that is fundamentally different from anything we have ever seen with our telescopes or measured in our laboratories. It is called dark matter, and it constitutes one of the most pressing challenges of modern science. In this book, aimed at the general reader with an interest in science, the author illustrates in non-technical terms, borrowing concepts and ideas from other branches of art and literature, the far-reaching implications of this discovery. It has led to a worldwide race to identify the nature of this mysterious form of matter. We may be about to witness a pivotal paradigm shift in Physics, as we set out to test the existence of dark matter particles with a wide array of experiments, including the Large Hadron Collider at CERN, as well as with a new generation of Astroparticle experiments underground and in space.
This book offers construction of a renormalizable effective theory of electroweak-interacting spin-1 dark matter (DM). The effective theory realizes minimal but essential features of DM predicted in extra-dimension models, and enables to systematically treat non-perturbative corrections such as the Sommerfeld effects. Deriving an annihilation cross section including the Sommerfeld effects based on the effective theory, the author discusses the future sensitivity of observations to gamma-ray from the Galactic Center. As a result, the author explains the monochromatic gamma-ray signatures originate from two photons (γγ) or photon and Z boson (γZ) produced in the process of DM annihilations, and concludes a possible scenario that unstable neutral spin-1 particles (Z’) appear and results in a spectral peak in addition to the one caused by γγ and γZ channels in gamma-ray observations. If those two spectral peaks are observed, the masses of spin-1 DM and Z’ would be reconstructed.