The effective theory of quantum gravity coupled to models of particle physics is being probed by cutting edge experiments in both high energy physics (searches for extra dimensions) and cosmology (testing models of inflation). This thesis derives new bounds that may be placed on these models both theoretically and experimentally. In models of extra dimensions, the internal consistency of the theories at high energies are investigated via perturbative unitarity bounds. Similarly it is shown that recent models of Higgs inflation suffer from a breakdown of perturbative unitarity during the inflationary period. In addition, the thesis uses the latest LHC data to derive the first ever experimental bound on the size of the Higgs boson's non-minimal coupling to gravity.

This book is a collection of lectures given in August 2006 at the Les Houches Summer School on "Particle Physics and Cosmology: the Fabric of Spacetime. It provides a pedagogical introduction to the various aspects of both particle physics beyond the Standard Model and Cosmology of the Early Universe, covering each topic from the basics to the most recent developments.· Provides a pedagogical introduction to topics at the interface of particle physics and cosmology· Addresses each topic from the basis to the most recent developments· Provides necessary tools to build new theoretical models addressing various issues both in cosmology and particle physics· Covers the lectures by internationally-renowned and leading experts· Faces the predictions of theoretical models against collider experimental data as well as from cosmological observations

Current Problems in Particle Physics and Cosmology covers the proceedings of the workshop ""Current Problems in Particle Physics and Cosmology"", held in Ioannina, Greece on June 25-29, 1990. The book focuses on the reactions, problems, methodologies, and processes involved in particle physics and cosmology. The selection first offers information on the search for cosmic axions and experimental limits on light scalars/pseudoscalars and experimental tests of the standard model using the recently collected UA2 data. Topics include limits on the production of light scalar and pseudoscalar particles; measurement of SM parameters; transverse momenta distributions of the W and Z bosons; and mass spectroscopy with jets. The text then takes a look at heavy top quark, fermion mixings, and electroweak multi-particle-production at TeV energies. Discussions focus on third and second generation masses and mixing; neutrino sector; threshold energy; total inelastic multiparticle cross sections; and geometrical flavor interactions at very high energies. The publication examines supersymmetry breaking and dynamical determination of superstring parameters; four-dimensional strings and low energy predictions; and gravity from superstrings. The selection is a vital source of data for readers interested in particle physics and cosmology.

This work investigates the theoretical and cosmological implications of modifying Einstein's theory of general relativity. It explores two classes of modifications to gravity: those in which the graviton is given a small mass, and those in which Lorentz invariance is spontaneously broken. It elucidates the nature of cosmological perturbations in theories of massive bimetric gravity, including a potentially deadly instability. Theories of gravity beyond general relativity could explain why the expansion of the Universe is accelerating, obviating the need for a dark energy, and can also affect the evolution of the early Universe. Next, it investigates the nature of spacetime in massive gravity theories that contain two different spacetime metrics. Lastly, the strongest constraints to date are placed on the size of Lorentz-violating effects in the gravity sector during inflation.

Despite the success of general relativity in explaining classical gravitational phenomena, several problems at the interface between gravitation and high energy physics still remain open. The purpose of this thesis is to explore quantum gravity and its phenomenological consequences for dark matter, gravitational waves and inflation. A new formalism to classify gravitational theories based on their degrees of freedom is introduced and, in light of this classification, it is argued that dark matter is no different from modified gravity. Gravitational waves are shown to be damped due to quantum degrees of freedom. The consequences for gravitational wave events are also discussed. The non-minimal coupling of the Higgs boson to gravity is studied in connection with Starobinsky inflation and its implications for the vacuum instability problem is analyzed.

The wealth of recent cosmic microwave background and large-scale structure data has transformed the field of cosmology. These observations have not only become precise enough to answer questions about the universe on the largest scales, but also to address puzzles in the microscopic description of Nature. This thesis investigates new ways of probing the early universe, the properties of neutrinos and the possible existence of other light particles. In particular, based on detailed theoretical insights and novel analyses, new evidence for the cosmic neutrino background is found in the distribution of galaxies and in cosmic microwave background data. This tests the Standard Model of particle physics and the universe back to a time when it was about one second old. Furthermore, it is demonstrated that future observations will be capable of probing physics beyond the Standard Model since they can achieve a particular target which would either allow the detection of any light particles that have ever been in thermal equilibrium or imply strong bounds on their properties.

Dark matter in the Universe has become one of the most exciting and central fields of astrophysics, particle physics and cosmology. The lectures and talks in this book emphasize the experimental and theoretical status and perspectives of the ongoing search for dark matter, and the future potential of the field into the next millennium, stressing in particular the interplay between astro- and particle physics.