NON PERT QFT
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PHENOMENOLOGY NON PERT QFT STRINGS SOLITONS |
Phenomenology is research on the boundary between theory and experiment. It is concerned with identifying interesting physical observables, making theoretical predictions for them and then confronting experimental data gathered at the major international laboratories. We wish both to test the Standard Model (SM) of particle physics and to identify discrepancies that may be due to physics beyond the Standard Model. Close collaboration with our experimental colleagues is a vital aspect of our work.
The Standard Model of particle physics is a gauge quantum field theory incorporating strong interactions (QCD), weak interactions and electromagnetism. With the exception of gravity, it describes all of the fundamental laws of nature in terms of a few input parameters and so far there is very little solid evidence of physics beyond the standard model.
However, one of it's key features, the Higgs mechanism, which explains why the elementary particles carry mass is as yet untested and the postulated Higgs boson remains undiscovered. Even if the Higgs boson is found, many longstanding and fundamental questions remain, and it seems certain that more fundamental theories remain to be discovered.
It is convenient to define the following five broad overlapping categories of research that cover the whole range of phenomenology. In many cases, research projects will fall into more than one of these categories.
Patricia Ball, Nigel Glover, Alan Martin, Chris Maxwell, Mike Pennington, Adrian Signer, James Stirling
Quantum Chromodynamics (QCD) describes the strong interactions between quarks and gluons and in particular how they bind together to form hadrons such as the neutron and proton. This is the strongest of the four forces and most of the high energy scattering data is influenced by it. Understanding the strong force is therefore a prerequisite to identifying rare signatures of new physics that may be accessed at higher energies. At the smallest distance scales probed by current experiments (down to a few thousandths of the proton radius), the strong coupling constant is small and the interactions can be described by perturbation theory. However as the quarks and gluons separate (at distance scales of about 1 fm) the strong coupling becomes very large and non-perturbative techniques must be employed.
Nigel Glover, Alan Martin, Chris Maxwell, Mike Pennington, Adrian Signer, James Stirling, Georg Weiglein
The Electromagnetic Force is the force responsible for holding electrons inside atoms, and hence is responsible for making matter solid as well as all of chemistry. The Weak Force is the force responsible for nuclear decay and radioactivity. The best description that we have of these two forces is in a single unified theory known as electroweak theory. This electroweak theory is the one area of known physics that can not be made theoretically consistent with the particle spectrum currently observed. The difficulty arises because the weak force is carried by massive particles, and all mechanisms known for generating mass predict new physics beyond that currently observed. The minimal extension to current physics required for consistency is a single particle called the Higgs boson, unlike all other known particles this particle is predicted to have no intrinsic spin. The search for this particle is one of the burning issues for particle physics today.
Steve Abel, Sacha Davidson, Sakis Dedes, Adrian Signer, James Stirling, Georg Weiglein
The Standard Model (SM) of electroweak interactions has proven remarkably successful in describing the phenomena that are presently accessible at collider experiments and we know that the generic energy scale associated with electroweak mass generation (e.g. the mass of the Higgs boson) has to be close to the reach of the present-day experiments. So far, there are virtually no unambiguous hints of possible new structure beyond the SM. However, it would be rather unrealistic to expect that nature will have no more surprises in store between the electroweak energy scale and the very high energy scale (roughly 1016 times larger than present collider energies) at which gravitational effects are expected to become strong and cannot be ignored anymore. This immediately provokes the question Why is the electroweak scale so much smaller than the typical scale of the gravitational forces between masses? One way to circumvent this problem is by introducing a special cancellation mechanism, called supersymmetry which directly links the two fundamentally different types of particles in nature, the fermions (like electrons or quarks) and the bosons (like photons or Higgs bosons). As an added bonus, supersymmetry also makes it possible to achieve unification of the electroweak and strong forces at very high energies, which is excluded in the SM. For this reason supersymmetric models are very popular and are investigated extensively at collider experiments.
Patricia Ball, Alan Martin, Adrian Signer, James Stirling
The particles of the Standard Model are organized in three families, which, apart from large differences in the mass, are perfect copies of each other. Heavy flavor physics deals with the properties of the heaviest quarks that is the quarks of the third family (top and bottom) and to a lesser extent those of the second family (charm and strange). Long range goals are to understand why there are three families and why there is such an extreme mass pattern (the top quark is more than hundred times heavier than its counterpart in the second family, the charm quark). Another crucial aspect of heavy flavor physics is the study of CP violation (CP is the combined operation of interchanging particles with antiparticles, C, and looking at the world in a mirror, i.e. parity P). CP violation is one of the ingredients necessary to explain the huge abundance of matter over antimatter that is observed in the universe. The Standard model does predict CP violation, but only in processes where all three families take part and therefore involves processes with the bottom or top quark. These processes to be investigated at current and future experiments also provide us with a promising window for physics beyond the Standard Model.
Sacha Davidson, Sakis Dedes, Alan Martin
Neutrinos are the second most abundant particle in the universe, with only photons being more common. Nonetheless, they are one of the least well measured of all particles, because they are exceptionally weakly interacting. They pass through ordinary matter almost as if it were not there--- even when that matter is the size of the Earth! Enormous detectors, ranging from tons of ultrapure water deep in mines, to an instrumented cubic kilometre of the Antarctic icecap, are therefore required to detect neutrinos. Current experiments determine their properties with large uncertainty, and tell us that neutrinos are peculiarly different from other known particles---much lighter, possibly with a different type of mass, very mixed together. Experiments being built and planned should determine their properties accurately enough for neutrinos to be used as probes of the Universe near and far. This is possible, because neutrinos are almost massless, so travel close to the speed of light. And since neutrinos are very penetrating, they come from deep inside objects, such as the sun, supernovae, distant galaxies and other sources. For example, neutrinos escape directly from the centre of the sun in a few seconds, so tell us about what is happening at the centre; light, on the other hand, takes a thousand years for the same trip. Neutrinos are therefore a fascinatingly different animal in the particle physicist`s zoo, and a promising new type of telescope for astronomers and cosmologists.