New Physics on the Brane

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Like most subatomic theorists my broad objective is to understand the fundamental laws of nature. At present we have a very successful theory, the Standard Model with General Relativity, that until recently described all experiments that had been done. The three recent exceptions are terrestrial and astrophysical evidence for neutrino oscillations, together with cosmological observations revealing the existence of primordial density fluctuations as well as two unknown sources of gravitation: the so-called dark matter and dark energy. These show that the Standard Model fails; subatomic theorists seek its replacement.******Much of this evidence now comes from space, which is why cosmology has been my main focus. In the past I have proposed some of the leading models for dark matter, for dark energy and for the origins of primordial fluctuations. These models are motivated by simplicity and by the recognition that what we see is likely the low-energy limit of something more fundamental (which imposes 'naturalness' restrictions on candidate theories, particularly for dark energy). But we stand at the threshold of much new terrestrial information too, with the Large Hadron Collider (LHC) beginning its long-awaited full-energy run in the middle 2015.******My proposal comes in two parts. On the cosmology side I propose to continue exploring the implications of cosmology for fundamental physics in light of the on-going new observations, such as the much-anticipated updates from the Planck and BICEP collaborations. This itself comes in two parts: inferences about physics at very high energies coming from observations of primordial fluctuations, and searches for solutions to puzzles involving more 'recent' cosmology (like dark matter and dark energy). On the particle physics side I seek phenomena to be seen in collider experiments (and vice versa), particularly when these are motivated by problems in cosmology. I have identified several such connections in the past, and continue to seek them as more information arrives from the LHC.***One clue I try to use when doing so is to take ideas from string theory, which is the only candidate fundamental theory reconciling gravity with quantum mechanics for which predictions are precise enough to exploit systematically. String theory predicts that all of Nature is built from microscopic strings that can move along large, macroscopic surfaces (branes) within extra-dimensional space-time. One line of development on which I work examines how string theory impacts ideas for cosmology and particle physics, by changing what we see as natural in a low-energy theory. In particular, the potential existence of branes can strongly modify the kinds of features that the low-energy world might display.***For Canada my product is people: Fundamental physics draws fine young minds to learn transferable mathematical, computing and communications skills, which they can bring to the wider economy. **