Cosmology and Effective Field Theory in Warped Extra Dimension

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At the intersection of particle theory and cosmology lie fundamental questions. Why is gravity so different from other fundamental forces? Why is it so weak (the hierarchy problem)? What is the universe's dark energy? What drives inflation, smoothing the universe while seeding structure formation? String and M theories require extra spatial dimensions: how could they explain our perceived 3D universe? Recent work on this last question, extra dimension, illuminates all the others. In this project, the PI investigates a class of extra dimensional models: those where extra dimensions warp, or curve, around a 3-brane ? a 3D sub-universe trapping ordinary matter. Such branes are predicted by string and M theory; they warp space-time, due to general relativity; and their warp renders both gravity and particle interactions effectively 3D. The PI's work calibrates the warped particle interactions, using extra-dimensional field theory. Braneworlds thus predict a well-specified 3D universe, from one of higher dimension. Furthermore, they provide a dynamic means of dimensional reduction: a phase transition twists some field in the extra dimensions, spontaneously confining both gravity and ordinary matter, due to a massive 3-brane formed at the twisting defect?s core.