(De)constructing dimensions.

We construct renormalizable, asymptotically free, four-dimensional gauge theories that dynamically generate a fifth dimension.

New perspective on cosmic coincidence problems

Cosmological data suggest that we live in an interesting period in the history of the universe when rho(Lambda) approximately rho(M) approximately rho(R). The occurrence of any epoch with such a "triple coincidence" is puzzling, while the question of why we happen to live during this special epoch is the "Why now?" problem. We introduce a framework which makes the triple coincidence inevitable; furthermore, the "Why now?" problem is transformed and greatly ameliorated. The framework assumes that the only relevant mass scales are the electroweak scale M(EW), and the Planck scale M(Pl) and requires rho(1/4)(Lambda) approximately M(2)(EW)/M(Pl) parametrically. Assuming that the true vacuum energy vanishes, we present a simple model, where a false vacuum energy yields a cosmological constant of this form.

Infinitely large new dimensions

We construct intersecting brane configurations in anit-de Sitter (AdS) space which localize gravity to the intersection region, generalizing the trapping of gravity to any number n of infinite extra dimensions. Since the 4D Planck scale M(Pl) is determined by the fundamental Planck scale M(*) and the AdS radius L via the familiar relation M(2)(Pl) approximately M(2+n)(*)L(n), we get two kinds of theories with TeV scale quantum gravity and submillimeter deviations from Newton's law. With M(*) approximately TeV and L approximately submillimeter, we recover the phenomenology of theories with large extra dimensions. Alternatively, if M(*) approximately L-1 approximately M(Pl), and our 3-brane is at a distance of approximately 100M(-1)(Pl) from the intersection, we obtain a theory with an exponential determination of the weak/Planck hierarchy.