Stanford University

Project Title

Dimensionality in String Theory

Project Summary

One of the most basic classical observables is the dimensionality D of space-time, an input in general relativity and particle physics. In a more basic theory such as string theory, the dimensionality is not a priori fixed (or even well defined except in extreme limits), and in some sense the most generic regime is large D. In this limit, various cosmological phases can be obtained as particular solutions of the equations governing the theory. Moreover, a time-dependent process known as tachyon condensation can change the effective dimensionality. This project, pursued in part in collaboration with O. Aharony, will build on recent advances in these areas to address the following two main questions, while further developing the technical tools required for the analysis. (1) In cosmological backgrounds with an early large D phase, how do the horizon and flatness problems play out and what are the predictions for the spectrum of density perturbations which seed structure formation? (2) Higher effective dimensionality must arise in nontrivial ways in generic backgrounds with positive classical potential energy, such as compact negatively curved spaces where wound strings provide a corresponding exponentially growing number of states. How does this generalize?

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