Monday Colloquium

Liam McAllister
Professor, Department of Physics, Cornell University
 

STRING THEORY, THE COSMOLOGICAL CONSTANT, AND THE QUANTIZATION OF PARAMETERS
I will argue that the fundamental parameters in Nature are integers. In string theory these integers record the topology of six additional spatial dimensions. A task for theorists is to understand what values these numbers can take, and how experimental observables can be expressed in terms of them. One key observable is the dark energy density, which is 120 orders of magnitude smaller than the naive prediction from theory: this discrepancy is the famous cosmological constant problem. We have learned how to compute the fundamental integers in a vast class of geometries and have used this knowledge to construct solutions of string theory in which the dark energy density has an allowably small magnitude. But it has the wrong sign! I will explain how our results constitute progress on a toy model of the cosmological constant problem, and provide the foundation for a computational approach to cosmology in string theory.

Liam McAllister was an undergraduate physics and mathematics concentrator at Harvard, in the class of 2000. He received his PhD at Stanford in 2005 for work on inflation in string theory. He was a postdoc at Princeton, and in 2007 he joined the faculty at Cornell, where he has been ever since.

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