Axions from String Theory and Inflation
Katie Mack
Princeton University
The QCD axion is the leading contender to rid the standard model of the
strongCP problem. If the PecceiQuinn symmetry breaking occurs before
inflation, which is likely in string theory models, axions manifest
themselves cosmologically as a form of cold dark matter with a density
determined by the axion's initial conditions and by the energy scale of
inflation. Constraints on the dark matter density and on the amplitude
of CMB isocurvature perturbations currently demand an exponential degree
of finetuning of both axion and inflationary parameters beyond what is
required for particle physics. String theory models generally produce large
numbers of axionlike fields; the prospect that any of these fields exist
at scales close to that of the QCD axion makes the problem drastically
worse. I will discuss the challenge of accommodating stringtheoretic
axions in standard inflationary cosmology and show that the finetuning
problems cannot be fully addressed by anthropic principle arguments.
Date:  Thursday, 15 January 2009 
Time:  14:00 
Where:  McGill University 
 Ernest Rutherford Physics Building, R.E. Bell Conference Room (room 103) 
