Talks

Thanks to the ongoing Planck mission, a new window will be opened on the properties of the primordial density field, the cosmological parameters, and the physics of reionization. Much of Planck's new leverage on these quantities will come from temperature measurements at small angular scales and from polarization measurements. These both depend on the details of cosmological hydrogen recombination; use of the CMB as a probe of energies greater than 10^16 GeV compels us to get the ~eV scale atomic physics right. One question that remains is how high in hydrogen principle quantum number we have to go to make sufficiently accurate predictions for Planck. Using sparse matrix methods to beat computational difficulties, I have modeled the influence of very high (up to and including n=200) excitation states of atomic hydrogen on the recombination history of the primordial plasma, resolving all angular momentum sub-states separately and including, for the first time, the effect of hydrogen quadrupole transitions. I will review the basic physics, explain the resulting plasma properties, discuss recombination histories, and close by discussing the effects on CMB observables.

For generic field theories at finite temperature, a power-law falloff of correlation functions of conserved currents at long times is a prediction of non-linear hydrodynamics. We demonstrate, through a one-loop computation in Einstein gravity in Anti de Sitter space, that this effect is reproduced by the dynamics of black hole horizons. The result is in agreement with the gauge-gravity correspondence.

The validity of a local AdS supergravity description of SYM at strong coupling requires the existence of a parametrically large gap in the spectrum of dimensions of the local operators, separating the low dimension operators dual to supergravity fields from the others. We shall give evidence that the reverse is also true: a large gap in the spectrum of dimensions implies a local bulk dual.

Using this limit we can extract the scattering amplitudes of the bulk theory in flat space from the correlation functions of the dual CFT. This gives a non-perturbative definition of flat space string theory scattering amplitudes as a limit of the correlation functions of SYM.