Stuart Samuel

Neutrino oscillations in the early universe

Abstract Numerical studies are performed for neutrino oscillations for t > 1 3 seconds after the big bang. The effects of electron, positron and neutrino backgrounds are properly included. Flavor evolution of the neutrino background is dominantly smooth. However, in a certain parameter region, coherent undamped oscillations of the neutrino background are possible. In addition, neutrino CP asymmetry is found to be considerably smaller than expected. Reasons are provided for the above effects and some physical implications are discussed.

The Off-shell Koba-nielsen Formula

Abstract Starting with the Witten covariant string field theory and using conformal field-theoretic methods, the tree-level off-shell N -point tachyon amplitude in the open bosonic string is obtained. It is shown to agree on-shell with the Koba-Nielsen formula.

Solving the open bosonic string in perturbation theory

The integrand and integration region for the N-point amplitude in the open oriented bosonic string are obtained to all orders in perturbation theory. The result is derived from the Witten covariant string field theory by using on-shell and off-shell conformal methods and Riemann surface mathematics. Although only the off-shell g-loop tachyon amplitudes are computed explicitly, the methods generalize to other external states. We derive the g-loop ghost-Jacobi identity in which the ghost correlation function cancels the jacobian factor in changing from second-quantized to first-quantized variables. Moduli space is discussed from several viewpoints and it is shown that string field theory provides an algorithm for its determination.

Off-shell conformal field theory at the one-loop level

Abstract The one-loop off-shell N -point tachyon amplitude is obtained for Wittens covariant string field theory, using off-shell conformal methods. An identity is derived which relates the ghost correlation function to the javobian in changing to standard variables. This identity is used to show that the correct integration measure is obtained. The covering of moduli space by the field theory Feynman diagrams is shown. Complete on-shell agreement is found with first-quantized results. Finally, the off-shell singularity structure is discussed.