Particle theory

Abstract:

We study the Abelian projection of SU(2) instantons in the maximally Abelian gauge. We find that in this gauge an isolated instanton produces a closed monopole loop within its core and the size of this loop increases with the core size. We show that this result is robust against the introduction of small quantum fluctuations. We investigate the effects of neighbouring (anti-) instantons upon each other and show how overlapping (anti-) instantons can generate larger monopole loops. We find, however, that in fields that are typical of the fully quantised vacuum only some of the large monopole loops that are important for confinement have a topological origin. We comment on what this may imply for the rôle of instantons in confinement and chiral symmetry breaking.

Abstract:

Contrary to a recent claim, the inferred primordial abundances of the light elements are quite consistent with the expectations from standard big bang nucleosynthesis when attention is restricted to direct observations rather than results from chemical evolution models. The number of light neutrino (or equivalent particle) species ($N_\nu$) can be as high as 4.53 if the nucleon-to-photon ratio ($\eta$) is at its lower limit of $1.65 \times 10^{-10}$, as constrained by the upper bound on the deuterium abundance in high redshift quasar absorption systems. Alternatively, with $N_\nu = 3$, $\eta$ can be as high as $8.90 \times 10^{-10}$ if the deuterium abundance is bounded from below by its interstellar value.