18,410 research outputs found
Exploring arbitrarily high orders of optimized perturbation theory in QCD with nf -> 16.5
Perturbative QCD with nf flavours of massless quarks becomes simple in the
hypothetical limit nf -> 16.5, where the leading beta-function coefficient
vanishes. The Banks-Zaks (BZ) expansion in a0=(8/321)(16.5-nf) is
straightforward to obtain from perturbative results in MSbar or any
renormalization scheme (RS) whose nf dependence is `regular.' However,
`irregular' RS's are perfectly permissible and should ultimately lead to the
same BZ results. We show here that the `optimal' RS determined by the Principle
of Minimal Sensitivity does yield the same BZ-expansion results when all orders
of perturbation theory are taken into account. The BZ limit provides an arena
for exploring optimized perturbation theory at arbitrarily high orders. These
explorations are facilitated by a `master equation' expressing the optimization
conditions in the fixed-point limit. We find an intriguing strong/weak coupling
duality a -> a*^2/a about the fixed point a*.Comment: 32 pages, 4 figure
The lambda Phi^4 Miracle: lattice data and the zero-point potential
Recent lattice data for the effective potential of lambda Phi^4 theory fits
the massless one-loop formula with amazing precision. Any corrections are at
least 100 times smaller than is reasonable, perturbatively. This is strong
evidence for the "exactness conjecture" of Consoli and Stevenson.Comment: 6 pages, LaTe
Low-Energy Heavy-Ion Reactions and the Skyrme Effective Interaction
The Skyrme effective interaction, with its multitude of parameterisations,
along with its implemen- tation using the static and time-dependent density
functional (TDHF) formalism have allowed for a range of microscopic
calculations of low-energy heavy-ion collisions. These calculations allow
variation of the effective interaction along with an interpretation of the
results of this variation informed by a comparison to experimental data.
Initial progress in implementing TDHF for heavy-ion collisions necessarily used
many approximations in the geometry or the interaction. Over the last decade or
so, the implementations have overcome all restrictions, and studies have begun
to be made where details of the effective interaction are being probed. This
review surveys these studies in low energy heavy-ion reactions, finding
significant effects on observables from the form of the spin-orbit interaction,
the use of the tensor force, and the inclusion of time-odd terms in the density
functional.Comment: submitted to Prog. Part. Nucl. Phy
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