51 research outputs found
Sphaleron of a 4 dimensional SO(4) Higgs model
We construct the finite energy path between topologically distinct vacua of a
4 dimensional SO(4) Higgs model which is known to support an instanton, and
show that there is a sphaleron with Chern-Simons number N_CS=1/2 at the top of
the energy barrier. This is carried out using the original geometric loop
construction of Manton.Comment: 9 pages, 2 figures, LaTex format, minor text corrections. To be
published in Phys. Lett.
Quantum Tunneling and Phase Transitions in Spin Systems with an Applied Magnetic Field
Transitions from classical to quantum behaviour in a spin system with two
degenerate ground states separated by twin energy barriers which are asymmetric
due to an applied magnetic field are investigated. It is shown that these
transitions can be interpreted as first- or second-order phase transitions
depending on the anisotropy and magnetic parameters defining the system in an
effective Lagrangian description.Comment: 18 pages, 7 figure
N=2 String-String Duality and Holomorphic couplings
We review aspects of N=2 duality between the heterotic and the type IIA
string. After a description of string duality intended for the non-specialist
the computation of the heterotic prepotential and the function for the
ST, STU and STUV model (V a Wilson line) and the matching with the Calabi-Yau
instanton expansions are given in detail. Relations with BPS spectral sums in
various connections are pointed out.Comment: 86 pages, late
Significance of zero modes in path--integral quantization of solitonic theories with BRST invariance
The significance of zero modes in the path-integral quantization of some
solitonic models is investigated. In particular a Skyrme-like theory with
topological vortices in (1+2) dimensions is studied, and with a BRST invariant
gauge fixing a well defined transition amplitude is obtained in the one loop
approximation. We also present an alternative method which does not necessitate
evoking the time-dependence in the functional integral, but is equivalent to
the original one in dealing with the quantization in the background of the
static classical solution of the non-linear field equations. The considerations
given here are particularly useful in - but also limited to - the one-loop
approximation.Comment: 16 pages, LaTe
Calculation of Spin Tunneling Effects in the Presence of an Applied Magnetic Field
The tunneling splitting of the energy levels of a ferromagnetic particle in
the presence of an applied magnetic field - previously derived only for the
ground state with the path integral method - is obtained in a simple way from
Schroedinger theory. The origin of the factors entering the result is clearly
understood, in particular the effect of the asymmetry of the barriers of the
potential. The method should appeal particularly to experimentalists searching
for evidence of macroscopic spin tunneling.Comment: 10 pages, LaTex, 4 figures included using graphic
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