11,008 research outputs found
A proposed microcomputer implementation of an Omega navigation processor
A microprocessor navigation systems using the Omega process is discussed. Several methods for correcting incoming sky waves are presented along with the hardware design which depends on a microcomputer. The control program is discussed, and block diagrams of the Omega processor and interface systems are presented
Configurations of Rank-40r Extremal Even Unimodular Lattices (r=1,2,3)
We show that if L is an extremal even unimodular lattice of rank 40r with
r=1,2,3 then L is generated by its vectors of norms 4r and 4r+2. Our result is
an extension of Ozeki's result for the case r=1.Comment: 5 pages. To appear, Journal de Theorie des Nombres de Bordeau
R-symmetry and Supersymmetry Breaking at Finite Temperature
We analyze the spontaneous symmetry breaking at finite temperature
for the simple O'Raifeartaigh-type model introduced in [1] in connection with
spontaneous supersymmetry breaking. We calculate the finite temperature
effective potential (free energy) to one loop order and study the thermal
evolution of the model. We find that the R-symmetry breaking occurs through a
second order phase transition. Its associated meta-stable supersymmetry
breaking vacuum is thermodynamically favored at high temperatures and the model
remains trapped in this state by a potential barrier, as the temperature lowers
all the way until T=0.Comment: 19 pages, 4 figures - Minor revisions, references added. To appear in
JHE
Front propagation in laminar flows
The problem of front propagation in flowing media is addressed for laminar
velocity fields in two dimensions. Three representative cases are discussed:
stationary cellular flow, stationary shear flow, and percolating flow.
Production terms of Fisher-Kolmogorov-Petrovskii-Piskunov type and of Arrhenius
type are considered under the assumption of no feedback of the concentration on
the velocity. Numerical simulations of advection-reaction-diffusion equations
have been performed by an algorithm based on discrete-time maps. The results
show a generic enhancement of the speed of front propagation by the underlying
flow. For small molecular diffusivity, the front speed depends on the
typical flow velocity as a power law with an exponent depending on the
topological properties of the flow, and on the ratio of reactive and advective
time-scales. For open-streamline flows we find always , whereas for
cellular flows we observe for fast advection, and for slow advection.Comment: Enlarged, revised version, 37 pages, 14 figure
One-loop Yukawas on Intersecting Branes
We calculate Yukawa interactions at one-loop on intersecting D6 branes. We
demonstrate the non-renormalization theorem in supersymmetric configurations,
and show how Yukawa beta functions may be extracted. In addition to the usual
logarithmic running, we find the power-law dependence on the infra-red cut-off
associated with Kaluza-Klein modes. Our results may also be used to evaluate
coupling renormalization in non-supersymmetric cases.Comment: 48 pages, 9 figures; minor corrections, JHEP styl
Intersecting Brane Worlds at One Loop
We develop techniques for one-loop diagrams on intersecting branes. The
one-loop propagator of chiral intersection states on D6 branes is calculated
exactly and its finiteness is shown to be guaranteed by RR tadpole
cancellation. The result is used to demonstrate the expected softening of power
law running of Yukawa couplings at the string scale. We also develop methods to
calculate arbitrary N-point functions at one-loop, including those without
gauge bosons in the loop. These techniques are also applicable to heterotic
orbifold models.Comment: 35 pages, 3 figures; added reference, corrected typos, JHEP styl
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