1,201 research outputs found
Classification of the N=2, Z2 X Z2-symmetric type II orbifolds and their type II asymmetric duals
Using free world-sheet fermions, we construct and classify all the N=2, Z2 X
Z2 four-dimensional orbifolds of the type IIA/B strings for which the orbifold
projections act symmetrically on the left and right movers. We study the
deformations of these models out of the fermionic point, deriving the partition
functions at a generic point in the moduli of the internal torus T6=T2 X T2 X
T2. We investigate some of their perturbative and non-perturbative dualities
and construct new dual pairs of type IIA/type II asymmetric orbifolds, which
are related non-perturbatively and allow us to gain insight into some of the
non-perturbative properties of the type IIA/B strings in four dimensions. In
particular, we consider some of the (non-)perturbative gravitational
corrections.Comment: Latex, 47 pages, no figure
On the Heterotic Effective Action at One-Loop, Gauge Couplings and the Gravitational Sector
We present in detail the procedure for calculating the heterotic one-loop
effective action. We focus on gravitational and gauge couplings. We show that
the two-derivative couplings of the gravitational sector are not renormalized
at one loop when the ground state is supersymmetric. Arguments are presented
that this non-renormalization theorem persists to all orders in perturbation
theory. We also derive the full one-loop correction to the gauge coupling. For
a class of ground states, namely those that are obtained by toroidal
compactification to four dimensions of generic six-dimensional models, we
give an explicit formula for the gauge-group independent thresholds, and show
that these are equal within the whole family.Comment: LateX, 17pp. A minor correction mad
On the unification of geodetic leveling datums using satellite altimetry
Techniques are described for determining the height of Mean Sea Level (MSL) at coastal sites from satellite altimetry. Such information is of value in the adjustment of continental leveling networks. Numerical results are obtained from the 1977 GEOS-3 altimetry data bank at Goddard Space Flight Center using the Bermuda calibration of the altimeter. Estimates are made of the heights of MSL at the leveling datums for Australia and a hypothetical Galveston datum for central North America. The results obtained are in reasonable agreement with oceanographic estimates obtained by extrapolation. It is concluded that all gravity data in the Australian bank AUSGAD 76 and in the Rapp data file for central North America refer to the GEOS-3 altimeter geoid for 1976.0 with uncertainties which do not exceed + or - 0.1 mGal
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