175 research outputs found
New views of the spherical Bouguer gravity anomaly
This paper presents a number of new concepts concerning the gravity anomaly. First, it identifies a distinct difference between a surface (2-D) gravity anomaly (the difference between actual gravity on one surface and normal gravity on another surface) and a solid (3-D) gravity anomaly defined in the fundamental gravimetric equation. Second, it introduces the 'no topography' gravity anomaly (which turns out to be the complete spherical Bouguer anomaly) as a means to generate a quantity that is smooth, thus suitable for gridding, and harmonic, thus suitable for downward continuation. It is understood that the possibility of downward continuing a smooth gravity anomaly would simplify the task of computing an accurate geoid. It is also shown that the planar Bouguer anomaly is not harmonic, and thus cannot be downward continued
Toward the M(F)--Theory Embedding of Realistic Free-Fermion Models
We construct a Landau-Ginzburg model with the same data and symmetries as a
orbifold that corresponds to a class of realistic free-fermion
models. Within the class of interest, we show that this orbifolding connects
between different orbifold models and commutes with the mirror
symmetry. Our work suggests that duality symmetries previously discussed in the
context of specific and theory compactifications may be extended to the
special orbifold that characterizes realistic free-fermion
models.Comment: 15 pages. Standard Late
Testing Stokes-Helmert geoid model computation on a synthetic gravity field: experiences and shortcomings
We report on testing the UNB (University of New Brunswick) software suite for accurate regional geoid model determination by use of Stokes-Helmert’s method against an Australian Synthetic Field (ASF) as “ground truth”. This testing has taken several years and has led to discoveries of several significant errors (larger than 5mm in the resulting geoid models) both in the UNB software as well as the ASF. It was our hope that, after correcting the errors in UNB software, we would be able to come up with some definite numbers as far as the achievable accuracy for a geoid model computed by the UNB software. Unfortunately, it turned out that the ASF contained errors, some of as yet unknown origin, that will have to be removed before that ultimate goal can be reached. Regardless, the testing has taught us some valuable lessons, which we describe in this paper. As matters stand now, it seems that given errorless gravity data on 1’ by 1’ grid, a digital elevation model of a reasonable accuracy and no topographical density variations, the Stokes-Helmert approach as realised in the UNB software suite is capable of delivering an accuracy of the geoid model of no constant bias, standard deviation of about 25 mm and a maximum range of about 200 mm. We note that the UNB software suite does not use any corrective measures, such as biases and tilts or surface fitting, so the resulting errors reflect only the errors in modelling the geoid
Quantum field theory on manifolds with a boundary
We discuss quantum theory of fields \phi defined on (d+1)-dimensional
manifold {\cal M} with a boundary {\cal B}. The free action W_{0}(\phi) which
is a bilinear form in \phi defines the Gaussian measure with a covariance
(Green function) {\cal G}. We discuss a relation between the quantum field
theory with a fixed boundary condition \Phi and the theory defined by the Green
function {\cal G}. It is shown that the latter results by an average over \Phi
of the first. The QFT in (anti)de Sitter space is treated as an example. It is
shown that quantum fields on the boundary are more regular than the ones on
(anti) de Sitter space.Comment: The version to appear in Journal of Physics A, a discussion on the
relation to other works in the field is adde
Two-loop Yang-Mills diagrams from superstring amplitudes
Starting from the superstring amplitude describing interactions among
D-branes with a constant world-volume field strength, we present a detailed
analysis of how the open string degeneration limits reproduce the corresponding
field theory Feynman diagrams. A key ingredient in the string construction is
represented by the twisted (Prym) super differentials, as their periods encode
the information about the background field. We provide an efficient method to
calculate perturbatively the determinant of the twisted period matrix in terms
of sets of super-moduli appropriate to the degeneration limits. Using this
result we show that there is a precise one-to-one correspondence between the
degeneration of different factors in the superstring amplitudes and
one-particle irreducible Feynman diagrams capturing the gauge theory effective
action at the two-loop level.Comment: 42 pages plus appendices, 10 figure
Rigidity and defect actions in Landau-Ginzburg models
Studying two-dimensional field theories in the presence of defect lines
naturally gives rise to monoidal categories: their objects are the different
(topological) defect conditions, their morphisms are junction fields, and their
tensor product describes the fusion of defects. These categories should be
equipped with a duality operation corresponding to reversing the orientation of
the defect line, providing a rigid and pivotal structure. We make this
structure explicit in topological Landau-Ginzburg models with potential x^d,
where defects are described by matrix factorisations of x^d-y^d. The duality
allows to compute an action of defects on bulk fields, which we compare to the
corresponding N=2 conformal field theories. We find that the two actions differ
by phases.Comment: 53 pages; v2: clarified exposition of pivotal structures, corrected
proof of theorem 2.13, added remark 3.9; version to appear in CM
Strings from Tachyons
We propose a new interpretation of the c=1 matrix model as the world-line
theory of N unstable D-particles, in which the hermitian matrix is provided by
the non- abelian open string tachyon. For D-particles in 1+1-d string theory,
we find a direct quantitative match between the closed string emission due to a
rolling tachyon and that due to a rolling eigenvalue in the matrix model. We
explain the origin of the double-scaling limit, and interpret it as an extreme
representative of a large equivalence class of dual theories. Finally, we
define a concrete decoupling limit of unstable D-particles in IIB string theory
that reduces to the c=1 matrix model, suggesting that 1+1-d string theory
represents the near-horizon limit of an ultra-dense gas of IIB D-particles.Comment: 30 pages, 4 figures; v2: added references, improved discussion of
Liouville boundary states, v3: small correction
Deformations of flows from type IIB supergravity
We consider supersymmetric SL(3,R) deformations of various type IIB
supergravity backgrounds which exhibit flows away from an asymptotically
locally AdS_5 x S^5 fixed point. This includes the gravity dual of the Coulomb
branch of N=1 super Yang Mills theory, for which the deformed superpotential is
known. We also consider the gravity duals of field theories which live on
various curved backgrounds, such as Minkowski_2 x H^2, AdS_3 x S^1 and R x S^3.
Some of the deformed theories flow from a four-dimensional N=1 superconformal
UV fixed point to a two-dimensional (2,2) superconformal IR fixed point. We
study nonsupersymmetric generalizations of the deformations of the above
Coulomb branch flows.Comment: 29 pages, additional references and comment
Matrix Models and D-branes in Twistor String Theory
We construct two matrix models from twistor string theory: one by dimensional
reduction onto a rational curve and another one by introducing noncommutative
coordinates on the fibres of the supertwistor space P^(3|4)->CP^1. We comment
on the interpretation of our matrix models in terms of topological D-branes and
relate them to a recently proposed string field theory. By extending one of the
models, we can carry over all the ingredients of the super ADHM construction to
a D-brane configuration in the supertwistor space P^(3|4). Eventually, we
present the analogue picture for the (super) Nahm construction.Comment: 1+37 pages, reference added, JHEP style, published versio
On the complete classification of the unitary N=2 minimal superconformal field theories
Aiming at a complete classification of unitary N=2 minimal models (where the
assumption of space-time supersymmetry has been dropped), it is shown that each
modular invariant candidate of a partition function for such a theory is indeed
the partition function of a minimal model. A family of models constructed via
orbifoldings of either the diagonal model or of the space-time supersymmetric
exceptional models demonstrates that there exists a unitary N=2 minimal model
for every one of the allowed partition functions in the list obtained from
Gannon's work.
Kreuzer and Schellekens' conjecture that all simple current invariants can be
obtained as orbifolds of the diagonal model, even when the extra assumption of
higher-genus modular invariance is dropped, is confirmed in the case of the
unitary N=2 minimal models by simple counting arguments.Comment: 53 pages; Latex; minor changes in v2: intro expanded, references
added, typos corrected, footnote added on p31; renumbering of sections; main
theorem reformulated for clarity, but contents unchanged. Minor revisions in
v3: typos corrected, footnotes 5, 6 added, lemma 1 and section 3.3.2
rewritten for greater generality, section 3.3 review removed. To appear in
Comm. Math. Phy
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