19,623 research outputs found
Six-dimensional Methods for Four-dimensional Conformal Field Theories
The calculation of both spinor and tensor Green's functions in
four-dimensional conformally invariant field theories can be greatly simplified
by six-dimensional methods. For this purpose, four-dimensional fields are
constructed as projections of fields on the hypercone in six-dimensional
projective space, satisfying certain transversality conditions. In this way
some Green's functions in conformal field theories are shown to have structures
more general than those commonly found by use of the inversion operator. These
methods fit in well with the assumption of AdS/CFT duality. In particular, it
is transparent that if fields on AdS approach finite limits on the boundary
of AdS, then in the conformal field theory on this boundary these limits
transform with conformal dimensionality zero if they are tensors (of any rank),
but with conformal dimension 1/2 if they are spinors or spinor-tensors.Comment: Version accepted for publication in Physical Review D. References to
earlier work added in footnote 2. Minor errors corrected. 24 page
CO on Ru(001): Formation and dissolution of islands of CO at low coverages
The present paper deals with the benefits and difficulties of using ion scattering spectroscopy as a spectrometric technique
Aspects of Nucleon Chiral Perturbation Theory
I review recent progress made in the calculation of nucleon properties in the
framework of heavy baryon CHPT. Topics include: Compton scattering,
scattering, the anatomy of a low-energy constant and the induced pseudoscalar
form factor.Comment: plain TeX (macro included), 12pp, lecture delivered at the workshop
on "Chiral Dynamics: Theory and Experiments", MIT, July 25-29, 199
Comparison of liquid-metal magnetohydrodynamic power conversion cycles
Comparison of liquid metal magnetohydrodynamic power conversion cycle
Perturbation theory for the two-dimensional abelian Higgs model in the unitary gauge
In the unitary gauge the unphysical degrees of freedom of spontaneously
broken gauge theories are eliminated. The Feynman rules are simpler than in
other gauges, but it is non-renormalizable by the rules of power counting. On
the other hand, it is formally equal to the limit of the
renormalizable R-gauge. We consider perturbation theory to one-loop
order in the R-gauge and in the unitary gauge for the case of the
two-dimensional abelian Higgs model. An apparent conflict between the unitary
gauge and the limit of the R-gauge is resolved, and it is
demonstrated that results for physical quantities can be obtained in the
unitary gauge.Comment: 15 pages, LaTeX2e, uses the feynmf package, formulations correcte
Photoelectric polarimetry of the tail of comet Ikey-Seki (1975 VIII)
Post-perihelion measurements of Comet 1965 VIII made on four nights in October-November 1965 using a Fabry photometer atop 3,052 m Mt. Haleakala, Hawaii are described. Detailed results of observations at 5300A on October 29, 1965 are presented
Principles of Antifragile Software
The goal of this paper is to study and define the concept of "antifragile
software". For this, I start from Taleb's statement that antifragile systems
love errors, and discuss whether traditional software dependability fits into
this class. The answer is somewhat negative, although adaptive fault tolerance
is antifragile: the system learns something when an error happens, and always
imrpoves. Automatic runtime bug fixing is changing the code in response to
errors, fault injection in production means injecting errors in business
critical software. I claim that both correspond to antifragility. Finally, I
hypothesize that antifragile development processes are better at producing
antifragile software systems.Comment: see https://refuses.github.io
Cosmic Acceleration from Causal Backreaction with Recursive Nonlinearities
We revisit the causal backreaction paradigm, in which the need for Dark
Energy is eliminated via the generation of an apparent cosmic acceleration from
the causal flow of inhomogeneity information coming in towards each observer
from distant structure-forming regions. This second-generation formalism
incorporates "recursive nonlinearities": the process by which
already-established metric perturbations will then act to slow down all future
flows of inhomogeneity information. Here, the long-range effects of causal
backreaction are now damped, weakening its impact for models that were
previously best-fit cosmologies. Nevertheless, we find that causal backreaction
can be recovered as a replacement for Dark Energy via the adoption of larger
values for the dimensionless `strength' of the clustering evolution functions
being modeled -- a change justified by the hierarchical nature of clustering
and virialization in the universe, occurring on multiple cosmic length scales
simultaneously. With this, and with one new model parameter representing the
slowdown of clustering due to astrophysical feedback processes, an alternative
cosmic concordance can once again be achieved for a matter-only universe in
which the apparent acceleration is generated entirely by causal backreaction
effects. One drawback is a new degeneracy which broadens our predicted range
for the observed jerk parameter , thus removing what had
appeared to be a clear signature for distinguishing causal backreaction from
Cosmological Constant CDM. As for the long-term fate of the universe,
incorporating recursive nonlinearities appears to make the possibility of an
`eternal' acceleration due to causal backreaction far less likely; though this
does not take into account gravitational nonlinearities or the large-scale
breakdown of cosmological isotropy, effects not easily modeled within this
formalism.Comment: 53 pages, 7 figures, 3 tables. This paper is an advancement of
previous research on Causal Backreaction; the earlier work is available at
arXiv:1109.4686 and arXiv:1109.515
An Index Theorem for Domain Walls in Supersymmetric Gauge Theories
The supersymmetric abelian Higgs model with N scalar fields admits multiple
domain wall solutions. We perform a Callias-type index calculation to determine
the number of zero modes of this soliton. We confirm that the most general
domain wall has 2(N-1) zero modes, which can be interpreted as the positions
and phases of (N-1) constituent domain walls. This implies the existence of
moduli for a D-string interpolating between N D5-branes in IIB string theory.Comment: 9 pages, REVTeX4; v2: reference adde
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