151 research outputs found
ENERGY EXCHANGE WITHIN ECOSYSTEMS. Third Annual Technical Progress Report, May 15, 1969--May 14, 1970.
UV/IR Mixing for Noncommutative Complex Scalar Field Theory, II (Interaction with Gauge Fields)
We consider noncommutative analogs of scalar electrodynamics and N=2 D=4 SUSY
Yang-Mills theory. We show that one-loop renormalizability of noncommutative
scalar electrodynamics requires the scalar potential to be an anticommutator
squared. This form of the scalar potential differs from the one expected from
the point of view of noncommutative gauge theories with extended SUSY
containing a square of commutator. We show that fermion contributions restore
the commutator in the scalar potential. This provides one-loop
renormalizability of noncommutative N=2 SUSY gauge theory. We demonstrate a
presence of non-integrable IR singularities in noncommutative scalar
electrodynamics for general coupling constants. We find that for a special
ratio of coupling constants these IR singularities vanish. Also we show that IR
poles are absent in noncommutative N=2 SUSY gauge theory.Comment: 9 pages, 16 EPS figure
Earthshine observation of vegetation and implication for life detection on other planets - A review of 2001 - 2006 works
The detection of exolife is one of the goals of very ambitious future space
missions that aim to take direct images of Earth-like planets. While
associations of simple molecules present in the planet's atmosphere (,
, etc.) have been identified as possible global biomarkers, we
review here the detectability of a signature of life from the planet's surface,
i.e. the green vegetation. The vegetation reflectance has indeed a specific
spectrum, with a sharp edge around 700 nm, known as the "Vegetation Red Edge"
(VRE). Moreover vegetation covers a large surface of emerged lands, from
tropical evergreen forest to shrub tundra. Thus considering it as a potential
global biomarker is relevant. Earthshine allows to observe the Earth as a
distant planet, i.e. without spatial resolution. Since 2001, Earthshine
observations have been used by several authors to test and quantify the
detectability of the VRE in the Earth spectrum. The egetation spectral
signature is detected as a small 'positive shift' of a few percents above the
continuum, starting at 700 nm. This signature appears in most spectra, and its
strength is correlated with the Earth's phase (visible land versus visible
ocean). The observations show that detecting the VRE on Earth requires a
photometric relative accuracy of 1% or better. Detecting something equivalent
on an Earth-like planet will therefore remain challenging, moreover considering
the possibility of mineral artifacts and the question of 'red edge'
universality in the Universe.Comment: Invited talk in "Strategies for Life Detection" (ISSI Bern, 24-28
April 2006) to appear in a hardcopy volume of the ISSI Space Science Series,
Eds, J. Bada et al., and also in an issue of Space Science Reviews. 13 pages,
8 figures, 1 tabl
Why Does Inflation Start at the Top of the Hill?
We show why the universe started in an unstable de Sitter state. The quantum
origin of our universe implies one must take a `top down' approach to the
problem of initial conditions in cosmology, in which the histories that
contribute to the path integral, depend on the observable being measured. Using
the no boundary proposal to specify the class of histories, we study the
quantum cosmological origin of an inflationary universe in theories like trace
anomaly driven inflation in which the effective potential has a local maximum.
We find that an expanding universe is most likely to emerge in an unstable de
Sitter state, by semiclassical tunneling via a Hawking-Moss instanton. Since
the top down view is forced upon us by the quantum nature of the universe, we
argue that the approach developed here should still apply when the framework of
quantum cosmology will be based on M-Theory.Comment: 21 pages, 1 figur
Holography and Defect Conformal Field Theories
We develop both the gravity and field theory sides of the Karch-Randall
conjecture that the near-horizon description of a certain D5-D3 brane
configuration in string theory, realized as AdS_5 x S^5 bisected by an AdS_4 x
S^2 "brane", is dual to N=4 Super Yang-Mills theory in R^4 coupled to an R^3
defect. We propose a complete Lagrangian for the field theory dual, a novel
"defect superconformal field theory" wherein a subset of the fields of N=4 SYM
interacts with a d=3 SU(N) fundamental hypermultiplet on the defect preserving
conformal invariance and 8 supercharges. The Kaluza-Klein reduction of wrapped
D5 modes on AdS_4 x S^2 leads to towers of short representations of OSp(4|4),
and we construct the map to a set of dual gauge-invariant defect operators O_3
possessing integer conformal dimensions. Gravity calculations of and
are given. Spacetime and N-dependence matches expectations from dCFT,
while the behavior as functions of lambda = g^2 N at strong and weak coupling
is generically different. We comment on a class of correlators for which a
non-renormalization theorem may still exist. Partial evidence for the
conformality of the quantum theory is given, including a complete argument for
the special case of a U(1) gauge group. Some weak coupling arguments which
illuminate the duality are presented.Comment: 47 pages, LaTeX, 2 figures, feynmf. v2: fixed minor errors, added
references. v3: fixed more typo
On the perturbative chiral ring for marginally deformed N=4 SYM theories
For \cal{N}=1 SU(N) SYM theories obtained as marginal deformations of the
\cal{N}=4 parent theory we study perturbatively some sectors of the chiral ring
in the weak coupling regime and for finite N. By exploiting the relation
between the definition of chiral ring and the effective superpotential we
develop a procedure which allows us to easily determine protected chiral
operators up to n loops once the superpotential has been computed up to (n-1)
order. In particular, for the Lunin-Maldacena beta-deformed theory we determine
the quantum structure of a large class of operators up to three loops. We
extend our procedure to more general Leigh-Strassler deformations whose chiral
ring is not fully understood yet and determine the weight-two and weight-three
sectors up to two loops. We use our results to infer general properties of the
chiral ring.Comment: LaTex, 40 pages, 4 figures, uses JHEP3; v2: minor correction
On the Background Field Method Beyond One Loop: A manifestly covariant derivative expansion in super Yang-Mills theories
There are currently many string inspired conjectures about the structure of
the low-energy effective action for super Yang-Mills theories which require
explicit multi-loop calculations. In this paper, we develop a manifestly
covariant derivative expansion of superspace heat kernels and present a scheme
to evaluate multi-loop contributions to the effective action in the framework
of the background field method. The crucial ingredient of the construction is a
detailed analysis of the properties of the parallel displacement propagators
associated with Yang-Mills supermultiples in N-extended superspace.Comment: 32 pages, latex, 7 EPS figures. v2: references, comments added, typos
corrected, incorrect `skeleton' conjecture in sect. 3 replaced by a more
careful treatment. v3: typos corrected, final version published in JHE
Comparing the Anglo-American and Israeli-American special relationships in the Obama era: an alliance persistence perspective
The Anglo-American and Israeli-American security relationships have proved to be unusually close and have confounded expectations that they would wither away with the changing international environment. In order to explain this, the article proposes a theory of âalliance persistenceâ that is based on reciprocity over shared geostrategic interests, sentimental attachments and institutionalized security relations. The article employs this theoretical framework to explore how Anglo-American and Israeli-American relations have developed during the Obama administration. It argues that the Anglo-American relationship has been closer because of the two countriesâ shared strategic interests, whilst the Israeli-American relationship has experienced divergences in how the security interests of the two sides have been pursued. The article concludes by assessing how the two relationships will fair in the post-Obama era and argues that there are numerous areas of tension in the US-Israeli relationship that risk future tensions.
Keywords: Alliance, US-UK, US-Israel, Special Relationship, Obam
Re-storying and visualizing the changing entrepreneurial identities of Bill Gates and Richard Branson.
The storytelling in textual and visual re-constructions of Bill Gates and Richard Branson by their organizations produces entrepreneurial identities bound into particular social power-knowledge relations. Our purpose is to examine how these organizations, and their critics, mobilize storytelling in acts of re-storying (enlivening) or re-narrating (branding a monologic) practices using Internet technologies to invite viewers to frame the world of entrepreneurship. We use visual discourse and storytelling methods to analyze how Microsoft and Virgin Group use various kinds of entrepreneurial images and textual narratives to re-narrate and produce particular brands of capitalism. These organizations' scoptic regimes of representation are contested in counter-visualizing and counterstory practices of external stakeholders. We suggest that the image and textual practices of storytelling have changed as both entrepreneurs court philanthropic and social entrepreneur identity markers. Our contribution to entrepreneurial identity is to apply double and multiple narrations, the appropriation of another's narrative words (or images) into another's narrative, and relate such storytelling moves to visuality
Temporal dynamics of spectral reflectance and vegetation indices during canola crop cycle in southern Brazil
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