125 research outputs found
Non-Perturbative Planar Equivalence and the Absence of Closed String Tachyons
We consider 'orbifold' and 'orientifold' field theories from the dual closed
string theory side. We argue that a necessary condition for planar equivalence
to hold is the absence of a closed string tachyonic mode in the dual
non-supersymmetric string. We analyze several gauge theories on R3xS1. In the
specific case of U(N) theories with symmetric/anti-symmetric fermions
('orientifold field theories') the relevant closed string theory is
tachyon-free at large compactification radius (due to winding modes), but it
develops a tachyonic mode below a critical radius. Our finding is with
agreement with field theory expectations of a phase transition from a C-parity
violating phase to a C-parity preserving phase as the compactification radius
increases. In the case of U(N)xU(N) theories with bi-fundamental matter
('orbifold field theories') a tachyon is always present in the string spectrum,
at any compactification radius. We conclude that on R4 planar equivalence holds
for 'orientfiold field theories', but fails for 'orbifold field theories'
daughters of N=4 SYM and suggest the same for daughters of N=1 SYM. We also
discuss examples of SO/Sp gauge theories with symmetric/anti-symmetric
fermions. In this case planar equivalence holds at any compactification radius
-in agreement with the absence of tachyons in the string dual.Comment: 14 pages, Latex. 3 eps figures. v2: ref. added. v3: clarifying
sentences added in the abstract and at the end of section 4. version accepted
to JHE
Simplifying superstring and D-brane actions in AdS(4) x CP(3) superbackground
By making an appropriate choice for gauge fixing kappa-symmetry we obtain a
relatively simple form of the actions for a D=11 superparticle in AdS(4) x
S(7)/Z_k, and for a D0-brane, fundamental string and D2-branes in the AdS(4) x
CP(3) superbackground. They can be used to study various problems of string
theory and the AdS4/CFT3 correspondence, especially in regions of the theory
which are not reachable by the OSp(6|4)/U(3) x SO(1,3) supercoset sigma-model.
In particular, we present a simple form of the gauge-fixed superstring action
in AdS(4) x CP(3) and briefly discuss issues of its T-dualization.Comment: 1+36 pages, v2,v3 clarifications and references adde
Invariant Distances
In this chapter we shall define the (invariant) distance we are going to use, and collect some of its main properties we shall need later on
Review of AdS/CFT Integrability, Chapter IV.3: N=6 Chern-Simons and Strings on AdS4xCP3
We review the duality and integrability of N=6 superconformal Chern-Simons
theory in three dimensions and IIA superstring theory on the background
AdS4xCP3. We introduce both of these models and describe how their degrees of
freedom are mapped to excitations of a long-range integrable spin-chain.
Finally, we discuss the properties of the Bethe equations, the S-matrix and the
algebraic curve that are special to this correspondence and differ from the
case of N=4 SYM theory and strings on AdS5xS5.Comment: 22 pages, see also overview article arXiv:1012.3982, v2: references
to other chapters updated, v3: references added, v4: brief discussion of
giant magnons added, further minor changes, published version, v5: union of
v3 and v4 because changes made in v3 were accidentally lost in v
A cognitive framework for the categorisation of auditory objects in urban soundscapes
Categorisation is a fundamental cognitive process that plays a central role in
everyday behaviour and action. Whereas previous studies have investigated the
categorisation of isolated everyday sounds, this paper presents an experiment to
investigate the cognitive categorisation of everyday sounds within their original
context. A group of eighteen expert and non-expert listeners took part in a free
sorting task using 110 sounds identified within ambisonic reproductions of urban
soundscapes. The participants were asked to sort the objects into groups of
sounds that served a similar purpose in the overall perception of the soundscape.
Following this, the participants were asked to provide descriptive labels for the
groups they had formed. The results were analysed using hierarchical agglomerative
clustering and non-metric multidimensional scaling (MDS) to explore
both the structure and dimensionality of the data. The resulting hierarchical
clustering of objects show three top level categories relating to transient sounds,
continuous sounds, and speech and vocalisations. Sub-categories were identified
in each of the top level categories which included harmonic and non-harmonic
continuous sounds, clear speech, unintelligible speech, vocalisations, transient
sounds that indicate actions, and non-salient transient sounds. The first two
dimensions revealed by the MDS analysis relate to temporal extent and intelligibility
respectively. Interpretation of the third dimension is less clear, but may be related to harmonic content
Organic matter chemistry controls greenhouse gas emissions from permafrost peatlands
Large tracts of arctic and subarctic peatlands are underlain by permafrost. These peatlands store large quantities of carbon (C), and are currently under severe threat from climate change. The aim of this study was to determine the size and organic chemistry of the easily degradable C pool in permafrost peatlands and link the functional organic chemistry to temperature and moisture controls of greenhouse gas emissions. First, we used a combination of field measurements and laboratory experiments to assess the influence of increased temperature and flooding on CO₂ and CH₄ emissions from sixteen permafrost peatlands in subarctic Sweden and Canada. Second, we determined the variation in organic matter chemistry and the associated microbial community composition of the peat active layer, with depth using quantitative ¹³C solid-state NMR and molecular biomarkers respectively. We demonstrate that the peat organic chemistry strongly controls CO₂ release from peat and that ca. 35 and 26% of the peat organic matter, at the Swedish and Canadian peatlands sites, respectively, is easily degradable by heterotrophic microorganisms. In contrast to CO₂, CH₄ emissions were decoupled from peat functional organic chemistry. We show a strong relationship between the microbial community structure and the peat organic chemistry suggesting that substrate type and abundance is an important driver of microbial composition in sub-arctic peatlands. Despite considerable variation in peat chemistry and microbial community composition with depth the temperature sensitivity was comparable throughout the active layer. Our study shows that functional organic chemistry controls both soil respiration rates and the composition of the microbial community. Furthermore, if these peatlands collapse and flood on thawing, they are unlikely to become large emitters of CH₄ without additional input of labile substrates
Giant Magnons on CP^3 by Dressing Method
We consider classical string spectrum of R x CP^3, and construct a family of
solutions with residual SU(2) symmetry by the dressing method on SU(4)/U(3)
sigma model. All of them obey the square-root type dispersion relation, as is
expected from the su(2|2) symmetry. A single dyonic giant magnon is not found
in this approach.Comment: 1+29 pages, 1 figure, v2: a figure and references added, minor
corrections, v3: remarks on semiclassical quantization added. To be published
in JHE
The surface detector array of the Telescope Array experiment
The Telescope Array (TA) experiment, located in the western desert of
Utah,USA, is designed for observation of extensive air showers from extremely
high energy cosmic rays. The experiment has a surface detector array surrounded
by three fluorescence detectors to enable simultaneous detection of shower
particles at ground level and fluorescence photons along the shower track. The
TA surface detectors and fluorescence detectors started full hybrid observation
in March, 2008. In this article we describe the design and technical features
of the TA surface detector.Comment: 32 pages, 17 figure
New air fluorescence detectors employed in the Telescope Array experiment
Since 2007, the Telescope Array (TA) experiment, based in Utah, USA, has been
observing ultra high energy cosmic rays to understand their origins. The
experiment involves a surface detector (SD) array and three fluorescence
detector (FD) stations. FD stations, installed surrounding the SD array,
measure the air fluorescence light emitted from extensive air showers (EASs)
for precise determination of their energies and species. The detectors employed
at one of the three FD stations were relocated from the High Resolution Fly's
Eye experiment. At the other two stations, newly designed detectors were
constructed for the TA experiment. An FD consists of a primary mirror and a
camera equipped with photomultiplier tubes. To obtain the EAS parameters with
high accuracies, understanding the FD optical characteristics is important. In
this paper, we report the characteristics and installation of new FDs and the
performances of the FD components. The results of the monitored mirror
reflectance during the observation time are also described in this report.Comment: 44 pages, 23 figures, submitted to NIM-
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