2,846 research outputs found
General (Anti-)de Sitter Black Holes in Five Dimensions
We find a general class of rotating charged black hole solutions to N=2, D=5
gauged supergravity coupled to vector supermultiplets. The supersymmetry
properties of these solutions are studied, and their mass and angular momenta
are obtained. We also compute the stress tensor of the dual D=4, N=4 super
Yang-Mills theory in the limit of strong `t Hooft coupling. It is shown that
closed timelike curves occur outside the horizon, indicating loss of unitarity
in the dual CFT. For imaginary coupling constant of the gravitini to the gauge
fields, one can obtain multi-centered rotating charged de Sitter black holes.
Some physical properties of these solutions are also discussed.Comment: 22 pages, LaTeX, some explanations concerning the appearance of
closed timelike curves outside the horizon added in section 5.1, updated
references, published versio
Nonperturbative Effective Actions of N=2 Supersymmetric Gauge Theories
We elaborate on our previous work on N=2 supersymmetric Yang-Mills theory. In
particular, we show how to explicitly determine the low energy quantum
effective action for from the underlying hyperelliptic Riemann
surface, and calculate the leading instanton corrections. This is done by
solving Picard-Fuchs equations and asymptotically evaluating period integrals.
We find that the dynamics of the theory is governed by an Appell system
of type , and compute the exact quantum gauge coupling explicitly in terms
of Appell functions.Comment: 57p, harvmac with hyperlinks, 9 uuencoded ps figure
K3--Fibrations and Heterotic-Type II String Duality
We analyze the map between heterotic and type II N=2 supersymmetric string
theories for certain two and three moduli examples found by Kachru and Vafa.
The appearance of elliptic j-functions can be traced back to specializations of
the Picard-Fuchs equations to systems for surfaces. For the three-moduli
example we write the mirror maps and Yukawa couplings in the weak coupling
limit in terms of j-functions; the expressions agree with those obtained in
perturbative calculations in the heterotic string in an impressive way. We also
discuss symmetries of the world-sheet instanton numbers in the type II theory,
and interpret them in terms of S--duality of the non-perturbative heterotic
string.Comment: 16p, harvmac with hyperlink
On the Monodromies of N=2 Supersymmetric Yang-Mills Theory
We review the generalization of the work of Seiberg and Witten on N=2
supersymmetric SU(2) Yang-Mills theory to SU(n) gauge groups. The quantum
moduli spaces of the effective low energy theory parametrize a special family
of hyperelliptic genus n-1 Riemann surfaces. We discuss the massless spectrum
and the monodromies.Comment: 15p, harvmac/lanlmac with hyperlinks, 4 uuencoded compressed
postscript figures appende
Causality Violation and Naked Time Machines in AdS_5
We study supersymmetric charged rotating black holes in AdS, and show
that closed timelike curves occur outside the event horizon. Also upon lifting
to rotating D3 brane solutions of type IIB supergravity in ten dimensions,
closed timelike curves are still present. We believe that these causal
anomalies correspond to loss of unitarity in the dual , D=4 super
Yang-Mills theory, i.e. the chronology protection conjecture in the AdS bulk is
related to unitarity bounds in the boundary CFT. We show that no charged or
uncharged geodesic can penetrate the horizon, so that the exterior region is
geodesically complete. These results still hold true in the quantum case,
i.~e.~the total absorption cross section for Klein-Gordon scalars propagating
in the black hole background is zero. This suggests that the effective
temperature is zero instead of assuming the naively found imaginary value.Comment: 22 pages, Latex, uses JHEP.cls, 1 figure. v3: comments on unitarity
in CFT and 2 references added. v4: changes in final remarks, final version to
appear in JHE
Why Does Rem Sleep Occur? A Wake-Up Hypothesis1
Brain activity differs in the various sleep stages and in conscious wakefulness. Awakening from sleep requires restoration of the complex nerve impulse patterns in neuronal network assemblies necessary to re-create and sustain conscious wakefulness. Herein I propose that the brain uses rapid eye movement (REM) to help wake itself up after it has had a sufficient amount of sleep. Evidence suggesting this hypothesis includes the facts that, (1) when first going to sleep, the brain plunges into Stage N3 (formerly called Stage IV), a deep abyss of sleep, and, as the night progresses, the sleep is punctuated by episodes of REM that become longer and more frequent toward morning, (2) conscious-like dreams are a reliable component of the REM state in which the dreamer is an active mental observer or agent in the dream, (3) the last awakening during a night's sleep usually occurs in a REM episode during or at the end of a dream, (4) both REM and awake consciousness seem to arise out of a similar brainstem ascending arousal system (5) N3 is a functionally perturbed state that eventually must be corrected so that embodied brain can direct adaptive behavior, and (6) cortico-fugal projections to brainstem arousal areas provide a way to trigger increased cortical activity in REM to progressively raise the sleeping brain to the threshold required for wakefulness. This paper shows how the hypothesis conforms to common experience and has substantial predictive and explanatory power regarding the phenomenology of sleep in terms of ontogeny, aging, phylogeny, abnormal/disease states, cognition, and behavioral physiology. That broad range of consistency is not matched by competing theories, which are summarized herein. Specific ways to test this wake-up hypothesis are suggested. Such research could lead to a better understanding of awake consciousness
We Three: My Brain, My Homunculus, and Me
An unconscious sense of the body in all higher mammals is located in somatosensory and motor cortices, colloquially referred to as the Homunculus (H). The time has arrived to consider how H might engage in the dimensions of selfhood that go beyond embodiment. Surely, the neural network modules that process various dimensions of selfhood must at least access and interact with the H or a stored memory of it. In this review, I suggest that our traditional understanding of H is much too simplistic. This review specifies a set of experimental approaches that should enlarge our understanding of the brain mechanisms of selfhood
Possible indicators for low dimensional superconductivity in the quasi-1D carbide Sc3CoC4
The transition metal carbide Sc3CoC4 consists of a quasi-one-dimensional (1D)
structure with [CoC4]_{\inft} polyanionic chains embedded in a scandium
matrix. At ambient temperatures Sc3CoC4 displays metallic behavior. At lower
temperatures, however, charge density wave formation has been observed around
143K which is followed by a structural phase transition at 72K. Below T^onset_c
= 4.5K the polycrystalline sample becomes superconductive. From Hc1(0) and
Hc2(0) values we could estimate the London penetration depth ({\lambda}_L ~=
9750 Angstroem) and the Ginsburg-Landau (GL) coherence length ({\xi}_GL ~= 187
Angstroem). The resulting GL-parameter ({\kappa} ~= 52) classifies Sc3CoC4 as a
type II superconductor. Here we compare the puzzling superconducting features
of Sc3CoC4, such as the unusual temperature dependence i) of the specific heat
anomaly and ii) of the upper critical field H_c2(T) at T_c, and iii) the
magnetic hysteresis curve, with various related low dimensional
superconductors: e.g., the quasi-1D superconductor (SN)_x or the 2D
transition-metal dichalcogenides. Our results identify Sc3CoC4 as a new
candidate for a quasi-1D superconductor.Comment: 4 pages, 5 figure
The effect of soil acidity on crop and pasture production.
SUMMARY The effects of lime and molybdenum applications on wheat and subterranean Clover were studied further. Wheat. In relation to lime use, my aim is to develop soil tests to be used to predict when a soil requires lime to produce maximum yield, and to predict the optimum rate of lime. Using the results from field trials commenced in 1980 and 1981 the soil parameters which may be used to predict lime responses in wheat have been narrowed down. From the relationships between soil data and lime responses it appears that soil ph (measured in 1:5 H20 or 1:5 N kcl), extractable aluminium (in 1:5 N kcl), and exchangeable aluminium expressed as a percentage of total kcl- or NH4Cl- exchangeable cations are poor predictors of the lime responsiveness of wheat on soils in the low rainfall areas of the wheatbelt. The soils are being analysed further to attempt to find an accurate predictor of lime response. Unfortunately, the Government Chemical laboratories which do our analyses, are grossly understaffed, resulting in long delays in analyses being completed. To predict the optimum rate of lime to use on a soil it is necessary to be able to predict the effect of a given rate of lime on the soil properties of interest. It was found that laboratory measurements of ph buffer capacity did not reflect the changes in soil ph induced by lime application at 13 field sites. Molybdenum responses in wheat were common in the 1981 growing season (Table 1). The biggest yield increases were on low yielding trials (80ME3 and 81M02). However, on average, molybdenum application increased yield by 130 kg/ha, or 15 per cent of the yield without molybdenum. All but one (81LG12) of these trial sites have previously received applications of molybdenum. Two long term trials (81M2 and 81LG12) were commenced to study the residual value of molybdenum on acid soils. Subterranean clover grew poorly on all sites and, although molybdenum responses were observed they were not measurable because of the low productivity and high variability of the clover. Progress towards defining a model to predict acidification rates has been made. The conceptual framework of the model has been refined through studies of the scientific literature. A trial to obtain a first approximation of the effect of acidity on the effectiveness of phosphate fertiliser was commenced east of Hyden. 79GE10, 80GE5, 80GE6, 81GL5, 81JE1, 81LG8, 80ME3, 80ME4, 81ME4, 80M29, 80M30, 80M31, 81M2, 81M5/, 81M6, 81M54, 79M027, 80M04, 80M05, 81M02, 81M03, 80NA3, 80NA4, 81N06, 81N07, 79TS1, 79TS2, 80TS6, 81TS1, 81TS2, 81TS30, 81JE2, 81LG12, 79M027
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