11,605 research outputs found

    Gauge Fields and Singletons of AdS2p+1AdS_{2p+1}

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    We show that pp-forms on AdS2p+1AdS_{2p+1} describe both singletons and massless particles. On the 2p2p-dimensional boundary the singleton pp-form Lagrangian reduces to the conformally invariant functional ∫F2\int F^2. All the representations, singletons as well as massless, are zero center modules and involve a vacuum mode. Two- and three-form singleton fields are required by supersymmetry in AdS5_5 and AdS7_7 supergravity respectively.Comment: tex file, 13 page

    Forecasting Euro-area recessions using time-varying binary response models for financial.

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    Recent macroeconomic evolutions during the years 2008 and 2009 have pointed out the impact of financial markets on economic activity. In this paper, we propose to evaluate the ability of a set of financial variables to forecast recessions in the euro area by using a non-linear binary response model associated with information combination. Especially, we focus on a time-varying probit model whose parameters evolve according to a Markov chain. For various forecast horizons, we provide a readable and leading signal of recession by combining information according to two combining schemes over the sample 1970-2006. First we average recession probabilities and second we linearly combine variables through a dynamic factor model in order to estimate an innovative factor-augmented probit model. Out-of-sample results over the period 2007-2008 show that financial variables would have been helpful in predicting a recession signal as September 2007, that is around six months before the effective start of the 2008-2009 recession in the euro area.Macroeconomic forecasting, Business cycles, Turning points, Financial markets, Non-linear time series, Combining forecasts.

    Mass formulae and natural hierarchy in string effective supergravities

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    We study some conditions for the hierarchy m3/2<<MPm_{3/2} << M_P to occur naturally in a generic effective supergravity theory. Absence of fine-tuning and perturbative calculability require that the effective potential has a sliding gravitino mass and vanishing cosmological constant, up to O(m3/24){\cal O}(m_{3/2}^4) corrections. In particular, cancellation of quadratically divergent contributions to the one-loop effective potential should take place, including the `hidden sector' of the theory. We show that these conditions can be met in the effective supergravities derived from four-dimensional superstrings, with supersymmetry broken either at the string tree level via compactification, or by non-perturbative effects such as gaugino condensation. A crucial role is played by some approximate scaling symmetries, which are remnants of discrete target-space dualities in the large moduli limit. We derive explicit formulae for the soft breaking terms arising from this class of `large hierarchy compatible' (LHC) supergravities.Comment: 40 pages, no figures, CERN-TH.7192/94, LPTENS -94/12, UCLA/94/TEP13 (plain LATEX, to be run twice). Some trivial misprints and references have been correcte

    Simulating intergalactic quasar scintillation

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    Intergalactic scintillation of distant quasars is sensitive to free electrons and therefore complements Lyα\alpha absorption line experiments probing the neutral intergalactic medium (IGM). We present a new scheme to compute IGM refractive scintillation effects on distant sources in combination with Adaptive Mesh Refinement cosmological simulations. First we validate our model by reproducing the well-known interstellar scintillation (ISS) of Galactic sources. The simulated cosmic density field is then used to infer the statistical properties of intergalactic scintillation. Contrary to previous claims, we find that the scattering measure of the simulated IGM at z<2z<2 is \langle \mbox{SM}_{\equ}\rangle=3.879, i.e. almost 40 times larger than for the usually assumed smooth IGM. This yield an average modulation index ranging from 0.01 (Îœs=5\nu_s=5 GHz) up to 0.2 (Îœs=50\nu_s=50 GHz); above \nu_{s}\gsim30 GHz the IGM contribution dominates over ISS modulation. We compare our model with data from a 0.3≀z≀20.3\leq z\leq 2 quasar sample observed at \nu_{\obs}=8.4 GHz. For this high frequency (10.92≀Μs≀25.210.92\leq \nu_s \leq 25.2), high galactic latitude sample ISS is negligible, and IGM scintillation can reproduce the observed modulation with a 4% accuracy, without invoking intrinsic source variability. We conclude by discussing the possibility of using IGM scintillation as a tool to pinpoint the presence of intervening high-zz groups/clusters along the line of sight, thus making it a probe suitably complementing Sunyaev-Zeldovich data recently obtained by \textit{Planck}.Comment: 14 pages, 13 figures, accepted for publication in MNRA

    Flat Symplectic Bundles of N-Extended Supergravities, Central Charges and Black-Hole Entropy

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    In these lectures we give a geometrical formulation of N-extended supergravities which generalizes N=2 special geometry of N=2 theories. In all these theories duality symmetries are related to the notion of "flat symplectic bundles" and central charges may be defined as "sections" over these bundles. Attractor points giving rise to "fixed scalars" of the horizon geometry and Bekenstein-Hawking entropy formula for extremal black-holes are discussed in some details.Comment: Based on lectures given by S. Ferrara at the 5th Winter School on Mathematical Physics held at the Asia Pacific Center for Theoretical Physics, Seul (Korea), February 199


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    Recent conflicts over fish stocks, such as salmon and turbot, have revived public interest in the optimal management of transboundary renewable natural resources. Given that enforcement of binding contracts is often a major obstacle, dynamically consistent or self-enforcing contracting, as proposed by Vislie (1987), must be relied upon. A more general model is developed which recognizes that, in the absence of a cooperative agreement, two countries may enjoy differing economic payoffs. The predictions of the model are consistent with, and provide insights into, the particulars of recent disputes.Resource /Energy Economics and Policy,

    11-Dimensional Supergravity Compactified on Calabi-Yau Threefolds

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    We consider generic features of eleven dimensional supergravity compactified down to five dimensions on an arbitrary Calabi-Yau threefold.Comment: TeX, harvmac, 8 pg

    Finite-Size Effects and Operator Product Expansions in a CFT for d>2

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    The large momentum expansion for the inverse propagator of the auxiliary field λ(x)\lambda(x) in the conformally invariant O(N) vector model is calculated to leading order in 1/N, in a strip-like geometry with one finite dimension of length LL for 2<d<42<d<4. Its leading terms are identified as contributions from λ(x)\lambda(x) itself and the energy momentum tensor, in agreement with a previous calculation based on conformal operator product expansions. It is found that a non-trivial cancellation takes place by virtue of the gap equation. The leading coefficient of the energy momentum tensor contribution is shown to be related to the free energy density.Comment: 10 pages LaTeX 2 eps figures, minor changes in text. Revised version to be published in Phys.Lett. B. email: [email protected] [email protected]