11,357 research outputs found

    The Hubble Deep Field Reveals a Supernova at z~0.95

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    We report the discovery of a variable object in the Hubble Deep Field North (HDF-N) which has brightened, during the 8.5 days sampled by the data, by more than 0.9 mag in I and about 0.7 mag in V, remaining stable in B. Subsequent observations of the HDF-N show that two years later this object has dimmed back to about its original brightness in I. The colors of this object, its brightness, its time behavior in the various filters and the evolution of its morphology are consistent with being a Type Ib supernova in a faint galaxy at z~0.95.Comment: 5 pages including 2 figures. Accepted for publication in MNRA

    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

    Inhomogeneous Reionization Regulated by Radiative and Stellar Feedbacks

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    We study the inhomogeneous reionization in a critical density CDM universe due to stellar sources, including Population III objects. The spatial distribution of the sources is obtained from high resolution numerical N-body simulations. We calculate the source properties taking into account a self-consistent treatment of both radiative (ie ionizing and H2 -photodissociating photons) and stellar (ie SN explosions) feedbacks regulated by massive stars. This allows us to describe the topology of the ionized and dissociated regions at various cosmic epochs and derive the evolution of H, He, and H2 filling factors, soft UV background, cosmic star formation rate and the final fate of ionizing objects. The main results are: (i) galaxies reionize the IGM by z~10 (with some uncertainty related to the gas clumping factor), whereas H2 is completely dissociated already by z~25; (ii) reionization is mostly due to the relatively massive objects which collapse via H line cooling, while objects whose formation relies on H2 cooling alone are insufficient to this aim; (iii) the diffuse soft UV background is the major source of radiative feedback effects for z<15; at higher z direct flux from neighboring objects dominates; (iv) the match of the calculated cosmic star formation history with the one observed at lower redshifts suggests that the conversion efficiency of baryons into stars is ~1%; (v) we find that a very large population of dark objects which failed to form stars is present by z~8. We discuss and compare our results with similar previous studies.Comment: 34 pages, emulateapj.sty, LaTeX, 13 figures. MNRAS, submitte

    The European way out of recession

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    This paper proposes a two-regime Bounce-Back Function augmented Self-Exciting Threshold AutoRegression (SETAR) which allows for various shapes of recoveries from the recession regime. It relies on the bounce-back effects first analyzed in a Markov-Switching setup by Kim, Morley and Piger [2005] and recently extended by Bec, Bouabdallah and Ferrara [2011a]. This approach is then applied to post-1973 quarterly growth rates of French, German, Italian, Spanish and Euro area real GDPs. Both the linear autoregression and the standard SETAR without bounce-back effect null hypotheses are strongly rejected against the Bounce-Back augmented SETAR alternative in all cases but Italy. The relevance of our proposed model is further assessed by the comparison of its short-term forecasting performances with the ones obtained from a linear autoregression and a standard SETAR. It turns out that the bounce-back models one-step ahead forecasts generally outperform the other ones, and particularly so during the last recovery period in 2009Q3-2010Q4.Threshold autoregression, bounce-back effects, asymmetric business cycles.

    Two-Centered Magical Charge Orbits

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    We determine the two-centered generic charge orbits of magical N = 2 and maximal N = 8 supergravity theories in four dimensions. These orbits are classified by seven U-duality invariant polynomials, which group together into four invariants under the horizontal symmetry group SL(2,R). These latter are expected to disentangle different physical properties of the two-centered black-hole system. The invariant with the lowest degree in charges is the symplectic product (Q1,Q2), known to control the mutual non-locality of the two centers.Comment: 1+17 pages, 1 Table; v2: Eq. (3.23) corrected; v3: various refinements in text and formulae, caption of Table 1 expanded, Footnote and Refs. added. To appear on JHE

    On Black Attractors in 8D and Heterotic/Type IIA Duality

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    Motivated by the study of black attractors in 8D supergravity with 16 supersymmetries, we use the field theory approach and 8D supersymmetry with non trivial central charges to shed light on the exact duality between heterotic string on T^2 and type IIA on real connected and compact surfaces {\Sigma}2. We investigate the two constraints that should be obeyed by {\Sigma}2 and give their solutions in terms of intersecting 2-cycles as well their classification using Dynkin diagrams of affine Kac-Moody algebras. It is shown as well that the moduli space of these dual theories is given by SO(1,1)x((SO(2,r+2))/(SO(2)xSO(r+2))) where r stands for the rank of the gauge symmetry G_{r} of the 10D heterotic string on T^2. The remarkable cases r=-2,-1,0 as well as other features are also investigated.Comment: LaTex, 18 pages, 2 figures, To appear in JHE

    Laparoendoscopic extraperitoneal surgical techniques for ventral hernias and diastasis recti repair: a systematic review

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    Purposethis systematic review aims to classify and summarize the characteristics and outcomes of the different laparoendoscopic extraperitoneal approaches for the repair of ventral hernias and diastasis recti described in the last 10 years.Methodsa literature search was performed by two reviewers in December 2023 including articles from January 2013, 01 to December 2023, 15. The techniques were selected according to the surgical access site (anterior or posterior to the rectus sheath), the access type (laparoendoscopic, single incision laparoscopic, mini or less open), the main space used to repair the defect (subcutaneous or retromuscular) and the mesh place (onlay, sublay-retromuscular or sublay-preperitoneal) and classified as anterior or posterior approaches.Resultsthe literature search retrieved 1755 results and 27 articles were included in the study. The studies included 1874 patients, the mean age ranged from 37.8 to 60.2 years. The access site was anterior in 16 cases and posterior in 11 cases. The mesh was positioned onlay in 13 cases and sublay in 13 cases, with only one study using no mesh. Complications were: seroma, ranging from 0.8 to 81%, followed by skin complications (leak, ischemia, necrosis) from 0.8 to 6.4%, surgical site infections and bleeding. Recurrences ranged from 0% to 12,5%, with a mean follow-up from 1 to 24 months.Conclusionthis systematic review confirms the presence of several new minimally invasive extraperitoneal techniques for the repair of abdominal wall defects, with different advantages and disadvantages. Further studies, with more extensive follow-up data and wider patient groups, are necessary to define specific indications for each technique
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