Top Quark Production Dynamics in QCD

A calculation of the total cross section for top quark production in hadron-hadron collisions is presented based on an all-orders perturbative resummation of initial-state gluon radiative contributions to the basic quantum chromodynamics subprocesses. Principal-value resummation is used to evaluate all relevant large threshold contributions. In this method there are no arbitrary infrared cutoffs, and the perturbative regime of applicability is well defined, two attributes that significantly reduce the estimated uncertainty of the results. For $p\bar{p}$ collisions at center-of-mass energy $\sqrt{s}=1.8$ TeV and a top mass of 175 GeV, we obtain $\sigma(t\bar{t})=5.52^{+0.07}_{-0.45} pb$, in agreement with experiment. Predicted cross sections are provided as a function of top mass in $p\bar{p}$ collisions at $\sqrt{s}=2.0$ TeV and in $p p$ collisions at CERN LHC energies.Comment: 12 pages. Latex file plus 8 ps files of figures submitted altogther in uuencoded form; Invited talk presented by E. L. Berger at the International Symposium on Heavy Flavor and Electroweak Theory, Beijing, August 16 - 19, 199

The Perturbative Resummed Series for Top Production

Our calculation of the total cross section for inclusive production of $t\bar{t}$ pairs in hadron collisions is summarized. The principal ingredient of this calculation is resummation of the universal leading-logarithm effects of gluon radiation to all orders in the quantum chromodynamics coupling strength, restricted to the region of phase space that is manifestly perturbative. We present predictions of the physical cross section as a function of top quark mass in proton-antiproton reactions at center-of-mass energies of 1.8 and 2.0 TeV.Comment: 9 pages. Latex file plus 6 ps files of figures submitted togther in uuencoded form; invited talk presented by Harry Contopanagos at the XXXI Rencontres de Moriond on QCD and High Energy Hadronic Interactions, Les Arcs, France, March, 1996. New version to correct problem with unsuccessful posting of figures on May

Threshold Resummation and the Total Cross Section for Top Quark Production

We discuss the motivation for resummation of the effects of initial-state soft-gluon radiation, to all orders in the strong coupling strength, for processes in which the near-threshold region in the partonic subenergy is important. We summarize our calculation of the total cross section for top quark production at hadron colliders. Comments are included on the differences between our treatment of subleading logarithmic terms and other methods.Comment: 7 pages, 1 figure, uses aipproc.sty; Paper presented by E. L. Berger, to be published in the Proceedings of DIS'97, Fifth International Workshop on Deep Inelastic Scattering and QCD, Chicago, IL, April 14 - 18, 199

Calculation of the Cross Section for Top Quark Production

We summarize calculations of the cross section for top quark production at hadron colliders within the context of perturbative quantum chromodynamics, including resummation of the effects of initial-state soft gluon radiation to all orders in the strong coupling strength. In our approach we resum the universal leading-logarithm contributions, and we restrict the calculation to the region of phase space that is demonstrably perturbative. We compare our approach with other methods. We present predictions of the physical cross section as a function of the top quark mass in proton-antiproton reactions at center-of-mass energies of 1.8 and 2.0 TeV, and we discuss estimated uncertainties.Comment: 13 pages, LaTeX, including 6 ps files of figures. Invited paper presented by E. L. Berger at the XIth Topical Workshop on Hadron Collider Physics, Abano Terme, Padova, Italy, May, 199

Future scenarios for the charity sector in 2045

Rapid change is affecting the demography, technology and availability of resources (both financial and volunteer) on which charities draw. This paper presents four different scenarios that could describe the charity sector one generation from now as it responds to a different world. We highlight the dangers if any one scenario becomes dominant. While it is inevitable that change will occur, these drawbacks should be minimized and it is important that public funders and policy makers steer intelligently through this changing world. Also, charity leaders must prepare and plan for inevitable change in the sector

Homotransplantation of multiple visceral organs

It was technically possible to perform simultaneous homotransplantation of multiple visceral organs including the liver, spleen, pancreas, omentum and the entire gastrointestinal tract. Arterialization of the cooled graft was accomplished through the donor aorta which was removed with the graft and attached to that of the recipient dog. Gastrointestinal hemorrhage after surgery accounted for a high operative mortality and was thought to be due to denervation of the graft. The five dogs which survived the immediate trauma of surgery lived for five and a half to nine days. After the second day, these animals were physically active and able to resume oral alimentation. In three dogs, there was metabolic evidence of rejection of the liver. In two others, jaundice did not develop. These observations were compared with chemical, hematologic and pathologic data obtained in previous experiments involving homotransplantation of the liver alone. In some cases, there was less evidence of host versus graft rejection after the multiple organ transplants. Other data in the present study suggested the possibility that a significant graft versus host reaction may have been an important contributory cause of death. © 1962

Localizing compact binary inspirals on the sky using ground-based gravitational wave interferometers

The inspirals and mergers of compact binaries are among the most promising events for ground-based gravitational-wave (GW) observatories. The detection of electromagnetic (EM) signals from these sources would provide complementary information to the GW signal. It is therefore important to determine the ability of gravitational-wave detectors to localize compact binaries on the sky, so that they can be matched to their EM counterparts. We use Markov Chain Monte Carlo techniques to study sky localization using networks of ground-based interferometers. Using a coherent-network analysis, we find that the Laser Interferometer Gravitational Wave Observatory (LIGO)-Virgo network can localize 50% of their ~8 sigma detected neutron star binaries to better than 50 sq.deg. with 95% confidence region. The addition of the Large Scale Cryogenic Gravitational Wave Telescope (LCGT) and LIGO-Australia improves this to 12 sq.deg.. Using a more conservative coincident detection threshold, we find that 50% of detected neutron star binaries are localized to 13 sq.deg. using the LIGO-Virgo network, and to 3 sq.deg. using the LIGO-Virgo-LCGT-LIGO-Australia network. Our findings suggest that the coordination of GW observatories and EM facilities offers great promise.Comment: 6 pages, 4 figures, 1 table, matches published version in ApJ (incorporates referee's comments

Sentiment bubbles

We examine cumulative changes in investor sentiment and find that these changes relate to extended periods of increasing overvaluation, followed by price corrections. The relation between sentiment and returns is path dependent — short-term increases in sentiment precede strong positive returns, while prolonged periods of increasing sentiment precede negative returns. Positive short-run returns are consistent with bubble dynamics and mitigate the backwards induction conundrum described by Abreu and Brunnermeier (2003). Our results hold for the market portfolio, and are especially strong for opaque portfolios with high levels of uncertainty, as well as portfolios with greater market frictions that limit arbitrage.Keywords: Bubbles, Investor sentiment, Price-correctio

Constraints on the Heating of High Temperature Active Region Loops: Observations from Hinode and SDO

We present observations of high temperature emission in the core of a solar active region using instruments on Hinode and SDO. These multi-instrument observations allow us to determine the distribution of plasma temperatures and follow the evolution of emission at different temperatures. We find that at the apex of the high temperature loops the emission measure distribution is strongly peaked near 4 MK and falls off sharply at both higher and lower temperatures. Perhaps most significantly, the emission measure at 0.5 MK is reduced by more than two orders of magnitude from the peak at 4 MK. We also find that the temporal evolution in broad-band soft X-ray images is relatively constant over about 6 hours of observing. Observations in the cooler SDO/AIA bandpasses generally do not show cooling loops in the core of the active region, consistent with the steady emission observed at high temperatures. These observations suggest that the high temperature loops observed in the core of an active region are close to equilibrium. We find that it is possible to reproduce the relative intensities of high temperature emission lines with a simple, high-frequency heating scenario where heating events occur on time scales much less than a cooling time. In contrast, low-frequency heating scenarios, which are commonly invoked to describe nanoflare models of coronal heating, do not reproduce the relative intensities of high temperature emission lines and predict low-temperature emission that is approximately an order of magnitude too large. We also present an initial look at images from the SDO/AIA 94 A channel, which is sensitive to Fe XVIII.Comment: Movies are available at http://tcrb.nrl.navy.mil/~hwarren/temp/papers/active_region_core/ Paper has been refereed and revise

Toward an optimal search strategy of optical and gravitational wave emissions from binary neutron star coalescence

Observations of an optical source coincident with gravitational wave emission detected from a binary neutron star coalescence will improve the confidence of detection, provide host galaxy localisation, and test models for the progenitors of short gamma ray bursts. We employ optical observations of three short gamma ray bursts, 050724, 050709, 051221, to estimate the detection rate of a coordinated optical and gravitational wave search of neutron star mergers. Model R-band optical afterglow light curves of these bursts that include a jet-break are extrapolated for these sources at the sensitivity horizon of an Advanced LIGO/Virgo network. Using optical sensitivity limits of three telescopes, namely TAROT (m=18), Zadko (m=21) and an (8-10) meter class telescope (m=26), we approximate detection rates and cadence times for imaging. We find a median coincident detection rate of 4 yr^{-1} for the three bursts. GRB 050724 like bursts, with wide opening jet angles, offer the most optimistic rate of 13 coincident detections yr^{-1}, and would be detectable by Zadko up to five days after the trigger. Late time imaging to m=26 could detect off-axis afterglows for GRB 051221 like bursts several months after the trigger. For a broad distribution of beaming angles, the optimal strategy for identifying the optical emissions triggered by gravitational wave detectors is rapid response searches with robotic telescopes followed by deeper imaging at later times if an afterglow is not detected within several days of the trigger.Comment: 6 pages, 1 figure, Accepted for publication in MNRAS Letters (2011 April 22