Scattering AMplitudes from Unitarity-based Reduction Algorithm at the Integrand-level

SAMURAI is a tool for the automated numerical evaluation of one-loop corrections to any scattering amplitudes within the dimensional-regularization scheme. It is based on the decomposition of the integrand according to the OPP-approach, extended to accommodate an implementation of the generalized d-dimensional unitarity-cuts technique, and uses a polynomial interpolation exploiting the Discrete Fourier Transform. SAMURAI can process integrands written either as numerator of Feynman diagrams or as product of tree-level amplitudes. We discuss some applications, among which the 6- and 8-photon scattering in QED, and the 6-quark scattering in QCD. SAMURAI has been implemented as a Fortran90 library, publicly available, and it could be a useful module for the systematic evaluation of the virtual corrections oriented towards automating next-to-leading order calculations relevant for the LHC phenomenology.Comment: 35 pages, 7 figure

Idiopathic gastric infarction in childhood

The case of a 6-year-old female with gastric infarction is presented. Despite a careful evaluation, no etiology could be determined in this child or, retrospectively, in several similar children described by other authors in the past. Vascular compromise was present although it is not possible to know whether this was a primary or a secondary event. It is important to recognize that gastric infarction can occur in children without obvious explanation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47178/1/383_2004_Article_BF00182780.pd

Vector boson pair production at the LHC

We present phenomenological results for vector boson pair production at the LHC, obtained using the parton-level next-to-leading order program MCFM. We include the implementation of a new process in the code, pp -> \gamma\gamma, and important updates to existing processes. We incorporate fragmentation contributions in order to allow for the experimental isolation of photons in \gamma\gamma, W\gamma, and Z\gamma production and also account for gluon-gluon initial state contributions for all relevant processes. We present results for a variety of phenomenological scenarios, at the current operating energy of \sqrt{s} = 7 TeV and for the ultimate machine goal, \sqrt{s} = 14 TeV. We investigate the impact of our predictions on several important distributions that enter into searches for new physics at the LHC.Comment: 35 pages, 14 figure

Infrared Spectroscopy of U Equulei's Warm Circumstellar Gas

Medium and high resolution spectroscopy of U Equulei from 1 to 4 microns during 1997-2003 has revealed information about its unusual circumstellar envelope, observed previously at optical and radio wavelengths. Strong absorption bands of H2O and of CO dominate the 1-4um spectrum. The gas has a mean temperature of 600 K and 12C/13C =< 10. The CO 2-0 line profiles and velocities imply no net ejection or infall and indicate either rapid radial gas motions being seen along a narrow continuum beam, or absorption by orbiting gas that is nearly coincident with a highly extended continuum source. The gas could be located in a disk-like structure. The observed high column densities of warm CO and H2 normally would be associated with sufficient dust to completely obscure the star at optical wavelengths. The observations thus indicate either a highly abnormal gas-to-dust ratio, consistent with the earlier optical observation of abundant refractory metal oxides in the circumstellar gas, or peculiar geometry and/or illumination.Comment: 21 pages incl. 8 postscript figures and 1 table; typos correcte

Improving NLO-parton shower matched simulations with higher order matrix elements

In recent times the algorithms for the simulation of hadronic collisions have been subject to two substantial improvements: the inclusion, within parton showering, of exact higher order tree level matrix elements (MEPS) and, separately, next-to-leading order corrections (NLOPS). In this work we examine the key criteria to be met in merging the two approaches in such a way that the accuracy of both is preserved, in the framework of the POWHEG approach to NLOPS. We then ask to what extent these requirements may be fulfilled using existing simulations, without modifications. The result of this study is a pragmatic proposal for merging MEPS and NLOPS events to yield much improved MENLOPS event samples. We apply this method to W boson and top quark pair production. In both cases results for distributions within the remit of the NLO calculations exhibit no discernible changes with respect to the pure NLOPS prediction; conversely, those sensitive to the distribution of multiple hard jets assume, exactly, the form of the corresponding MEPS results.Comment: 38 pages, 17 figures. v2: added citations and brief discussion of related works, MENLOPS prescription localized in a subsection. v3: cited 4 more MEPS works in introduction

MINLO: Multi-scale improved NLO

In the present work we consider the assignment of the factorization and renormalization scales in hadron collider processes with associated jet production, at next-to-leading order (NLO) in perturbation theory. We propose a simple, definite prescription to this end, including Sudakov form factors to consistently account for the distinct kinematic scales occuring in such collisions. The scheme yields results that are accurate at NLO and, for a large class of observables, it resums to all orders the large logarithms that arise from kinematic configurations involving disparate scales. In practical terms the method is most simply understood as an NLO extension of the matrix element reweighting procedure employed in tree level matrix element-parton shower merging algorithms. By way of a proof-of-concept, we apply the method to Higgs and Z boson production in association with up to two jets.Comment: 27 pages, 17 figure

School-related subjective well-being promotes subsequent adaptability, achievement, and positive behavioural conduct.

BACKGROUND: Previous studies have shown that subjective well-being and adaptability are linked to adaptive educational outcomes, including higher achievement and lower anxiety. It is not presently clear, however, how school-related subjective well-being and adaptability are related, or predict behavioural outcomes such as student conduct. AIM: The aim of the present study was to test a bidirectional model of school-related subjective well-being and adaptability, and how they relate to achievement and behavioural conduct. METHOD: Data were collected from 539 Year 12 students over four waves. Achievement and behavioural conduct were measured in the first wave of data collection (T1 ), school-related subjective well-being and adaptability at the second and third waves (T2 and T3 ), and achievement and behavioural conduct again in the fourth wave of data collection (T4 ). RESULTS: A structural equation model showed that T2 school-related subjective well-being predicted higher T3 adaptability, but not vice versa. T3 school-related subjective well-being predicted greater T4 achievement and positive behavioural conduct, and T3 adaptability predicted greater T4 positive behavioural conduct. CONCLUSION: School-related subjective well-being promotes adaptability, achievement, and positive behavioural conduct, and adaptability is also related to positive behavioural conduct. Attempts to foster well-being and adaptability could show educational gains for students

Atomic Dark Matter

We propose that dark matter is dominantly comprised of atomic bound states. We build a simple model and map the parameter space that results in the early universe formation of hydrogen-like dark atoms. We find that atomic dark matter has interesting implications for cosmology as well as direct detection: Protohalo formation can be suppressed below $M_{proto} \sim 10^3 - 10^6 M_{\odot}$ for weak scale dark matter due to Ion-Radiation interactions in the dark sector. Moreover, weak-scale dark atoms can accommodate hyperfine splittings of order 100 \kev, consistent with the inelastic dark matter interpretation of the DAMA data while naturally evading direct detection bounds.Comment: 17 pages, 3 figure