Monte Carlo calculations for the hard Pomeron

Starting from the same input as the standard BFKL Pomeron, we directly calculate the ``hard'' Pomeron as a gluonic ladder by using Monte Carlo methods. We reproduce the characteristic features of the the BFKL Pomeron and are now also able to evaluate new observables. The applicability of the BFKL approach under realistic kinematical conditions can be tested and the influence of the running coupling constant examined.Comment: 9 pages and 4 figures included. To appear in Phys.Lett.

Lattice Gauge Theory and the Origin of Mass

Most of the mass of everyday objects resides in atomic nuclei; the total of the electrons' mass adds up to less than one part in a thousand. The nuclei are composed of nucleons---protons and neutrons---whose nuclear binding energy, though tremendous on a human scale, is small compared to their rest energy. The nucleons are, in turn, composites of massless gluons and nearly massless quarks. It is the energy of these confined objects, via $M=E/c^2$, that is responsible for everyday mass. This article discusses the physics of this mechanism and the role of lattice gauge theory in establishing its connection to quantum chromodynamics.Comment: prepared for "100 Years of Subatomic Physics," edited by Ernest Henley and Stephen Ellis. Submitted version with typos corrected and refs added. 26 pp., 6 figure

Status and Future Perspectives for Lattice Gauge Theory Calculations to the Exascale and Beyond

In this and a set of companion whitepapers, the USQCD Collaboration lays out a program of science and computing for lattice gauge theory. These whitepapers describe how calculation using lattice QCD (and other gauge theories) can aid the interpretation of ongoing and upcoming experiments in particle and nuclear physics, as well as inspire new ones.Comment: 44 pages. 1 of USQCD whitepapers

Solar X-ray Flare Hazards on the Surface of Mars

Putative organisms on the Martian surface would be exposed to potentially high doses of ionizing radiation during strong solar X-ray flares. We extrapolate the observed flare frequency-energy release scaling relation to releases much larger than seen so far for the sun, an assumption supported by observations of flares on other solar- and subsolar-mass main sequence stars. We calculate the surficial reprocessed X-ray spectra using a Monte Carlo code we have developed. Biological doses from indirect genome damage are calculated for each parameterized flare spectrum by integration over the X-ray opacity of water. We estimate the mean waiting time for solar flares producing a given biological dose of ionizing radiation on Mars and compare with lethal dose data for a wide range of terrestrial organisms. These timescales range from decades for significant human health risk to 0.5 Myr for D. radiodurans lethality. Such doses require total flare energies of 10^33--10^38 erg, the lower range of which has been observed for other stars. Flares are intermittent bursts, so acute lethality will only occur on the sunward hemisphere during a sufficiently energetic flare, unlike low-dose-rate, extended damage by cosmic rays. We estimate the soil and CO_2 ice columns required to provide 1/e shielding as 4--9 g cm^-2, depending on flare mean energy and atmospheric column density. Topographic altitude variations give a factor of two variation in dose for a given flare. Life in ice layers that may exist ~ 100 g cm^-2 below the surface would be well protected.Comment: To be published in Planetary and Space Science; 33 pages, 3 figure

Insights into the content and spatial distribution of dust from the integrated spectral properties of galaxies

[Abridged] We present a new approach to investigate the content and spatial distribution of dust in structurally unresolved star-forming galaxies from the observed dependence of integrated spectral properties on galaxy inclination. We develop an innovative combination of generic models of radiative transfer (RT) in dusty media with a prescription for the spectral evolution of galaxies, via the association of different geometric components of galaxies with stars in different age ranges. We show that a wide range of RT models all predict a quasi-universal relation between slope of the attenuation curve at any wavelength and V-band attenuation optical depth in the diffuse interstellar medium (ISM), at all galaxy inclinations. This relation predicts steeper (shallower) dust attenuation curves than both the Calzetti and MW curves at small (large) attenuation optical depths, which implies that geometry and orientation effects have a stronger influence on the shape of the attenuation curve than changes in the optical properties of dust grains. We use our combined RT and spectral evolution model to interpret the observed dependence of the H\alpha/H\beta\ ratio and ugrizYJH attenuation curve on inclination in a sample of ~23 000 nearby star-forming galaxies. From a Bayesian MCMC fit, we measure the central face-on B-band optical depth of this sample to be tau_B\perp~1.8\pm0.2. We also quantify the enhanced optical depth towards newly formed stars in their birth clouds, finding this to be significantly larger in galaxies with bulges than in disc-dominated galaxies, while tau_B\perp is roughly similar in both cases. Finally, we show that neglecting the effect of geometry and orientation on attenuation can severely bias the interpretation of galaxy spectral energy distributions, as the impact on broadband colours can reach up to 0.3-0.4 mag at optical wavelengths and 0.1 mag at near-infrared ones.Comment: 32 pages, 3 tables, 41 figures, MNRAS in-pres

Sensitivity Study on Canadian Air Quality Measurements from Geostationary Orbit

Tropospheric Emissions: Monitoring of Pollution (TEMPO) is a satellite-based remote sensing air quality instrument destined for geostationary orbit over North America beginning in 2022. TEMPO will take hourly measurements with unprecedented resolution which will greatly benefit air quality forecasting, monitoring of emission sources, and health impact studies related to air quality. The field of regard of TEMPO contains a significant portion of Canada, including regions of particular interest such as major population centers and the Alberta oil sands. However, the standard retrieval algorithms that will be used to process TEMPO data do not explicitly account for some of the challenges that exist for measurements over Canada, such as pervasive snow cover, shallow lines of sight, and limited daylight hours. With the ultimate goal of creating new or optimized algorithms that address these challenges and allow Canada to take full advantage of TEMPO, standard retrieval algorithms for nitrogen dioxide and ozone have been replicated and studied. These algorithms use differential optical absorption spectroscopy (DOAS), the technique that will be used to create the standard TEMPO products, and they will serve as a baseline for comparison with future algorithms. The SASKTRAN radiative transfer framework, developed at the University of Saskatchewan, has been utilized to calculate air mass factors, key quantities in the DOAS-style retrieval, using three complementary methods which are all in agreement with each other. End-to-end retrievals modelled after cutting-edge algorithms used by modern instruments have been implemented, and they have been used to conduct a preliminary sensitivity study that quantifies the major sources of uncertainty in DOAS retrievals using synthetic TEMPO measurements

The QCD/SM Working Group: Summary Report

This Report documents the results obtained by the Working Group on Quantum ChromoDynamics and the Standard Model for the Workshop ``Physics at TeV Colliders'', Les Houches, France, 21 May - 1 June 2001. The account of uncertainties in Parton Distribution Functions is reviewed. Progresses in the description of multiparton final states at Next-to-Leading Order and the extension of calculations for precision QCD observables beyond this order are summarized. Various issues concerning the relevance of resummation for observables at TeV colliders is examined. Improvements to algorithms of jet reconstruction are discussed and predictions for diphoton and photon pi-zero production at the LHC are made for kinematic variables of interest regarding searches for a Higgs boson decaying into two photons. Finally, several improvements implemented in Monte-Carlo event generators are documented