Threshold Resummation in Momentum Space from Effective Field Theory

Methods from soft-collinear effective theory are used to perform the threshold resummation of Sudakov logarithms for the deep-inelastic structure function F_2(x,Q^2) in the endpoint region x->1 directly in momentum space. An explicit all-order formula is derived, which expresses the short-distance coefficient function C in the convolution F_2=C*phi_q in terms of Wilson coefficients and anomalous dimensions defined in the effective theory. Contributions associated with the physical scales Q^2 and Q^2(1-x) are separated from non-perturbative hadronic physics in a transparent way. A crucial ingredient to the momentum-space resummation is the exact solution to the integro-differential evolution equation of the jet function, which is derived. The methods developed in this Letter can be applied to many other hard QCD processes.Comment: 4 pages, 1 figure. Version to appear in PR

An experimental study on performance portability of OpenCL kernels

Accelerator processors allow energy-efficient computation at high performance, especially for computationintensive applications. There exists a plethora of different accelerator architectures, such as GPUs and the Cell Broadband Engine. Each accelerator has its own programming language, but the recently introduced OpenCL language unifies accelerator programming languages. Hereby, OpenCL achieves functional protability, allowing to reduce the development time of kernels. Functional portability however has limited value without performance portability: the possibility to re-use optimized kernels with good performance. This paper investigates the specificity of code optimizations to accelerator architecture and the severity of lack of performance portability

Leaky Fermi accelerators

A Fermi accelerator is a billiard with oscillating walls. A leaky accelerator interacts with an environment of an ideal gas at equilibrium by exchange of particles through a small hole on its boundary. Such interaction may heat the gas: we estimate the net energy flow through the hole under the assumption that the particles inside the billiard do not collide with each other and remain in the accelerator for sufficiently long time. The heat production is found to depend strongly on the type of the Fermi accelerator. An ergodic accelerator, i.e. one which has a single ergodic component, produces a weaker energy flow than a multi-component accelerator. Specifically, in the ergodic case the energy gain is independent of the hole size, whereas in the multi-component case the energy flow may be significantly increased by shrinking the hole size.Comment: 7 pages, 5 figure

Accelerator systems for the international design study of the neutrino factory

The Neutrino Factory produces high-energy neutrino beams with a well-defined flavour content and energy spectrum from the decay of intense, high-energy, stored muon beams. The muon stor- age rings include long straight sections that are directed toward neutrino detectors that are sited several thousand kilometers away. This paper outlines the status of the accelerator facility de- scribed in the Interim Design Report (IDR) recently completed by the International Design Study for a Neutrino Factory (IDS-NF). We give a baseline specification for the accelerator, describe the accelerator subsystems that comprise it and briefly indicate some of the accelerator-physics challenges that such a facility presents