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Reiter T.,Nikhef
Computer Physics Communications | Year: 2010

This article describes haggies, a program for the generation of optimised programs for the efficient numerical evaluation of mathematical expressions. It uses a multivariate Horner-scheme and Common Subexpression Elimination to reduce the overall number of operations. The package can serve as a back-end for virtually any general purpose computer algebra program. Built-in type inference that allows to deal with non-standard data types in strongly typed languages and a very flexible, pattern-based output specification ensure that haggies can produce code for a large variety of programming languages. We currently use haggies as part of an automated package for the calculation of one-loop scattering amplitudes in quantum field theories. The examples in this articles, however, demonstrate that its use is not restricted to the field of high energy physics. Program summary: Program title: haggies. Catalogue identifier: AEGF_v1_0. Program summary: URL: Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland. Licensing provisions: GNU GPL v3. No. of lines in distributed program, including test data, etc.: 56 220. No. of bytes in distributed program, including test data, etc.: 579 010. Distribution format: tar.gz. Programming language: Java, JavaCC. Computer: Any system that runs the Java Virtual Machine. Operating system: Any system that runs the Java Virtual Machine. RAM: Determined by the size of the problem. Classification: 4.14, 5, 6.2, 6.5, 11.1. Nature of problem: Generation of optimised programs for the evaluation of possibly large algebraic expressions. Solution method: Java implementation. Running time: Determined by the size of the problem. © 2010 Elsevier B.V. All rights reserved.

Montanus J.M.C.,Nikhef
Astroparticle Physics | Year: 2014

The Heitler-Matthews model for hadronic air showers will be extended to all the generations of electromagnetic subshowers in the hadronic cascade. The analysis is outlined in detail for showers initiated by primary protons. For showers initiated by iron primaries the part of the analysis is given for as far as it differs from the analysis for a primary proton. Predictions for shower sizes and the depth of maximum shower size are compared with results of Monte Carlo simulations. The depth of maximum as it follows from the extrapolation of the Heitler-Matthews model restricted to the first generation of electromagnetic subshowers is too small with respect to Monte Carlo predictions. It is shown that the inclusion of all the generations of electromagnetic subshowers leads to smaller predictions for the depth of maximum and to smaller predictions for the elongation rate. The discrepancy between discrete model predictions and Monte Carlo predictions for the depth of maximum can therefore not be explained from the number of generations that is taken into consideration. An alternative explanation will be proposed. © 2014 Elsevier B.V. All rights reserved.

Christakoglou P.,Nikhef
Journal of Physics G: Nuclear and Particle Physics | Year: 2011

Separation of charges along the extreme magnetic field created in non-central relativistic heavy-ion collisions is predicted to be a signature of local parity violation in strong interactions. We report on results for charge-dependent two-particle azimuthal correlations with respect to the reaction plane for PbPb collisions at √SNN = 2.76 TeV recorded in 2010 with ALICE at the LHC. The results are compared with measurements at RHIC energies and against currently available model predictions for LHC. Systematic studies of possible background effects including comparison with conventional (parityeven) correlations simulated with Monte Carlo event generators of heavy-ion collisions are also presented. © CERN 2011.

Krzewicki M.,NIKHEF
Journal of Physics G: Nuclear and Particle Physics | Year: 2011

We report on the first measurements of the elliptic and triangular flow for charged pions, kaons and anti-protons in leadlead collisions at √ sNN = 2.76 TeV measured with the ALICE detector at the LHC. We compare the observed mass splitting of differential elliptic flow at LHC energies to RHIC measurements at lower energies and theory predictions. We test the quark coalescence picture with the quark number scaling of elliptic and triangular flow. © 2011 CERN.

Botje M.,Nikhef
Computer Physics Communications | Year: 2011

The qcdnum program numerically solves the evolution equations for parton densities and fragmentation functions in perturbative QCD. Un-polarised parton densities can be evolved up to next-to-next-to-leading order in powers of the strong coupling constant, while polarised densities or fragmentation functions can be evolved up to next-to-leading order. Other types of evolution can be accessed by feeding alternative sets of evolution kernels into the program. A versatile convolution engine provides tools to compute parton luminosities, cross-sections in hadron-hadron scattering, and deep inelastic structure functions in the zero-mass scheme or in generalised mass schemes. Input to these calculations are either the qcdnum evolved densities, or those read in from an external parton density repository. Included in the software distribution are packages to calculate zero-mass structure functions in un-polarised deep inelastic scattering, and heavy flavour contributions to these structure functions in the fixed flavour number scheme. © 2010 Elsevier B.V. All rights reserved.

Schellekens A.N.,Nikhef
Reviews of Modern Physics | Year: 2013

If the results of the first LHC run are not betraying us, many decades of particle physics are culminating in a complete and consistent theory for all nongravitational physics: the standard model. But despite this monumental achievement there is a clear sense of disappointment: many questions remain unanswered. Remarkably, most unanswered questions could just be environmental, and disturbingly to some the existence of life may depend on that environment. Meanwhile there has been increasing evidence that the seemingly ideal candidate for answering these questions, string theory, gives an answer few people initially expected: a large "landscape" of possibilities that can be realized in a multiverse and populated by eternal inflation. At the interface of "bottom-up" and "top-down" physics, a discussion of anthropic arguments becomes unavoidable. Developments in this area are reviewed, focusing especially on the last decade. © 2013 American Physical Society.

Postma M.,Nikhef | Volponi M.,Nikhef
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

No experiment can measure an absolute scale: every dimensionful quantity has to be compared to some fixed unit scale in order to be measured, and thus only dimensionless quantities are really physical. The Einstein and Jordan frames are related by a conformal transformation of the metric, which amounts to rescaling all length scales. Since the absolute scale cannot be measured, both frames describe the same physics and are equivalent. In this article we make this explicit by rewriting the action in terms of dimensionless variables, which are invariant under a conformal transformation. For definitiveness, we concentrate on the action of Higgs inflation, but the results can easily be generalized. In addition, we show that the action for f(R) gravity, which includes Starobinsky inflation, can be written in a frame-independent form. © 2014 American Physical Society.

Montanus J.M.C.,Nikhef
Astroparticle Physics | Year: 2012

Cosmic rays impacting on the atmosphere cause particle-showers. Several descriptions exist for the evolution of the shower size along the atmospheric depth. The well known functions for shower profiles, Greisen, Gaisser-Hillas and 'Gaussian in Age', are intimately connected in that they all are approximate solutions of versions of the Rossi and Greisen diffusion equations. The mathematical connection will be demonstrated by means of two simple models for the longitudinal electromagnetic shower profile. Both models can be regarded either as a generalization of the Heitler model or as a simplification of the diffusion model of Rossi and Greisen. These models are far closer to reality than the Heitler model, while they are not as close to reality as the model of Rossi and Greisen. Therefore, they will be referred to as intermediate models. For each intermediate model the evolution of the shower is governed by either a single differential equation or a single integro-differential equation. The approximate solution of the differential equation is a Gaisser-Hillas function and can be adjusted such that it almost matches the Greisen profile. The approximate solution of the integro-differential equation is a 'Gaussian in Age' function. The corresponding profile is, after suitable adjustment, in excellent agreement with the Greisen profile. The analysis also leads to an alternative functional form for the age parameter. © 2012 Elsevier B.V. All rights reserved.

Nikhef and Cern | Date: 2011-09-09

In an integrated two-phase accumulator controlled loop cooling system, the pumped refrigerant is employed to cool the supply of refrigerant in the accumulator vessel. No external cooling of the accumulator vessel is required, and a standard heater in the accumulator is sufficient to regulate the boiling pressure. This allows to provide a cooling system in which sub-cooling in the pump is guaranteed by the laws of nature, and which is hence more reliable, structurally simpler, better to control and cheaper.

Petraki K.,Nikhef | Volkas R.R.,University of Melbourne
International Journal of Modern Physics A | Year: 2013

Asymmetric dark matter models are based on the hypothesis that the present-day abundance of dark matter has the same origin as the abundance of ordinary or "visible" matter: an asymmetry in the number densities of particles and antiparticles. They are largely motivated by the observed similarity in the mass densities of dark and visible matter, with the former observed to be about five times the latter. This review discusses the construction of asymmetric dark matter models, summarizes cosmological and astrophysical bounds, and touches on direct detection prospects and collider signatures. © 2013 World Scientific Publishing Company.

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