In the last 30 days

• Open/close The anti-k_t jet clustering algorithm OPEN ACCESS

  Matteo Cacciari et al JHEP04(2008)063 Tag this article

  Article References Full text PDF (336 KB)

  The k _t and Cambridge/Aachen inclusive jet finding algorithms for hadron-hadron collisions can be seen as belonging to a broader class of sequential recombination jet algorithms, parametrised by the power of the energy scale in the distance measure. We examine some properties of a new member of this class, for which the power is negative. This ``anti- k <sub>t</sub> '' algorithm essentially behaves like an idealised cone algorithm, in that jets with only soft fragmentation are conical, active and passive areas are equal, the area anomalous dimensions are zero, the non-global logarithms are those of a rigid boundary and the Milan factor is universal. None of these properties hold for existing sequential recombination algorithms, nor for cone algorithms with split-merge steps, such as SISCone. They are however the identifying characteristics of the collinear unsafe plain ``iterative cone'' algorithm, for which the anti- k _t algorithm provides a natural, fast, infrared and collinear safe replacement.
• Open/close Bounds on scalar masses in two Higgs doublet models

  P.M. Ferreira and D.R.T. Jones JHEP08(2009)069 Tag this article

  Article References Full text PDF (3.78 MB)

  A thorough analysis of stability and perturbativity bounds is performed in several versions of the two-Higgs doublet model, for both CP-conserving and spontaneously broken CP minima. LEP results further aid in establishing very strict constraints on the mass of the lighter Higgs particle.
• Open/close PYTHIA 6.4 physics and manual

  Torbjörn Sjöstrand et al JHEP05(2006)026 Tag this article

  Article References Full text PDF (4.04 MB)

  The Pythia program can be used to generate high-energy-physics `events', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, within and beyond the Standard Model, with emphasis on those where strong interactions play a rôle, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, underlying events and beam remnants, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.

  The code and further information may be found on the Pythia web page: http://www.thep.lu.se/~torbjorn/Pythia.html .

• Open/close String theory and noncommutative geometry

  Nathan Seiberg and Edward Witten JHEP09(1999)032 Tag this article

  Article References Full text PDF (995 KB)

  We extend earlier ideas about the appearance of noncommutative geometry in string theory with a nonzero B-field. We identify a limit in which the entire string dynamics is described by a minimally coupled (supersymmetric) gauge theory on a noncommutative space, and discuss the corrections away from this limit. Our analysis leads us to an equivalence between ordinary gauge fields and noncommutative gauge fields, which is realized by a change of variables that can be described explicitly. This change of variables is checked by comparing the ordinary Dirac-Born-Infeld theory with its noncommutative counterpart. We obtain a new perspective on noncommutative gauge theory on a torus, its T-duality, and Morita equivalence. We also discuss the D0/ D4 system, the relation to M-theory in DLCQ, and a possible noncommutative version of the six-dimensional (2,0) theory.

• Open/close Generalised geometry for M-theory

  Christopher M. Hull JHEP07(2007)079 Tag this article

  Article References Full text PDF (341 KB)

  Generalised geometry studies structures on a d-dimensional manifold with a metric and 2-form gauge field on which there is a natural action of the group SO( d,  d). This is generalised to d-dimensional manifolds with a metric and 3-form gauge field on which there is a natural action of the group E _d . This provides a framework for the discussion of M-theory solutions with flux. A different generalisation is to d-dimensional manifolds with a metric, 2-form gauge field and a set of p-forms for p either odd or even on which there is a natural action of the group E _d+1. This is useful for type IIA or IIB string solutions with flux. Further generalisations give extended tangent bundles and extended spin bundles relevant for non-geometric backgrounds. Special structures that arise for supersymmetric backgrounds are discussed.
• Open/close Eternal black holes in anti-de Sitter

  Juan Maldacena JHEP04(2003)021 Tag this article

  Article References Full text PDF (267 KB)

  We propose a dual non-perturbative description for maximally extended Schwarzschild Anti-de-Sitter spacetimes. The description involves two copies of the conformal field theory associated to the AdS spacetime and an initial entangled state. In this context we also discuss a version of the information loss paradox and its resolution.

• Open/close Transport coefficients in high temperature gauge theories, 2. Beyond leading log

  Peter Arnold et al JHEP05(2003)051 Tag this article

  Article References Full text PDF (507 KB)

  Results are presented of a full leading-order evaluation of the shear viscosity, flavor diffusion constants, and electrical conductivity in high temperature QCD and QED. The presence of Coulomb logarithms associated with gauge interactions imply that the leading-order results for transport coefficients may themselves be expanded in an infinite series in powers of 1/log (1/ g); the utility of this expansion is also examined. A next-to-leading-log approximation is found to approximate the full leading-order result quite well as long as the Debye mass is less than the temperature.

• Open/close Precise prediction for M_W in the MSSM

  Sven Heinemeyer et al JHEP08(2006)052 Tag this article

  Article References Full text PDF (765 KB)

  We present the currently most accurate evaluation of the W boson mass, M _W , in the Minimal Supersymmetric Standard Model (MSSM). The full complex phase dependence at the one-loop level, all available MSSM two-loop corrections as well as the full Standard Model result have been included. We analyse the impact of the different sectors of the MSSM at the one-loop level with a particular emphasis on the effect of the complex phases. We discuss the prediction for M _W based on all known higher-order contributions in representative MSSM scenarios. Furthermore we obtain an estimate of the remaining theoretical uncertainty from unknown higher-order corrections.
• Open/close New Generation of Parton Distributions with Uncertainties from Global QCD Analysis

  Jonathan Pumplin et al JHEP07(2002)012 Tag this article

  Article References Full text PDF (864 KB)

  A new generation of parton distribution functions with increased precision and quantitative estimates of uncertainties is presented. This work significantly extends previous CTEQ and other global analyses on two fronts: (i) a full treatment of available experimental correlated systematic errors for both new and old data sets; (ii) a systematic and pragmatic treatment of uncertainties of the parton distributions and their physical predictions, using a recently developed eigenvector-basis approach to the hessian method. The new gluon distribution is considerably harder than that of previous standard fits. A number of physics issues, particularly relating to the behavior of the gluon distribution, are addressed in more quantitative terms than before. Extensive results on the uncertainties of parton distributions at various scales, and on parton luminosity functions at the Tevatron RunII and the LHC, are presented. The latter provide the means to quickly estimate the uncertainties of a wide range of physical processes at these high-energy hadron colliders, based on current knowledge of the parton distributions. In particular, the uncertainties on the production cross sections of the W, Z at the Tevatron and the LHC are estimated to be ±4% and ±5%, respectively, and that of a light Higgs at the LHC to be ±5%.

• Open/close Trialogue on the number of fundamental constants

  Michael J. Duff et al JHEP03(2002)023 Tag this article

  Article References Full text PDF (404 KB)

  This paper consists of three separate articles on the number of fundamental dimensionful constants in physics. We started our debate in summer 1992 on the terrace of the famous CERN cafeteria. In the summer of 2001 we returned to the subject to find that our views still diverged and decided to explain our current positions. LBO develops the traditional approach with three constants, GV argues in favor of at most two (within superstring theory), while MJD advocates zero.