Renormalization and resummation in the O(N) model

In the O(N) model for the large N expansion one needs resummation which makes the renormalization of the model difficult. In the paper it is discussed, how can one perform a consistent perturbation theory at zero as well as at finite temperature with the help of momentum dependent renormalization schemes.Comment: 4 pages, presented at International Conference on Strong and Electroweak matter (SEWM 2008), Amsterdam, The Netherlands, 26-29 Aug 200

Three loop HTL perturbation theory at finite temperature and chemical potential

In this proceedings contribution we present a recent three-loop hard-thermal-loop perturbation theory (HTLpt) calculation of the thermodynamic potential for a finite temperature and chemical potential system of quarks and gluons. We compare the resulting pressure, trace anomaly, and diagonal/off-diagonal quark susceptibilities with lattice data. We show that there is good agreement between the three-loop HTLpt analytic result and available lattice data.Comment: 4 pages, 4 figure

Buckling and d-Wave Pairing in HiTc-Superconductors

We have investigated whether the electron-phonon interaction can support a d-wave gap-anisotropy. On the basis of models derived from LDA calculations, as well as LDA linear-response calculations we argue that this is the case, for materials with buckled or dimpled CuO2 planes, for the so-called buckling modes, which involve out-of-plane movements of the plane oxygens.Comment: 5pages, Latex2e, 6 Postscript figure

Charge asymmetry in W + jets production at the LHC

The charge asymmetry in W + jets production at the LHC can serve to calibrate the presence of New Physics contributions. We study the ratio {\sigma}(W^+ + n jets)/{\sigma}(W^- + n jets) in the Standard Model for n <= 4, paying particular attention to the uncertainty in the prediction from higher-order perturbative corrections and uncertainties in parton distribution functions. We show that these uncertainties are generally of order a few percent, making the experimental measurement of the charge asymmetry ratio a particularly useful diagnostic tool for New Physics contributions.Comment: 13 pages, 7 figures. Reference added. Slightly modified tex

Hard-loop dynamics of non-abelian plasma instabilities

I discuss recent advances in the understanding of non-equilibrium gauge field dynamics in plasmas which have particle distributions which are locally anisotropic in momentum space. In contrast to locally isotropic plasmas such anisotropic plasmas have a spectrum of soft unstable modes which are characterized by exponential growth of transverse (chromo)-magnetic fields at short times. The long-time behavior of such instabilities depends on whether or not the gauge group is abelian or non-abelian. Here I will report on recent numerical simulations which attempt to determine the long-time behavior of an anisotropic non-abelian plasma within hard-loop effective theory.Comment: 4 pages, 1 figure; Contribution to proceedings of Quark Matter 2005, Budapest, Hungary, Aug 4-9 200

Patterns, Information, and Causation

This paper articulates an account of causation as a collection of information-theoretic relationships between patterns instantiated in the causal nexus. I draw on Dennett’s account of real patterns to characterize potential causal relata as patterns with specific identification criteria and noise tolerance levels, and actual causal relata as those patterns instantiated at some spatiotemporal location in the rich causal nexus as originally developed by Salmon. I develop a representation framework using phase space to precisely characterize causal relata, including their degree of counterfactual robustness, causal profiles, causal connectivity, and privileged grain size. By doing so, I show how the philosophical notion of causation can be rendered in a format that is amenable for direct application of mathematical techniques from information theory such that the resulting informational measures are causal informational measures. This account provides a metaphysics of causation that supports interventionist semantics and causal modeling and discovery techniques

Demarcating misconduct from misinterpretations and mistakes

Within recent years, scientific misconduct has become an increasingly important topic, not only in the scientific community, but in the general public as well. Spectacular cases have been extensively covered in the news media, such as the cases of the Korean stem cell researcher Hwang, the German nanoscientist Schön, or the Norwegian cancer researcher Sudbø. In Science's latest annual "breakthrough of the year" report from December 2006, the descriptions of the year's hottest breakthroughs were accompanied by a similar description of "the breakdown of the year: scientific fraud". Official guidelines for dealing with scientific misconduct were introduced in the 1990s. At this time, research agencies, universities and other research institutions around the world developed guidelines for good scientific practice and formed committees to handle cases of scientific misconduct. In this process it was widely debated how to define scientific misconduct. Most definitions centered on falsification, fabrication, and plagiarism (the so-called FFP definition), but suggestions were also made for definitions that were broader and more open-ended, such as the 1995 suggestion from the US Commission of Research Integrity to replace FFP with misappropriation, interference and misrepresentation (the so-called MIM definition). The MIM definition was not adopted in the US, but MIM-like definitions have been adopted in several other countries. In this paper, I shall describe these MIM-related definitions of scientific misconduct and analyze the arguments that have been advanced in their favor. I shall discuss some of the difficulties inherent in the MIM-related definitions, such as the distinction between misrepresentation and mistake, and the demarcation of misrepresentation in areas characterized by uncertainty or by diverging research paradigms. I shall illustrate the problems inherent in the MIM-definition through a particular case: the ruling of the Danish Committee on Scientific Dishonesty (DCSD) about Bjørn Lomborg's best-selling book The Skeptical Environmentalist in which he argued that contrary to what was claimed in the “litany” of the environmentalists, the state of the environment is getting better rather than worse. Lomborg was reported to the DCSD by several environmental scientists, and this controversial case from 2003 ended with a verdict that characterized Lomborg’s conclusions as misrepresentations, but acquitted Lomborg of misconduct due to his ignorance. I shall analyze this verdict and the problems it reveals with respect to the MIM-related definitions of misconduct

Vector-valued modular forms and the Mock Theta Conjectures

The mock theta conjectures are ten identities involving Ramanujan's fifth-order mock theta functions. The conjectures were proven by Hickerson in 1988 using q-series methods. Using methods from the theory of harmonic Maass forms, specifically work of Zwegers and Bringmann-Ono, Folsom reduced the proof of the mock theta conjectures to a finite computation. Both of these approaches involve proving the identities individually, relying on work of Andrews-Garvan. Here we give a unified proof of the mock theta conjectures by realizing them as an equality between two nonholomorphic vector-valued modular forms which transform according to the Weil representation. We then show that the difference of these vectors lies in a zero-dimensional vector space.Comment: 11 page