Refine
Year of publication
- 2004 (55) (remove)
Document Type
- Preprint (55) (remove)
Has Fulltext
- yes (55)
Is part of the Bibliography
- no (55) (remove)
Keywords
- Semantik (4)
- Syntax (4)
- Optimalitätstheorie (3)
- Aufsatzsammlung (2)
- Deutsch (2)
- Frage (2)
- Phonologie (2)
- Prosodie (2)
- Albert (1)
- Antiteilchen (1)
Institute
- Physik (31)
- Frankfurt Institute for Advanced Studies (FIAS) (14)
- Extern (13)
- Mathematik (3)
- Rechtswissenschaft (2)
- Zentrum für Weiterbildung (1)
String theory suggests modifications of our spacetime such as extra dimensions and the existence of a mininal length scale. In models with addidional dimensions, the Planck scale can be lowered to values accessible by future colliders. Effective theories which extend beyond the standart-model by including extra dimensions and a minimal length allow computation of observables and can be used to make testable predictions. Expected effects that arise within these models are the production of gravitons and black holes. Furthermore, the Planck-length is a lower bound to the possible resolution of spacetime which might be reached soon.
We discuss modifications of the gyromagnetic moment of electrons and muons due to a minimal length scale combined with a modified fundamental scaleMf . First-order deviations from the theoretical standard model value for g-2 due to these String Theory-motivated e ects are derived. Constraints for the new fundamental scale Mf are given.
We investigate hadron production and transverse hadron spectra in nucleus-nucleus collisions from 2 A·GeV to 21.3 A·TeV within two independent transport approaches (UrQMD and HSD) based on quark, diquark, string and hadronic degrees of freedom. The enhancement of pion production in central Au+Au (Pb+Pb) collisions relative to scaled pp collisions (the ’kink’) is described well by both approaches without involving a phase transition. However, the maximum in the K+ p+ ratio at 20 to 30 A·GeV (the ’horn’) is missed by ~ 40%. Also, at energies above ~5 A·GeV, the measured K± mT-spectra have a larger inverse slope than expected from the models. Thus the pressure generated by hadronic interactions in the transport models at high energies is too low. This finding suggests that the additional pressure - as expected from lattice QCD at finite quark chemical potential and temperature - might be generated by strong interactions in the early pre-hadronic/partonic phase of central heavy-ion collisions. Finally, we discuss the emergence of density perturbations in a first-order phase transition and why they might affect relative hadron multiplicities, collective flow, and hadron mean-free paths at decoupling. A minimum in the collective flow v2 excitation function was discovered experimentally at 40 A·GeV - such a behavior has been predicted long ago as signature for a first order phase transition.
Report from NA49
(2004)
The most recent data of NA49 on hadron production in nuclear collisions at CERN SPS energies are presented. Anomalies in the energy dependence of pion and kaon production in central Pb+Pb collisions are observed. They suggest that the onset of deconfinement is located at about 30 AGeV. Large multiplicity and transverse momentum fluctuations are measured for collisions of intermediate mass systems at 158 AGeV. The need for a new experimental programme at the CERN SPS is underlined.
The purpose of this paper is to describe recent developments in the morphological, syntactic, and semantic annotation of the TüBa-D/Z treebank of German. The TüBa-D/Z annotation scheme is derived from the Verbmobil treebank of spoken German [4, 10], but has been extended along various dimensions to accommodate the characteristics of written texts. TüBa-D/Z uses as its data source the "die tageszeitung" (taz) newspaper corpus. The Verbmobil treebank annotation scheme distinguishes four levels of syntactic constituency: the lexical level, the phrasal level, the level of topological fields, and the clausal level. The primary ordering principle of a clause is the inventory of topological fields, which characterize the word order regularities among different clause types of German, and which are widely accepted among descriptive linguists of German [3, 6]. The TüBa-D/Z annotation relies on a context-free backbone (i.e. proper trees without crossing branches) of phrase structure combined with edge labels that specify the grammatical function of the phrase in question. The syntactic annotation scheme of the TüBa-D/Z is described in more detail in [12, 11]. TüBa-D/Z currently comprises approximately 15 000 sentences, with approximately 7 000 sentences being in the correction phase. The latter will be released along with an updated version of the existing treebank before the end of this year. The treebank is available in an XML format, in the NEGRA export format [1] and in the Penn treebank bracketing format. The XML format contains all types of information as described above, the NEGRA export format contains all sentenceinternal information while the Penn treebank format includes only those layers of information that can be expressed as pure tree structures. Over the course of the last year, more fine grained linguistic annotations have been added along the following dimensions: 1. the basic Stuttgart-Tübingen tagset, STTS, [9] labels have been enriched by relevant features of inflectional morphology, 2. named entity information has been encoded as part of the syntactic annotation, and 3. a set of anaphoric and coreference relations has been added to link referentially dependent noun phrases. In the following sections, we will describe each of these innovations in turn and will demonstrate how the additional annotations can be incorporated into one comprehensive annotation scheme.
Preliminary results on pion-pion Bose-Einstein correlations in central Pb+Pb collisions measured by the NA49 experiment are presented. Rapidity as well as transverse momentum dependence of the HBT-radii are shown for collisions at 20, 30, 40, 80, and 158 AGeV beam energy. Including results from AGS and RHIC experiments only a weak energy dependence of the radii is observed. Based on hydrodynamical models parameters like lifetime and geometrical radius of the source are derived from the dependence of the radii on transverse momentum.
We investigate the effects of strong color fields and of the associated enhanced intrinsic transverse momenta on the phi-meson production in ultrarelativistic heavy ion collisions at RHIC. The observed consequences include a change of the spectral slopes, varying particle ratios, and also modified mean transverse momenta. In particular, the composition of the production processes of phi-mesons, that is, direct production vs. coalescence-like production, depends strongly on the strength of the color fields and intrinsic transverse momenta and thus represents a sensitive probe for their measurement.
We study the phase diagram of dense, locally neutral three-flavor quark matter as a function of the strange quark mass, the quark chemical potential, and the temperature, employing a general nine-parameter ansatz for the gap matrix. At zero temperature and small values of the strange quark mass, the ground state of matter corresponds to the color-flavor-locked (CFL) phase. At some critical value of the strange quark mass, this is replaced by the recently proposed gapless CFL (gCFL) phase. We also find several other phases, for instance, a metallic CFL (mCFL) phase, a so-called uSC phase where all colors of up quarks are paired, as well as the standard two-flavor color-superconducting (2SC) phase and the gapless 2SC (g2SC) phase.
Fluctuations of charged particle number are studied in the canonical ensemble. In the infinite volume limit the fluctuations in the canonical ensemble are different from the fluctuations in the grand canonical one. Thus, the well-known equivalence of both ensembles for the average quantities does not extend for the fluctuations. In view of a possible relevance of the results for the analysis of fluctuations in nuclear collisions at high energies, a role of the limited kinematical acceptance is studied.