Refine
Year of publication
- 1999 (41)
- 1998 (30)
- 2002 (29)
- 2000 (25)
- 2003 (23)
- 1997 (22)
- 2001 (19)
- 2006 (18)
- 2004 (17)
- 1995 (15)
- 2005 (15)
- 1996 (13)
- 2018 (9)
- 1994 (8)
- 1992 (7)
- 1993 (7)
- 2019 (7)
- 1983 (6)
- 1987 (6)
- 1988 (6)
- 1991 (6)
- 2020 (6)
- 2023 (6)
- 1990 (5)
- 2007 (5)
- 2021 (5)
- 2022 (5)
- 1981 (4)
- 1984 (4)
- 1986 (4)
- 1989 (4)
- 2009 (4)
- 2017 (3)
- 1985 (2)
- 2016 (2)
- 1976 (1)
- 1979 (1)
- 1980 (1)
- 2008 (1)
- 2010 (1)
- 2013 (1)
- 2014 (1)
- 2024 (1)
Document Type
- Preprint (227)
- Article (158)
- Conference Proceeding (7)
- Report (2)
- Doctoral Thesis (1)
- Working Paper (1)
Has Fulltext
- yes (396)
Is part of the Bibliography
- no (396)
Keywords
- Kollisionen schwerer Ionen (47)
- heavy ion collisions (41)
- Quark-Gluon-Plasma (17)
- equation of state (14)
- QGP (13)
- quark-gluon plasma (12)
- Hadron (11)
- heavy-ion collisions (11)
- Quark Gluon Plasma (10)
- Zustandsgleichung (10)
The lightest supersymmetric particle, most likely the lightest neutralino, is one of the most prominent particle candidates for cold dark matter (CDM). We show that the primordial spectrum of density fluctuations in neutralino CDM has a sharp cut-off, induced by two different damping mechanisms. During the kinetic decoupling of neutralinos, non-equilibrium processes constitute viscosity effects, which damp or even absorb density perturbations in CDM. After the last scattering of neutralinos, free streaming induces neutralino flows from overdense to underdense regions of space. Both damping mechanisms together define a minimal mass scale for perturbations in neutralino CDM, before the inhomogeneities enter the non- linear epoch of structure formation. We find that the very first gravitationally bound neutralino clouds ought to have masses above 10-6M , which is six orders of magnitude above the mass of possible axion miniclusters.
A significant drop of the vector meson masses in nuclear matter is observed in a chiral SU(3) model due to the e ects of the baryon Dirac sea. This is taken into account through the summation of baryonic tadpole diagrams in the relativistic Hartree approximation. The appreciable decrease of the in-medium vector meson masses is due to the vacuum polarisation e ects from the nucleon sector and is not observed in the mean field approximation.
The SENECA model, a new hybrid approach to air shower simulations, is presented. It combines the use of efficient cascade equations in the energy range where a shower can be treated as one-dimensional, with a traditional Monte Carlo method which traces individual particles. This allows one to reproduce natural fluctuations of individual showers as well as the lateral spread of low energy particles. The model is quite efficient in computation time. As an application of the new approach, the influence of the low energy hadronic models on shower properties for AUGER energies is studied. We conclude that these models have a significant impact on the tails of lateral distribution functions, and deserve therefore more attention.
The in-medium properties of the vector mesons are known to be modified significantly in hot and dense hadronic matter due to vacuum polarisation e ects from the baryon sector in the Walecka model. The vector meson mass drops significantly in the medium due to the e ects of the Dirac sea. In the variational approach adopted in the present paper, these e ects are taken into account through a realignment of the ground state with baryon condensates. Such a realignment of the ground state becomes equivalent to summing of the baryonic tadpole diagrams in the relativistic Hartree approximation (RHA). The approximation scheme adopted here goes beyond RHA to include quantum e ects from the scalar meson and is nonperturbative and self consistent. It includes multiloop e ects, thus corresponding to a di erent approximation as compared to the one loop approximation of including scalar field quantum corrections. In the present work, we study the properties of the vector mesons in the hot and dense matter as modified due to such quantum correction e ects from the baryon as well as scalar meson sectors. These medium modifications of the properties of the vector mesons are reflected, through the shifting and broadening of the respective peaks, in the low mass dilepton spectra. There is broadening of the peaks due to corrections from scalar meson quantum e ects as compared to the relativistic Hartree approximation. It is seen to be rather prominent for the ! meson in the invariant mass plot. PACS number: 21.65.+f,12.40.Yx
The amount of proton stopping in central Pb+Pb collisions from 20 160 A·GeV as well as hyperon and antihyperon rapidity distributions are calcu- lated within the UrQMD model in comparison to experimental data at 40, 80 and 160 A·GeV taken recently from the NA49 collaboration. Further- more, the amount of baryon stopping at 160 A·GeV for Pb + Pb collisions is studied as a function of centrality in comparison to the NA49 data. We find that the strange baryon yield is reasonably described for central colli- sions, however, the rapidity distributions are somewhat more narrow than the data. Moreover, the experimental antihyperon rapidity distributions at 40, 80 and 160 A·GeV are underestimated by up to factors of 3 - depending on the annihilation cross section employed - which might be addressed to missing multi-meson fusion channels in the UrQMD model. PACS 25.75.+r
We study central collision of Pb + Pb at 20, 40, 80 and 160 A·GeV within the UrQMD transport approach and compare rapidity distributions of ,K+,K and with the recent measurements from the NA49 Collaboration at 40, 80 and 160 A·GeV. It is found that the UrQMD model reasonably describes the data, however, systematically overpredicts the yield by < 20%, whereas the K+ yield is underestimated by < 15%. The K yields are in a good agreement with the experimental data, the yields are also in a reasonable correspondence with the data for all energies. We find that hadronic flavour exchange reactions largely distort the information about the initial strangeness production mechanism at all energies considered. PACS: 25.75.+r
The lightest supersymmetric particle, most likely the neutralino, might account for a large fraction of dark matter in the Universe.We show that the primordial spectrum of density fluctuations in neutralino cold dark matter (CDM) has a sharp cut-off due to two damping mechanisms: collisional damping during the kinetic decoupling of the neutralinos at (10 MeV) and free streaming after last scattering of neutralinos. The cut-off in the primordial spectrum defines a minimal mass for CDM objects in hierarchical structure formation. For typical neutralino and sfermion masses the first gravitionally bound neutralino clouds have masses above 10 -6 M .
Recent progress in the understanding of the high density phase of neutron stars advances the view that a substantial fraction of the matter consists of hyperons. The possible impacts of a highly attractive interaction between hyperons on the properties of compact stars are investigated.We find that a hadronic equation of state with hyperons allows for a first order phase transition to hyperonic matter. The corresponding hyperon stars can have rather small radii of R 8 km.
The production of black holes at Tevatron and LHC in spacetimes with compactified space-like large extra dimensions is studied. Either black holes can already be observed in ¯ pp collisions at s = 1.8 TeV or the fundamental gravity scale has to be above 1.4 TeV. At LHC the creation of a large number of quasi-stable black holes is predicted, with lifetimes beyond several hundred fm/c. A cut-off in the high-PT jet cross section is shown to be a unique signature of black hole production. This signal is compared to the jet plus missing energy signature due to graviton production in the final state as proposed by the ATLAS collaboration.
The measured particle ratios in central heavy-ion collisions at RHIC-BNL are investigated within a chemical and thermal equilibrium chiral SU(3) theta - omega approach. The commonly adopted noninteracting gas calculations yield temperatures close to or above the critical temperature for the chiral phase transition, but without taking into account any interactions. Contrary, the chiral SU(3) model predicts temperature and density dependent e ective hadron masses and e ective chemical potentials in the medium and a transition to a chirally restored phase at high temperatures or chemical potentials. Three di erent parametrizations of the model, which show di erent types of phase transition behaviour, are investigated. We show that if a chiral phase transition occured in those collisions, freezing of the relative hadron abundances in the symmetric phase is excluded by the data. Therefore, either very rapid chemical equilibration must occur in the broken phase, or the measured hadron ratios are the outcome of the dynamical symmetry breaking. Furthermore, the extracted chemical freeze-out parameters di er considerably from those obtained in simple noninteracting gas calculations. In particular, the three models yield up to 35 MeV lower temperatures than the free gas approximation. The in-medium masses turn out di er up to 150 MeV from their vacuum values.