5,039 research outputs found
Size of Fireballs Created in High Energy Lead-Lead Collisions as Inferred from Coulomb Distortions of Pion Spectra
We compute the Coulomb effects produced by an expanding, highly charged
fireball on the momentum distribution of pions. We compare our results to data
on Au+Au at 11.6 A GeV from E866 at the BNL AGS and to data on Pb+Pb at 158 A
GeV from NA44 at the CERN SPS. We conclude that the distortion of the spectra
at low transverse momentum and mid-rapidity can be explained in both
experiments by the effect of the large amount of participating charge in the
central rapidity region. By adjusting the fireball expansion velocity to match
the average transverse momentum of protons, we find a best fit when the
fireball radius is about 10 fm, as determined by the moment when the pions
undergo their last scattering. This value is common to both the AGS and CERN
experiments.Comment: Enlarged discussion, new references added, includes new analysis of
pi-/pi+ at AGS energies. 12 pages 5 figures, uses LaTex and epsfi
Cooper pairing and finite-size effects in a NJL-type four-fermion model
Starting from a NJL-type model with N fermion species fermion and difermion
condensates and their associated phase structures are considered at nonzero
chemical potential and zero temperature in spaces with nontrivial
topology of the form and . Special
attention is devoted to the generation of the superconducting phase. In
particular, for the cases of antiperiodic and periodic boundary conditions we
have found that the critical curve of the phase transitions between the chiral
symmetry breaking and superconducting phases as well as the corresponding
condensates and particle densities strongly oscillate vs ,
where is the length of the circumference . Moreover, it is shown that
at some finite values of the superconducting phase transition is shifted to
smaller values both of and particle density in comparison with the case
of .Comment: 13 pages, 13 figures; minor changes; new references added; version
accepted to PR
Advances in increment coring system for large tropical trees with high wood densities
Incremental coring of trees is the key method used in non-destructive dendrochronological sampling. Despite the advances in developing such methods, the sampling of large, high-density trees still poses a challenge in remote tropical forests. Manually operated incremental drills, while easy to transport across difficult terrain, limit sample size and can often get damaged in the sampling process, especially when trees have wood densities above 0.8 g/cmÂł. Here, we discuss the existing available alternatives and present an up-to-date incremental coring system composed of a borer coupled to a hand-held drilling machine and a support attached to the tree which can collect incremental cores of 1.5 mm in diameter and over 1.0 m in length. The support ensures stability for the drill throughout the sampling process. This system is relatively lightweight and portable, offering field flexibility and suitability for sampling in remote locations. It provides a core sample of an appropriate diameter and amount for carrying out ring-width measurements, stable isotope and radiocarbon analyses on some of the large, older trees which are now being found in the tropics. We expect that this methodology will broaden the possibilities in the now-blossoming sub-field of tropical dendrochronology.1. Introduction 2. Description 2.1. Drilling machine 2.2. Drill 2.3. Support 3. Operating instructions and system testing 4. Discussion 5. Conclusion
Large magnetic dipole moments for neutrinos with arbitrary masses
We show that there is a general sort of models in which it is possible to
have large magnetic dipole moments for neutrinos while keeping their masses
arbitrarily small. Some examples of these models are considered.Comment: REVTEX, 8 pages, 2 .eps figure
Mechanistic insights into bacterial metabolic reprogramming from omics-integrated genome-scale models.
Understanding the adaptive responses of individual bacterial strains is crucial for microbiome engineering approaches that introduce new functionalities into complex microbiomes, such as xenobiotic compound metabolism for soil bioremediation. Adaptation requires metabolic reprogramming of the cell, which can be captured by multi-omics, but this data remains formidably challenging to interpret and predict. Here we present a new approach that combines genome-scale metabolic modeling with transcriptomics and exometabolomics, both of which are common tools for studying dynamic population behavior. As a realistic demonstration, we developed a genome-scale model of Pseudomonas veronii 1YdBTEX2, a candidate bioaugmentation agent for accelerated metabolism of mono-aromatic compounds in soil microbiomes, while simultaneously collecting experimental data of P. veronii metabolism during growth phase transitions. Predictions of the P. veronii growth rates and specific metabolic processes from the integrated model closely matched experimental observations. We conclude that integrative and network-based analysis can help build predictive models that accurately capture bacterial adaptation responses. Further development and testing of such models may considerably improve the successful establishment of bacterial inoculants in more complex systems
Low-energy theorems of QCD and bulk viscosity at finite temperature and baryon density in a magnetic field
The nonperturbative QCD vacuum at finite temperature and a finite baryon
density in an external magnetic field is studied. Equations relating
nonperturbative condensates to the thermodynamic pressure for , and are obtained, and low-energy theorems are derived. A bulk
viscosity is expressed in terms of basic thermodynamical
quantities describing the quark-gluon matter at , , and
. Various limiting cases are also considered.Comment: 12 pages; v2: title changed, new section about bulk viscosity and new
references added; v3: new discussion adde
Additional Suppression from High Density Effects
At high energies the saturation effects associated to the high parton density
should modify the behavior of the observables in proton-nucleus and
nucleus-nucleus scattering. In this paper we investigate the saturation effects
in the nuclear production and estimate the modifications in the energy
dependence of the cross section as well as in the length of the nuclear medium.
In particular, we calculate the ratio of to Drell-Yan cross sections
and show that it is strongly modified if the high density effects are included.
Moreover, our results are compared with the data from the NA50 Collaboration
and predictions for the RHIC and LHC kinematic regions are presented. We
predict an additional suppression associated to the high density
effects.Comment: 13 pages, 5 figures, version to be published in Eur. Phys. J.
Dilepton low suppression as an evidence of the Color Glass Condensate
The dilepton production is investigated in proton-nucleus collisions in the
forward region using the Color Glass Condensate approach. The transverse
momentum distribution (), more precisely the low region, where the
saturation effects are expected to increase, is analyzed. The ratio between
proton-nucleus and proton-proton differential cross section for RHIC and LHC
energies is evaluated, showing the effects of saturation at small , and
presenting a Cronin type peak at moderate . These features indicate the
dilepton as a most suitable probe to study the properties of the saturated
regime and the Cronin effect.Comment: 10 pages, 8 figures, replaced with the version to appear in Physical
Review
Radiative Neutrino Decay in Media
In this letter we introduce a new method to determine the radiative neutrino
decay rate in the presence of a medium. Our approach is based on the
generalisation of the optical theorem at finite temperature and density.
Differently from previous works on this subject, our method allows to account
for dispersive and dissipative electromagnetic properties of the medium. Some
inconsistencies that are present in the literature are pointed-out and
corrected here. We shortly discuss the relevance of our results for neutrino
evolution in the early universe.Comment: 11 pages, 3 encapsulated figure
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