3,271 research outputs found
General analysis of self-dual solutions for the Einstein-Maxwell-Chern-Simons theory in (1+2) dimensions
The solutions of the Einstein-Maxwell-Chern-Simons theory are studied in
(1+2) dimensions with the self-duality condition imposed on the Maxwell field.
We give a closed form of the general solution which is determined by a single
function having the physical meaning of the quasilocal angular momentum of the
solution. This function completely determines the geometry of spacetime, also
providing the direct computation of the conserved total mass and angular
momentum of the configurations.Comment: 3 pages, REVTEX file, no figure
On an asymptotic estimate of the -loop correction in perturbative QCD
A recently proposed method of estimating the asymptotic behaviour of QCD
perturbation theory coefficients is critically reviewed and shown to contain
numerous invalid mathematical operations and unsubstantiated assumptions. We
discuss in detail why this procedure, based solely on renormalization group
(RG) considerations and analyticity constraints, cannot lead to such estimates.
We stress the importance of correct renormalization scheme (RS) dependence of
any meaningful asymptotic estimate and argue that the unambiguous summation of
QCD perturbation expansions for physical quantities requires information from
outside of perturbation theory itself.Comment: PRA-HEP-92/17, Latex, 20 pages of text plus 5 figures contained in 5
separate PS files. Four of them (corresponding to Figs.1,2,3,5) are appended
at the end of this file, the (somewhat larger one) corresponding to Fig.4 can
be obtained from any of the mentioned E-mail addresses upon request. E-mail
connections: J. Chyla - [email protected]) or h1kchy@dhhdesy3 P. Kolar -
[email protected]
Systematic thermal reduction of neutronization in core-collapse supernovae
We investigate to what extent the temperature dependence of the nuclear
symmetry energy can affect the neutronization of the stellar core prior to
neutrino trapping during gravitational collapse. To this end, we implement a
one-zone simulation to follow the collapse until beta equilibrium is reached
and the lepton fraction remains constant. Since the strength of electron
capture on the neutron-rich nuclei associated to the supernova scenario is
still an open issue, we keep it as a free parameter. We find that the
temperature dependence of the symmetry energy consistently yields a small
reduction of deleptonization, which corresponds to a systematic effect on the
shock wave energetics: the gain in dissociation energy of the shock has a small
yet non-negligible value of about 0.4 foe (1 foe = 10^51 erg) and this result
is almost independent from the strength of nuclear electron capture. The
presence of such a systematic effect and its robustness under changes of the
parameters of the one-zone model are significative enough to justify further
investigations with detailed numerical simulations of supernova explosions.Comment: 15 pages, 2 tables, 3 figure
Entropy for Asymptotically AdS_3 Black Holes
We propose that Strominger's method to derive the BTZ black hole entropy is
in fact applicable to other asymptotically AdS_3 black holes and gives the
correct functional form of entropies. We discuss various solutions in the
Einstein-Maxwell theory, dilaton gravity, Einstein-scalar theories, and
Einstein-Maxwell-dilaton theory. In some cases, solutions approach AdS_3
asymptotically, but their entropies do not have the form of Cardy's formula.
However, it turns out that they are actually not "asymptotically "
solutions. On the other hand, for truly asymptotically AdS_3 solutions, their
entropies have the form of Cardy's formula. In this sense, all known solutions
are consistent with our proposal.Comment: 21 pages, LaTeX; v2: added discussion for section 3.
Scale Setting in QCD and the Momentum Flow in Feynman Diagrams
We present a formalism to evaluate QCD diagrams with a single virtual gluon
using a running coupling constant at the vertices. This method, which
corresponds to an all-order resummation of certain terms in a perturbative
series, provides a description of the momentum flow through the gluon
propagator. It can be viewed as a generalization of the scale-setting
prescription of Brodsky, Lepage and Mackenzie to all orders in perturbation
theory. In particular, the approach can be used to investigate why in some
cases the ``typical'' momenta in a loop diagram are different from the
``natural'' scale of the process. It offers an intuitive understanding of the
appearance of infrared renormalons in perturbation theory and their connection
to the rate of convergence of a perturbative series. Moreover, it allows one to
separate short- and long-distance contributions by introducing a hard
factorization scale. Several applications to one- and two-scale problems are
discussed in detail.Comment: eqs.(51) and (83) corrected, minor typographic changes mad
First Direct Measurement of Jets in GeV Heavy Ion Collisions by STAR
We present the first measurement of reconstructed jets in ultra-relativistic
heavy ion collisions. Utilizing the large coverage of the STAR Time Projection
Chamber and Electromagnetic Calorimeter, we apply several modern jet
reconstruction algorithms and background subtraction techniques and explore
their systematic uncertainties in heavy ion events. The differential spectrum
for inclusive jet production in central Au+Au collisions at GeV is presented. In order to assess the jet reconstruction biases, this
spectrum is compared with the jet cross section measured in GeV
p+p collisions scaled by the number of binary N-N collisions to account for
nuclear geometric effects.Comment: Proceedings of the 3rd International Conference on Hard and Electro-
Magnetic Probes of High-Energy Nuclear Collisions 8-14 June 2008, Illa da
Toxa (Galicia-Spain
SCIENCECRAFT
The technological capabilities are now at hand to design an integrated system that combine science instruments, spacecraft and propulsion elements into a single system. The authors have called this a Sciencecraft since it is intended to provide automatic scientific observations of planetary and astrophysical objects. Integration of function allows lower mass and cost and supports a short development cycle. A specific science mission is described in this paper, a flyby of Neptune, Triton and an object in the Kuiper belt. The SCIENCECRAFT system is described. It has electric propulsion and is capable of measuring the surface constituents and morphology of the objects visited and characterizing their atmospheres both in emission and absorption (against the sun). Miniature fields and particles experiments are incorporated that will provide interplanetary information together with details of the magnetic and electric attributes of each object. The SCIENCECRAFT is Delta launched and has a flight time to the Kuiper belt of 7 years. The design is such that the craft functions in a largely autonomous mode to provide low cost mission operations
Further Studies of Unusual Fission Mass Distributions using 190 MeV Protons
This research was sponsored by the National Science Foundation Grant NSF PHy 87-1440
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