178,191 research outputs found
The First Stars: Final Remarks
How did star formation begin in the universe? Some of the questions addressed
at this first meeting on "The First Stars" are summarized here from a
theoretical perspective, and some brief comments are made on what we may have
learned so far.Comment: 5 pages, text only, contains final remarks made at the ESO/MPA
conference on "The First Stars", Garching, August 1999; to be published by
ES
On the moduli description of local models for ramified unitary groups
Local models are schemes which are intended to model the \'etale-local
structure of p-adic integral models of Shimura varieties. Pappas and Zhu have
recently given a general group-theoretic construction of flat local models with
parahoric level structure for any tamely ramified group, but it remains an
interesting problem to characterize the local models, when possible, in terms
of an explicit moduli problem. In the setting of local models for ramified,
quasi-split GU_n, work towards an explicit moduli description was initiated in
the general framework of Rapoport and Zink's book and was subsequently advanced
by Pappas and Pappas-Rapoport. In this paper we propose a further refinement to
their moduli problem, which we show is both necessary and sufficient to
characterize the (flat) local model in a certain special maximal parahoric case
with signature (n-1,1).Comment: New section 5.3 giving an explicit application to Shimura varieties,
and other minor revisions. To appear in IMRN. 29 page
Reevaluation of the density dependence of nucleon radius and mass in the global color symmetry model of QCD
With the global color symmetry model (GCM) at finite chemical potential, the
density dependence of the bag constant, the total energy and the radius of a
nucleon in nuclear matter is investigated. A relation between the nuclear
matter density and the chemical potential with the action of QCD being taken
into account is obtained. A maximal nuclear matter density for the existence of
the bag with three quarks confined within is given. The calculated results
indicate that, before the maximal density is reached, the bag constant and the
total energy of a nucleon decrease, and the radius of a nucleon increases
slowly, with the increasing of the nuclear matter density. As the maximal
nuclear matter density is reached, the mass of the nucleon vanishes and the
radius becomes infinite suddenly. It manifests that a phase transition from
nucleons to quarks takes place.Comment: 18 pages, 3 figure
Density Dependence of Nucleon Bag Constant, Radius and Mass in an Effective Field Theory Model of QCD
With the global color symmetry model (GCM) being extended to finite chemical
potential, the density dependence of the bag constant, the total energy and the
radius of a nucleon, as well as the quark condensate in nuclear matter are
investigated. A maximal nuclear matter density for the existence of the bag
with three quarks confined within is obtained. The calculated results indicate
that, before the maximal density is reached, the bag constant, the total energy
of a nucleon and the quark condensate decrease gradually, and the radius of a
nucleon increases, with the increasing of the nuclear matter density.
Nevertheless no sudden change emerges. As the maximal nuclear matter density is
reached, a phase transition from nucleons to quarks takes place and the chiral
symmetry is restored.Comment: Latex, 15 postscript pages, 6 postscript files, To be published in
Nuclear Physics
HKT Geometry and Fake Five Dimensional Supergravity
Recent results on the relation between hyper-Kahler geometry with torsion and
solutions admitting Killing spinors in minimal de sitter supergravity are
extended to more general supergravity models with vector multiplets.Comment: 14 pages, latex. Minor typos corrected, references adde
Asymptotic silence-breaking singularities
We discuss three complementary aspects of scalar curvature singularities:
asymptotic causal properties, asymptotic Ricci and Weyl curvature, and
asymptotic spatial properties. We divide scalar curvature singularities into
two classes: so-called asymptotically silent singularities and non-generic
singularities that break asymptotic silence. The emphasis in this paper is on
the latter class which have not been previously discussed. We illustrate the
above aspects and concepts by describing the singularities of a number of
representative explicit perfect fluid solutions.Comment: 25 pages, 6 figure
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