18,341 research outputs found
Nonlinear screening and stopping power in two-dimensional electron gases
We have used density functional theory to study the nonlinear screening
properties of a two-dimensional (2D) electron gas. In particular, we consider
the screening of an external static point charge of magnitude Z as a function
of the distance of the charge from the plane of the gas. The self-consistent
screening potentials are then used to determine the 2D stopping power in the
low velocity limit based on the momentum transfer cross-section. Calculations
as a function of Z establish the limits of validity of linear and quadratic
response theory calculations, and show that nonlinear screening theory already
provides significant corrections in the case of protons. In contrast to the 3D
situation, we find that the nonlinearly screened potential supports a bound
state even in the high density limit. This behaviour is elucidated with the
derivation of a high density screening theorem which proves that the screening
charge can be calculated perturbatively in the high density limit for arbitrary
dimensions. However, the theorem has particularly interesting implications in
2D where, contrary to expectations, we find that perturbation theory remains
valid even when the perturbing potential supports bound states.Comment: 23 pages, 15 figures in RevTeX
From Quark Gluon Plasma to a Perfect Fluid of Quarks and Beyond
With high energy heavy ion collisions one tries to create a new forms of
matter that is similar to the one present at the birth of our Universe. Recent
development on flow pattern, initial energy-density and freeze-out temperature
shows that most likely this new form of matter is in a deconfined state, has
colored degrees of freedom and is more fluid-like than gas-like. In present
paper we calculate estimations on the physical properties of this new-old
matter.Comment: 10 pages, 5 figures, to appear in the proceedings of the 44th
International School of Subnuclear Physics, Erice, Sicily, 29 August - 7
September 200
Spontaneous Breaking of Chiral Symmetry as a Consequence of Confinement
We show that at the leading order in the large- expansion a lattice QCD
motivated linear rising confinement potential at large distances leads to a
non-local four-quark interaction that realizes spontaneous breaking of chiral
symmetry (SBCS) in the same way the Nambu-Jona-Lasinio model does. The
dynamical quark mass , which represents the solution of the gap-equation, is
proportional to the square root of the string tension and takes the
form at the leading order in the large- expansion
with GeV. The Nambu-Jona-Lasinio phenomenological constant
, which is responsible for SBCS, is expressed in terms of the string
tension and the confinement radius.Comment: 10 pages, 0 figures, latex, IK-TUW-Preprint 930540
Global symmetries of Yang-Mills squared in various dimensions
Tensoring two on-shell super Yang-Mills multiplets in dimensions
yields an on-shell supergravity multiplet, possibly with additional matter
multiplets. Associating a (direct sum of) division algebra(s) with
each dimension we obtain formulae for the algebras
and of the U-duality group and its maximal
compact subgroup , respectively, in terms of the internal global symmetry
algebras of each super Yang-Mills theory. We extend our analysis to include
supergravities coupled to an arbitrary number of matter multiplets by allowing
for non-supersymmetric multiplets in the tensor product.Comment: 25 pages, 2 figures, references added, minor typos corrected, further
comments on sec. 2.4 included, updated to match version to appear in JHE
Merged infrared catalogue
A compilation of equatorial coordinates, spectral types, magnitudes, and fluxes from five catalogues of infrared observations is presented. This first edition of the Merged Infrared Catalogue contains 11,201 oservations from the Two-Micron Sky Survey, Observations of Infrared Radiation from Cool Stars, the Air Force Geophysics Laboratory four Color Infrared Sky Survey and its Supplemental Catalog, and from Catalog of 10 micron Celestial Objects (HALL). This compilation is a by-product of a computerized infrared data base under development at Goddard Space Flight Center; the objective is to maintain a complete and current record of all infrared observations from 1 micron m to 1000 micron m of nonsolar system objects. These observations are being placed into a standardized system
An octonionic formulation of the M-theory algebra
We give an octonionic formulation of the N = 1 supersymmetry algebra in D =
11, including all brane charges. We write this in terms of a novel outer
product, which takes a pair of elements of the division algebra A and returns a
real linear operator on A. More generally, with this product comes the power to
rewrite any linear operation on R^n (n = 1,2,4,8) in terms of multiplication in
the n-dimensional division algebra A. Finally, we consider the reinterpretation
of the D = 11 supersymmetry algebra as an octonionic algebra in D = 4 and the
truncation to division subalgebras
A magic pyramid of supergravities
By formulating N = 1, 2, 4, 8, D = 3, Yang-Mills with a single Lagrangian and
single set of transformation rules, but with fields valued respectively in
R,C,H,O, it was recently shown that tensoring left and right multiplets yields
a Freudenthal-Rosenfeld-Tits magic square of D = 3 supergravities. This was
subsequently tied in with the more familiar R,C,H,O description of spacetime to
give a unified division-algebraic description of extended super Yang-Mills in D
= 3, 4, 6, 10. Here, these constructions are brought together resulting in a
magic pyramid of supergravities. The base of the pyramid in D = 3 is the known
4x4 magic square, while the higher levels are comprised of a 3x3 square in D =
4, a 2x2 square in D = 6 and Type II supergravity at the apex in D = 10. The
corresponding U-duality groups are given by a new algebraic structure, the
magic pyramid formula, which may be regarded as being defined over three
division algebras, one for spacetime and each of the left/right Yang-Mills
multiplets. We also construct a conformal magic pyramid by tensoring conformal
supermultiplets in D = 3, 4, 6. The missing entry in D = 10 is suggestive of an
exotic theory with G/H duality structure F4(4)/Sp(3) x Sp(1).Comment: 30 pages, 6 figures. Updated to match published version. References
and comments adde
- …