870 research outputs found

### On projective group properties of the $6D$ pseudo-Riemannian space

We study the six-dimensional pseudo-Riemannian spaces with two time-like
coordinates that admit non-homothetic infinitesimal projective transformations.
The metrics are manifestly obtained and the projective group properties are
determined. We also find a generic defining of projective motion in the
6-dimensional rigid h-space.Comment: 4 pages, talk presented at the "Integrable Systems-2005", Prague,
200

### The Orbifolds of Permutation-Type as Physical String Systems at Multiples of c=26 IV. Orientation Orbifolds Include Orientifolds

In this fourth paper of the series, I clarify the somewhat mysterious
relation between the large class of {\it orientation orbifolds} (with twisted
open-string CFT's at $\hat c=52$) and {\it orientifolds} (with untwisted open
strings at $c=26$), both of which have been associated to division by
world-sheet orientation-reversing automorphisms. In particular -- following a
spectral clue in the previous paper -- I show that, even as an {\it interacting
string system}, a certain half-integer-moded orientation orbifold-string system
is in fact equivalent to the archetypal orientifold. The subtitle of this
paper, that orientation orbifolds include and generalize standard orientifolds,
then follows because there are many other orientation orbifold-string systems
-- with higher fractional modeing -- which are not equivalent to untwisted
string systems.Comment: 22 pages, typos correcte

### Toxicity of lunar dust

The formation, composition and physical properties of lunar dust are
incompletely characterised with regard to human health. While the physical and
chemical determinants of dust toxicity for materials such as asbestos, quartz,
volcanic ashes and urban particulate matter have been the focus of substantial
research efforts, lunar dust properties, and therefore lunar dust toxicity may
differ substantially. In this contribution, past and ongoing work on dust
toxicity is reviewed, and major knowledge gaps that prevent an accurate
assessment of lunar dust toxicity are identified. Finally, a range of studies
using ground-based, low-gravity, and in situ measurements is recommended to
address the identified knowledge gaps. Because none of the curated lunar
samples exist in a pristine state that preserves the surface reactive chemical
aspects thought to be present on the lunar surface, studies using this material
carry with them considerable uncertainty in terms of fidelity. As a
consequence, in situ data on lunar dust properties will be required to provide
ground truth for ground-based studies quantifying the toxicity of dust exposure
and the associated health risks during future manned lunar missions.Comment: 62 pages, 9 figures, 2 tables, accepted for publication in Planetary
and Space Scienc

### Classification of Static Plane Symmetric Spacetimes according to their Matter Collineations

In this paper we classify static plane symmetric spacetimes according to
their matter collineations. These have been studied for both cases when the
energy-momentum tensor is non-degenerate and also when it is degenerate. It
turns out that the non-degenerate case yields either {\it four}, {\it five},
{\it six}, {\it seven} or {\it ten} independent matter collineations in which
{\it four} are isometries and the rest are proper. There exists three
interesting cases where the energy-momentum tensor is degenerate but the group
of matter collineations is finite-dimensional. The matter collineations in
these cases are either {\it four}, {\it six} or {\it tenComment: 15 pages, LaTex, no figure

### The Hagedorn temperature Revisited

The Hagedorn temperature, T_H is determined from the number of hadronic
resonances including all mesons and baryons. This leads to a stable result T_H
= 174 MeV consistent with the critical and the chemical freeze-out temperatures
at zero chemical potential. We use this result to calculate the speed of sound
and other thermodynamic quantities in the resonance hadron gas model for a wide
range of baryon chemical potentials following the chemical freeze-out curve. We
compare some of our results to those obtained previously in other papers.Comment: 13 pages, 4 figure

### On the SO(2,1) symmetry in General Relativity

The role of the SO(2,1) symmetry in General Relativity is analyzed.
Cosmological solutions of Einstein field equations invariant with respect to a
space-like Lie algebra G_r, with r between 3 and 6 and containing so(2,1) as a
subalgebra, are also classified.Comment: 10 pages, latex, no figure

### Global Analysis of Data on the Proton Structure Function g1 and Extraction of its Moments

Inspired by recent measurements with the CLAS detector at Jefferson Lab, we
perform a self-consistent analysis of world data on the proton structure
function g1 in the range 0.17 < Q2 < 30 (GeV/c)**2. We compute for the first
time low-order moments of g1 and study their evolution from small to large
values of Q2. The analysis includes the latest data on both the unpolarized
inclusive cross sections and the ratio R = sigmaL / sigmaT from Jefferson Lab,
as well as a new model for the transverse asymmetry A2 in the resonance region.
The contributions of both leading and higher twists are extracted, taking into
account effects from radiative corrections beyond the next-to-leading order by
means of soft-gluon resummation techniques. The leading twist is determined
with remarkably good accuracy and is compared with the predictions obtained
using various polarized parton distribution sets available in the literature.
The contribution of higher twists to the g1 moments is found to be
significantly larger than in the case of the unpolarized structure function F2.Comment: 18 pages, 13 figures, to appear in Phys. Rev.

### Quantum Newtonian Dynamics on a Light Front

We recall the special features of quantum dynamics on a light-front (in an
infinite momentum frame) in string and field theory. The reason this approach
is more effective for string than for fields is stressed: the light-front
dynamics for string is that of a true Newtonian many particle system, since a
string bit has a fixed Newtonian mass. In contrast, each particle of a field
theory has a variable Newtonian mass P^+, so the Newtonian analogy actually
requires an infinite number of species of elementary Newtonian particles. This
complication substantially weakens the value of the Newtonian analogy in
applying light-front dynamics to nonperturbative problems. Motivated by the
fact that conventional field theories can be obtained as infinite tension
limits of string theories, we propose a way to recast field theory as a
standard Newtonian system. We devise and analyze some simple quantum mechanical
systems that display the essence of the proposal, and we discuss prospects for
applying these ideas to large N_c QCD.Comment: 13 pages, 3 figures, LaTex, psfig, references added, APS copyrigh

### Power counting with one-pion exchange

Techniques developed for handing inverse-power-law potentials in atomic
physics are applied to the tensor one-pion exchange potential to determine the
regions in which it can be treated perturbatively. In S-, P- and D-waves the
critical values of the relative momentum are less than or of the order of 400
MeV. The RG is then used to determine the power counting for short-range
interaction in the presence of this potential. In the P-and D-waves, where
there are no low-energy bound or virtual states, these interactions have
half-integer RG eigenvalues and are substantially promoted relative to naive
expectations. These results are independent of whether the tensor force is
attractive or repulsive. In the 3S1 channel the leading term is relevant, but
it is demoted by half an order compared to the counting for the effective-range
expansion with only a short-range potential. The tensor force can be treated
perturbatively in those F-waves and above that do not couple to P- or D-waves.
The corresponding power counting is the usual one given by naive dimensional
analysis.Comment: 18 pages, RevTeX (further details, explanation added

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