32,300 research outputs found
Latest Results on the Hot-Dense Partonic Matter at RHIC
At the Relativistic Heavy Ion Collider (RHIC) collisions of heavy ions at
nucleon-nucleon energies of 200 GeV appear to have created a new form of matter
thought to be a deconfined state of the partons that ordinarily are bound in
nucleons.We discuss the evidence that a thermalized partonic medium, usually
called a Quark Gluon Plasma (QGP), has been produced. Then we discuss the
effect of this high-density medium on the production of jets and their pair
correlations. Next we look at direct photons as a clean electro-magnetic probe
to constrain the initial hard scatterings. Finally we review the developing
picture for the effect of this medium on the production of open heavy quarks
and on the screening by the QGP of heavy-quark bound states.Comment: 6 pages, 14 figures, proceedings for QNP06 (5-10 June, 2006) invited
tal
The three-fold theoretical basis of the Gravity Probe B gyro precession calculation
The Gravity Probe B (GP-B) experiment is complete and the results are in
agreement with the predictions of general relativity (GR) for both the geodetic
precession, 6.6 arcsec/yr to about 0.3%, and the Lense-Thirring precession, 39
marcsec to about 19%. This note is concerned with the theoretical basis for the
predictions. The predictions depend on three elements of gravity theory,
firstly that macroscopic gravity is described by a metric theory such as
general relativity, secondly that the Lense-Thirring metric provides an
approximate description of the gravitational field of the spinning earth, and
thirdly that the spin axis of a gyroscope is parallel displaced in spacetime,
which gives its equation of motion. We look at each of these three elements to
show how each is solidly based on previous experiments and well-tested theory.
The agreement of GP-B with theory strengthens our belief that all three
elements are correct and increases our confidence in applying GR to
astrophysical phenomena. Conversely, if GP-B had not verified the predictions a
major theoretical quandary would have occurred.Comment: To appear as one of 21 articles in a special issue of Classical and
Quantum Gravity devoted to the GP-B experiment. 16 pages, 1 figur
Euler Integration of Gaussian Random Fields and Persistent Homology
In this paper we extend the notion of the Euler characteristic to persistent
homology and give the relationship between the Euler integral of a function and
the Euler characteristic of the function's persistent homology. We then proceed
to compute the expected Euler integral of a Gaussian random field using the
Gaussian kinematic formula and obtain a simple closed form expression. This
results in the first explicitly computable mean of a quantitative descriptor
for the persistent homology of a Gaussian random field.Comment: 21 pages, 1 figur
Modeling the flyby anomalies with dark matter scattering
We continue our exploration of whether the flyby anomalies can be explained
by scattering of spacecraft nucleons from dark matter gravitationally bound to
the earth. We formulate and analyze a simple model in which inelastic and
elastic scatterers populate shells generated by the precession of circular
orbits with normals tilted with respect to the earth's axis. Good fits to the
data published by Anderson et al. are obtained.Comment: Latex, 20 pages; revised version has moved derivations to Appendices
and gives further numerical results in Sec. III and in added Tables VI and
VI
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