3,831 research outputs found
On Poisson Structure and Curvature
We consider a curved space-time whose algebra of functions is the commutative
limit of a noncommutative algebra and which has therefore an induced Poisson
structure. In a simple example we determine a relation between this structure
and the Riemann tensor.Comment: 8 pages, Late
Sigma One
We demonstrate that it is possible to calculate not only the mean of an
underlying population but also its dispersion, given only a single observation
and physically reasonable constraints (i.e., that the quantities under
consideration are non-negative and bounded). We suggest that this
counter-intuitive conclusion is in fact at the heart of most modeling of
astronomical data.Comment: Accepted to the Astronomical Journal. 13 pages, 4 figure
Classical Gravity on Fuzzy Space-Time
A review is made of recent efforts to find relations between the commutation
relations which define a noncommutative geometry and the gravitational field
which remains as a shadow in the commutative limit.Comment: Lecture given at the 30th International Symposium Ahrenshoop on the
Theory of Elementary Particles, Buckow, Germany, August 27-31, 1996; 11 Pages
LaTe
Fuzzy Space-Time
A review is made of recent efforts to define linear connections and their
corresponding curvature within the context of noncommutative geometry. As an
application it is suggested that it is possible to identify the gravitational
field as a phenomenological manifestation of space-time commutation relations
and to thereby clarify its role as an ultraviolet regularizer.Comment: 17 pages LaTe
Two New Tests of the Metallicity Sensitivity of the Cepheid Period-Luminosity Relation (The Leavitt Law)
We undertake a new test of the metallicity sensitivity of the Leavitt Law for
Classical Cepheids. We derive an empirical calibration of the apparent
luminosities of Cepheids as measured from the optical through the mid-infrared
(0.45-8.0um) as a function of spectroscopic [Fe/H] abundances of individual
Cepheids in the Large Magellanic Cloud from Romaniello et al. (2008). The
cumulative trend over the entire wavelength range shows a nearly monotonic
behavior. The sense of the trend is consistent with differential
line-blanketing in the optical, leading to stars of high metallicity being
fainter in the optical. This is followed by a reversal in the trend at longer
wavelengths, with the cross-over occurring near the K band at about 2.2um,
consistent with a subsequent redistribution of energy resulting in a mild
brightening of Cepheids (with increased metallicity) at mid-infrared
wavelengths. This conclusion agrees with that of Romaniello et al. based on a
differential comparison of the mean V- and K-band Leavitt Laws for the Galaxy,
SMC and LMC, but is opposite in sign to most other empirical tests of the
sensitivity of Cepheid distances to mean [O/H] HII region abundances. We also
search for a correlation of Cepheid host-galaxy metallicity with deviations of
the galaxy's Cepheid distance from that predicted from a pure Hubble flow.
Based on Cepheid distances to 26 nearby galaxies in the local flow, only a very
weak signal is detected giving Dmu_o = -0.17 (+/- 0.31) ([O/H] - 8.80) - 0.21
(+/-0.10). This is in agreement with previous determinations, but statistically
inconclusive.Comment: Accepted to the Astrophysical Journal. 8 pages, 5 figures, 1 tabl
Connes' Model Building Kit
Alain Connes' applications of non-commutative geometry to interaction physics
are described for the purpose of model building.Comment: 35 pages, LATeX, CPT-93/P.296
Fuzzy Surfaces of Genus Zero
A fuzzy version of the ordinary round 2-sphere has been constructed with an
invariant curvature. We here consider linear connections on arbitrary fuzzy
surfaces of genus zero. We shall find as before that they are more or less
rigidly dependent on the differential calculus used but that a large number of
the latter can be constructed which are not covariant under the action of the
rotation group. For technical reasons we have been forced to limit our
considerations to fuzzy surfaces which are small perturbations of the fuzzy
sphere.Comment: 11 pages, Late
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