1,146,855 research outputs found
Invariant Kinematics on a One-Dimensional Lattice in Noncommutative Geometry
In a one-dimensional lattice, the induced metric (from a noncommutative
geometry calculation) breaks translation invariance. This leads to some
inconsistencies among different spectator frames, in the observation of the
hoppings of a test particle between lattice sites. To resolve the
inconsistencies between the different spectator frames, we replace the test
particle's bare mass by an effective locally dependent mass. This effective
mass also depends on the lattice constant - i.e. it is a scale dependent
variable (a "running" mass). We also develop an alternative approach based on a
compensating potential. The induced potential between a spectator frame and the
test particle is attractive on the average. We then show that the entire
formalism holds for a quantum particle represented by a wave function, just as
it applies to the mechanics of a classical point particle.Comment: 17 pages, latex, epsf, amssymbols, 2 figures. Final version to be
published in IJMP
Scalar transport in compressible flow
Transport of scalar fields in compressible flow is investigated. The
effective equations governing the transport at scales large compared to those
of the advecting flow are derived by using multi-scale techniques. Ballistic
transport generally takes place when both the solenoidal and the potential
components of the velocity do not vanish, despite of the fact that it has zero
average value. The calculation of the effective ballistic velocity is
reduced to the solution of one auxiliary equation. An analytic expression for
is derived in some special instances, i.e. flows depending on a single
coordinate, random with short correlation times and slightly compressible
cellular flow. The effective mean velocity vanishes for velocity fields
which are either incompressible or potential and time-independent. For generic
compressible flow, the most general conditions ensuring the absence of
ballistic transport are isotropy and/or parity invariance. When vanishes
(or in the frame of reference moving with velocity ), standard diffusive
transport takes place. It is known that diffusion is always enhanced by
incompressible flow. On the contrary, we show that diffusion is depleted in the
presence of time-independent potential flow. Trapping effects due to potential
wells are responsible for this depletion. For time-dependent potential flow or
generic compressible flow, transport rates are enhanced or depleted depending
on the detailed structure of the velocity field.Comment: 27 pages, submitted to Physica
The Luminous Convolution Model as an alternative to dark matter in spiral galaxies
The Luminous Convolution Model (LCM) demonstrates that it is possible to
predict the rotation curves of spiral galaxies directly from estimates of the
luminous matter. We consider two frame-dependent effects on the light observed
from other galaxies: relative velocity and relative curvature. With one free
parameter, we predict the rotation curves of twenty-three (23) galaxies
represented in forty-two (42) data sets. Relative curvature effects rely upon
knowledge of both the gravitational potential from luminous mass of the
emitting galaxy and the receiving galaxy, and so each emitter galaxy is
compared to four (4) different Milky Way luminous mass models. On average in
this sample, the LCM is more successful than either dark matter or modified
gravity models in fitting the observed rotation curve data.
Implications of LCM constraints on populations synthesis modeling are
discussed in this paper. This paper substantially expands the results in
arXiv:1309.7370.Comment: Implications of LCM constraints on populations synthesis modeling are
discussed in this paper. This paper substantially expands the results in
arxiv:1309.737
The Average Physical Properties and Star Formation Histories of the UV-Brightest Star-Forming Galaxies at z~3.7
[Abridged] We investigate the average physical properties and star formation
histories of the most UV-luminous star-forming galaxies at z~3.7. Our results
are derived from analyses of the average spectral energy distributions (SEDs),
constructed from stacked optical to infrared photometry, of a sample of the
1,902 most UV-luminous star-forming galaxies found in 5.3 square degrees of the
NOAO Deep Wide-Field Survey. We bin the sample according to UV luminosity, and
find that the shape of the average SED in the rest-frame optical and infrared
is fairly constant with UV luminosity: i.e., more UV luminous galaxies are, on
average, also more luminous at longer wavelengths. In the rest-UV, however, the
spectral slope (measured at 0.13-0.28 um) rises steeply with the median UV
luminosity from -1.8 at L L* to -1.2 in the brightest bin (L~4-5L*). We use
population synthesis analyses to derive the average physical properties of
these galaxies and find that: (1) L_UV, and thus star formation rates (SFRs),
scale closely with stellar mass such that more UV-luminous galaxies are also
more massive; (2) The median ages indicate that the stellar populations are
relatively young (200-400 Myr) and show little correlation with UV luminosity;
and (3) More UV-luminous galaxies are dustier than their less-luminous
counterparts, such that L~4-5L* galaxies are extincted up to A(1600)=2 mag
while L L* galaxies have A(1600)=0.7-1.5 mag. Based on these observations, we
argue that the average star formation histories of UV-luminous galaxies are
better described by models in which SFR increases with time in order to
simultaneously reproduce the tight correlation between the observed SFR and
stellar mass, and the universally young ages of these galaxies. We demonstrate
the potential of measurements of the SFR-M* relation at multiple redshifts to
discriminate between simple models of star formation histories.Comment: 14 pages, 7 figures. Accepted for publication in Astrophysical
Journa
Exploratory X-ray Monitoring of Luminous Radio-Quiet Quasars at High Redshift: No Evidence for Evolution in X-ray Variability
We report on the second installment of an X-ray monitoring project of seven
luminous radio-quiet quasars (RQQs). New {\sl Chandra} observations of four of
these, at , yield a total of six X-ray epochs, per source,
with temporal baselines of days in the rest frame. These data
provide the best X-ray light curves for RQQs at , to date, enabling
qualitative investigations of the X-ray variability behavior of such sources
for the first time. On average, these sources follow the trend of decreasing
variability amplitude with increasing luminosity, and there is no evidence for
X-ray variability increasing toward higher redshifts, in contrast with earlier
predictions of potential evolutionary scenarios. An ensemble variability
structure function reveals that their variability level remains relatively flat
across days in the rest frame and it is generally lower than
that of three similarly luminous RQQs at over the same
temporal range. We discuss possible explanations for the increased variability
of the lower-redshift subsample and, in particular, whether higher accretion
rates play a leading role. Near-simultaneous optical monitoring of the sources
at indicates that none is variable on -day
timescales, although flux variations of up to \% are observed on
-day timescales, typical of RQQs at similar redshifts. Significant
optical-X-ray spectral slope variations observed in two of these sources are
consistent with the levels observed in luminous RQQs and are dominated by X-ray
variations.Comment: 11 pages (emulateapj), 4 figures. Accepted for publication in Ap
- …