66,329 research outputs found
Chern-Simons Actions and Their Gaugings in 4D, N=1 Superspace
We gauge the abelian hierarchy of tensor fields in 4D by a Lie algebra. The
resulting non-abelian tensor hierarchy can be interpreted via an equivariant
chain complex. We lift this structure to N=1 superspace by constructing
superfield analogs for the tensor fields, along with covariant superfield
strengths. Next we construct Chern-Simons actions, for both the bosonic and N=1
cases, and note that the condition of gauge invariance can be presented
cohomologically. Finally, we provide an explicit realization of these
structures by dimensional reduction, for example by reducing the three-form of
eleven-dimensional supergravity into a superspace with manifest 4D, N=1
supersymmetry.Comment: 40pp, v2 added reference
The Deep Lens Survey Transient Search I : Short Timescale and Astrometric Variability
We report on the methodology and first results from the Deep Lens Survey
transient search. We utilize image subtraction on survey data to yield all
sources of optical variability down to 24th magnitude. Images are analyzed
immediately after acquisition, at the telescope and in near-real time, to allow
for followup in the case of time-critical events. All classes of transients are
posted to the web upon detection. Our observing strategy allows sensitivity to
variability over several decades in timescale. The DLS is the first survey to
classify and report all types of photometric and astrometric variability
detected, including solar system objects, variable stars, supernovae, and short
timescale phenomena. Three unusual optical transient events were detected,
flaring on thousand-second timescales. All three events were seen in the B
passband, suggesting blue color indices for the phenomena. One event (OT
20020115) is determined to be from a flaring Galactic dwarf star of spectral
type dM4. From the remaining two events, we find an overall rate of \eta = 1.4
events deg-2 day-1 on thousand-second timescales, with a 95% confidence limit
of \eta < 4.3. One of these events (OT 20010326) originated from a compact
precursor in the field of galaxy cluster Abell 1836, and its nature is
uncertain. For the second (OT 20030305) we find strong evidence for an extended
extragalactic host. A dearth of such events in the R passband yields an upper
95% confidence limit on short timescale astronomical variability between 19.5 <
R < 23.4 of \eta_R < 5.2. We report also on our ensemble of astrometrically
variable objects, as well as an example of photometric variability with an
undetected precursor.Comment: 24 pages, 12 figures, 3 tables. Accepted for publication in ApJ.
Variability data available at http://dls.bell-labs.com/transients.htm
Abelian Tensor Hierarchy in 4D, N=1 Superspace
With the goal of constructing the supersymmetric action for all fields,
massless and massive, obtained by Kaluza-Klein compactification from type II
theory or M-theory in a closed form, we embed the (Abelian) tensor hierarchy of
p-forms in four-dimensional, N=1 superspace and construct its Chern-Simons-like
invariants. When specialized to the case in which the tensors arise from a
higher-dimensional theory, the invariants may be interpreted as
higher-dimensional Chern-Simons forms reduced to four dimensions. As an
application of the formalism, we construct the eleven-dimensional Chern-Simons
form in terms of four-dimensional, N=1 superfields.Comment: 31 page
Molecular and functional characterization of gap junctions in the avian inner ear.
To analyze the fundamental role of gap junctions in the vertebrate inner ear, we examined molecular and functional characteristics of gap junctional communication (GJC) in the auditory and vestibular system of the chicken. By screening inner ear tissues for connexin isoforms using degenerate reverse transcription-PCR, we identified, in addition to chicken Cx43 (cCx43) and the inner-ear-specific cCx30, an as yet uncharacterized connexin predicted to be the ortholog of the mammalian Cx26. In situ hybridization indicated that cCx30 and cCx26 transcripts were both widely expressed in the cochlear duct and utricle in an overlapping pattern, suggesting coexpression of these isoforms similar to that in the mammalian inner ear. Immunohistochemistry demonstrated that cCx43 was present in gap junctions connecting supporting cells of the basilar papilla, in which its immunofluorescence colocalized with that of cCx30. However, cCx43 was absent from supporting cell gap junctions of the utricular macula. This variation in the molecular composition of gap junction plaques coincided with differences in the functional properties of GJC between the auditory and vestibular sensory epithelia. Fluorescence recovery after photobleaching, adapted to examine the diffusion of calcein in inner ear explants, revealed asymmetric communication pathways among supporting cells in the basilar papilla but not in the utricular macula. This study supports the hypothesis that the coexpression of Cx26/Cx30 is unique to gap junctions in the vertebrate inner ear. Furthermore, it demonstrates asymmetric GJC within the supporting cell population of the auditory sensory epithelium, which might mediate potassium cycling and/or intercellular signaling
New Measurements of the Ionizing Ultraviolet Background over 2 < z < 5 and Implications for Hydrogen Reionization
We present new measurements of the intensity of the ionizing ultraviolet
background and the global emissivity of ionizing photons over 2 < z < 5. Our
results are based on a suite of updated measurements of physical properties of
the high-redshift intergalactic medium (IGM), including gas temperatures and
the opacity of the IGM to Ly-alpha and ionizing photons. Consistent with
previous works, we find a relatively flat hydrogen photoionization rate over 2
< z < 5, although our measurements are roughly a factor of two higher than the
2008 values of Faucher-Giguere et al., due primarily to our lower gas
temperatures. The ionizing emissivity we derive is also generally higher than
other recent estimates due to a combination of lower gas temperatures, higher
ionizing opacity, and an accounting of cosmological radiative transfer effects.
We find evidence that the emissivity increases from z~3 to 5, reaching ~5
ionizing photons per atom per gigayear at z=4.75 for realistic galaxy spectra.
We further find that galaxies must dominate the emissivity near 1 Ryd at z > 4,
and possibly at all redshifts z > 2.4. Our results suggest that the
globally-averaged ionizing "efficiency" of star-forming galaxies increases
substantially with redshift over 3.2 < z < 4.75. This trend is consistent with
the conclusion often drawn from reionization models that the ionizing
efficiency of galaxies must be higher during reionization in order for galaxies
to reionize the IGM by z=6. Our emissivity values at z~5 suggest that ionizing
photons may have been a factor of two more abundant during the final stages of
reionization than previously indicated. The evolution of the ionizing
emissivity over 2 < z < 5 suggests, moreover, that the steep decline in the
photoionization rate from z~5 to 6 may indicate a rapid evolution in the mean
free path at z > 5.Comment: 19 pages, 14 figures, MNRAS, in pres
Metal-Insulator Transition in a Generalized Hubbard Model with Correlated Hopping at Half-Filling
In the present paper metal-insulator transition is studied in a generalized
Hubbard model with correlated hopping at half-filling and zero temperature.
Single-particle Green function and energy spectrum of electron system are
calculated. The expressions for energy gap width and the concentration of polar
states (holes or doublons) are obtained. The conditions for metallic and
insulating states are found.Comment: 11 pages, 2 eps figures, Latex 2.09, submitted to Phys. Stat. Sol.
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