27,784 research outputs found
Analysis of the Low-Energy Theorem for \gamma p \to p \pi^0
The derivation of the `classical' low-energy theorem (LET) for \gamma p
\rightarrow p\pi^0 is re-examined and compared to chiral perturbation theory.
Both results are correct and are not contradictory; they differ because
different expansions of the same quantity are involved. Possible modifications
of the extended partially conserved axial-vector current relation, one of the
starting points in the derivation of the LET, are discussed. An alternate, more
transparent form of the LET is presented.Comment: 5 pages, Revtex, no figures, no table
Two Higgs doublets to explain the excesses and
The two Higgs doublet model emerges as a minimal scenario in which to
address, at the same time, the excess at 750 GeV and the lepton
flavour violating decay into of the 125 GeV Higgs boson.
The price to pay is additional matter to enhance the rate, and a
peculiar pattern for the lepton Yukawa couplings. We add TeV scale vector-like
fermions and find parameter space consistent with both excesses, as well as
with Higgs and electroweak precision observables.Comment: 15 pages, 1 figure; v2: discussion of tau-->mu gamma added, leading
to an additional constraint. v3: references added, figure 1 recovered and
figure 2 adde
Sulfate and MSA in the air and snow on the Greenland Ice Sheet
Sulfate and methanesulfonic acid (MSA) concentrations in aerosol, surface snow, and snowpit samples have been measured at two sites on the Greenland Ice Sheet. Seasonal variations of the concentrations observed for these chemical species in the atmosphere are reproduced in the surface snow and preserved in the snowpit sequence. The amplitude of the variations over a year are smaller in the snow than in the air, but the ratios of the concentrations are comparable. The seasonal variations for sulfate are different at the altitude of the Ice Sheet compared to those observed at sea level, with low concentrations in winter and short episodes of elevated concentrations in spring. In contrast, the variations in concentrations of MSA are similar to those measured at sea level, with a first sequence of elevated concentrations in spring and another one during summer, and a winter low resulting from low biogenic production. The ratio MSA/sulfate clearly indicates the influence of high-latitude sources for the summer maximum of MSA, but the large impact of anthropogenic sulfate precludes any conclusion for the spring maximum. The seasonal pattern observed for these species in a snowpit sampled according to stratigraphy indicates a deficit in the accumulation of winter snow at the summit of the Greenland Ice Sheet, in agreement with some direct observations. A deeper snowpit covering the years 1985–1992 indicates the consistency of the seasonal pattern for MSA over the years, which may be linked to transport and deposition processes
A comparison of soil moisture characteristics predicted by the Arya-Paris model with laboratory-measured data
Soil moisture characteristics predicted by the Arya-Paris model were compared with the laboratory measured data for 181 New Jersey soil horizons. For a number of soil horizons, the predicted and the measured moisture characteristic curves are almost coincident; for a large number of other horizons, despite some disparity, their shapes are strikingly similar. Uncertainties in the model input and laboratory measurement of the moisture characteristic are indicated, and recommendations for additional experimentation and testing are made
Machine Learning and Irresponsible Inference: Morally Assessing the Training Data for Image Recognition Systems
Just as humans can draw conclusions responsibly or irresponsibly, so too can computers. Machine learning systems that have been trained on data sets that include irresponsible judgments are likely to yield irresponsible predictions as outputs. In this paper I focus on a particular kind of inference a computer system might make: identification of the intentions with which a person acted on the basis of photographic evidence. Such inferences are liable to be morally objectionable, because of a way in which they are presumptuous. After elaborating this moral concern, I explore the possibility that carefully procuring the training data for image recognition systems could ensure that the systems avoid the problem. The lesson of this paper extends beyond just the particular case of image recognition systems and the challenge of responsibly identifying a person’s intentions. Reflection on this particular case demonstrates the importance (as well as the difficulty) of evaluating machine learning systems and their training data from the standpoint of moral considerations that are not encompassed by ordinary assessments of predictive accuracy
Richness and Abundance of Carabidae and Staphylinidae (Coleoptera), in Northeastern Dairy Pastures Under Intensive Grazing
Dairy cattle has become popular to dairy farmers in the Northeast looking for management schemes to cut production costs. Carabidae (ground beetles) and Staphylinidae (rove beetles) are indicators of habitat disturbances, such as drainage of wetlands, or grassland for grazing animals, and their monitoring could provide one measure of ecosystem sustainability if intensive management systems expand or intensify in the future. Our objective was assess the abundance and species richness of these two beetle families under intensive grazing throughout Pennsylvania, southern New York and Vermont. We collected 4365 ground beetles (83 species) and 4,027 rove beetles (79 species) by pitfall traps in three years in Pennsylvania. Nine ground beetle species, Amara aenea, Poecilus chalcites, Pterostichus melanarius, Bembidion quadrimaculatum oppositum, Amara familiaris, Poecilus lucublandus, Agonum muelleri, Bembidion obtusum and Bembidion mimus represented 80% of the Carabidae collected.
Five other species were new to Pennsylvania. Four rove beetle species, Philonthus cognatus, Meronera venustula, Amischa analis, and Philonthus various = (carbonarius), comprised 74% of the total Staphylinidae collected. Yearly distributions of the dominant species did not change significantly in the three years with A. aenea and P. cognatus being most abundant every year. A parasitic rove beetle, Aleochara tristis, was recovered for the first time in Pennsylvania and Vermont since its release in the 1960\u27s to control face fly, Musca autumnalis.
Similar results were found in New York and Vermont. We collected 1,984 ground beetles (68 species). Pterostichus melanarius was most abundant. Pterostichus vernalis was detected for the first time in the United States (Vermont). It was previously reported from Montreal, Canada. We collected 843 rove beetles (45 species). Philonthus cognatus was the most abundant rove beetle. In addition, Tachinus corticinus, previously known only from Canada, was discovered for the first time in the United States in Vermont.
Pastures in Pennsylvania were diverse, containing 14 species of forage plants and 17 weed species. Botanical composition was similar in New York and Vermont. Sixteen species of grasses and legumes made up 90% of the plant composition and 36 species of weeds made up the remainder. This diÂverse plant ecosystem may explain the richness of ground and rove beetles in northeastern U.S. pastures because the heterogeneity in the plant population provided additional resources which can support a rich assemblage of beetles. Monitoring richness and abundance of Carabidae and Staphylinidae over three years in Pennsylvania suggests intensive grazing systems are ecoÂlogically sustainable
Localized U(1) Gauge Fields, Millicharged Particles, and Holography
We consider U(1) gauge fields in a slice of AdS_5 with bulk and boundary mass
parameters. The zero mode of a bulk U(1) gauge field can be localized either on
the UV or IR brane. This leads to a simple model of millicharged particles in
which fermions can have arbitrarily small electric charge. In the electroweak
sector we also discuss phenomenological implications of a localized U(1)_Y
gauge boson. Using the AdS/CFT correspondence we present the 4D holographic
interpretation of the 5D model. In particular the photon is shown to be a
composite particle when localized near the IR brane, whereas it is elementary
when localized near the UV brane. In the dual interpretation the
``millicharge'' results from an elementary fermion coupling to a composite
photon via a vector current with large anomalous dimension.Comment: 26 pages, 1 figur
Photoionization and Photoelectric Loading of Barium Ion Traps
Simple and effective techniques for loading barium ions into linear Paul
traps are demonstrated. Two-step photoionization of neutral barium is achieved
using a weak intercombination line (6s2 1S0 6s6p 3P1, 791 nm) followed by
excitation above the ionization threshold using a nitrogen gas laser (337 nm).
Isotopic selectivity is achieved by using a near Doppler-free geometry for
excitation of the triplet 6s6p 3P1 state. Additionally, we report a
particularly simple and efficient trap loading technique that employs an
in-expensive UV epoxy curing lamp to generate photoelectrons.Comment: 5 pages, Accepted to PRA 3/20/2007 -fixed typo -clarified figure 3
caption -added reference [15
The eta-photon transition form factor
The eta-photon transition form factor is evaluated in a formalism based on a
phenomenological description at low values of the photon virtuality, and a
QCD-based description at high photon virtualities, matching at a scale
. The high photon virtuality description makes use of a Distribution
Amplitude calculated in the Nambu-Jona-Lasinio model with Pauli-Villars
regularization at the matching scale , and QCD evolution from
to higher values of . A good description of the available
data is obtained. The analysis indicates that the recent data from the BaBar
collaboration on pion and eta transition form factor can be well reproduced, if
a small contribution of twist three at the matching scale is
included.Comment: 14 pages, 3 figures, revised version, minor corrections, references
added, conclusions unchanged. Accepted for publication in Phys. Rev.
- …