7,325 research outputs found
Subleading corrections to parity-violating pion photoproduction
We compute the photon asymmetry Bγ for near threshold parity-violating (PV) pion photoproduction through subleading order. We show that subleading contributions involve a new combination of PV couplings not included in previous analyses of hadronic PV. We argue that existing constraints on the leading order contribution to Bγ—obtained from the PV γ-decay of 18F—suggest that the impact of the subleading contributions may be more significant than expected from naturalness arguments
Chiral Symmetry and the Parity-Violating Yukawa Coupling
We construct the complete SU(2) parity-violating (PV)
interaction Lagrangian with one derivative, and calculate the chiral
corrections to the PV Yukawa coupling constant through in the leading order of heavy baryon expansion. We
discuss the relationship between the renormalized \hpi, the measured value of
\hpi, and the corresponding quantity calculated microscopically from the
Standard Model four-quark PV interaction.Comment: RevTex, 26 pages + 5 PS figure
The infrared morphology of galactic centers
Initial results are presented of a program to map the centers of galaxies in the mid-infrared using the NASA-MSFC 20 pixel bolometer array. Maps at 10.8 micrometer of the galaxies NGC 5236 (M82), NGC 1808, NGC 4536, and NGC 4527 reveal complex emitting regions ranging in size from 500 pc to 2 kpc. The infrared spatial distributions generally resemble those in the visible and radio. In all cases a large fraction of the IRAS 12 micrometer flux originates in spatial structures prominent in the maps
Gravity Waves from a Cosmological Phase Transition: Gauge Artifacts and Daisy Resummations
The finite-temperature effective potential customarily employed to describe
the physics of cosmological phase transitions often relies on specific gauge
choices, and is manifestly not gauge-invariant at finite order in its
perturbative expansion. As a result, quantities relevant for the calculation of
the spectrum of stochastic gravity waves resulting from bubble collisions in
first-order phase transitions are also not gauge-invariant. We assess the
quantitative impact of this gauge-dependence on key quantities entering
predictions for gravity waves from first order cosmological phase transitions.
We resort to a simple abelian Higgs model, and discuss the case of R_xi gauges.
By comparing with results obtained using a gauge-invariant Hamiltonian
formalism, we show that the choice of gauge can have a dramatic effect on
theoretical predictions for the normalization and shape of the expected gravity
wave spectrum. We also analyze the impact of resumming higher-order
contributions as needed to maintain the validity of the perturbative expansion,
and show that doing so can suppress the amplitude of the spectrum by an order
of magnitude or more. We comment on open issues and possible strategies for
carrying out "daisy resummed" gauge invariant computations in non-Abelian
models for which a gauge-invariant Hamiltonian formalism is not presently
available.Comment: 25 pages, 10 figure
Electroweak Baryogenesis with Vector-like Leptons and Scalar Singlets
We investigate the viability of electroweak baryogenesis in a model with a
first order electroweak phase transition induced by the addition of two gauge
singlet scalars. A vector-like lepton doublet is introduced in order to provide
CP violating interactions with the singlets and Standard Model leptons, and the
asymmetry generation dynamics are examined using the vacuum expectation value
insertion approximation. We find that such a model is readily capable of
generating sufficient baryon asymmetry while satisfying electron electric
dipole moment and collider phenomenology constraints.Comment: 38 pages, 8 figures. Citations added. Benchmarks, figures and tables
updated, error fixed in calculations. Matches version published in JHE
Ejecta patterns of Meteor Crater, Arizona derived from the linear un-mixing of TIMS data and laboratory thermal emission spectra
Accurate interpretation of thermal infrared data depends upon the understanding and removal of complicating effects. These effects may include physical mixing of various mineralogies and particle sizes, atmospheric absorption and emission, surficial coatings, geometry effects, and differential surface temperatures. The focus is the examination of the linear spectral mixing of individual mineral or endmember spectra. Linear addition of spectra, for particles larger than the wavelength, allows for a straight-forward method of deconvolving the observed spectra, predicting a volume percent of each endmember. The 'forward analysis' of linear mixing (comparing the spectra of physical mixtures to numerical mixtures) has received much attention. The reverse approach of un-mixing thermal emission spectra was examined with remotely sensed data, but no laboratory verification exists. Understanding of the effects of spectral mixing on high resolution laboratory spectra allows for the extrapolation to lower resolution, and often more complicated, remotely gathered data. Thermal Infrared Multispectral Scanner (TIMS) data for Meteor Crater, Arizona were acquired in Sep. 1987. The spectral un-mixing of these data gives a unique test of the laboratory results. Meteor Crater (1.2 km in diameter and 180 m deep) is located in north-central Arizona, west of Canyon Diablo. The arid environment, paucity of vegetation, and low relief make the region ideal for remote data acquisition. Within the horizontal sedimentary sequence that forms the upper Colorado Plateau, the oldest unit sampled by the impact crater was the Permian Coconino Sandstone. A thin bed of the Toroweap Formation, also of Permian age, conformably overlays the Coconino. Above the Toroweap lies the Permian Kiabab Limestone which, in turn, is covered by a thin veneer of the Moenkopi Formation. The Moenkopi is Triassic in age and has two distinct sub-units in the vicinity of the crater. The lower Wupatki member is a fine-grained sandstone, while the upper Moqui member is a fissile siltstone. Ejecta from these units are preserved as inverted stratigraphy up to 2 crater radii from the rim. The mineralogical contrast between the units, relative lack of post-emplacement erosion and ejecta mixing provide a unique site to apply the un-mixing model. Selection of the aforementioned units as endmembers reveals distinct patterns in the ejecta of the crater
Constraints on T-Odd, P-Even Interactions from Electric Dipole Moments
We construct the relationship between nonrenormalizable,effective,
time-reversal violating (TV) parity-conserving (PC) interactions of quarks and
gauge bosons and various low-energy TVPC and TV parity-violating (PV)
observables. Using effective field theory methods, we delineate the scenarious
under which experimental limits on permanent electric dipole moments (EDM's) of
the electron, neutron, and neutral atoms as well as limits on TVPC observables
provide the most stringent bounds on new TVPC interactions. Under scenarios in
which parity invariance is restored at short distances, the one-loop EDM of
elementary fermions generate the most severe constraints. The limits derived
from the atomic EDM of Hg are considerably weaker. When parity symmetry
remains broken at short distances, direct TVPC search limits provide the least
ambiguous bounds. The direct limits follow from TVPC interactions between two
quarks.Comment: 43 pages, 9 figure
Aerolian erosion, transport, and deposition of volcaniclastic sands among the shifting sand dunes, Christmas Lake Valley, Oregon: TIMS image analysis
Remote sensing is a tool that, in the context of aeolian studies, offers a synoptic view of a dune field, sand sea, or entire desert region. Blount et al. (1990) presented one of the first studies demonstrating the power of multispectral images for interpreting the dynamic history of an aeolian sand sea. Blount's work on the Gran Desierto of Mexico used a Landsat TM scene and a linear spectral mixing model to show where different sand populations occur and along what paths these sands may have traveled before becoming incorporated into dunes. Interpretation of sand transport paths and sources in the Gran Desierto led to an improved understanding of the origin and Holocene history of the dunes. With the anticipated advent of the EOS-A platform and ASTER thermal infrared capability in 1998, it will become possible to look at continental sand seas and map sand transport paths using 8-12 mu m bands that are well-suited to tracking silicate sediments. A logical extension of Blount's work is to attempt a similar study using thermal infrared images. One such study has already begun by looking at feldspar, quartz, magnetite, and clay distributions in the Kelso Dunes of southern California. This paper describes the geology and application of TIMS image analysis of a less-well known Holocene dune field in south central Oregon using TIMS data obtained in 1991
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