370 research outputs found
Quenching of the Deuteron in Flight
We investigate the Lorentz contraction of a deuteron in flight. Our starting
point is the Blankenbecler-Sugar projection of the Bethe-Salpeter equation to a
3-dimensional quasi potential equation, wqhich we apply for the deuteron bound
in an harmonic oscillator potential (for an analytical result) and by the Bonn
NN potential for a more realistic estimate. We find substantial quenching with
increasing external momenta and a significant modification of the high momentum
spectrum of the deuteron.Comment: 11 pages, 4 figure
Silica in a Mars analog environment: Ka'u Desert, Kilauea Volcano, Hawaii
Airborne Visible/Near-Infrared Imaging Spectrometer (AVIRIS) data acquired over the Ka'u Desert are atmospherically corrected to ground reflectance and used to identify the mineralogic components of relatively young basaltic materials, including 250â700 and 200â400 year old lava flows, 1971 and 1974 flows, ash deposits, and solfatara incrustations. To provide context, a geologic surface units map is constructed, verified with field observations, and supported by laboratory analyses. AVIRIS spectral end-members are identified in the visible (0.4 to 1.2 ÎŒm) and short wave infrared (2.0 to 2.5 ÎŒm) wavelength ranges. Nearly all the spectral variability is controlled by the presence of ferrous and ferric iron in such minerals as pyroxene, olivine, hematite, goethite, and poorly crystalline iron oxides or glass. A broad, nearly ubiquitous absorption feature centered at 2.25 ÎŒm is attributed to opaline (amorphous, hydrated) silica and is found to correlate spatially with mapped geologic surface units. Laboratory analyses show the silica to be consistently present as a deposited phase, including incrustations downwind from solfatara vents, cementing agent for ash duricrusts, and thin coatings on the youngest lava flow surfaces. A second, Ti-rich upper coating on young flows also influences spectral behavior. This study demonstrates that secondary silica is mobile in the Ka'u Desert on a variety of time scales and spatial domains. The investigation from remote, field, and laboratory perspectives also mimics exploration of Mars using orbital and landed missions, with important implications for spectral characterization of coated basalts and formation of opaline silica in arid, acidic alteration environments
Oxidative photopolymerization of thiol-terminated polysulfide resins. Application in antibacterial coatings
A UV photoinduced cross-linking of non-modified commercial poly(disulfide) resins (Thioplast) is reported via the air oxidative photocoupling of terminal thiol functions. Catalyzed by a photogenerated guanidine base (TBD), this step-growth photopolymerization is useful to maximize disulfide functions content. The mechanism proceeds through thiol deprotonation into thiolate anions, further oxidized into thiyl radicals, eventually dimerizing into disulfide cross-links. Starting with a detailed structural characterization of the thiol-terminated resin, photooxidative kinetics are studied under exposure to a polychromatic medium-pressure Hg arc using Raman and infrared spectroscopy. The effects of irradiance, film thickness, photobase concentration, resin molar mass, and content of an additional polythiol monomer (reactive diluent) have been investigated. In an effort of upscaling, irradiation under a 365 nm LED panel has enabled the fast preparation of 1.5 ÎŒm thick cross-linked poly(disulfide) coatings in a matter of minutes. Capitalizing on the ability of residual thiol groups to react with silver cations, a post-functionalization has been successfully performed, leading to films exhibiting at their surface stable thiolate-silver bonds as proved by X-ray photoelectron spectroscopy. Despite the well-established biocide action of silver ions, no antibacterial action has been evidenced by confocal fluorescence microscopy because of insufficient release
Exotic baryon multiplets at large number of colours
We generalize the usual octet, decuplet and exotic antidecuplet and higher
baryon multiplets to any number of colours Nc. We show that the multiplets fall
into a sequence of bands with O(1/Nc) splittings inside the band and
O(1)splittings between the bands characterized by "exoticness", that is the
number of extra quark-antiquark pairs needed to compose the multiplet. Each
time one adds a pair the baryon mass is increased by the same constant which
can be interpreted as a mass of a quark-antiquark pair. At the same time, we
prove that masses of exotic rotational multiplets are reliably determined at
large Nc from collective quantization of chiral solitons.Comment: 13 p., 5 figs. New section and references adde
The LHC String Hunter's Companion (II): Five-Particle Amplitudes and Universal Properties
We extend the study of scattering amplitudes presented in ``The LHC String
Hunter's Companion'' to the case of five-point processes that may reveal the
signals of low mass strings at the LHC and are potentially useful for detailed
investigations of fundamental Regge excitations. In particular, we compute the
full-fledged string disk amplitudes describing all 2->3 parton scattering
subprocesses leading to the production of three hadronic jets. We cast our
results in a form suitable for the implementation of stringy partonic cross
sections in the LHC data analysis. We discuss the universal, model-independent
features of multi-parton processes and point out the existence of even stronger
universality relating N-gluon amplitudes to the amplitudes involving N-2 gluons
and one quark-antiquark pair. We construct a particularly simple basis of two
functions describing all universal five-point amplitudes. We also discuss
model-dependent amplitudes involving four fermions and one gauge boson that may
be relevant for studying jets associated to Drell-Yan pairs and other processes
depending on the spectrum of Kaluza-Klein particles, thus on the geometry of
compact dimensions.Comment: 71 pages, LaTeX v2: very few typos removed, final version to appear
in NP
Polarized Single Top Production at Leptonic Colliders from Broken R Parity Interactions Incorporating CP Violation
The contribution from the R parity violating interactions in the associated
production of a top quark with a charm antiquark is examined for high energy
leptonic colliders. We concentrate on the reactions associated with the
semileptonic top decay. A set of characteristic dynamical distributions for the
signal events is evaluated and the results contrasted against those from the
standard model W-boson pair production background. Next, we turn to a study of
a CP-odd observable, associated with the top spin, which leads to an asymmetry
in the energy distribution of the emitted charged leptons for the pair of
CP-conjugate final states, and . A
non vanishing asymmetry arises from a CP-odd phase, embedded in the R parity
violating coupling constants, through interference terms between the R parity
violating amplitudes at both the tree and loop levels.Comment: revtex file. 17 pages. 7 postscript figures. 1 table. The revised
version includes an estimate of experimental uncertainties. Submitted to
Phys. Rev.
Microscopic calculation of 6Li elastic and transition form factors
Variational Monte Carlo wave functions, obtained from a realistic Hamiltonian
consisting of the Argonne v18 two-nucleon and Urbana-IX three-nucleon
interactions, are used to calculate the 6Li ground-state longitudinal and
transverse form factors as well as transition form factors to the first four
excited states. The charge and current operators include one- and two-body
components, leading terms of which are constructed consistently with the
two-nucleon interaction. The calculated form factors and radiative widths are
in good agreement with available experimental data.Comment: 9 pages, 2 figures, REVTeX, submitted to Physical Review Letters,
with updated introduction and reference
The Gluon Exchange Interaction Between Constituent Quarks
The interaction mediated by irreducible pion and gluon exchange between
constituent quarks is calculated and shown to have a strong tensor component,
which tends to cancel the pion exchange tensor interaction between quarks. Its
spin-spin component is somewhat weaker than the pion exchange spin-spin
interaction, while its central and spin-orbit components are small in
comparison to the corresponding single gluon exchange interactions. The
combination of the gluon exchange interaction with the single pion
exchange interaction and a weak gluon exchange interaction between constituent
quarks has the qualitative features required for understanding the hyperfine
splittings of the spectra of the nucleon and the resonances.Comment: LaTeX, 17 pages, 5 Postscript figure
Chiral soliton models, large N_c consistency and the Theta^+ exotic baryon
Predictions for a light collective baryon state (with strangeness
+1) based on the collective quantization of chiral soliton models are shown to
be inconsistent with large QCD. The lightest strangeness +1 state to
emerge from the analysis has an excitation energy which at large scales
as while collective quantization is legitimate only for excitations
which go to zero as . This inconsistency strongly suggests that
predictions for properties based on collective quantization of
chiral solitons are not valid.Comment: 5 pages, 1 figure. This is the version to be published; minor typos
have been corrected and a reference adde
- âŠ