73 research outputs found
Compton scattering on the proton, neutron, and deuteron in chiral perturbation theory to O(Q^4)
We study Compton scattering in systems with A=1 and 2 using chiral
perturbation theory up to fourth order. For the proton we fit the two
undetermined parameters in the O(Q^4) p amplitude of McGovern to
experimental data in the region MeV, obtaining a
chi^2/d.o.f. of 133/113. This yields a model-independent extraction of proton
polarizabilities based solely on low-energy data: alpha_p=12.1 +/- 1.1 (stat.)
+/- 0.5 (theory) and beta_p=3.4 +/- 1.1 (stat.) +/- 0.1 (theory), both in units
of 10^{-4} fm^3. We also compute Compton scattering on deuterium to O(Q^4). The
d amplitude is a sum of one- and two-nucleon mechanisms, and contains
two undetermined parameters, which are related to the isoscalar nucleon
polarizabilities. We fit data points from three recent d scattering
experiments with a chi^2/d.o.f.=26.6/20, and find alpha_N=13.0 +/- 1.9 (stat.)
+3.9/-1.5 (theory) and a beta_N that is consistent with zero within sizeable
error bars.Comment: 57 pages, 16 figures. Substantial changes. Correction of errors in
deuteron calculation results in different values for isoscalar
polarizabilities. Results for the proton are unaffected. Text modified to
reflect this change, and also to clarify various point
Unitarized Chiral Perturbation Theory in a finite volume: scalar meson sector
We develop a scheme for the extraction of the properties of the scalar mesons
f0(600), f0(980), and a0(980) from lattice QCD data. This scheme is based on a
two-channel chiral unitary approach with fully relativistic propagators in a
finite volume. In order to discuss the feasibility of finding the mass and
width of the scalar resonances, we analyze synthetic lattice data with a fixed
error assigned, and show that the framework can be indeed used for an accurate
determination of resonance pole positions in the multi-channel scattering.Comment: 15 pages, 17 figure
Scalar mesons moving in a finite volume and the role of partial wave mixing
Phase shifts and resonance parameters can be obtained from finite-volume
lattice spectra for interacting pairs of particles, moving with nonzero total
momentum. We present a simple derivation of the method that is subsequently
applied to obtain the pi pi and pi K phase shifts in the sectors with total
isospin I=0 and I=1/2, respectively. Considering different total momenta, one
obtains extra data points for a given volume that allow for a very efficient
extraction of the resonance parameters in the infinite-volume limit.
Corrections due to the mixing of partial waves are provided. We expect that our
results will help to optimize the strategies in lattice simulations, which aim
at an accurate determination of the scattering and resonance properties.Comment: 19 pages, 12 figure
Insecticide use and breast cancer risk among farmers’ wives in the agricultural health study
BACKGROUND: Some epidemiologic and laboratory studies suggest that insecticides are related to increased breast cancer risk, but the evidence is inconsistent. Women engaged in agricultural work or who reside in agricultural areas may experience appreciable exposures to a wide range of insecticides. OBJECTIVE: We examined associations between insecticide use and breast cancer incidence among wives of pesticide applicators (farmers) in the prospective Agricultural Health Study. METHODS: Farmers and their wives provided information on insecticide use, demographics, and reproductive history at enrollment in 1993–1997 and in 5-y follow-up interviews. Cancer incidence was determined via cancer registries. Among 30,594 wives with no history of breast cancer before enrollment, we examined breast cancer risk in relation to the women’s and their husbands’ insecticide use using Cox proportional hazards regression to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (CIs). RESULTS: During an average 14.7-y follow-up, 39% of the women reported ever using insecticides, and 1,081 were diagnosed with breast cancer. Although ever use of insecticides overall was not associated with breast cancer risk, risk was elevated among women who had ever used the organophosphates chlorpyrifos [HR = 1:4 (95% CI: 1.0, 2.0)] or terbufos [HR = 1:5 (95% CI: 1.0, 2.1)], with nonsignificantly increased risks for coumaphos [HR = 1:5 (95% CI: 0.9, 2.5)] and heptachlor [HR = 1:5 (95% CI: 0.7, 2.9)]. Risk in relation to the wives’ use was associated primarily with premenopausal breast cancer. We found little evidence of differential risk by tumor estrogen receptor status. Among women who did not apply pesticides, the husband’s use of fonofos was associated with elevated risk, although no exposure–response trend was observed. CONCLUSION: Use of several organophosphate insecticides was associated with elevated breast cancer risk. However, associations for the women’s and husbands’ use of these insecticides showed limited concordance. Ongoing cohort follow-up may help clarify the relationship, if any, between individual insecticide exposures and breast cancer risk
Predictive powers of chiral perturbation theory in Compton scattering off protons
We study low-energy nucleon Compton scattering in the framework of baryon
chiral perturbation theory (BPT) with pion, nucleon, and (1232)
degrees of freedom, up to and including the next-to-next-to-leading order
(NNLO). We include the effects of order , and , with
MeV the -resonance excitation energy. These are
all "predictive" powers in the sense that no unknown low-energy constants enter
until at least one order higher (i.e, ). Estimating the theoretical
uncertainty on the basis of natural size for effects, we find that
uncertainty of such a NNLO result is comparable to the uncertainty of the
present experimental data for low-energy Compton scattering. We find an
excellent agreement with the experimental cross section data up to at least the
pion-production threshold. Nevertheless, for the proton's magnetic
polarizability we obtain a value of fm, in
significant disagreement with the current PDG value. Unlike the previous
PT studies of Compton scattering, we perform the calculations in a
manifestly Lorentz-covariant fashion, refraining from the heavy-baryon (HB)
expansion. The difference between the lowest order HBPT and BPT
results for polarizabilities is found to be appreciable. We discuss the chiral
behavior of proton polarizabilities in both HBPT and BPT with the
hope to confront it with lattice QCD calculations in a near future. In studying
some of the polarized observables, we identify the regime where their naive
low-energy expansion begins to break down, thus addressing the forthcoming
precision measurements at the HIGS facility.Comment: 24 pages, 9 figures, RevTeX4, revised version published in EPJ
Drum vortons in high density QCD
Recently it was shown that high density QCD supports of number of topological
defects. In particular, there are U(1)_Y strings that arise due to K^0
condensation that occurs when the strange quark mass is relatively large. The
unique feature of these strings is that they possess a nonzero K^+ condensate
that is trapped on the core. In the following we will show that these strings
(with nontrivial core structure) can form closed loops with conserved charge
and currents trapped on the string worldsheet. The presence of conserved
charges allows these topological defects, called vortons, to carry angular
momentum, which makes them classically stable objects. We also give arguments
demonstrating that vortons carry angular momentum very efficiently (in terms of
energy per unit angular momentum) such that they might be the important degrees
of freedom in the cores of neutron stars.Comment: 11 pages, accepted for publication in Physical Review
The hyperon-nucleon interaction: conventional versus effective field theory approach
Hyperon-nucleon interactions are presented that are derived either in the
conventional meson-exchange picture or within leading order chiral effective
field theory. The chiral potential consists of one-pseudoscalar-meson exchanges
and non-derivative four-baryon contact terms. With regard to meson-exchange
hyperon-nucleon models we focus on the new potential of the Juelich group,
whose most salient feature is that the contributions in the scalar--isoscalar
(\sigma) and vector--isovector (\rho) exchange channels are constrained by a
microscopic model of correlated \pi\pi and KKbar exchange.Comment: 28 pages, 8 figures, submitted to Lecture Notes in Physic
SO(2,1) conformal anomaly: Beyond contact interactions
The existence of anomalous symmetry-breaking solutions of the SO(2,1)
commutator algebra is explicitly extended beyond the case of scale-invariant
contact interactions. In particular, the failure of the conservation laws of
the dilation and special conformal charges is displayed for the two-dimensional
inverse square potential. As a consequence, this anomaly appears to be a
generic feature of conformal quantum mechanics and not merely an artifact of
contact interactions. Moreover, a renormalization procedure traces the
emergence of this conformal anomaly to the ultraviolet sector of the theory,
within which lies the apparent singularity.Comment: 11 pages. A few typos corrected in the final versio
Universal Correlations in Pion-less EFT with the Resonating Group Model: Three and Four Nucleons
The Effective Field Theory "without pions" at next-to-leading order is used
to analyze universal bound state and scattering properties of the 3- and
4-nucleon system. Results of a variety of phase shift equivalent nuclear
potentials are presented for bound state properties of 3H and 4He, and for the
singlet S-wave 3He-neutron scattering length a_0(3He-n). The calculations are
performed with the Refined Resonating Group Method and include a full treatment
of the Coulomb interaction and the leading-order 3-nucleon interaction. The
results compare favorably with data and values from AV18(+UIX) model
calculations. A new correlation between a_0(3He-n) and the 3H binding energy is
found. Furthermore, we confirm at next-to-leading order the correlations,
already found at leading-order, between the 3H binding energy and the 3H charge
radius, and the Tjon line. With the 3H binding energy as input, we get
predictions of the Effective Field Theory "without pions" at next-to-leading
order for the root mean square charge radius of 3H of (1.6\pm 0.2) fm, for the
4He binding energy of (28\pm 2.5) MeV, and for Re(a_0(3He-n)) of (7.5\pm
0.6)fm. Including the Coulomb interaction, the splitting in binding energy
between 3H and 3He is found to be (0.66\pm 0.03) MeV. The discrepancy to data
of (0.10\mp 0.03) MeV is model independently attributed to higher order charge
independence breaking interactions. We also demonstrate that different results
for the same observable stem from higher order effects, and carefully assess
that numerical uncertainties are negligible. Our results demonstrate the
convergence and usefulness of the pion-less theory at next-to-leading order in
the 4He channel. We conclude that no 4-nucleon interaction is needed to
renormalize the theory at next-to-leading order in the 4-nucleon sector.Comment: 24 pages revtex4, including 8 figures as .eps files embedded with
includegraphicx, leading-order results added, calculations include the LO
three-nucleon interaction explicitly, comment on Wigner bound added, minor
modification
Downgraded curriculum? An analysis of knowledge in new curricula in Scotland and New Zealand
The development, since 2000, of new National Curricula across the Anglophone world signals a number of policy trends, including: a move from the explicit specification of content towards a more generic, skills-based approach; a greater emphasis on the centrality of the learner; and [ostensibly] greater autonomy for teachers in developing the curriculum in school. These policy shifts have attracted some criticism, especially from social realist writers, who claim that the new curricula downgrade knowledge. This paper offers a contribution to this debate; an empirically-based analysis of two new curricula, New Zealand’s Curriculum Framework and Scotland’s Curriculum for Excellence. We conclude that, while these curricula continue to accord considerable importance to knowledge in their statements of policy intent, the social realist critique is at least partially justified, since both curricula are characterised by a lack of coherence and mixed messages about the place of knowledge
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