870 research outputs found
Compton scattering from the proton: An analysis using the delta expansion up to N3LO
We report on a chiral effective field theory calculation of Compton
scattering from the proton. Our calculation includes pions, nucleons, and the
Delta(1232) as explicit degrees of freedom. It uses the "delta expansion", and
so implements the hierarchy of scales m_pi < M_Delta-M_N < Lambda_chi. In this
expansion the power counting in the vicinity of the Delta peak changes, and
resummation of the loop graphs associated with the Delta width is indicated.
We have computed the nucleon Compton amplitude in the delta expansion up to
N3LO for photon energies of the order of m_pi. This is the first order at which
the proton Compton scattering amplitudes receive contributions from contact
operators which encode contributions to the spin-independent polarisabilities
from states with energies of the order of Lambda_chi. We fit the coefficients
of these two operators to the experimental proton Compton data that has been
taken in the relevant photon-energy domain, and are in a position to extract
new results for the proton polarisabilities alpha and beta.Comment: 6 pages. Proceeding of Sixth International Workshop on Chiral
Dynamics, Bern (Switzerland), 6th -- 10th July 2009. To be published in Po
Using EFT to analyze low-energy Compton scattering from protons and light nuclei
We discuss the application of an effective field theory (EFT) which
incorporates the chiral symmetry of QCD to Compton scattering from the proton
and deuteron. We describe the chiral EFT analysis of the proton Compton
scattering database presented in our recent review (arXiv:1203.6834), which
gives: alpha^{(p)}=10.5 +/- 0.5(stat) +/- 0.8(theory); beta^{(p)}= 2.7 +/-
0.5(stat) +/- 0.8(theory), for the electric and magnetic dipole polarizability
of the proton. We also summarize the chiral EFT analysis of the world data on
coherent Compton scattering from deuterium presented in arXiv:1203.6834. That
yields: alpha^{(s)}=10.5 +/- 2.0(stat) +/- 0.8(theory); beta^{(s)}=3.6 +/-
1.0(stat) +/- 0.8(theory).Comment: 5 pages. Invited talk, presented by Phillips at the 11th Conference
on the Intersections of Nuclear and Particle Physics (CIPANP 2012), St.
Petersburg, FL, May 201
Nucleon Polarisabilities at and Beyond Physical Pion Masses
We examine the results of Chiral Effective Field Theory (EFT) for the
scalar- and spin-dipole polarisabilities of the proton and neutron, both for
the physical pion mass and as a function of . This provides chiral
extrapolations for lattice-QCD polarisability computations. We include both the
leading and sub-leading effects of the nucleon's pion cloud, as well as the
leading ones of the resonance and its pion cloud. The analytic
results are complete at NLO in the -counting for pion masses close
to the physical value, and at leading order for pion masses similar to the
Delta-nucleon mass splitting. In order to quantify the truncation error of our
predictions and fits as \% degree-of-belief intervals, we use a Bayesian
procedure recently adapted to EFT expansions. At the physical point, our
predictions for the spin polarisabilities are, within respective errors, in
good agreement with alternative extractions using experiments and
dispersion-relation theory. At larger pion masses we find that the chiral
expansion of all polarisabilities becomes intrinsically unreliable as
approaches about MeV---as has already been seen in other observables.
EFT also predicts a substantial isospin splitting above the physical
point for both the electric and magnetic scalar polarisabilities; and we
speculate on the impact this has on the stability of nucleons. Our results
agree very well with emerging lattice computations in the realm where EFT
converges. Curiously, for the central values of some of our predictions, this
agreement persists to much higher pion masses. We speculate on whether this
might be more than a fortuitous coincidence.Comment: 39 pages LaTeX2e (pdflatex) including 12 figures as 16 .pdf files
using includegraphics. Version approved for publication in EPJA includes
modifications, clarifications and removal of typographical errors in
refereeing and publication proces
Compton scattering from the proton in an effective field theory with explicit Delta degrees of freedom
We analyse the proton Compton-scattering differential cross section for
photon energies up to 325 MeV using Chiral Effective Field Theory and extract
new values for the electric and magnetic polarisabilities of the proton. Our
EFT treatment builds in the key physics in two different regimes: photon
energies around the pion mass ("low energy") and the higher energies where the
Delta(1232) resonance plays a key role. The Compton amplitude is complete at
N4L0, O(e^2 delta^4), in the low-energy region, and at NLO, O(e^2 delta^0), in
the resonance region. Throughout, the Delta-pole graphs are dressed with pi-N
loops and gamma-N-Delta vertex corrections. A statistically consistent database
of proton Compton experiments is used to constrain the free parameters in our
amplitude: the M1 gamma-N-Delta transition strength b_1 (which is fixed in the
resonance region) and the polarisabilities alpha and beta (which are fixed from
data below 170 MeV). In order to obtain a reasonable fit we find it necessary
to add the spin polarisability gammaM1 as a free parameter, even though it is,
strictly speaking, predicted in chiral EFT at the order to which we work. We
show that the fit is consistent with the Baldin sum rule, and then use that sum
rule to constrain alpha+beta. In this way we obtain
alpha=[10.65+/-0.35(stat})+/-0.2(Baldin)+/-0.3(theory)]10^{-4} fm^3, and beta
=[3.15-/+0.35(stat)-/+0.2(Baldin)-/+0.3(theory)]10^{-4} fm^3, with chi^2 =
113.2 for 135 degrees of freedom. A detailed rationale for the theoretical
uncertainties assigned to this result is provided.Comment: 36 pages, 15 figures Version 2 is shortened for publication; version
1 is more self-contained. Results section unchange
Comprehensive Study of Observables in Compton Scattering on the Nucleon
We present an analysis of observables in Compton scattering on the
proton. Cross sections, asymmetries with polarised beam and/or targets, and
polarisation-transfer observables are investigated for energies up to the
resonance to determine their sensitivity to the proton's dipole
scalar and spin polarisabilities. The Chiral Effective Field Theory Compton
amplitude we use is complete at NLO, , for photon
energies , and so has an accuracy of a few per cent there. At
photon energies in the resonance region it is complete at NLO,
, and so its accuracy there is about \%. We find
that for energies from pion-production threshold to about ,
multiple asymmetries have significant sensitivity to presently ill-determined
combinations of proton spin polarisabilities. We also argue that the broad
outcomes of this analysis will be replicated in complementary theoretical
approaches, e.g., dispersion relations. Finally, we show that below the
pion-production threshold, observables suffice to reconstruct the Compton
amplitude, and above it are required. Although not necessary for
polarisability extractions, this opens the possibility to perform "complete"
Compton-scattering experiments. An interactive Mathematica notebook, including
results for the neutron, is available from [email protected] .Comment: 75 pages LaTeX2e (pdflatex) including 37 figures as .pdf files using
includegraphics; minor corrections. Text-identical to published version but
including the Online Supplement. Higher-resolution figures are available at
http://home.gwu.edu/~hgrie/Compton/one-N-comprehensive-observables-delta4.v2.0.high-resolution-figures.tg
Compton Scattering and Nucleon Polarisabilities in Chiral EFT: Update and Future
We review theoretical progress and prospects for determining the nucleon's
static dipole polarisabilities from Compton scattering on few-nucleon targets,
including new values; see Refs. [1-5] for details and a more thorough
bibliography.Comment: 6 pages LaTeX2e (pdflatex) including 11 figures as .pdf files. First
presented by Griesshammer at the 12th Conference on the Intersections of
Nuclear and Particle Physics CIPANP2015, 19-24 May 2015, Vail (CO), USA;
updated for 22nd International Spin Symposium (SPIN 2016), University of
Illinois, Urbana (USA), 26-30 September 2016. Corrected 2 figures, added
clarifying tex
What different variants of chiral EFT predict for the proton Compton differential cross section - and why
We compare the predictions of different variants of chiral effective field
theory for the gamma-p elastic scattering differential cross section. We pay
particular attention to the role of pion loops, and the impact that a
heavy-baryon expansion has on the behavior of those loops. We also correct
erroneous results for these loops that were published in Phys. Rev. C 67,
055202 (2003) [ arXiv:nucl-th/0212024 ].Comment: 4 pages, 2 figure
Using effective field theory to analyse low-energy Compton scattering data from protons and light nuclei
Compton scattering provides important insight into the structure of the
nucleon. For photons up to about 300 MeV, it is parameterised by six dynamical
dipole polarisabilities which characterise the response of the nucleon to a
monochromatic photon of fixed frequency and multipolarity. Their zero-energy
limit yields the well-known static electric and magnetic dipole
polarisabilities \alpha and \beta, and the four dipole spin polarisabilities.
Chiral Effective Field Theory (ChiEFT) describes nucleon, deuteron and 3-He
Compton scattering, using consistent nuclear currents, rescattering and wave
functions. It can thus also be used to extract useful information on the
neutron amplitude from Compton scattering on light nuclei. We summarise past
work in ChiEFT on all of these reactions and compare with other theoretical
approaches. We also discuss all proton experiments up to about 400 MeV, as well
as the three modern elastic deuteron data sets, paying particular attention to
precision and accuracy of each set. Constraining the Delta(1232) parameters
from the resonance region, we then perform new fits to the proton data up to
omega(lab)=170 MeV, and a new fit to the deuteron data. After checking in each
case that a two-parameter fit is compatible with the respective Baldin sum
rules, we obtain, using the sum-rule constraints in a one-parameter fit,
\alpha=10.7\pm0.3(stat)\pm0.2(Baldin)\pm0.8(theory),
\beta=3.1\mp0.3(stat)\pm0.2(Baldin)\pm0.8(theory), for the proton
polarisabilities, and \alpha =10.9\pm 0.9(stat)\pm0.2(Baldin)\pm0.8(theory),
\beta =3.6\mp 0.9(stat)\pm0.2(Baldin)\pm0.8(theory), for the isoscalar
polarisabilities, each in units of 10^(-4) fm^3. We discuss plans for polarised
Compton scattering, their promise as tools to access spin polarisabilities, and
other future avenues for theoretical and experimental investigation.Comment: 82 pages LaTeX2e including 24 figures as .eps file embedded with
includegraphicx; review for Prog. Part Nucl Phys. Final version identical to
published areticle; spelling and grammar correcte
Non-degree Recital: Maria Phillips, soprano
Maria Phillips is a Senior pursuing a Bachelor of Music in Music Education. Ms. Phillips studies voice with Leah Partridge.https://digitalcommons.kennesaw.edu/musicprograms/1798/thumbnail.jp
Enlightenment, education and entertainment : a study of the Chautauqua movement in Kentucky.
The Chautauqua movement has been called culture under canvas and the university of the people. What began as a training camp for Sunday School teachers on the shores of Lake Chautauqua in western New York State in the 1870\u27s, grew and spread over the midwest for the next fifty years. There were some other permanent Chautauqua establishments, but none seemed to last as long as the original. What did last were traveling tent shows called Chautauquas that brought enlightenment, education, and entertainment to thousands of people over the summer months until the movement died because of technological advancements such as talking movies, radio, and the automobile. The circuit Chautauquas were quite well known in Iowa, Kansas, Missouri, and Illinois, but newspaper accounts show that they also spread into many states of the Ohio Valley and the South. Although there was a standard Chautauqua pattern that evolved over the years, each state and even each town added its own particular flavor to the pattern. Chautauqua in Kentucky was similar to Chautauqua in other states, and while it was not a major cultural phenomenon, it did have an impact on people who lived in rural and mountainous regions and thus were isolated from metropolitan areas and all that they had to offer. As the various circuits traveled throughout Kentucky from June through September, lecturers brought ideas, world news, and culture to those who might not otherwise have been exposed to such informative refinement. The Chautauquas faded away and as a cultural influence had little lasting impact on Kentuckians, except in individual memories. However, one cannot say that the Chautauquas were, therefore, unimportant; they were significant but primarily only during the times they were popular
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