8,053 research outputs found

### Coulomb effects in nucleon-deuteron polarization-transfer coefficients

Coulomb effects in the neutron-deuteron and proton-deuteron
polarization-transfer coefficients $K_y^{y'}$, $K_z^{x'}$, $K_y^{x'x'-y'y'}$
and $K_y^{z'z'}$ are studied at energies above the deuteron breakup threshold.
Theoretical predictions for these observables are evaluated in the framework of
the Kohn Variational Principle using correlated basis functions to expand the
three-nucleon scattering wave function. The two-nucleon Argonne $v_{18}$ and
the three-nucleon Urbana IX potentials are considered. In the proton-deuteron
case, the Coulomb interaction between the two protons is included explicitly
and the results are compared to the experimental data available at
$E_{lab}=10,19,22.7$ MeV. In the neutron-deuteron case, a comparison to a
recent measurement of $K_y^{y'}$ by Hempen {\sl et al.} at $E_{lab}=19$ MeV
evidences a contribution of the calculated Coulomb effects opposite to those
extracted from the experiment.Comment: 7 pages, 3 figure

### Electromagnetic transitions for A=3 nuclear systems

Recent advances in the study of pd radiative capture in a wide range of
center-of-mass energy below and above deuteron breakup threshold are presented
and discussed.Comment: Invited lead talk at the 19th European Conference on Few-Body
Problems in Physics, Groningen, The Netherlands, 8/23 - 8/27 2004, 5 pages, 4
figure

### Evolution in the iron abundance of the ICM

We present a Chandra analysis of the X-ray spectra of 56 clusters of galaxies
at $z>0.3$, which cover a temperature range of $3> kT > 15$ keV. Our analysis
is aimed at measuring the iron abundance in the ICM out to the highest redshift
probed to date. We find that the emission-weighted iron abundance measured
within $(0.15-0.3) R_{vir}$ in clusters below 5 keV is, on average, a factor of
$\sim2$ higher than in hotter clusters, following $Z(T)\simeq 0.88 T^{-0.47}
Z_\odot$, which confirms the trend seen in local samples. We made use of
combined spectral analysis performed over five redshift bins at $0.3> z > 1.3$
to estimate the average emission weighted iron abundance. We find a constant
average iron abundance $Z_{Fe}\simeq 0.25 Z_\odot$ as a function of redshift,
but only for clusters at $z>0.5$. The emission-weighted iron abundance is
significantly higher ($Z_{Fe}\simeq0.4 Z_\odot$) in the redshift range
$z\simeq0.3-0.5$, approaching the value measured locally in the inner $0.15
R_{vir}$ radii for a mix of cool-core and non cool-core clusters in the
redshift range $0.1<z<0.3$. The decrease in $Z_{Fe}$ with $z$ can be
parametrized by a power law of the form $\sim(1+z)^{-1.25}$. The observed
evolution implies that the average iron content of the ICM at the present epoch
is a factor of $\sim2$ larger than at $z\simeq 1.2$. We confirm that the ICM is
already significantly enriched ($Z_{Fe}\simeq0.25 Z_\odot$) at a look-back time
of 9 Gyr. Our data provide significant constraints on the time scales and
physical processes that drive the chemical enrichment of the ICM.Comment: 4 pages, 4 figures, to appear in the Proceedings of "The Extreme
Universe in the Suzaku Era", Dicember 2006, Kyoto (Japan

### Electromagnetic structure of A=2 and 3 nuclei and the nuclear current operator

Different models for conserved two- and three-body electromagnetic currents
are constructed from two- and three-nucleon interactions, using either
meson-exchange mechanisms or minimal substitution in the momentum dependence of
these interactions. The connection between these two different schemes is
elucidated. A number of low-energy electronuclear observables, including (i)
$np$ radiative capture at thermal neutron energies and deuteron
photodisintegration at low energies, (ii) $nd$ and $pd$ radiative capture
reactions, and (iii) isoscalar and isovector magnetic form factors of $^3$H and
$^3$He, are calculated in order to make a comparative study of these models for
the current operator. The realistic Argonne $v_{18}$ two-nucleon and Urbana IX
or Tucson-Melbourne three-nucleon interactions are taken as a case study. For
$A$=3 processes, the bound and continuum wave functions, both below and above
deuteron breakup threshold, are obtained with the correlated
hyperspherical-harmonics method. Three-body currents give small but significant
contributions to some of the polarization observables in the
$^2$H($p,\gamma$)$^3$He process and the $^2$H($n,\gamma$)$^3$H cross section at
thermal neutron energies. It is shown that the use of a current which did not
exactly satisfy current conservation with the two- and three-nucleon
interactions in the Hamiltonian was responsible for some of the discrepancies
reported in previous studies between the experimental and theoretical
polarization observables in $pd$ radiative capture.Comment: 48 pages, 25 figures, 4 tables, revtex4. Submitted to Phys. Rev.

### Chiral effective field theory predictions for muon capture on deuteron and 3He

The muon-capture reactions 2H(\mu^-,\nu_\mu)nn and 3He(\mu^-,\nu_\mu)3H are
studied with nuclear strong-interaction potentials and charge-changing weak
currents, derived in chiral effective field theory. The low-energy constants
(LEC's) c_D and c_E, present in the three-nucleon potential and (c_D)
axial-vector current, are constrained to reproduce the A=3 binding energies and
the triton Gamow-Teller matrix element. The vector weak current is related to
the isovector component of the electromagnetic current via the
conserved-vector-current constraint, and the two LEC's entering the contact
terms in the latter are constrained to reproduce the A=3 magnetic moments. The
muon capture rates on deuteron and 3He are predicted to be 399(3) sec^{-1} and
1494 (21) sec^{-1}, respectively, where the spread accounts for the cutoff
sensitivity as well as uncertainties in the LEC's and electroweak radiative
corrections. By comparing the calculated and precisely measured rates on 3He, a
value for the induced pseudoscalar form factor is obtained in good agreement
with the chiral perturbation theory prediction.Comment: 4 pages, 2 figures, revisited version accepted for publication on
Phys. Rev. Let

### Electrodisintegration of $^3$He below and above deuteron breakup threshold

Recent advances in the study of electrodisintegration of 3He are presented
and discussed. The pair-correlated hyperspherical harmonics method is used to
calculate the initial and final state wave functions, with a realistic
Hamiltonian consisting of the Argonne v18 two-nucleon and Urbana IX
three-nucleon interactions. The model for the nuclear current and charge
operators retains one- and many-body contributions. Particular attention is
made in the construction of the two-body current operators arising from the
momentum-dependent part of the two-nucleon interaction. Three-body current
operators are also included so that the full current operator is strictly
conserved. The present model for the nuclear current operator is tested
comparing theoretical predictions and experimental data of pd radiative capture
cross section and spin observables.Comment: 5 pages, 5 figures, submitted to Eur. Phys. J.

### Explanation, Vindication, and the Role of Normative Theory in Legal Scholarship

I find Yuracko\u27s inquiry quite intriguing, but I have doubts about the central thesis. My aim, in the discussion that follows, is to press Yuracko on two fronts, one methodological, the other substantive. As concerns substance, I shall say a bit as this commentary progresses about why Yuracko would need much more support to make good on her claim that an implicit perfectionism explains decisional antidiscrimination law. My chief interest, however, lies with certain questions as to what methodology she means to follow in her efforts to develop a more complete theory of employment discrimination law. Yuracko\u27s approach is one that seems to me to be quite common in legal scholarship, at least in legal scholarship with more theoretical ambitions. For reasons that I shall offer shortly, I find the approach puzzling and problematic. I want to be clear, however, that in pressing methodological questions, my aim is not so much to pose a problem for Yuracko, who understandably adopts what seems the usual approach of scholars in her field. Rather, I mean to point out how and why, in my view, legal theorists need to pay far greater attention to methodology than they generally have. As for Yuracko, I greatly admire her efforts, in this article and elsewhere, to tackle complex questions about the theoretical unity and underpinnings of employment discrimination law. For that very reason, I want to urge her to adopt an approach better suited to exploring theoretical issues and to supporting her most central ideas

### What is the Meaning of Marriage ?

There is legitimacy to the conservative approach that goes beyond looking at the impact on people\u27s welfare. This article responds to Professor Arneson by offering a different framework to investigate the underlying theoretical values behind appropriate state policies regarding private relationships. Neither the prioritarian consequentialist, nor the lockean libertarian captures the other side of the marriage debate, that is, the traditional ideal. The state’s interest in fostering the conservative, traditional marriage relationships begins to emerge through the author\u27s assumptions that Kantian ethics is correct, that social stability depends on others—inviolate value, and that through love one can apprehend the value of another. Therefore, the author concludes that to the extent that same-sex marriage helps to encourage these assumptions—that is, encouraging a regard for the value of others—the state also has compelling reasons to extend the boundaries of legal marriage to encompass same sex-unions

- …