427 research outputs found
The Nuclear Physics of Hyperfine Structure in Hydrogenic Atoms
The theory of QED corrections to hyperfine structure in light hydrogenic
atoms and ions has recently advanced to the point that the uncertainty of these
corrections is much smaller than 1 part per million (ppm), while the
experiments are even more accurate. The difference of the experimental results
and the corresponding QED theory is due to nuclear effects, which are primarily
the result of the finite nuclear charge and magnetization distributions. This
difference varies from tens to hundreds of ppm. We have calculated the dominant
nuclear component of the 1s hyperfine interval for deuterium, tritium and
singly ionized helium, using a unified approach with modern second-generation
potentials. The calculated nuclear corrections are within 3% of the
experimental values for deuterium and tritium, but are roughly 20% discrepant
for helium. The nuclear corrections for the trinucleon systems can be
qualitatively understood by invoking SU(4) symmetry.Comment: 12 pages, 1 figure, latex - submitted to Physics Letters
A Finite-Volume Version of Aizenman-Higuchi Theorem for the 2d Ising Model
In the late 1970s, in two celebrated papers, Aizenman and Higuchi
independently established that all infinite-volume Gibbs measures of the
two-dimensional ferromagnetic nearest-neighbor Ising model are convex
combinations of the two pure phases. We present here a new approach to this
result, with a number of advantages: (i) We obtain an optimal finite-volume,
quantitative analogue (implying the classical claim); (ii) the scheme of our
proof seems more natural and provides a better picture of the underlying
phenomenon; (iii) this new approach might be applicable to systems for which
the classical method fails.Comment: A couple of typos corrected. To appear in Probab. Theory Relat.
Field
The reciprocal relation between children’s attachment representations and their cognitive ability
This study explores reciprocal relations between children’s attachment representations and their cognitive ability. Previous literature has mainly focused on the prediction of cognitive abilities from attachment, rarely on the reverse prediction. This was explored in the current research. Attachment representations were assessed with the Attachment Story Completion Task (Bretherton, Ridgeway, & Cassidy, 1990); the IQ was measured with the WPPSI-III (Wechsler, 2004). Data were collected twice, at a two-year interval, from about 400 preschoolers. Reasoning IQ was found to influence the development of secure attachment representations, while attachment security and disorganization influenced later verbal IQ. The implications of the findings for both clinical and research purposes are discussed in the light of the interactions between cognitive abilities and attachment representations
Expansion for Excited Baryons
We derive consistency conditions which constrain the possible form of the
strong couplings of the excited baryons to the pions. The consistency
conditions follow from requiring the pion-excited baryon scattering amplitudes
to satisfy the large-N_c Witten counting rules and are analogous to consistency
conditions used by Dashen, Jenkins and Manohar and others for s-wave baryons.
The consistency conditions are explicitly solved, giving the most general
allowed form of the strong vertices for excited baryons in the large-N_c limit.
We show that the solutions to the large-N_c consistency conditions coincide
with the predictions of the nonrelativistic quark model for these states,
extending the results previously obtained for the s-wave baryons. The 1/N_c
corrections to these predictions are studied in the quark model with arbitrary
number of colors N_c.Comment: 56 pages, REVTeX; one new Appendix added containing a discussion of
the results in the language of quark operator
Negative Parity 70-plet Baryon Masses in the 1/Nc Expansion
The masses of the negative parity SU(6) 70-plet baryons are analyzed in the
1/Nc expansion to order 1/Nc and to first order in SU(3) breaking. At this
level of precision there are twenty predictions. Among them there are the well
known Gell-Mann Okubo and equal spacing relations, and four new relations
involving SU(3) breaking splittings in different SU(3) multiplets. Although the
breaking of SU(6) symmetry occurs at zeroth order in 1/Nc, it turns out to be
small. The dominant source of the breaking is the hyperfine interaction which
is of order 1/Nc. The spin-orbit interaction, of zeroth order in 1/Nc, is
entirely fixed by the splitting between the singlet states Lambda(1405) and
Lambda(1520), and the spin-orbit puzzle is solved by the presence of other
zeroth order operators involving flavor exchange.Comment: 31 pages, 3 figure
Probing Lorentz and CPT violation with space-based experiments
Space-based experiments offer sensitivity to numerous unmeasured effects
involving Lorentz and CPT violation. We provide a classification of clock
sensitivities and present explicit expressions for time variations arising in
such experiments from nonzero coefficients in the Lorentz- and CPT-violating
Standard-Model Extension.Comment: 15 page
Lorentz and CPT Violation in Neutrinos
A general formalism is presented for violations of Lorentz and CPT symmetry
in the neutrino sector. The effective hamiltonian for neutrino propagation in
the presence of Lorentz and CPT violation is derived, and its properties are
studied. Possible definitive signals in existing and future
neutrino-oscillation experiments are discussed. Among the predictions are
direction-dependent effects, including neutrino-antineutrino mixing, sidereal
and annual variations, and compass asymmetries. Other consequences of Lorentz
and CPT violation involve unconventional energy dependences in oscillation
lengths and mixing angles. A variety of simple models both with and without
neutrino masses are developed to illustrate key physical effects. The
attainable sensitivities to coefficients for Lorentz violation in the
Standard-Model Extension are estimated for various types of experiments. Many
experiments have potential sensitivity to Planck-suppressed effects, comparable
to the best tests in other sectors. The lack of existing experimental
constraints, the wide range of available coefficient space, and the variety of
novel effects imply that some or perhaps even all of the existing data on
neutrino oscillations might be due to Lorentz and CPT violation.Comment: 25 pages REVTe
Recommended from our members
Junior staffing changes and the temporal ecology of adverse incidents in acute psychiatric wards
Aim. This paper reports an examination of the relationship between adverse incident rates, the arrival of new junior staff on wards, and days of the week on acute psychiatric wards.
Background. Incidents of violence, absconding and self-harm in acute inpatient services pose risks to patients and staff. Previous research suggests that the arrival of inexperienced new staff may trigger more adverse incidents. Findings on the relationship between incidents and the weekly routine are inconsistent.
Method. A retrospective analysis was conducted of formally reported incident rates, records of nursing student allocations and junior doctor rotation patterns, using Poisson Regression. Variance between days of the week was explored using contingency table analysis. The data covered 30 months on 17 psychiatric wards, and were collected in 2002–2004.
Findings. The arrival of new and inexperienced staff on the wards was not associated with increases in adverse incident rates. Most types of incidents were less frequent at weekends and midweek. Incident rates were unchanged on ward-round days, but increased rates were found on the days before and after ward rounds.
Conclusion. Increased patient tension is associated with raised incident rates. It may be possible to reduce incident rates by moderating stimulation in the environment and by mobilizing support for patients during critical periods
Operator Analysis of L=1 Baryon Masses in Large N_c QCD
We consider in detail the mass operator analysis for the nonstrange L=1
excited baryons in large N_c QCD. We present a straightforward procedure for
constructing the large N_c baryon wavefunctions, and provide complete analytic
expressions for the matrix elements of all the independent isosinglet mass
operators. We discuss the relationship between the old-fashioned operator
analyses based on nonrelativistic SU(6) symmetry and the modern large N_c
approach, which has a firmer theoretical foundation. We then suggest a possible
dynamical interpretation for the subset of operators preferred strongly by the
data.Comment: 36 pages LaTe
A resonant-term-based model including a nascent disk, precession, and oblateness: application to GJ 876
Investigations of two resonant planets orbiting a star or two resonant
satellites orbiting a planet often rely on a few resonant and secular terms in
order to obtain a representative quantitative description of the system's
dynamical evolution. We present a semianalytic model which traces the orbital
evolution of any two resonant bodies in a first- through fourth-order
eccentricity or inclination-based resonance dominated by the resonant and
secular arguments of the user's choosing. By considering the variation of
libration width with different orbital parameters, we identify regions of phase
space which give rise to different resonant ''depths,'' and propose methods to
model libration profiles. We apply the model to the GJ 876 extrasolar planetary
system, quantify the relative importance of the relevant resonant and secular
contributions, and thereby assess the goodness of the common approximation of
representing the system by just the presumably dominant terms. We highlight the
danger in using ''order'' as the metric for accuracy in the orbital solution by
revealing the unnatural libration centers produced by the second-order, but not
first-order, solution, and by demonstrating that the true orbital solution lies
somewhere ''in-between'' the third- and fourth-order solutions. We also present
formulas used to incorporate perturbations from central-body oblateness and
precession, and a protoplanetary or protosatellite thin disk with gaps, into a
resonant system. We quantify these contributions to the GJ 876 system, and
thereby highlight the conditions which must exist for multi-planet exosystems
to be significantly influenced by such factors. We find that massive enough
disks may convert resonant libration into circulation; such disk-induced
signatures may provide constraints for future studies of exoplanet systems.Comment: 39 pages of body text, 21 figures, 5 tables, 1 appendix, accepted for
publication in Celestial Mechanics and Dynamical Astronom
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