2,803 research outputs found
Radium single-ion optical clock
We explore the potential of the electric quadrupole transitions
7s\,^2S_{1/2} - 6d\,^2D_{3/2}, 6d\,^2D_{5/2} in radium isotopes as
single-ion optical frequency standards. The frequency shifts of the clock
transitions due to external fields and the corresponding uncertainties are
calculated. Several competitive Ra candidates with 223 - 229 are
identified. In particular, we show that the transition
7s\,^2S_{1/2}\,(F=2,m_F=0) - 6d\,^2D_{3/2}\,(F=0,m_F=0) at 828 nm in
Ra, with no linear Zeeman and electric quadrupole shifts, stands
out as a relatively simple case, which could be exploited as a compact, robust,
and low-cost atomic clock operating at a fractional frequency uncertainty of
. With more experimental effort, the Ra clocks
could be pushed to a projected performance reaching the level.Comment: 20 pages, 1 figur
CNET and APT : a comparison of two methods for measuring mental representations underlying activity-travel choices
This paper presents and compares the potential of online versions of two interview techniques (APT and CNET) which have been developed for measuring mental representations underlying activity-travel choices. The comparison is based on the results of a first online survey administered in the Netherlands. Resulting mental representations for a simple activity-travel task are analysed and compared. Conclusions for further investigations are drawn
Atomic Electric Dipole Moments: The Schiff Theorem and Its Corrections
Searches for the permanent electric dipole moments (EDMs) of diamagnetic
atoms provide powerful probes of CP-violating hadronic and semileptonic
interactions. The theoretical interpretation of such experiments, however,
requires careful implementation of a well-known theorem by Schiff that implies
a vanishing net EDM for an atom built entirely from point-like, nonrelativistic
constituents that interact only electrostatically. Any experimental observation
of a nonzero atomic EDM would result from corrections to the point-like,
nonrelativistic, electrostatic assumption. We reformulate Schiff's theorem at
the operator level and delineate the electronic and nuclear operators whose
atomic matrix elements generate corrections to "Schiff screening". We obtain a
form for the operator responsible for the leading correction associated with
finite nuclear size -- the so-called "Schiff moment" operator -- and observe
that it differs from the corresponding operator used in previous Schiff moment
computations. We show that the more general Schiff moment operator reduces to
the previously employed operator only under certain approximations that are not
generally justified. We also identify other corrections to Schiff screening
that may not be included properly in previous theoretical treatments. We
discuss practical considerations for obtaining a complete computation of
corrections to Schiff screening in atomic EDM calculations.Comment: 31 pages, 2 figures, typeset by REVTe
Electric Dipole Moments of Light Nuclei From Chiral Effective Field Theory
We set up the framework for the calculation of electric dipole moments (EDMs)
of light nuclei using the systematic expansion provided by chiral effective
field theory (EFT). We take into account parity (P) and time-reversal (T)
violation which, at the quark-gluon level, originates from the QCD vacuum angle
and dimension-six operators capturing physics beyond the Standard Model. We
argue that EDMs of light nuclei can be expressed in terms of six low-energy
constants that appear in the P- and T-violating nuclear potential and electric
current. As examples, we calculate the EDMs of the deuteron, the triton, and
3He in leading order in the EFT expansion
Thermalization of an impurity cloud in a Bose-Einstein condensate
We study the thermalization dynamics of an impurity cloud inside a
Bose-Einstein condensate at finite temperature, introducing a suitable
Boltzmann equation. Some values of the temperature and of the initial impurity
energy are considered. We find that, below the Landau critical velocity, the
macroscopic population of the initial impurity state reduces its depletion
rate. For sufficiently high velocities the opposite effect occurs. For
appropriate parameters the collisions cool the condensate. The maximum cooling
per impurity atom is obtained with multiple collisions.Comment: 4 pages 6 figure
Pion and photon couplings of N* resonances from scattering on the proton
Results of a relativistic model for pion- and photon-induced reactions on the
proton are presented. The model is crossing symmetric and gauge invariant. The
nucleon resonances P_11 (1440), P_11 (1710), D_13 (1520), S_11 (1535), S_11
(1650), P_33 (1232), P_33 (1600), S_31 (1620), and D_33 (1700) have been
included explicitly in the calculation. Unitarity within the channel space \pi
N + \gamma N below the two-pion production threshold has been achieved by using
the K-matrix approach. Strong and electromagnetic coupling parameters of the N*
resonances have been determined from a fit to the pion-nucleon phase shifts,
pion-photoproduction multipoles and Compton-scattering cross sections. The
model is shown to describe simultaneously most of the available data. Results
for the electric and magnetic polarizabilities of the nucleon are presented.Comment: 12 pages, 3 figures, Revte
- …