26,895 research outputs found
Ab initio calculations of structures and stabilities of (NaI)_nNa+ and (CsI)_nCs+ cluster ions
Ab initio calculations using the Perturbed Ion model, with correlation
contributions included, are presented for nonstoichiometric (NaI)_nNa+ and
(CsI)_nCs+ (n=1-14) cluster ions. The ground state and several low-lying
isomers are identified and described. Rocksalt ground states are common and
appear at cluster sizes lower than in the corresponding neutral systems. The
most salient features of the measured mobilities seem to be explained by
arguments related to the changes of the compactness of the clusters as a
function of size. The stability of the cluster ions against evaporation of a
single alkali halide molecule shows variations that explain the enhanced
stabilities found experimentally for cluster sizes n=4, 6, 9, and 13. Finally,
the ionization energies and the orbital eigenvalue spectrum of two (NaI)_13Na+
isomers are calculated and shown to be a fingerprint of the structure.Comment: 8 pages plus 13 postscript figures, LaTeX. Accepted for publication
in Phys, Rev. B; minor changes including a more complete comparison to pair
potential result
Chiral low-energy constants from tau data
We analyze how the recent precise hadronic tau-decay data on the V-A spectral
function and general properties of QCD such as analyticity, the operator
product expansion and chiral perturbation theory (ChPT), can be used to improve
the knowledge of some of the low-energy constants of ChPT. In particular we
find the most precise values of L_{9,10} (or equivalently l_{5,6}) at order p^4
and p^6 and the first phenomenological determination of C_87 (c_50).Comment: Proceedings of the 6th International Workshop on Chiral Dynamics
(Bern, Switzerland, July 6-10, 2009). 9 pages, 3 figure
On the semiclassical mass of -kinks
One-loop mass shifts to the classical masses of stable kinks arising in a
massive non-linear -sigma model are computed. Ultraviolet
divergences are controlled using the heat kernel/zeta function regularization
method. A comparison between the results achieved from exact and
high-temperature asymptotic heat traces is analyzed in depth.Comment: RevTex file, 15 pages, 2 figures. Version to appear in Journal of
Physics
Time relaxation of interacting single--molecule magnets
We study the relaxation of interacting single--molecule magnets (SMMs) in
both spatially ordered and disordered systems. The tunneling window is assumed
to be, as in Fe8, much narrower than the dipolar field spread. We show that
relaxation in disordered systems differs qualitatively from relaxation in fully
occupied cubic and Fe_8 lattices. We also study how line shapes that develop in
''hole--digging'' experiments evolve with time t in these fully occupied
lattices. We show (1) that the dipolar field h scales as t^p in these hole line
shapes and show (2) how p varies with lattice structure. Line shapes are not,
in general, Lorentzian. More specifically, in the lower portion of the hole,
they behave as (h/t^p)^{(1/p)-1} if h is outside the tunnel window. This is in
agreement with experiment and with our own Monte Carlo results.Comment: 21 LaTeX pages, 6 eps figures. Submitted to PRB on 15 June 2005.
Accepted on 13 August 200
Cyclotrons as Drivers for Precision Neutrino Measurements
As we enter the age of precision measurement in neutrino physics, improved
flux sources are required. These must have a well-defined flavor content with
energies in ranges where backgrounds are low and cross section knowledge is
high. Very few sources of neutrinos can meet these requirements. However,
pion/muon and isotope decay-at-rest sources qualify. The ideal drivers for
decay-at-rest sources are cyclotron accelerators, which are compact and
relatively inexpensive. This paper describes a scheme to produce decay-at-rest
sources driven by such cyclotrons, developed within the DAEdALUS program.
Examples of the value of the high precision beams for pursuing Beyond Standard
Model interactions are reviewed. New results on a combined DAEdALUS--Hyper-K
search for CP-violation that achieve errors on the mixing matrix parameter of 4
degrees to 12 degrees are presented.Comment: This paper was invited by the journal Advances in High Energy Physics
for their upcoming special issue on "Neutrino Masses and Oscillations," which
will be published on the 100th anniversary of Pontecorvo's birt
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