6,390 research outputs found
Unitary coupled-channels model for three-mesons decays of heavy mesons
A unitary coupled-channels model is presented for investigating the decays of
heavy mesons and excited meson states into three light pseudoscalar mesons. The
model accounts for the three-mesons final state interactions in the decay
processes, as required by both the three-body and two-body unitarity
conditions. In the absence of the Z-diagram mechanisms that are necessary
consequences of the three-body unitarity, our decay amplitudes are reduced to a
form similar to those used in the so-called isobar-model analysis. We apply our
coupled-channels model to the three-pions decays of a1(1260), pi2(1670),
pi2(2100), and D0 mesons, and show that the Z-diagram mechanisms can contribute
to the calculated Dalitz plot distributions by as much as 30% in magnitudes in
the regions where f0(600), rho(770), and f2(1270) dominate the distributions.
Also, by fitting to the same Dalitz plot distributions, we demonstrate that the
decay amplitudes obtained with the unitary model and the isobar model can be
rather different, particularly in the phase that plays a crucial role in
extracting the CKM CP-violating phase from the data of B meson decays. Our
results indicate that the commonly used isobar model analysis must be extended
to account for the final state interactions required by the three-body
unitarity to reanalyze the three-mesons decays of heavy mesons, thereby
exploring hybrid or exotic mesons, and signatures of physics beyond the
standard model.Comment: 32 pages, 10 figures. Version to appear in PR
Testing Magnetic Star Formation Theory
We report here observations of the Zeeman effect in the 18-cm lines of OH in
the envelope regions surrounding four molecular cloud cores toward which
detections of B(LOS) have been achieved in the same lines, and evaluate the
ratio of mass to magnetic flux, M/Phi, between the cloud core and envelope.
This relative M/Phi measurement reduces uncertainties in previous studies, such
as the angle between B and the line of sight and the value of [OH/H]. Our
result is that for all four clouds, the ratios R of the core to the envelope
values of M/Phi are less than 1. Stated another way, the ratios R' of the core
to the total cloud M/Phi are less than 1. The extreme case or idealized (no
turbulence) ambipolar diffusion theory of core formation requires the ratio of
the central to total M/Phi to be approximately equal to the inverse of the
original subcritical M/Phi, or R' > 1. The probability that all four of our
clouds have R' > 1 is 3 x 10^{-7}; our results are therefore significantly in
contradiction with the hypothesis that these four cores were formed by
ambipolar diffuson. Highly super-Alfvenic turbulent simulations yield a wide
range of relative M/Phi, but favor a ratio R < 1, as we observe. Our experiment
is limited to four clouds, and we can only directly test the predictions of the
extreme-case "idealized" models of ambipolar-diffusion driven star formation
that have a regular magnetic field morphology. Nonetheless, our experimental
results are not consistent with the "idealized" strong field, ambipolar
diffusion theory of star formation.Comment: 30 pages, 6 figures; paper revised after journal review, now accepted
by Ap
Determination of the strange nucleon form factors
The strange contribution to the electric and magnetic form factors of the
nucleon is determined at a range of discrete values of up to
GeV. This is done by combining recent lattice QCD results for the
electromagnetic form factors of the octet baryons with experimental
determinations of those quantities. The most precise result is a small negative
value for the strange magnetic moment: . At
larger values of both the electric and magnetic form factors are
consistent with zero to within -sigma
Charge Symmetry Violation in the Electromagnetic Form Factors of the Proton
Experimental tests of QCD through its predictions for the strange-quark
content of the proton have been drastically restricted by our lack of knowledge
of the violation of charge symmetry (CSV). We find unexpectedly tiny CSV in the
proton's electromagnetic form factors by performing the first extraction of
these quantities based on an analysis of lattice QCD data. The resulting values
are an order of magnitude smaller than current bounds on proton strangeness
from parity violating electron-proton scattering experiments. This result paves
the way for a new generation of experimental measurements of the proton's
strange form factors to challenge the predictions of QCD
Octet baryon electromagnetic form factors in nuclear medium
We study the octet baryon electromagnetic form factors in nuclear matter
using the covariant spectator quark model extended to the nuclear matter
regime. The parameters of the model in vacuum are fixed by the study of the
octet baryon electromagnetic form factors. In nuclear matter the changes in
hadron properties are calculated by including the relevant hadron masses and
the modification of the pion-baryon coupling constants calculated in the
quark-meson coupling model. In nuclear matter the magnetic form factors of the
octet baryons are enhanced in the low region, while the electric form
factors show a more rapid variation with . The results are compared with
the modification of the bound proton electromagnetic form factors observed at
Jefferson Lab. In addition, the corresponding changes for the bound neutron are
predicted.Comment: Version accepted for publication in J.Phys. G. Few changes. 40 pages,
14 figures and 8 table
Ferromagnetic Luttinger Liquids
We study weak itinerant ferromagnetism in one-dimensional Fermi systems using
perturbation theory and bosonization. We find that longitudinal spin
fluctuations propagate ballistically with velocity v_m << v_F, where v_F is the
Fermi velocity. This leads to a large anomalous dimension in the spin-channel
and strong algebraic singularities in the single-particle spectral function and
in the transverse structure factor for momentum transfers q ~ 2 Delta/v_F,
where 2 Delta is the exchange splitting.Comment: 4 pages, 3 figure
Implementing an apparent-horizon finder in three dimensions
Locating apparent horizons is not only important for a complete understanding
of numerically generated spacetimes, but it may also be a crucial component of
the technique for evolving black-hole spacetimes accurately. A scheme proposed
by Libson et al., based on expanding the location of the apparent horizon in
terms of symmetric trace-free tensors, seems very promising for use with
three-dimensional numerical data sets. In this paper, we generalize this scheme
and perform a number of code tests to fully calibrate its behavior in
black-hole spacetimes similar to those we expect to encounter in solving the
binary black-hole coalescence problem. An important aspect of the
generalization is that we can compute the symmetric trace-free tensor expansion
to any order. This enables us to determine how far we must carry the expansion
to achieve results of a desired accuracy. To accomplish this generalization, we
describe a new and very convenient set of recurrence relations which apply to
symmetric trace-free tensors.Comment: 14 pages (RevTeX 3.0 with 3 figures
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