2,628 research outputs found
Extrapolation of K to \pi\pi decay amplitude
We examine the uncertainties involved in the off-mass-shell extrapolation of
the decay amplitude with emphasis on those aspects that
have so far been overlooked or ignored. Among them are initial-state
interactions, choice of the extrapolated kaon field, and the relation between
the asymptotic behavior and the zeros of the decay amplitude. In the inelastic
region the phase of the decay amplitude cannot be determined by strong
interaction alone and even its asymptotic value cannot be deduced from
experiment. More a fundamental issue is intrinsic nonuniqueness of off-shell
values of hadronic matrix elements in general. Though we are hampered with
complexity of intermediate-energy meson interactions, we attempt to obtain a
quantitative idea of the uncertainties due to the inelastic region and find
that they can be much larger than more optimistic views portray.Comment: 16 pages with 5 eps figures in REVTE
Kaon photoproduction on the nucleon: Contributions of kaon-hyperon final states to the magnetic moment of the nucleon
By using the Gerasimov-Drell-Hearn (GDH) sum rule and an isobaric model of
kaon photoproduction, we calculate contributions of kaon-hyperon final states
to the magnetic moment of the proton and the neutron. We find that the
contributions are small. The approximation of sigma_{TT'} by sigma_{T} clearly
overestimates the value of the GDH integral. We find a smaller upper bound for
the contributions of kaon-hyperon final states to the proton's anomalous
magnetic moment in kaon photoproduction, and a positive contribution for the
square of the neutron's magnetic moment.Comment: 6 pages, revtex, 1 postscript figure, to appear in Phys. Rev.
Type Ia Supernovae, Evolution, and the Cosmological Constant
We explore the possible role of evolution in the analysis of data on SNe Ia
at cosmological distances. First, using a variety of simple sleuthing
techniques, we find evidence that the properties of the high and low redshift
SNe Ia observed so far differ from one another. Next, we examine the effects of
including simple phenomenological models for evolution in the analysis. The
result is that cosmological models and evolution are highly degenerate with one
another, so that the incorporation of even very simple models for evolution
makes it virtually impossible to pin down the values of and
, the density parameters for nonrelativistic matter and for the
cosmological constant, respectively. Moreover, we show that if SNe Ia evolve
with time, but evolution is neglected in analyzing data, then, given enough SNe
Ia, the analysis hones in on values of and which
are incorrect. Using Bayesian methods, we show that the probability that the
cosmological constant is nonzero (rather than zero) is unchanged by the SNe Ia
data when one accounts for the possibility of evolution, provided that we do
not discriminate among open, closed and flat cosmologies a priori. The case for
nonzero cosmological constant is stronger if the Universe is presumed to be
flat, but still depends sensitively on the degree to which the peak
luminosities of SNe Ia evolve as a function of redshift. The estimated value of
, however, is only negligibly affected by accounting for possible
evolution.Comment: 45 pages, 15 figures; accepted for publication in The Astrophysical
Journal. Minor revisions and clarifications made including addition of recent
reference
Factorization of Fermion Doubles on the Lattice
We address the problem of the fermion species doubling on the Lattice. Our
strategy is to factorize the fermion doubles from the action. The mass term of
the Dirac-Wilson action is changed. In this case the extra roots which appear
in the action of free fermions in the moment representation are independent of
the mass and can be factorized from the fermion propagator. However the gauge
couplings suffer from the pathological ghost poles which are common to
non-local actions. This action can be used to find a solution of the Ginsparg
Wilson relation, which is cured from the non-local pathology. Finally we
compare this factorized action with solutions of The Ginsparg Wilson relation.
We find that the present is equivalent to the Zenkin action, and that is not
quite as local as the Neuberger action.Comment: 7 Latex Revtex pages, 4 ps figures. The paper was improoved due to
Comments received. It has a new section and several new reference
The Nucleon Spin Polarizability at Order ) in Chiral Perturbation Theory
We calculate the forward spin-dependent photon-nucleon Compton amplitude as a
function of photon energy at the next-to-leading () order in
chiral perturbation theory, from which we extract the contribution to nucleon
spin polarizability. The result shows a large correction to the leading order
contribution.Comment: 7 pages, latex, 2 figures included as .eps file
Is the ground state of Yang-Mills theory Coulombic?
We study trial states modelling the heavy quark-antiquark ground state in
SU(2) Yang-Mills theory. A state describing the flux tube between quarks as a
thin string of glue is found to be a poor description of the continuum ground
state; the infinitesimal thickness of the string leads to UV artifacts which
suppress the overlap with the ground state. Contrastingly, a state which
surrounds the quarks with non-abelian Coulomb fields is found to have a good
overlap with the ground state for all charge separations. In fact, the overlap
increases as the lattice regulator is removed. This opens up the possibility
that the Coulomb state is the true ground state in the continuum limit.Comment: 10 pages, 9 .eps figure
A Perturbative Construction of Lattice Chiral Fermions
We perform a renormalization group transformation to construct a lattice
theory of chiral fermions. The field variables of the continuum theory are
averaged over hypercubes to define lattice fields. Integrating out the
continuum variables in perturbation theory we derive a chirally invariant
effective action for the lattice fields. This is consistent with the
Nielsen-Niniomiya theorem because the effective action is nonlocal. We also
construct the axial current on the lattice and we show that the axial anomaly
of the continuum theory is reproduced in the Schwinger model. This shows that
chiral fermions can be regularized on the lattice.Comment: 8 pages, LaTe
The asymptotic behaviour of the vertex
The Bjorken-Johnson-Low theorem applied to the process provides us with a rather remarkable asymptotic behaviour for
the vertex. We compare our result with previous
QCD- inspired estimates and argue that the predicted behaviour is quite
consistent with the present data on hadronic decays and ensures the
matching of long- and short-distance radiative corrections to .Comment: 10 pages, latex, no figure
Gerasimov-Drell-Hearn Sum Rule and the Discrepancy between the New CLAS and SAPHIR Data
Contribution of the K^+\Lambda channel to the Gerasimov-Drell-Hearn (GDH) sum
rule has been calculated by using the models that fit the recent SAPHIR or CLAS
differential cross section data. It is shown that the two data sets yield quite
different contributions. Contribution of this channel to the forward spin
polarizability of the proton has been also calculated. It is also shown that
the inclusion of the recent CLAS C_x and C_z data in the fitting data base does
not significantly change the result of the present calculation. Results of the
fit, however, reveal the role of the S_{11}(1650), P_{11}(1710), P_{13}(1720),
and P_{13}(1900) resonances for the description of the C_x and C_z data. A
brief discussion on the importance of these resonances is given. Measurements
of the polarized total cross section \sigma_{TT'} by the CLAS, LEPS, and MAMI
collaborations are expected to verify this finding.Comment: 15 pages, 8 figure
Renormalization of Anisotropy and Glueball Masses on Tadpole Improved Lattice Gauge Action
The Numerical calculations for tadpole-improved U(1) lattice gauge theory in
three-dimensions on anisotropic lattices have been performed using standard
path integral Monte Carlo techniques. Using average plaquette tadpole
renormalization scheme, simulations were done with temporal lattice spacings
much smaller than the spatial ones and results were obtained for the string
tension, the renormalized anisotropy and scalar glueball masses. We find, by
comparing the `regular' and `sideways' potentials, that tadpole improvement
results in very little renormalization of the bare anisotropy and reduces the
discretization errors in the static quark potential and in the glueball masses.Comment: 6 pages, 6 figures. Accepted for publication in Eur. Phys. J.
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