1,047 research outputs found
The Lambda_Q-Lambda_Q Potential
Lattice QCD simulations of the potential between two baryons, each containing
a heavy quark and two light quarks, such as the Lambda_Q-Lambda_Q potential,
will provide insight into the nucleon-nucleon interaction. As one-pion exchange
does not contribute to the Lambda_Q-Lambda_Q potential, the long-distance
behavior is dominated by physics that contributes to the intermediate-range
attraction between two nucleons. We compute the leading long-distance
contributions to the Lambda_Q-Lambda_Q potential in QCD and in
partially-quenched QCD in the low-energy effective field theory.Comment: 10 pages LaTeX, 3 eps figs, 3 ps fig
Bridging over p-wave pi-production and weak processes in few-nucleon systems with chiral perturbation theory
I study an aspect of chiral perturbation theory (\chi PT) which enables one
to ``bridge'' different reactions. That is, an operator fixed in one of the
reactions can then be used to predict the other. For this purpose, I calculate
the partial wave amplitude for the p-wave pion production (pp\to pn\pi^+) using
the pion production operator from the lowest and the next nonvanishing orders.
The operator includes a contact operator whose coupling has been fixed using a
matrix element of a low-energy weak process (pp\to de^+\nu_e). I find that this
operator does not reproduce the partial wave amplitude extracted from
experimental data, showing that the bridging over the reactions with
significantly different kinematics is not necessarily successful. I study the
dependence of the amplitude on the various inputs such as the NN potential, the
\pi N\Delta coupling, and the cutoff. I argue the importance of a higher order
calculation. In order to gain an insight into a higher order calculation, I add
a higher order counter term to the operator used above, and fit the couplings
to both the low-energy weak process and the pion production. The energy
dependence of the partial wave amplitude for the pion production is described
by the operator consistently with the data. However, I find a result which
tells us to be careful about the convergence of the chiral expansion for the
pp\to pn\pi^+ reaction.Comment: 30 pages, 13 figures, figures changed, compacted tex
Pions in the Pionless Effective Field Theory
We show that processes involving pions that remain very near their mass-shell
can be reliably computed in the pionless effective field theory, with the pion
integrated in as a heavy field. As an application, we compute the pion-deuteron
scattering amplitude near threshold to next-to-leading order in the momentum
expansion. This amplitude is formally dominated by an infrared logarithm of the
form log(gamma/mpi), where gamma is the deuteron binding momentum, and mpi is
the mass of the pion. The coefficient of this logarithm is determined by the
S-wave pion-nucleon scattering lengths.Comment: 10 pages LaTeX, 4 eps fig
High Energy Theorems at Large-N
Sum rules for products of two, three and four QCD currents are derived using
chiral symmetry at infinite momentum in the large-N limit. These exact
relations among meson decay constants, axialvector couplings and masses
determine the asymptotic behavior of an infinite number of QCD correlators. The
familiar spectral function sum rules for products of two QCD currents are among
the relations derived. With this precise knowledge of asymptotic behavior, an
infinite number of large-N QCD correlators can be constructed using dispersion
relations. A detailed derivation is given of the exact large-N pion vector form
factor and forward pion-pion scattering amplitudes.Comment: 34 pages TeX and mtexsis.tex, 10 figures (uses epsf
A Conjecture about Hadrons
We conjecture that in the chiral limit of QCD the spectrum of hadrons is
comprised of decoupled, reducible chiral multiplets. A simple rule is developed
which identifies the chiral representations filled out by the ground-state
hadrons. Our arguments are based on the algebraic structure of superconvergence
relations derived by Weinberg from the high-energy behavior of pion-hadron
scattering amplitudes.Comment: 15 pages LaTe
Nucleon-Nucleon Scattering From Fully-Dynamical Lattice QCD
We present results of the first fully-dynamical lattice QCD determination of
nucleon-nucleon scattering lengths in the 1S0 channel and 3S1-3D1 coupled
channels. The calculations are performed with domain-wall valence quarks on the
MILC staggered configurations with lattice spacing of b=0.125 fm in the
isospin-symmetric limit, and in the absence of electromagnetic interactions.Comment: 4 pages, 4 figure
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