1,616 research outputs found
Lowest Order Effective Field Theory for the weak interaction
The interaction, responsible for the decay of
hypernuclei, is studied by means of an Effective Field Theory where the long
range physics is described by pion and kaon exchange mechanisms, and its short
range counterpart is obtained from the most general non-derivative local
four-fermion interaction. We show that, including the Lowest Order Parity
Conserving contact terms, allows us to reproduce the total decay rates for
, and with
a reasonable value of , while in order to get a prediction for
the Parity Violating (PV) asymmetry compatible with experiments, we have to
include the Lowest Order PV contact pieces.Comment: 3 pages, no figures. Contribution to the 17th International IUPAP
Conference on Few-body Problems in Physics, June 5-10, 2003 Durham, North
Carolina, USA. Uses espcrc1.st
Neutrino Physics
The basic concepts of neutrino physics are presented at a level appropriate
for integration into elementary courses on quantum mechanics and/or modern
physics.Comment: Prepared for the American Journal of Physics; 50 pages; 11 figures
(10 included); late
Extracting Electric Polarizabilities from Lattice QCD
Charged and neutral, pion and kaon electric polarizabilities are extracted
from lattice QCD using an ensemble of anisotropic gauge configurations with
dynamical clover fermions. We utilize classical background fields to access the
polarizabilities from two-point correlation functions. Uniform background
fields are achieved by quantizing the electric field strength with the proper
treatment of boundary flux. These external fields, however, are implemented
only in the valence quark sector. A novel method to extract charge particle
polarizabilities is successfully demonstrated for the first time.Comment: 17 pages, 6 figures, a few clarifications added, published versio
Polaron self-trapping in a honeycomb net
Small polaron behavior in a two dimensional honeycomb net is studied by
applying the strong coupling perturbative method to the Holstein molecular
crystal model. We find that small optical polarons can be mobile also if the
electrons are strongly coupled to the lattice. Before the polarons localize and
become very heavy, there is infact a window of {\it e-ph} couplings in which
the polarons are small and have masses of order times the bare
band mass according to the value of the adiabaticity parameter. The 2D
honeycomb net favors the mobility of small optical polarons in comparison with
the square lattice.Comment: 6 pages, 3 figures, to appear in J.Phys.:Condensed Matter {PACS:
63.10.+a, 63.20.Dj, 71.38.+i
Exotic Meson Decay Widths using Lattice QCD
A decay width calculation for a hybrid exotic meson h, with JPC=1-+, is
presented for the channel h->pi+a1. This quenched lattice QCD simulation
employs Luescher's finite box method. Operators coupling to the h and pi+a1
states are used at various levels of smearing and fuzzing, and at four quark
masses. Eigenvalues of the corresponding correlation matrices yield energy
spectra that determine scattering phase shifts for a discrete set of relative
pi+a1 momenta. Although the phase shift data is sparse, fits to a Breit-Wigner
model are attempted, resulting in a decay width of about 60 MeV when averaged
over two lattice sizes.Comment: 9 pages, 8 figures, RevTex4, minor change to Fig.
Resonances in weak nonleptonic Omega^- decay
We examine the importance of J^P = 1/2^+, 1/2^- resonances for weak
nonleptonic Omega^- decays within the framework of chiral perturbation theory.
The spin-1/2 resonances are included into an effective theory and tree
contributions to the Omega^- decays are calculated. We find significant
contributions to the decay amplitudes and satisfactory agreement with
experiment. This confirms and extends previous results wherein such spin-1/2
resonances were included in nonleptonic and radiative-nonleptonic hyperon
decays.Comment: 12 pages, 2 figure
Resonances in radiative hyperon decays
The importance of resonances for the radiative hyperon decays is examined in
the framework of chiral perturbation theory. Low lying baryon resonances are
included into the effective theory and tree contributions to these decays are
calculated. We find significant contributions to both the parity-conserving and
parity-violating decay amplitudes and a large negative value for the asymmetry
parameter in polarized Sigma^+ -> p gamma is found, in agreement with the
experimental result alpha(p Sigma^+) = -0.76 +/- 0.08.Comment: 14 pages, 2 figure
On Quantum Groups in the Hubbard Model with Phonons
The correct Hamiltonian for an extended Hubbard model with quantum group
symmetry as introduced by A. Montorsi and M. Rasetti is derived for a
D-dimensional lattice. It is shown that the superconducting SUq(2) holds as a
true quantum symmetry only for D = 1 and that terms of higher order in the
fermionic operators in addition to phonons are required for a quantum symmetric
hamiltonian. The condition for quantum symmetry is "half filling" and there is
no local electron-phonon coupling. A discussion of Quantum symmetries in
general is given in a formalism that should be readily accessible to non
Hopf-algebraists.Comment: latex, 17 page
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