335 research outputs found

### Nucleons Properties at Finite Lattice Spacing in Chiral Perturbation Theory

Properties of the proton and neutron are studied in partially-quenched chiral
perturbation theory at finite lattice spacing. Masses, magnetic moments, the
matrix elements of isovector twist-2 operators and axial-vector currents are
examined at the one-loop level in a double expansion in the light-quark masses
and the lattice spacing. This work will be useful in extrapolating the results
of simulations using Wilson valence and sea quarks, as well as simulations
using Wilson sea quarks and Ginsparg-Wilson valence quarks, to the continuum.Comment: 16 pages LaTe

### Negative Parity 70-plet Baryon Masses in the 1/Nc Expansion

The masses of the negative parity SU(6) 70-plet baryons are analyzed in the
1/Nc expansion to order 1/Nc and to first order in SU(3) breaking. At this
level of precision there are twenty predictions. Among them there are the well
known Gell-Mann Okubo and equal spacing relations, and four new relations
involving SU(3) breaking splittings in different SU(3) multiplets. Although the
breaking of SU(6) symmetry occurs at zeroth order in 1/Nc, it turns out to be
small. The dominant source of the breaking is the hyperfine interaction which
is of order 1/Nc. The spin-orbit interaction, of zeroth order in 1/Nc, is
entirely fixed by the splitting between the singlet states Lambda(1405) and
Lambda(1520), and the spin-orbit puzzle is solved by the presence of other
zeroth order operators involving flavor exchange.Comment: 31 pages, 3 figure

### Long distance regularization in chiral perturbation theory with decuplet

We investigate the use of long distance regularization in SU(3) baryon chiral
perturbation theory with decuplet fields. The one-loop decuplet contributions
to the octet baryon masses, axial couplings, S-wave nonleptonic hyperon decays
and magnetic moments are evaluated in a chirally consistent fashion by
employing a cutoff to implement long distance regularization. The convergence
of the chiral expansions of these quantities is improved compared to the
dimensionally regularized version which indicates that the propagation of
Goldstone bosons over distances smaller than a typical hadronic size, which is
beyond the regime of chiral perturbation theory but included by dimensional
regularization, is removed by use of a cutoff.Comment: 31 page

### Decay Modes of Narrow Molecular Resonances

prĂ©sentĂ© par Sandrine Courtin (DRS-IPHC)The heavy-ion radiative capture reactions $^{12}C(^{12}C,\gamma)^{24}Mg$ and $^{12}C(^{16}O,\gamma)^{28}Si$ have been performed on and off resonance at TRIUMF using the Dragon separator and its associated BGO array. The decay of the studied narrow resonances has been shown to proceed predominantly through quasi-bound doorway states which cluster and deformed configurations would have a large overlap with the entry resonance states

### Generation of Primordial Cosmological Perturbations from Statistical Mechanical Models

The initial conditions describing seed fluctuations for the formation of
structure in standard cosmological models, i.e.the Harrison-Zeldovich
distribution, have very characteristic ``super-homogeneous'' properties: they
are statistically translation invariant, isotropic, and the variance of the
mass fluctuations in a region of volume V grows slower than V. We discuss the
geometrical construction of distributions of points in ${\bf R}^3$ with similar
properties encountered in tiling and in statistical physics, e.g. the Gibbs
distribution of a one-component system of charged particles in a uniform
background (OCP). Modifications of the OCP can produce equilibrium correlations
of the kind assumed in the cosmological context. We then describe how such
systems can be used for the generation of initial conditions in gravitational
$N$-body simulations.Comment: 7 pages, 3 figures, final version with minor modifications, to appear
in PR

- â€¦