14,135 research outputs found
Two loops calculation in chiral perturbation theory and the unitarization program of current algebra
In this paper we compare two loop Chiral Perturbation Theory (ChPT)
calculation of pion-pion scattering with the unitarity second order correction
to the current algebra soft-pion theorem. It is shown that both methods lead to
the same analytic structure for the scattering amplitude.Comment: 13 pages, Revtex 3.0, no figures, submitted to Phys. Lett.
Families of nested completely regular codes and distance-regular graphs
In this paper infinite families of linear binary nested completely regular
codes are constructed. They have covering radius equal to or ,
and are -th parts, for of binary (respectively,
extended binary) Hamming codes of length (respectively, ), where
. In the usual way, i.e., as coset graphs, infinite families of embedded
distance-regular coset graphs of diameter equal to or are
constructed. In some cases, the constructed codes are also completely
transitive codes and the corresponding coset graphs are distance-transitive
Symmetry breaking patterns of the 3-3-1 model at finite temperature
We consider the minimal version of an extension of the standard electroweak
model based on the gauge symmetry (the
3-3-1 model). We analyze the most general potential constructed from three
scalars in the triplet representation of , whose neutral components
develop nonzero vacuum expectation values, giving mass for all the model's
massive particles. {}For different choices of parameters, we obtain the
particle spectrum for the two symmetry breaking scales: one where the group is broken down to and a lower scale
similar to the standard model one. Within the considerations used, we show that
the model encodes two first-order phase transitions, respecting the pattern of
symmetry restoration. The last transition, corresponding to the standard
electroweak one, is found to be very weak first-order, most likely turning
second-order or a crossover in practice. However, the first transition in this
model can be strongly first-order, which might happen at a temperature not too
high above the second one. We determine the respective critical temperatures
for symmetry restoration for the model.Comment: 13 pages, 8 figures. Minor changes to match published versio
Unitarized pion-nucleon scattering amplitude from inverse amplitude method
In a recent work on low energy pion-nucleon scattering, instead of using
chiral perturbation theory (ChPT) amplitude, we started from a pion-nucleon
{\it soft-pion} result and used elastic unitarity directly as a dynamical
constraint to construct first-order unitarity corrected amplitudes. The
resulting amplitudes are crossing symmetric but, as the ChPT ones, satisfy only
approximate unitarity relation. In the present work, we reconsider our approach
and we apply the inverse amplitude method (IAM) in order to access the energy
resonance region. We present the resulting S- and P-wave phase shifts that are
shown to be in qualitative agreement with experimental data.Comment: 6 pages, 3 figure
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