6,021 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.
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
Stationary Black Holes in a Generalized Three-Dimensional Theory of Gravity
We consider a generalized three-dimensional theory of gravity which is
specified by two fields, the graviton and the dilaton, and one parameter. This
theory contains, as particular cases, three-dimensional General Relativity and
three-dimensional String Theory. Stationary black hole solutions are generated
from the static ones using a simple coordinate transformation. The stationary
black holes solutions thus obtained are locally equivalent to the corresponding
static ones, but globally distinct. The mass and angular momentum of the
stationary black hole solutions are computed using an extension of the Regge
and Teitelboim formalism. The causal structure of the black holes is described.Comment: 12 pages, Late
Explicit Soliton for the Laplacian Co-Flow on a Solvmanifold
We apply the general Ansatz in geometric flows on homogeneous spaces proposed
by Jorge Lauret for the Laplacian co-flow of invariant -structures on a
Lie group, finding an explicit soliton on a particular almost Abelian
-manifold.Comment: Minor corrections, proof's Lemma 4.1 modified. To appear in the S\~ao
Paulo Journal of mathematical scienc
Analytical r-mode solution with gravitational radiation reaction force
We present and discuss the analytical r-mode solution to the linearized
hydrodynamic equations of a slowly rotating, Newtonian, barotropic,
non-magnetized, perfect-fluid star in which the gravitational radiation
reaction force is present.Comment: 3 pages, in Proceedings of the 5th International Workshop "New Worlds
in Astroparticle Physics", Faro, Portugal, 8-10 January 200
Top quark forward-backward asymmetry from the model
The forward-backward asymmetry in top quark pair production,
measured at the Tevatron, is probably related to the contribution of new
particles. The Tevatron result is more than a deviation from the
standard model prediction and motivates the application of alternative models
introducing new states.
However, as the standard model predictions for the total cross section
and invariant mass distribution for this process are in
good agreement with experiments, any alternative model must reproduce these
predictions. These models can be placed into two categories: One introduces the
s-channel exchange of new vector bosons with chiral couplings to the light
quarks and to the top quark and another relies on the t-channel exchange of
particles with large flavor-violating couplings in the quark sector. In this
work we employ a model which introduces both s- and t-channel nonstandard
contributions for the top quark pair production in proton antiproton
collisions. We use the minimal version of the model (3-3-1 model) that predicts the existence of a new neutral gauge
boson, called . This gauge boson has both flavor-changing couplings
to up and top quarks and chiral coupling to the light quarks and to the top
quark. This very peculiar model coupling can correct the for top quark
pair production for two ranges of mass while leading to cross
section and invariant mass distribution quite similar to the standard model
ones. This result reinforces the role of the 3-3-1 model for any new physics
effect.Comment: 12 pages, 4 figures, 2 table
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