8,801 research outputs found

### Dirac's hole theory versus quantum field theory

Dirac's hole theory and quantum field theory are usually considered
equivalent to each other. For models of a certain type, however, the
equivalence may not hold as we discuss in this Letter. This problem is closely
related to the validity of the Pauli principle in intermediate states of
perturbation theory.Comment: No figure

### Two definitions of the electric polarizability of a bound system in relativistic quantum theory

For the electric polarizability of a bound system in relativistic quantum
theory, there are two definitions that have appeared in the literature. They
differ depending on whether or not the vacuum background is included in the
system. A recent confusion in this connection is clarified

### Validity of Feynman's prescription of disregarding the Pauli principle in intermediate states

Regarding the Pauli principle in quantum field theory and in many-body
quantum mechanics, Feynman advocated that Pauli's exclusion principle can be
completely ignored in intermediate states of perturbation theory. He observed
that all virtual processes (of the same order) that violate the Pauli principle
cancel out. Feynman accordingly introduced a prescription, which is to
disregard the Pauli principle in all intermediate processes. This ingeneous
trick is of crucial importance in the Feynman diagram technique. We show,
however, an example in which Feynman's prescription fails. This casts doubts on
the general validity of Feynman's prescription

### Top quark forward-backward asymmetry from the $3-3-1$ model

The forward-backward asymmetry $A_{FB}$ 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 $2\sigma$ 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
$\sigma_{tt}$ and invariant mass distribution $M_{tt}$ 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 $SU(3)_C \otimes SU(3)_L \otimes
U (1)_X$ model (3-3-1 model) that predicts the existence of a new neutral gauge
boson, called $Z^\prime$. 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 $A_{FB}$ for top quark
pair production for two ranges of $Z^\prime$ 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

### Bounds on $Z^\prime$ from 3-3-1 model at the LHC energies

The Large Hadron Collider will restart with higher energy and luminosity in
2015. This achievement opens the possibility of discovering new phenomena
hardly described by the Standard Model, that is based on two neutral gauge
bosons: the photon and the $Z$. This perspective imposes a deep and systematic
study of models that predicts the existence of new neutral gauge bosons. One of
such models is based on the gauge group $SU(3)_C \times SU(3)_L \times U(1)_N$
called 3-3-1 model for short.
In this paper we perform a study with $Z^\prime$ predicted in two versions of
the 3-3-1 model and compare the signature of this resonance in each model
version. By considering the present and future LHC energy regimes, we obtain
some distributions and the total cross section for the process $p + p
\longrightarrow \ell^{+} + \ell^{-} + X$. Additionally, we derive lower bounds
on $Z^\prime$ mass from the latest LHC results. Finally we analyze the LHC
potential for discovering this neutral gauge boson at 14 TeV center-of-mass
energy.Comment: 6 pages, 9 figures, 2 table

### Some remarks on Dirac's hole theory versus quantum field theory

Dirac's hole theory and quantum field theory are generally considered to be
equivalent to each other. However, it has recently been shown that this is not
necessarily the case. In this article we will discuss the reason for this lack
of equivalence and suggest a possible solution.Comment: Correction to title and other minor changes to reflect the version to
be published in the Canadian Journal of Physic

- â€¦