5,687 research outputs found

### Compositeness Effects in the Anomalous Weak-Magnetic Moment of Leptons

We investigate the effects induced by excited leptons, at the one-loop level,
in the anomalous magnetic and weak-magnetic form factors of the leptons. Using
a general effective Lagrangian approach to describe the couplings of the
excited leptons, we compute their contributions to the weak-magnetic moment of
the $\tau$ lepton, which can be measured on the $Z$ peak, and we compare it
with the contributions to $g_\mu - 2$, measured at low energies.Comment: Latex File using Rev Tex. 16 pages 5 .eps figure

### Standard Model: An Introduction

We present a primer on the Standard Model of the electroweak interaction.
Emphasis is given to the historical aspects of the theory's formulation. The
radiative corrections to the Standard Model are presented and its predictions
for the electroweak parameters are compared with the precise experimental data
obtained at the Z pole. Finally, we make some remarks on the perspectives for
the discovery of the Higgs boson, the most important challenge of the Standard
Model.Comment: 101 pages, 14 figures, To be published in "Particle and Fields",
Proceedings of the X J. A. Swieca Summer School (World Scientific, Singapore,
2000

### Fermion Helicity Flip in Weak Gravitational Fields

The helicity flip of a spin-${\textstyle \frac{1}{2}}$ Dirac particle
interacting gravitationally with a scalar field is analyzed in the context of
linearized quantum gravity. It is shown that massive fermions may have their
helicity flipped by gravity, in opposition to massless fermions which preserve
their helicity.Comment: RevTeX 3.0, 8 pages, 3 figures (available upon request), Preprint
IFT-P.013/9

### New Higgs Interactions in ZZ\gamma and Z\gamma\gamma Production

The effect of new operators that only modify the bosonic couplings of the
Higgs boson, without altering the WW\gamma or WWZ three-point functions, are
examined in the e+e- -> ZZ\gamma and Z\gamma\gamma processes. We analyse the
constraints on these interactions that can be imposed by the LEP II collider at
CERN and at the Next Linear Collider.Comment: 7 pages, RevTeX, 3 postscript figure

### A new correlator in quantum spin chains

We propose a new correlator in one-dimensional quantum spin chains, the
$s-$Emptiness Formation Probability ($s-$EFP). This is a natural generalization
of the Emptiness Formation Probability (EFP), which is the probability that the
first $n$ spins of the chain are all aligned downwards. In the $s-$EFP we let
the spins in question be separated by $s$ sites. The usual EFP corresponds to
the special case when $s=1$, and taking $s>1$ allows us to quantify non-local
correlations. We express the $s-$EFP for the anisotropic XY model in a
transverse magnetic field, a system with both critical and non-critical
regimes, in terms of a Toeplitz determinant. For the isotropic XY model we find
that the magnetic field induces an interesting length scale.Comment: 6 pages, 1 figur

### Bounds on Contact Interactions from LEP1 Data and the High-$Q^2$ HERA Events

A contact four-fermion interaction between light quarks and electrons has been evoked as a possible explanation for the excess of events observed by HERA at high-$Q^2$. We explore the 1-loop effects of such interaction in limit of the effective scale. Our results are able to discard some of the contact interactions as possible explanation for the HERA events

### Detecting Large Concept Extensions for Conceptual Analysis

When performing a conceptual analysis of a concept, philosophers are
interested in all forms of expression of a concept in a text---be it direct or
indirect, explicit or implicit. In this paper, we experiment with topic-based
methods of automating the detection of concept expressions in order to
facilitate philosophical conceptual analysis. We propose six methods based on
LDA, and evaluate them on a new corpus of court decision that we had annotated
by experts and non-experts. Our results indicate that these methods can yield
important improvements over the keyword heuristic, which is often used as a
concept detection heuristic in many contexts. While more work remains to be
done, this indicates that detecting concepts through topics can serve as a
general-purpose method for at least some forms of concept expression that are
not captured using naive keyword approaches

### Supersymmetric Higgs pair discovery prospects at hadron colliders

We study the potential of hadron colliders in the search for the pair
production of neutral Higgs bosons in the framework of the Minimal
Supersymmetric Standard Model. Using analytical expressions for the relevant
amplitudes, we perform a detailed signal and background analysis, working out
efficient kinematical cuts for the extraction of the signal. The important role
of squark loop contributions to the signal is emphasised. If the signal is
sufficiently enhanced by these contributions, it could even be observable at
the next run of the upgraded Tevatron collider in the near future. At the LHC
the pair production of light and heavy Higgs bosons might be detectable
simultaneously.Comment: 5 pages, hep99, 6 figures; Presented at the International Europhysics
Conference on High Energy Physics, Tampere, Finland, 15-21 July 199

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