1,750 research outputs found
A Global Fit to Extended Oblique Parameters
The STU formalism of Peskin and Takeuchi is an elegant method for encoding
the measurable effects of new physics which couples to light fermions
dominantly through its effects on electroweak boson propagation. However, this
formalism cannot handle the case where the scale of new physics is not much
larger than the weak scale. In this case three new parameters (V, W and X) are
required. We perform a global fit to precision electroweak data for these six
parameters. Our results differ from what is found for just STU. In particular
we find that the preference for S < 0 is not maintained.Comment: Plain TeX, 11 pages, one figure (ps file enclosed), (replaced version
corrects minor TeX problem, text unchanged) UdeM-LPN-TH-93-166, McGill-93/24,
OCIP/C-93-
Coherent transmission through a one dimensional lattice
Based on the Keldysh nonequilibrium Green function (NGF) technique, a general
formula for the current and transmission coefficient through a one dimensional
lattice is derived without the consideration of electron-electron interactions.
We obtain an analytical condition for perfect resonant transmission when the
levels of sites are aligned, which depends on the parity of the number of
sites. Localization-delocalization transition in a generic one dimensional
disordered lattice is also analyzed, depending on the correlation among the
hopping parameters and the strength of the coupling to reservoirs. The
dependence of the number and lineshape of resonant transmission and linear
conductance peaks on the structure parameters of the lattice is also given in
several site cases.Comment: 22 pages, 3 figures, Revtex, minor revision mad
The Top Mass Upper Bound and Electroweak Radiative Corrections
We investigated the possibility of introducing sizeable negative corrections
to the () parameter without affecting
. We have found that a proper vector-like family of fermions
can imply such corrections. Differently from supersymmetry \cite{bcf}, this can
be realized without introducing light particles easily observable at LEP II.
Our example can be of particular interest if no new particle is found at LEP II
and the value is found to be small compared to the one
expected in the case of a large top mass.Comment: 7 pages, Latex, IFUP-TH 3/9
The Relationship Between HR Practices and Firm Performance: Examining Causal Order
Significant research attention has been devoted to examining the relationship between HR practices and firm performance, and the research support has assumed HR as the causal variable. Using data from 45 business units (with 62 data points), this study examines how measures of HR practices correlate with past, concurrent, and future operational performance measures. The results indicate that correlations with performance measures at all three times are both high and invariant, and that controlling for past or concurrent performance virtually eliminates the correlation of HR with future performance. Implications are discussed
Technicolor Theories with Negative S
We show that the pseudo Nambu--Goldstone boson contribution to the
Peskin--Takeuchi electroweak parameter can be negative in a class of
technicolor theories. This negative contribution can be large enough to cancel
the positive techni-hadron contribution, showing that electroweak precision
tests alone cannot be used to rule out technicolor as the mechanism of
electroweak symmetry breaking.Comment: (LBL-32893, UCB-PTH 92/34, 10 pages; we added a discussion of
uncertainties, fine-tuning, and SU(2) asymptotic freedom; the conclusions are
unchanged.
Upper bound on the scale of Majorana-neutrino mass generation
We derive a model-independent upper bound on the scale of Majorana-neutrino
mass generation. The upper bound is , where GeV is the weak scale and is the Majorana neutrino mass. For
neutrino masses implied by neutrino oscillation experiments, all but one of
these bounds are less than the Planck scale, and they are all within a few
orders of magnitude of the grand-unification scale.Comment: 6 pages, 3 figures; REVTeX; published versio
The impact of contact tracing in clustered populations
The tracing of potentially infectious contacts has become an important part of the control strategy for many infectious diseases, from early cases of novel infections to endemic sexually transmitted infections. Here, we make use of mathematical models to consider the case of partner notification for sexually transmitted infection, however these models are sufficiently simple to allow more general conclusions to be drawn. We show that, when contact network structure is considered in addition to contact tracing, standard “mass action” models are generally inadequate. To consider the impact of mutual contacts (specifically clustering) we develop an improvement to existing pairwise network models, which we use to demonstrate that ceteris paribus, clustering improves the efficacy of contact tracing for a large region of parameter space. This result is sometimes reversed, however, for the case of highly effective contact tracing. We also develop stochastic simulations for comparison, using simple re-wiring methods that allow the generation of appropriate comparator networks. In this way we contribute to the general theory of network-based interventions against infectious disease
Vectorlike Confinement at the LHC
We argue for the plausibility of a broad class of vectorlike confining gauge
theories at the TeV scale which interact with the Standard Model predominantly
via gauge interactions. These theories have a rich phenomenology at the LHC if
confinement occurs at the TeV scale, while ensuring negligible impact on
precision electroweak and flavor observables. Spin-1 bound states can be
resonantly produced via their mixing with Standard Model gauge bosons. The
resonances promptly decay to pseudo-Goldstone bosons, some of which promptly
decay to a pair of Standard Model gauge bosons, while others are charged and
stable on collider time scales. The diverse set of final states with little
background include multiple photons and leptons, missing energy, massive stable
charged particles and the possibility of highly displaced vertices in dilepton,
leptoquark or diquark decays. Among others, a novel experimental signature of
resonance reconstruction out of massive stable charged particles is
highlighted. Some of the long-lived states also constitute Dark Matter
candidates.Comment: 33 pages, 6 figures. v4: expanded discussion of Z_2 symmetry for
stability, one reference adde
Surprises in the doping dependence of the Fermi surface in Bi(Pb)-2212
A detailed and systematic ARPES investigation of the doping-dependence of the
normal state Fermi surface (FS) of modulation-free (Pb,Bi)-2212 is presented.
The FS does not change in topology away from hole-like at any stage. The data
reveal, in addition, a number of surprises. Firstly the FS area does not follow
the usual curve describing Tc vs x for the hole doped cuprates, but is
down-shifted in doping by ca. 0.05 holes per Cu site, indicating either the
break-down of Luttinger's theorem or the consequences of a significant bi-layer
splitting of the FS. Secondly, the strong k-dependence of the FS width is shown
to be doping independent. Finally, the relative strength of the shadow FS has a
doping dependence mirroring that of Tc.Comment: 5 pages, 4 figures (revtex
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