11,642 research outputs found
Constraints on the mass and mixing of Z' bosons
We tested several models in which the Standard Model (SM) gauge group is
extended by an additional U(1) gauge symmetry, against available electroweak
precision data to impose limits on the mass of the neutral Z' boson, M_Z',
predicted in all such models, and on the Z-Z' mixing angle, theta_ZZ', at 95%
C.L. We found lower limits on M_Z' of order 1 TeV in most cases, while
theta_ZZ' was found to be constrained to very small values.Comment: Format fixed, 5 pages, 2 figures, Talk given at the 17th
International Conference on Supersymmetry and the Unification of Fundamental
Interactions (SUSY09), Boston, MA, USA, 5-10 June 2009, to be published in
the conference proceedings (AIP
Z' Searches: From Tevatron to LHC
The CDF collaboration has set lower limits on the masses of the Z' bosons
occurring in a range of E_6 GUT based models. We revisit their analysis and
extend it to certain other E_6 scenarios as well as to some general classes of
models satisfying the anomaly cancellation conditions, which are not included
in the CDF analysis. We also suggest a Bayesian statistical method for finding
exclusion limits on the Z' mass, which allows one to explore a wide range of
the U(1)' gauge coupling parameter. This method also takes into account the
effects of interference between the Z' and the SM gauge bosons.Comment: 5 pages. Talk given at the XXIInd Rencontres de Blois, Loire, France,
16-20 July 201
Frequency correlation requirements on the biphoton wavefunction in an induced coherence experiment between separate sources
There is renewed interest in using the coherence between beams generated in
separate down-converter sources for new applications in imaging, spectroscopy,
microscopy and optical coherence tomography (OCT). These schemes make use of
continuous wave (CW) pumping in the low parametric gain regime, which produces
frequency correlations, and frequency entanglement, between signal-idler pairs
generated in each single source. But can induced coherence still be observed if
there is no frequency correlation, so the biphoton wavefunction is factorable?
We will show that this is the case, and this might be an advantage for OCT
applications. High axial resolution requires a large bandwidth. For CW pumping
this requires the use of short nonlinear crystals. This is detrimental since
short crystals generate small photon fluxes. We show that the use of ultrashort
pump pulses allows improving axial resolution even for long crystal that
produce higher photon fluxes
(Pseudo)Scalar Charmonium in Finite Temperature QCD
The hadronic parameters of pseudoscalar () and scalar ()
charmonium are determined at finite temperature from Hilbert moment QCD sum
rules. These parameters are the hadron mass, leptonic decay constant, total
width, and continuum threshold (). Results for in both channels
indicate that starts approximately constant, and then it decreases
monotonically with increasing until it reaches the QCD threshold, , at a critical temperature T = T_c \simeq 180 \; \mbox{MeV}
interpreted as the deconfinement temperature. The other hadronic parameters
behave qualitatively similarly to those of the , as determined in this
same framework. The hadron mass is essentially constant, the total width is
initially independent of T, and after it begins to increase
with increasing up to for
(), and subsequently it decreases sharply up to , for (), beyond which the sum rules are no
longer valid. The decay constant of at first remains basically flat up
to , then it starts to decrease up to , and finally it increases sharply with increasing . In the case of
the decay constant does not change up to where
it begins a gentle increase up to beyond which it
increases dramatically with increasing . This behaviour contrasts with that
of light-light and heavy-light quark systems, and it suggests the survival of
the and the states beyond the critical temperature, as
already found for the from similar QCD sum rules. These conclusions
are very stable against changes in the critical temperature in the wide range
T_c = 180 - 260 \; \mbox{MeV}.Comment: 12 pages, 5 figures. A wide range of critical temperatures has been
considered. No qualitative changes to the conclusion
A Study of Non-Neutral Networks with Usage-based Prices
Hahn and Wallsten wrote that network neutrality "usually means that broadband
service providers charge consumers only once for Internet access, do not favor
one content provider over another, and do not charge content providers for
sending information over broadband lines to end users." In this paper we study
the implications of non-neutral behaviors under a simple model of linear
demand-response to usage-based prices. We take into account advertising
revenues and consider both cooperative and non-cooperative scenarios. In
particular, we model the impact of side-payments between service and content
providers. We also consider the effect of service discrimination by access
providers, as well as an extension of our model to non-monopolistic content
providers
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