473 research outputs found
The effects of non-universal extra dimensions on the radiative lepton flavor decays \mu\to e\gamma and \tau\to \mu\gamma in the two Higgs doublet model
We study the effect of non-universal extra dimensions on the branching ratios
of the lepton flavor violating processes \mu\to e\gamma and \tau\to \mu\gamma
in the general two Higgs doublet model. We observe that these effects are small
for a single extra dimension, however, in the case of two extra dimensions
there is a considerable enhancement in the additional contributions.Comment: 16 Pages, 9 Figure
Precision Measurements and Fermion Geography in the Randall-Sundrum Model Revisited
We re-examine the implications of allowing fermion fields to propagate in the
five-dimensional bulk of the Randall-Sundrum (RS) localized gravity model. We
find that mixing between the Standard Model top quark and its Kaluza Klein
excitations generates large contributions to the rho parameter and consequently
restricts the fundamental RS scale to lie above 100 TeV. To circumvent this
bound we propose a `mixed' scenario which localizes the third generation
fermions on the TeV brane and allows the lighter generations to propagate in
the full five-dimensional bulk. We show that this construction naturally
reproduces the observed m_c / m_t and m_s / m_b hierarchies. We explore the
signatures of this scenario in precision measurements and future high energy
collider experiments. We find that the region of parameter space that addresses
the hierarchies of fermion Yukawa couplings permits a Higgs boson with a mass
of 500 GeV and remains otherwise invisible at the LHC. However, the entire
parameter region consistent with electroweak precision data is testable at
future linear colliders. We briefly discuss possible constraints on this
scenario arising from flavor changing neutral currents.Comment: 44 pages, 20 ps files; VII, typos fixed and refs adde
Recalculation of QCD Corrections to Decay
We give a more complete calculation of decay, including
leading log QCD corrections from to in addition to corrections
from to . We have included the full set of dimension-6 operators
and corrected numerical mistakes of anomalous dimensions in a previous
paper\cite{Cho}. Comparing with the calculations without QCD running from
to \cite{Mis}, the inclusive decay rate is found to be enhanced.
At GeV, it results in 12\% enhancement, and for GeV, 15\% is
found. The total QCD effect makes an enhanced factor of 4.2 at GeV,
and 3.2 for GeV.Comment: 16 pages, 7 figures (uuencoded ps files), Changes of description. To
appear in Phys. Rev.
Enhancement of Loop Induced Vertex in Two Higgs-doublet Model
The non-decoupling effects of heavy Higgs bosons as well as fermions on the
loop-induced vertex are discussed in the general two Higgs
doublet model. The decay width of the process is calculated
at one-loop level and the possibility of its enhancement is explored both
analytically and numerically. We find that the novel enhancement of the decay
width can be realized by the Higgs non-decoupling effects with large
mass-splitting between the charged Higgs boson and the CP-odd one. This is due
to the large breakdown of the custodial invariance in the Higgs
sector. The branching ratio can amount to for GeV within the constraint from the present experimental data. Hence this
mode may be detectable at LHC or future linear colliders.Comment: 31+1 pages, Latex with 8 eps-file
Universal Extra Dimensions and Kaluza Klein Bound States
We study the bound states of the Kaluza-Klein (KK) excitations of quarks in
certain models of Universal Extra Dimensions. Such bound states may be detected
at future lepton colliders in the cross section for the pair production of
KK-quarks near threshold. For typical values of model parameters, we find that
"KK-quarkonia" have widths in the 10 - 100 MeV range, and production cross
sections of order a few picobarns for the lightest resonances. Two body decays
of the constituent KK-quarks lead to distinctive experimental signatures. We
point out that such KK resonances may be discovered before any of the higher KK
modes.Comment: 21 pages LaTeX, 9 eps figure
Lepton Polarization and Forward-Backward Asymmetries in b -> s tau+ tau-
We study the spin polarizations of both tau leptons in the decay b -> s tau+
tau-. In addition to the polarization asymmetries involving a single tau, we
construct asymmetries for the case where both polarizations are simultaneously
measured. We also study forward-backward asymmetries with polarized tau's. We
find that a large number of asymmetries are predicted to be large, >~ 10%. This
permits the measurement of all Wilson coefficients and the b-quark mass, thus
allowing the standard model (SM) to be exhaustively tested. Furthermore, there
are many unique signals for the presence of new physics. For example,
asymmetries involving triple-product correlations are predicted to be tiny
within the SM, O(10^{-2}). Their observation would be a clear signal of new
physics.Comment: 21 pages, LaTeX, 4 figures (included). Paper somewhat reorganized,
references greatly expanded, conclusions unchange
FCNC Top Quark Decays in Extra Dimensions
The flavor changing neutral top quark decay t -> c X is computed, where X is
a neutral standard model particle, in a extended model with a single extra
dimension. The cases for the photon, X= \gammaR_\xi gauge. We find that
the branching ratios can be enhanced by the dynamics originated in the extra
dimension. In the limit where 1/R >> ->, we have found Br(t -> c \gamma) \simeq
10^{-10} for 1/R = 0.5 TeV. For the decay t -> c H, we have found Br(t -> cH)
\simeq 10^{-10} for a low Higgs mass value. The branching ratios go to zero
when 1/R -> \infty.Comment: Accepted to be published in the Europ. Phys. Jour. C; 16 pages, 2
figure
Static quantities of the W boson in the SU_L(3) X U_X(1) model with right-handed neutrinos
The static electromagnetic properties of the boson, and
, are calculated in the SU_L(3)} \times U_X(1) model with
right-handed neutrinos. The new contributions from this model arise from the
gauge and scalar sectors. In the gauge sector there is a new contribution from
a complex neutral gauge boson and a singly-charged gauge boson .
The mass of these gauge bosons, called bileptons, is expected to be in the
range of a few hundreds of GeV according to the current bounds from
experimental data. If the bilepton masses are of the order of 200 GeV, the size
of their contribution is similar to that obtained in other weakly coupled
theories. However the contributions to both and are
negligible for very heavy or degenerate bileptons. As for the scalar sector, an
scenario is examined in which the contribution to the form factors is
identical to that of a two-Higgs-doublet model. It is found that this sector
would not give large corrections to and .Comment: New material included. Final version to apppear in Physical Review
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An overview of the Amazonian Aerosol Characterization Experiment 2008 (AMAZE-08)
The Amazon Basin provides an excellent environment for studying the sources, transformations, and properties of natural aerosol particles and the resulting links between biological processes and climate. With this framework in mind, the Amazonian Aerosol Characterization Experiment (AMAZE-08), carried out from 7 February to 14 March 2008 during the wet season in the central Amazon Basin, sought to understand the formation, transformations, and cloud-forming properties of fine- and coarse-mode biogenic aerosol particles, especially as related to their effects on cloud activation and regional climate. Special foci included (1) the production mechanisms of secondary organic components at a pristine continental site, including the factors regulating their temporal variability, and (2) predicting and understanding the cloud-forming properties of biogenic particles at such a site. In this overview paper, the field site and the instrumentation employed during the campaign are introduced. Observations and findings are reported, including the large-scale context for the campaign, especially as provided by satellite observations. New findings presented include: (i) a particle number-diameter distribution from 10 nm to 10 μm that is representative of the pristine tropical rain forest and recommended for model use; (ii) the absence of substantial quantities of primary biological particles in the submicron mode as evidenced by mass spectral characterization; (iii) the large-scale production of secondary organic material; (iv) insights into the chemical and physical properties of the particles as revealed by thermodenuder-induced changes in the particle number-diameter distributions and mass spectra; and (v) comparisons of ground-based predictions and satellite-based observations of hydrometeor phase in clouds. A main finding of AMAZE-08 is the dominance of secondary organic material as particle components. The results presented here provide mechanistic insight and quantitative parameters that can serve to increase the accuracy of models of the formation, transformations, and cloud-forming properties of biogenic natural aerosol particles, especially as related to their effects on cloud activation and regional climate
Time-integrated luminosity recorded by the BABAR detector at the PEP-II e+e- collider
This article is the Preprint version of the final published artcile which can be accessed at the link below.We describe a measurement of the time-integrated luminosity of the data collected by the BABAR experiment at the PEP-II asymmetric-energy e+e- collider at the ϒ(4S), ϒ(3S), and ϒ(2S) resonances and in a continuum region below each resonance. We measure the time-integrated luminosity by counting e+e-→e+e- and (for the ϒ(4S) only) e+e-→μ+μ- candidate events, allowing additional photons in the final state. We use data-corrected simulation to determine the cross-sections and reconstruction efficiencies for these processes, as well as the major backgrounds. Due to the large cross-sections of e+e-→e+e- and e+e-→μ+μ-, the statistical uncertainties of the measurement are substantially smaller than the systematic uncertainties. The dominant systematic uncertainties are due to observed differences between data and simulation, as well as uncertainties on the cross-sections. For data collected on the ϒ(3S) and ϒ(2S) resonances, an additional uncertainty arises due to ϒ→e+e-X background. For data collected off the ϒ resonances, we estimate an additional uncertainty due to time dependent efficiency variations, which can affect the short off-resonance runs. The relative uncertainties on the luminosities of the on-resonance (off-resonance) samples are 0.43% (0.43%) for the ϒ(4S), 0.58% (0.72%) for the ϒ(3S), and 0.68% (0.88%) for the ϒ(2S).This work is supported by the US Department of Energy and National Science Foundation, the Natural Sciences and Engineering Research Council (Canada), the Commissariat à l’Energie Atomique and Institut National de Physique Nucléaire et de Physiquedes Particules (France), the Bundesministerium für Bildung und Forschung and Deutsche Forschungsgemeinschaft (Germany), the Istituto Nazionale di Fisica Nucleare (Italy), the Foundation for Fundamental Research on Matter (The Netherlands), the Research Council of Norway, the Ministry of Education and Science of the Russian Federation, Ministerio de Ciencia e Innovación (Spain), and the Science and Technology Facilities Council (United Kingdom). Individuals have received support from the Marie-Curie IEF program (European Union) and the A.P. Sloan Foundation (USA)
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