643 research outputs found
Identification of indirect new physics effects at e^+e^- colliders: the large extra dimensions case
We discuss indirect manifestations of graviton exchange, predicted by large
extra dimensions, in fermion-pair production at a high-energy e^+e^- collider.
By means of specifically defined asymmetries among integrated angular
distributions, the graviton exchange signal can be cleanly distinguished from
the effects of either vector-vector contact interactions or heavy scalar
exchanges. The role of initial electron and positron beams polarization is also
discussed. The method is applied to a quantitative assessment of the
sensitivity to the mass cut-off parameter M_H of the KK graviton tower in the
ADD scenario, and of the potential identification reach of this mechanism
obtainable at the currently planned Linear Collider.Comment: 21 pages, 11 figure
Resonating singlet valence plaquettes
We consider the simplest generalizations of the valence bond physics of SU(2)
singlets to SU(N) singlets that comprise objects with N sites -- these are
SU(N) singlet plaquettes with N=3 and N=4 in three spatial dimensions.
Specifically, we search for a quantum mechanical liquid of such objects -- a
resonating singlet valence plaquette phase that generalizes the celebrated
resonating valence bond phase for SU(2) spins. We extend the Rokhsar-Kivelson
construction of the quantum dimer model to the simplest SU(4) model for valence
plaquette dynamics on a cubic lattice. The phase diagram of the resulting
quantum plaquette model is analyzed both analytically and numerically. We find
that the ground state is solid everywhere, including at the Rokhsar-Kivelson
point where the ground state is an equal amplitude sum. By contrast, the equal
amplitude sum of SU(3) singlet triangular plaquettes on the face centered cubic
lattice is liquid and thus a candidate for describing a resonating single
valence plaquette phase, given a suitably defined local Hamiltonian.Comment: 12 pages, 15 figures, minor changes, references added, Phys Rev B
versio
Homoclinic standing waves in focussing DNLS equations --Variational approach via constrained optimization
We study focussing discrete nonlinear Schr\"{o}dinger equations and present a
new variational existence proof for homoclinic standing waves (bright
solitons). Our approach relies on the constrained maximization of an energy
functional and provides the existence of two one-parameter families of waves
with unimodal and even profile function for a wide class of nonlinearities.
Finally, we illustrate our results by numerical simulations.Comment: new version with revised introduction and improved condition (A3); 16
pages, several figure
Revealing the large extra dimension effective interaction at an e^+e^- collider with polarized beams
Contactlike nonstandard effective interactions can be revealed through
deviations of observables from the Standard Model predictions. If such
deviations were observed, the relevant source should be identified among the
possible models that could explain them. We estimate the expected
discrimination reach on the ADD model of gravity in large compactified extra
dimensions, against the compositeness-inspired four-fermion contact
interaction. As basic observables we take the differential cross sections for
fermion-pair production at a 0.5-1 TeV electron-positron linear collider with
both beams longitudinally polarized. For the four-fermion contact interaction,
we assume a general linear combination of the individual models with definite
chiralities, and arbitrary coupling constants. Accordingly, the estimated
identification reach on the ADD scenario can be considered as
`model-independent'. We emphasize the substantial role of beams polarization in
enhancing the identification sensitivity.Comment: 14 pages, 2 figure
Effect of low temperatures on osserous and cartilaginous tissues
The use of extreme cold to treat tumoral afflictions of the extremities is discussed. Cryogenic methods and instruments are discussed, and the levels of accumulated knowledge in this area (as well as the areas still in question) are evaluated. The overall promise for cryogenic methods of treatment is acknowledged, and areas which need further development are noted
Model-independent constraints on contact interactions from LEP2 data analysis
We derive model-independent constraints on four-fermion contact
interaction-type dynamics from the published preliminary LEP2 experimental data
on e^+e^- annihilation into \mu^+\mu^- and \tau^+\tau^- pairs, measured at
different energies between 130 and 207 GeV. The basic observables are chosen to
be the total cross section and the forward-backward asymmetry, and the analysis
realistically takes into account data uncertainties and correlations among
measurements at the various energies. The combination of data from different
energy points plays an important role in the determination of regions allowed
for the contact interaction coupling constants. In contrast to the more common
one-parameter analyses, we only obtain constraints on pairs of parameters
rather than limits on individual ones.Comment: 13 pages, LaTeX, including figures. v2: Included discussion of tau
data, version to appear in EPJ
Sneutrino identification in dilepton events at the LHC
Heavy neutral resonances appearing in the clean Drell-Yan channel may be the
first new physics to be observed at the proton-proton CERN LHC. If a new
resonance is discovered at the LHC as a (narrow) peak in the dilepton invariant
mass distribution, the characterization of its spin and couplings will proceed
via the measurement of production rates and angular distributions of the decay
products. We discuss the discrimination of a spin-0 resonance (sneutrino)
predicted by supersymmetric theories with R-parity breaking against the spin-1
of Z^\prime bosons and the Randall-Sundrum graviton resonance (spin-2) with the
same mass and producing the same number of events under the observed peak. To
assess the region of sneutrino parameters (couplings and masses) where the spin
determination can be performed to a given confidence level, we focus on the
event rate and the angular distributions of the Drell-Yan leptons, in
particular using the center-edge asymmetry, A_{\rm CE}. We find that although
the measured event rate permits solving the above problem partially, the
center-edge asymmetry, on the contrary allows to differentiate the various
spins entirely with a minimal number of events around 200.Comment: 20 pages; version to appear in PR
Distinguishing New Physics Scenarios at a Linear Collider with Polarized Beams
Numerous non-standard dynamics are described by contact-like effective
interactions that can manifest themselves through deviations of the cross
sections from the Standard Model predictions. If one such deviation were
observed, one should try to identify to a given confidence level the actual
source among the possible non-standard interactions that in principle can
explain it. We here estimate the potential identification reach on different
New Physics effective interactions, obtainable from the angular distributions
of lepton pair production processes at the planned International Linear
Collider with polarized beams. The models discussed are the interactions based
on gravity in large and in TeV^{-1} extra dimensions and the
compositeness-inspired four-fermion contact interactions. The availability of
both beams polarized in many cases plays an essential role in enhancing the
identification sensitivity.Comment: 21 pages, LaTex, 11 figures. One author was missing from the previous
version. The authors list has been completed, no other change
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