9,354 research outputs found
Unique Identification of Lee-Wick Gauge Bosons at Linear Colliders
Grinstein, O'Connell and Wise have recently presented an extension of the
Standard Model (SM), based on the ideas of Lee and Wick (LW), which
demonstrates an interesting way to remove the quadratically divergent
contributions to the Higgs mass induced by radiative corrections. This model
predicts the existence of negative-norm copies of the usual SM fields at the
TeV scale with ghost-like propagators and negative decay widths, but with
otherwise SM-like couplings. In earlier work, it was demonstrated that the LW
states in the gauge boson sector of these models, though easy to observe,
cannot be uniquely identified as such at the LHC. In this paper, we address the
issue of whether or not this problem can be resolved at an collider
with a suitable center of mass energy range. We find that measurements of the
cross section and the left-right polarization asymmetry associated with Bhabha
scattering can lead to a unique identification of the neutral electroweak gauge
bosons of the Lee-Wick type.Comment: 16 pages, 6 figures; discussion and references adde
Finite size corrections to disordered systems on Erd\"{o}s-R\'enyi random graphs
We study the finite size corrections to the free energy density in disorder
spin systems on sparse random graphs, using both replica theory and cavity
method. We derive an analytical expressions for the corrections in the
replica symmetric phase as a linear combination of the free energies of open
and closed chains. We perform a numerical check of the formulae on the Random
Field Ising Model at zero temperature, by computing finite size corrections to
the ground state energy density.Comment: Submitted to PR
Natural surface hydrocarbons and soil faunal biodiversity: A bioremediation perspective
Hydrocarbon pollution threatens aquatic and terrestrial ecosystems globally, but soil fauna in oil-polluted soils has been insufficiently studied. In this research, soil hydrocarbon toxicity was investigated in two natural oil seepage soils in Val D'Agri (Italy) using two different approaches: (i) toxicological tests with Folsomia candida (Collembola) and Eisenia fetida (Oligochaeta) and (ii) analysis of abundance and composition of micro- and meso-fauna. Soil sampling was done along 20 m-transepts starting from the natural oil seepages. Toxicological testing revealed that no exemplars of F. candida survived, whereas specimens of E. fetida not only survived but also increased in weight in soils with higher PAH concentrations, although no reproduction was observed. Analysis on microfauna showed that Nematoda was the most abundant group, with distance from seepages not affecting its abundance. Arthropoda results showed that Acarina, Collembola and Diptera larvae represented the most abundant taxa. The highest divergence in community composition was found between soils situated near seepages and at 5 m and 10 m distance. Arthropoda taxa numbers, total abundance and Acarina were lower in soils with high PAH concentration, while Diptera larvae were not significantly affected. Earthworms, together with Nematoda and Diptera larvae, could therefore represent ideal candidates in PAH degradation studies
t-channel production of heavy charged leptons
We study the pair production of heavy charged exotic leptons at e+ e-
colliders in the SU(2)_L x SU(2)_I x U(1)_Y model. This gauge group is a
subgroup of the grand unification group E6; SU(2)_I commutes with the electric
charge operator, and the three corresponding gauge bosons are electrically
neutral. In addition to the standard photon and Z boson contributions, we also
include the contributions from extra neutral gauge bosons. A t-channel
contribution due to W_I-boson exchange, which is unsuppressed by mixing angles,
is quite important. We calculate the left-right and forward-backward
asymmetries, and discuss how to differentiate different models.Comment: Increased discussion of experimental signatures. Version accepted by
PR
Single Production in Collisions at the NLC
Single production in collisions at the NLC can be used to
probe the Majorana nature of the heavy neutrinos present in the Left-Right
Symmetric Model below the kinematic threshold for their direct production. For
colliders in the TeV range, typical cross sections of order
are obtained, depending on the specific choice of model parameters.
Backgrounds arising from Standard Model processes are shown to be small. This
analysis greatly extends the kinematic range of previous studies wherein the
production of an on-shell, like-sign pair of 's at the NLC was considered.Comment: 13pp, 3 figures (available on request), LaTex, SLAC-PUB-647
Gauge Boson - Gauge Boson Scattering in Theories with Large Extra Dimensions
We consider the scattering amplitudes of the form V_1 V_2 -> V_3 V_4, where
V_i=\gamma, Z, W or g(=gluon) are the Standard Model gauge bosons, due to
graviton exchange in Kaluza-Klein theories with large extra dimensions. This
leads to a number of experimentally viable signatures at high energy leptonic
and hadronic colliders. We discuss the observability or future limits on the
scale of the gravitational interactions (m_D), that may be obtained at an e+e-
Next Linear Collider (NLC) and at the LHC, by studying some of these type of
gauge boson scattering processes. We find that the attainable limits through
these type of processes are: m_D > 3 TeV at the NLC and m_D > 6 TeV at the LHC.Comment: 27 pages, plain latex, 7 figures embadded in the text using epsfi
Reconstruction of the Extended Gauge Structure from Observables at Future Colliders
The discovery of a new neutral gauge boson with a mass in the TeV region
would allow for determination of gauge couplings of the to ordinary quarks
and leptons in a model independent way. We show that these couplings in turn
would allow us to determine the nature of the extended gauge structure. As a
prime example we study the group. In this case two discrete constraints
on experimentally determined couplings have to be satisfied. If so, the
couplings would then uniquely determine the two parameters, and
, which fully specify the nature of the within . If the
is part of the gauge structure, then for TeV and
could be determined to around at the future colliders. The NLC
provides a unique determination of the two constraints as well as of and , though with slightly larger error bars than at the LHC. On
the other hand, since the LHC primarily determines three out of four normalized
couplings, it provides weaker constraints for the underlying gauge structure.Comment: 14 pages LaTeX using RevTeX and psfig.sty. TeX source and 3 PS
figures, tarred, compressed and uuencoded; also available via anonymous ftp
to ftp://dept.physics.upenn.edu/pub/Cvetic/UPR-636-T
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