7,893 research outputs found
Comment on Leptophobic Bosons and Neutral Current Scattering Data
The relevance of existing deep inelastic scattering data to models
containing a leptophobic neutral vector boson is discussed. It is shown that
this neutral current data is in good agreement with the Standard Model and
disfavors such a leptophobic boson.Comment: LaTeX, 3 pages, 1 embedded PS figure, available at
http://cordelia.fnal.gov/~ksmcf/publications/moriond_comment.ps.gz .
Presented at the XXXIieme Rencontres de Moriond, Electroweak Interactions and
Unified Theorie
A Precision Measurement of Electroweak Parameters in Neutrino-Nucleon Scattering
The CCFR collaboration reports a precise measurement of electroweak
parameters derived from the ratio of neutral-current to charged-current
cross-sections in neutrino-nucleon scattering at the Fermilab Tevatron. This
ratio of cross-sections measures the neutral current couplings to quarks, which
implies a determination of sin^2 theta_W (on-shell) = 0.2236 +/- 0.0028(expt.)
+/- 0.0030(model) for m_top=175 GeV, m_Higgs=150 GeV. This is equivalent to
M_W=80.35+/-0.21 GeV. The good agreement of this measurement with Standard
Model expectations implies the exclusion of additional
neutrino-neutrino-quark-quark contact interactions at 95% confidence at a mass
scale of 1-8 TeV, depending on the form of the contact interaction.Comment: formatted in revtex, 5 pages, 3 eps figures included via psfig,
submitted to Physical Review Letter
A Small Target Neutrino Deep-Inelastic Scattering Experiment at the First Muon Collider
Several different scenarios for neutrino scattering experiments using a
neutrino beam from the muon collider complex are discussed. The physics reach
of a neutrino experiment at the front end of a muon collider is shown to extend
far beyond that of current neutrino experiments, since the high intensity
neutrino beams one would see at the muon collider allow for a large flexibility
in choosing neutrino targets. Measurements of quark spin, A-dependence of the
structure function and neutral current chiral couplings to quarks are
outlined.Comment: 7 pages, 2 figures, to appear in the proceedings of the Workshop on
Physics at the First Muon Collider and at the Front End of a Muon Collider,
November 1997, Fermila
A tug-of-war between driver and passenger mutations in cancer and other adaptive processes
Cancer progression is an example of a rapid adaptive process where evolving
new traits is essential for survival and requires a high mutation rate.
Precancerous cells acquire a few key mutations that drive rapid population
growth and carcinogenesis. Cancer genomics demonstrates that these few 'driver'
mutations occur alongside thousands of random 'passenger' mutations-a natural
consequence of cancer's elevated mutation rate. Some passengers can be
deleterious to cancer cells, yet have been largely ignored in cancer research.
In population genetics, however, the accumulation of mildly deleterious
mutations has been shown to cause population meltdown. Here we develop a
stochastic population model where beneficial drivers engage in a tug-of-war
with frequent mildly deleterious passengers. These passengers present a barrier
to cancer progression that is described by a critical population size, below
which most lesions fail to progress, and a critical mutation rate, above which
cancers meltdown. We find support for the model in cancer age-incidence and
cancer genomics data that also allow us to estimate the fitness advantage of
drivers and fitness costs of passengers. We identify two regimes of adaptive
evolutionary dynamics and use these regimes to rationalize successes and
failures of different treatment strategies. We find that a tumor's load of
deleterious passengers can explain previously paradoxical treatment outcomes
and suggest that it could potentially serve as a biomarker of response to
mutagenic therapies. Collective deleterious effect of passengers is currently
an unexploited therapeutic target. We discuss how their effects might be
exacerbated by both current and future therapies
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