273 research outputs found
Infrared behavior of graviton-graviton scattering
The quantum effective theory of general relativity, independent of the
eventual full theory at high energy, expresses graviton-graviton scattering at
one loop order O(E^4) with only one parameter, Newton's constant. Dunbar and
Norridge have calculated the one loop amplitude using string based techniques.
We complete the calculation by showing that the 1/(d-4) divergence which
remains in their result comes from the infrared sector and that the cross
section is finite and model independent when the usual bremsstrahlung diagrams
are included.Comment: 12 pages, uses axodra
Symmetry breaking via fermion 4-point functions
We construct the effective action and gap equations for nonperturbative
fermion 4-point functions. Our results apply to situations in which fermion
masses can be ignored, which is the case for theories of strong flavor
interactions involving standard quarks and leptons above the electroweak scale.
The structure of the gap equations is different from what a naive
generalization of the 2-point case would suggest, and we find for example that
gauge exchanges are insufficient to generate nonperturbative 4-point functions
when the number of colors is large.Comment: 36 pages, uses Revtex and eps files for figure
New Axial Interactions at a TeV
We consider a heavy fourth family with masses lying in the symmetry breaking
channel of a new strong gauge interaction. This interaction generates a heavy
quark axial-type operator, whose effects can be enhanced through multiple
insertions. In terms of the strength of this operator we can express new
negative contributions to the S and T parameters and the shifts of the Z
couplings to the third family. In particular we find that the new contribution
to T is strongly constrained by the experimental constraints on the Z coupling
to the tau.Comment: 14 pages, 1 figure, PRD versio
On the power counting of loop diagrams in general relativity
A class of loop diagrams in general relativity appears to have a behavior
which would upset the utility of the energy expansion for quantum effects. We
show through the study of specific diagrams that cancellations occur which
restore the expected behaviour of the energy expansion. By considering the
power counting in a physical gauge we show that the apparent bad behavior is a
gauge artifact, and that the quantum loops enter with a well behaved energy
expansion.Comment: 29 pages, uses axodraw and epsfig.tex, one small .eps file is
included. The full PostScript version is also available as
http://het.phast.umass.edu/students/kakukk/powercount_hepth.p
Dielectrophoresis of nanoscale dsDNA and humidity effects on its electrical conductivity
The dielectrophoresis method for trapping and attaching nanoscale
double-stranded DNA between nanoelectrodes was developed. The method gives a
high yield of trapping single or a few molecules only which enables transport
measurements at the single molecule level. Electrical conductivity of
individual 140-nm-long DNA molecules was measured, showing insulating behavior
in dry conditions. In contrast, clear enhancement of conductivity was observed
in moist conditions, relating to the interplay between the conformation of DNA
molecules and their conductivity.Comment: 4 pages, 2 figure
Charmonium production at neutrino factories
At existing and planned neutrino factories (high energy and high intensity
neutrino beam facilities) precision studies of QCD in neutrino-nucleon
interactions are a realistic opportunity. We investigate charmonium production
in fixed target neutrino experiments. We find that production in
neutrino-nucleon collision is dominated by the color octet NRQCD matrix
element in a neutral current process, which is not accessible in photo or
leptoproduction. Neutrino experiments at a future Muon Collider will acquire
sufficient event rate to accurately measure color octet matrix element
contributions. The currently running high energy neutrino experiments, NOMAD
and NuTeV could also observe several such events.Comment: 13 pages Latex, with five embedded eps figures. Cosmetic fixups in
the figures, otherwise unchange
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