3,161,555 research outputs found
About helicity conservation in gauge boson scattering at high energy
We remark that the high energy gauge boson scattering processes involving
two-body initial and final states, satisfy certain selection rules described as
helicity conservation of the \underline{gauge boson} amplitudes (GBHC). These
rules are valid at Born level, as well as at the level of the leading and
sub-leading 1-loop logarithmic corrections, in both the Standard Model (SM) and
the Minimal Supersymmetric Standard Model (MSSM). A "fermionic equivalence"
theorem is also proved, which suggests that GBHC is valid at all orders in MSSM
at sufficiently high energies, where the mass suppressed contributions are
neglected.Comment: 7 pages, 2 figures, version to appear in Phys. Rev. Letter
Solving the Constraints of General Relativity
I show in this letter that it is possible to solve some of the constraints of
the -ADM formalism for general relativity by using an approach similar
to the one introduced by Capovilla, Dell and Jacobson to solve the vector and
scalar constraints in the Ashtekar variables framework. I discuss the
advantages of using the ADM formalism and compare the result with similar
proposals for different Hamiltonian formulations of general relativity.Comment: 8 pages, LATEX, no figures, Preprint CGPG-94/11-
The processes of gluon fusion producing chargino or neutralino pairs at high energies
According to the helicity conservation (HCns) theorem, the sum of the
helicities should be conserved, in any 2-to-2 processes in MSSM with R-parity
conservation, at high energies; i.e. all amplitudes violating this rule, must
vanish asymptotically. The realization of HCns in gluon-fusion to charginos or
neutralinos is studied, at the one loop electroweak order (EW), and simple high
energy expressions are derived for the non-vanishing helicity conserving (HC)
amplitudes. These are very similar to the corresponding expressions for derived before. Asymptotic relations among
observable unpolarized cross sections for many such processes are then
obtained, some of which may hold at LHC-type energies.Comment: Extended version to appear in International Journal of Modern Physics
A 21 page
Probing the Structure of the Pomeron
We suggest that the pseudo-rapidity cut dependence of diffractive
deep-inelastic scattering events at HERA may provide a sensitive test of models
of diffraction. A comparison with the experimental cross section shows that the
Donnachie-Landshoff model and a simple two-gluon exchange model of the pomeron
model are disfavoured. However a model with a direct coupling of the pomeron to
quarks is viable for a harder quark--pomeron form factor, as is a model based
on the leading-twist operator contribution. We also consider a direct-coupling
scalar pomeron model. We comment on the implications of these results for the
determination of the partonic structure of the pomeron.Comment: 33 pages, LaTeX2e, 14 figures, uses axodra
Tone-burst technique measures high-intensity sound absorption
Tone-burst technique, in which narrow-bandwidth, short-duration sonic pulse is propagated down a standing-wave tube, measures sound absorbing capacity of materials used in jet engine noise abatement. Technique eliminates effects of tube losses and yields normal-incidence absorption coefficient of specimen
Correcting for selection bias via cross-validation in the classification of microarray data
There is increasing interest in the use of diagnostic rules based on
microarray data. These rules are formed by considering the expression levels of
thousands of genes in tissue samples taken on patients of known classification
with respect to a number of classes, representing, say, disease status or
treatment strategy. As the final versions of these rules are usually based on a
small subset of the available genes, there is a selection bias that has to be
corrected for in the estimation of the associated error rates. We consider the
problem using cross-validation. In particular, we present explicit formulae
that are useful in explaining the layers of validation that have to be
performed in order to avoid improperly cross-validated estimates.Comment: Published in at http://dx.doi.org/10.1214/193940307000000284 the IMS
Collections (http://www.imstat.org/publications/imscollections.htm) by the
Institute of Mathematical Statistics (http://www.imstat.org
Quantum symmetries and the Weyl-Wigner product of group representations
In the usual formulation of quantum mechanics, groups of automorphisms of
quantum states have ray representations by unitary and antiunitary operators on
complex Hilbert space, in accordance with Wigner's Theorem. In the phase-space
formulation, they have real, true unitary representations in the space of
square-integrable functions on phase-space. Each such phase-space
representation is a Weyl-Wigner product of the corresponding Hilbert space
representation with its contragredient, and these can be recovered by
`factorising' the Weyl-Wigner product. However, not every real, unitary
representation on phase-space corresponds to a group of automorphisms, so not
every such representation is in the form of a Weyl-Wigner product and can be
factorised. The conditions under which this is possible are examined. Examples
are presented.Comment: Latex2e file, 37 page
Graviton as a Goldstone boson: Nonlinear Sigma Model for Tensor Field Gravity
Spontaneous Lorentz invariance violation (SLIV) realized through a nonlinear
tensor field constraint H_{}^2=\pm M^2 (M is the proposed scale for Lorentz
violation) is considered in tensor field gravity theory, which mimics
linearized general relativity in Minkowski space-time. We show that such a SLIV
pattern, due to which the true vacuum in the theory is chosen, induces massless
tensor Goldstone modes some of which can naturally be associated with the
physical graviton. When expressed in terms of the pure Goldstone modes, this
theory looks essentially nonlinear and contains a variety of Lorentz and CPT
violating couplings. Nonetheless, all SLIV effects turn out to be strictly
cancelled in all the lowest order processes considered, provided that the
tensor field gravity theory is properly extended to general relativity (GR).
So, as we generally argue, the measurable effects of SLIV, induced by
elementary vector or tensor fields, are related to the accompanying gauge
symmetry breaking rather than to spontaneous Lorentz violation. The latter
appears by itself to be physically unobservable, only resulting in a
non-covariant gauge choice in an otherwise gauge invariant and Lorentz
invariant theory. However, while Goldstonic vector and tensor field theories
with exact local invariance are physically indistinguishable from conventional
gauge theories, there might appear some principal distinctions if this local
symmetry were slightly broken at very small distances controlled by quantum
gravity in an explicit, rather than spontaneous, way that could eventually
allow one to differentiate between them observationally.Comment: 15 pages, some minor additions mad
Line of Dirac monopoles embedded in a Bose-Einstein condensate
The gauge field of a uniform line of magnetic monopoles is created using a
single Laguerre-Gauss laser mode and a gradient in the physical magnetic field.
We study the effect of these monopoles on a Bose condensed atomic gas, whose
vortex structure transforms when more than six monopoles are trapped within the
cloud. Finally, we study this transition with the collective modes
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