1,081 research outputs found
QCD recursion relations from the largest time equation
We show how by reassembling the tree level gluon Feynman diagrams in a
convenient gauge, space-cone, we can explicitly derive the BCFW recursion
relations. Moreover, the proof of the gluon recursion relations hinges on an
identity in momentum space which we show to be nothing but the Fourier
transform of the largest time equation. Our approach lends itself to natural
generalizations to include massive scalars and even fermions.Comment: 18 pages, 2 figures, minor changes to Sect.
Closing the Symmetry at Electroweak Scale
We show that some models with gauge
symmetry can be realized at the electroweak scale and that this is a
consequence of an approximate global symmetry. This symmetry
implies a condition among the vacuum expectation value of one of the neutral
Higgs scalars, the 's coupling constant, , the sine of the weak
mixing angle , and the mass of the boson, . In the limit
in which this symmetry is valid it avoids the tree level mixing of the
boson of the Standard Model with the extra boson. We have verified
that the oblique parameter is within the allowed range indicating that the
radiative corrections that induce such a mixing at the 1-loop level are small.
We also show that a custodial symmetry implies that in some of
the models we have to include sterile (singlets of the 3-3-1 symmetry)
right-handed neutrinos with Majorana masses, being the see-saw mechanism
mandatory to obtain light active neutrinos. Moreover, the approximate
symmetry implies that the extra non-standard
particles of these 3-3-1 models can be considerably lighter than it had been
thought before so that new physics can be really just around the corner.Comment: 32 pages, no figure, RevTeX. Some typos correcte
Physics at \ggam and \egam colliders
I discuss, what really new could give Photon Colliders ( and
) after LHC and \epe Linear Collider operations.Comment: 7pages,LaTEX, To be published in proceedings "PHOTON99". The
forgotten title, author and abstract are added in the tex
Non locality and causal evolution in QFT
Non locality appearing in QFT during the free evolution of localized field
states and in the Feynman propagator function is analyzed. It is shown to be
connected to the initial non local properties present at the level of quantum
states and then it does not imply a violation of Einstein's causality. Then it
is investigated a simple QFT system with interaction, consisting of a classical
source coupled linearly to a quantum scalar field, that is exactly solved. The
expression for the time evolution of the state describing the system is given.
The expectation value of any arbitrary ``good'' local observable, expressed as
a function of the field operator and its space and time derivatives, is
obtained explicitly at all order in the field-matter coupling constant. These
expectation values have a source dependent part that is shown to be always
causally retarded, while the non local contributions are source independent and
related to the non local properties of zero point vacuum fluctuations.Comment: Submitted to Journal of Physics B: 16 pages: 1 figur
Invisible Events with Radiative Photons at LEP
A study of the radiative neutrino counting reaction at LEP1 and LEP2 energies is presented. An approximate expression
for the spectrum of the observed photon is derived within the framework of the
-dependent structure function approach. This is compared with an exact
expression and found in agreement within the foreseen experimental accuracy.
This model describing single-photon radiation can be applied to the more
general case of initial-state single-photon emission accompanying invisible
final-state events. Higher-order QED corrections due to undetected
initial-state radiation are also included. The implementation in a Monte Carlo
event generator is briefly described.Comment: 10 pages, LaTeX, 7 figures available via anonymous ftp at:
ftp://cobra1.pv.infn.it/pub/phot/, files fig#n.ps with #=1,...,
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