3,953 research outputs found

### The Parton Model and its Applications

This is a review of the program we started in 1968 to understand and
generalize Bjorken scaling and Feynman's parton model in a canonical quantum
field theory. It is shown that the parton model proposed for deep inelastic
electron scatterings can be derived if a transverse momentum cutoff is imposed
on all particles in the theory so that the impulse approximation holds. The
deep inelastic electron-positron annihilation into a nucleon plus anything else
is related by the crossing symmetry of quantum field theory to the deep
inelastic electron-nucleon scattering. We have investigated the implication of
crossing symmetry and found that the structure functions satisfy a scaling
behavior analogous to the Bjorken limit for deep inelastic electron scattering.
We then find that massive lepton pair production in collisions of two high
energy hadrons can be treated by the parton model with an interesting scaling
behavior for the differential cross sections. This turns out to be the first
example of a class of hard processes involving two initial hadrons.Comment: Contribution to a book to be published by World Scientific for the
occasion of 50 Years of Quarks. 17 pages, 4 figure

### Fixed Point Actions for Lattice Fermions

The fixed point actions for Wilson and staggered lattice fermions are
determined by iterating renormalization group transformations. In both cases a
line of fixed points is found. Some points have very local fixed point actions.
They can be used to construct perfect lattice actions for asymptotically free
fermionic theories like QCD or the Gross-Neveu model. The local fixed point
actions for Wilson fermions break chiral symmetry, while in the staggered case
the remnant $U(1)_e \otimes U(1)_o$ symmetry is preserved. In addition, for
Wilson fermions a nonlocal fixed point is found that corresponds to free chiral
fermions. The vicinity of this fixed point is studied in the Gross-Neveu model
using perturbation theory.Comment: 6 pages, figures 1 and 4 included, figures 2,3,5,6,7 can be obtained
from [email protected]

### Structure Functions are not Parton Probabilities

Parton distributions given by deep inelastic lepton scattering (DIS) are not
equal to the probabilities of finding those partons in the parent wave
function. Soft rescattering of the struck parton within the coherence length of
the hard process influences the DIS cross section and gives dynamical phases to
the scattering amplitudes. This gives rise to diffractive DIS, shadowing in
nuclear targets and transverse spin asymmetry.Comment: Talk at ICHEP 2002, Amsterdam (July 2002). 3 pages, 1 figur

### Holographic model for dilepton production in p-p collisions

We propose a holographic model for dilepton production in proton-proton
collisions based on the exchange of vector mesons. The holographic hard wall
model is used to describe the dynamics and interactions of vector mesons and
baryons. We estimate the parameters lambda, mu, nu that characterize the
angular distribution of the produced dileptons in a region of q_T^2 << Q^2,
where perturbative QCD presents an effective strong coupling due to large
logarithm corrections.Comment: Revision: V4 In this version we modified the dimension of the
fermionic operator to match the canonical dimension of a baryonic operator.
This modification affected slightly our results with respect to v3. 25 pages,
3 Latex figures + 6 eps figures, 5 tables. To appear in Nucl. Phys.

### Generalized Pauli-Villars regularization for undoubled lattice fermions

A manifestly gauge invariant formulation of chiral theories with fermions on
the lattice is developed. It combines SLAC lattice derivative \cite{DWY},
\cite{ACS}, \cite{S} and generalized Pauli-Villars regularization \cite{FS}.
The theory is free of fermion doubling, requires only local gauge invariant
counterterms and produces correct results when applied to exactly solvable two
dimensional models.Comment: 10 pages LATEX fil

### CORE and the Haldane Conjecture

The Contractor Renormalization group formalism (CORE) is a real-space
renormalization group method which is the Hamiltonian analogue of the Wilson
exact renormalization group equations. In an earlier paper\cite{QGAF} I showed
that the Contractor Renormalization group (CORE) method could be used to map a
theory of free quarks, and quarks interacting with gluons, into a generalized
frustrated Heisenberg antiferromagnet (HAF) and proposed using CORE methods to
study these theories. Since generalizations of HAF's exhibit all sorts of
subtle behavior which, from a continuum point of view, are related to
topological properties of the theory, it is important to know that CORE can be
used to extract this physics. In this paper I show that despite the folklore
which asserts that all real-space renormalization group schemes are necessarily
inaccurate, simple Contractor Renormalization group (CORE) computations can
give highly accurate results even if one only keeps a small number of states
per block and a few terms in the cluster expansion. In addition I argue that
even very simple CORE computations give a much better qualitative understanding
of the physics than naive renormalization group methods. In particular I show
that the simplest CORE computation yields a first principles understanding of
how the famous Haldane conjecture works for the case of the spin-1/2 and spin-1
HAF.Comment: 36 pages, 4 figures, 5 tables, latex; extensive additions to conten

### Tau Kinematics from Impact Parameters

The momenta of $\tau$ decay products in the reaction $e^+e^-\to\tau^+\tau^-$
do not constrain the $\tau$ direction unambiguously. It is shown how the
measurement of tracks of hadrons from semileptonic $\tau$ decays, in particular
their relative impact parameters, allows to resolve this ambiguity.Comment: 4[pag]es, 1 figure available by FAX, TTP93-1

### High-temperature X-ray-diffractometer study of oxidation of two superalloys, WI-52 and IN-100

High temperature X ray diffractometer study of oxidation of heat resistant alloy

- â€¦