17,334 research outputs found
Light-Front QCD in Light-Cone Gauge
The light-front (LF) quantization of QCD in light-cone (l.c.) gauge is
discussed. The Dirac method is employed to construct the LF Hamiltonian and
theory quantized canonically. The Dyson-Wick perturbation theory expansion
based on LF-time ordering is constructed. The framework incorporates in it
simultaneously the Lorentz gauge condition as an operator equation as well. The
propagator of the dynamical part of the free fermionic propagator is
shown to be causal while the gauge field propagator is found to be transverse.
The interaction Hamiltonian is re-expressed in the form closely resembling the
one in covariant theory, except for additional instantaneous interactions,
which can be treated systematically. Some explicit computations in QCD are
given.Comment: Presented at VII Hadron Physics 2000, Caraguatatuba, Sao Paulo,
Brazil, 10-15 April 200
LANDSAT-4 horizon scanner full orbit data averages
Averages taken over full orbit data spans of the pitch and roll residual measurement errors of the two conical Earth sensors operating on the LANDSAT 4 spacecraft are described. The variability of these full orbit averages over representative data throughtout the year is analyzed to demonstrate the long term stability of the sensor measurements. The data analyzed consist of 23 segments of sensor measurements made at 2 to 4 week intervals. Each segment is roughly 24 hours in length. The variation of full orbit average as a function of orbit within a day as a function of day of year is examined. The dependence on day of year is based on association the start date of each segment with the mean full orbit average for the segment. The peak-to-peak and standard deviation values of the averages for each data segment are computed and their variation with day of year are also examined
On Intrinsic Magnetic Moments In Black Hole Candidates
In previous work we found that many of the spectral properties of low mass
x-ray binaries, including galactic black hole candidates could be explained by
a magnetic propeller model that requires an intrinsically magnetized central
object. Here we describe how the Einstein field equations of General Relativity
and equipartition magnetic fields permit the existence of highly red shifted,
extremely long lived, collapsing, radiating objects. We examine the properties
of these collapsed objects and discuss characteristics that might lead to their
confirmation as the source of black hole candidate phenomena.Comment: 4 pages, emulateapj, accepted for ApJ Letters, October 20, 200
The general theory of convolutional codes
This article presents a self-contained introduction to the algebraic theory of convolutional codes. This introduction is partly a tutorial, but at the same time contains a number of new results which will prove useful for designers of advanced telecommunication systems. Among the new concepts introduced here are the Hilbert series for a convolutional code and the class of compact codes
Illuminating the 1/x moment of parton distribution functions
The Weisberger relation, an exact statement of the parton model, elegantly
relates a high-energy physics observable, the 1/x moment of parton distribution
functions, to a nonperturbative low-energy observable: the dependence of the
nucleon mass on the value of the quark mass or its corresponding quark
condensate. We show that contemporary fits to nucleon structure functions fail
to determine this 1/x moment; however, deeply virtual Compton scattering can be
described in terms of a novel F_{1/x}(t) form factor which illuminates this
physics. An analysis of exclusive photon-induced processes in terms of the
parton-nucleon scattering amplitude with Regge behavior reveals a failure of
the high Q^2 factorization of exclusive processes at low t in terms of the
Generalized Parton-Distribution Functions which has been widely believed to
hold in the past. We emphasize the need for more data for the DVCS process at
large t in future or upgraded facilities.Comment: 11 pages, 3 figures, invited contribution to the 11th International
Conference on Meson-Nucleon Physics and the Structure of the Nucleon, sept.
10th-14th 2007, Juelich, German
A Porosity-Length Formalism for Photon-Tiring-Limited Mass Loss from Stars Above the Eddington Limit
We examine radiatively driven mass loss from stars near and above the
Eddington limit (Ledd). We begin by reviewing the instabilities that are
expected to form extensive structure near Ledd. We investigate how this
"porosity" can reduce the effective coupling between the matter and radiation.
Introducing a new "porosity-length'' formalism, we derive a simple scaling for
the reduced effective opacity, and use this to derive an associated scaling for
the porosity-moderated, continuum-driven mass loss rate from stars that
formally exceed Ledd. For a simple super-Eddington model with a single porosity
length that is assumed to be on the order of the gravitational scale height,
the overall mass loss is similar to that derived in previous porosity work.
This is much higher than is typical of line-driven winds, but is still only a
few percent of the photon tiring limit--for which the luminosity becomes
insufficient to carry the flow out of the gravitational potential. To obtain
still stronger mass loss that approaches observationally inferred values near
this limit, we introduce a power-law-porosity model in which the associated
structure has a broad range of scales. We show that the mass loss rate can be
enhanced by a factor that increases with the Eddington parameter Gamma, such
that for moderately large Gamma (> 3-4), mass loss rates could approach the
photon tiring limit. Together with the ability to drive quite fast outflow
speeds, the derived mass loss could explain the large inferred mass loss and
flow speeds of giant outbursts in eta Carinae and other LBV stars.Comment: 17 pages, 6 figures, to appear in Ap
Hadron Spin Dynamics
Spin effects in exclusive and inclusive reactions provide an essential new
dimension for testing QCD and unraveling hadron structure. Remarkable new
experiments from SLAC, HERMES (DESY), and the Jefferson Laboratory present many
challenges to theory, including measurements at HERMES and SMC of the single
spin asymmetries in pion electroproduction, where the proton is polarized
normal to the scattering plane. This type of single spin asymmetry may be due
to the effects of rescattering of the outgoing quark on the spectators of the
target proton, an effect usually neglected in conventional QCD analyses. Many
aspects of spin, such as single-spin asymmetries and baryon magnetic moments
are sensitive to the dynamics of hadrons at the amplitude level, rather than
probability distributions. I illustrate the novel features of spin dynamics for
relativistic systems by examining the explicit form of the light-front
wavefunctions for the two-particle Fock state of the electron in QED, thus
connecting the Schwinger anomalous magnetic moment to the spin and orbital
momentum carried by its Fock state constituents and providing a transparent
basis for understanding the structure of relativistic composite systems and
their matrix elements in hadronic physics. I also present a survey of
outstanding spin puzzles in QCD, particularly the double transverse spin
asymmetry A_{NN} in elastic proton-proton scattering, the J/psi to rho-pi
puzzle, and J/psi polarization at the Tevatron.Comment: Concluding theory talk presented at SPIN2001, the Third
Circum-Pan-Pacific Symposium on High Energy Physics, October, 2001, Beijin
- …