5,400 research outputs found
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
TOP-INDUCED ELECTROWEAK BREAKING IN THE MINIMAL SUPERSYMMETRIC STANDARD MODEL
Severe constraints on parameters of the minimal supersymmetric standard model
follow from a dynamical electroweak symmetry breaking mechanism dominated by
top and stop loops. In particular, the lightest Higgs boson mass is expected to
be smaller than 100 GeV.Comment: 10 pages, Latex, 6 Postcript Figure
Probing the infrared quark mass from highly excited baryons
We argue that three-quark excited states naturally group into quartets, split
into two parity doublets, and that the mass splittings between these parity
partners decrease higher up in the baryon spectrum. This decreasing mass
difference can be used to probe the running quark mass in the mid-infrared
power-law regime. A measurement of masses of high-partial wave Delta*
resonances should be sufficient to unambiguously establish the approximate
degeneracy. We test this concept with the first computation of excited high-j
baryon masses in a chirally invariant quark model.Comment: 4 pages, 4 figures. submitted to Phys Rev Letter
Using highly excited baryons to catch the quark mass
Chiral symmetry in QCD can be simultaneously in Wigner and Goldstone modes,
depending on the part of the spectrum examined. The transition regime between
both, exploiting for example the onset of parity doubling in the high baryon
spectrum, can be used to probe the running quark mass in the mid-IR power-law
regime. In passing we also argue that three-quark states naturally group into
same-flavor quartets, split into two parity doublets, all splittings decreasing
high in the spectrum. We propose that a measurement of masses of high-partial
wave Delta* resonances should be sufficient to unambiguously establish the
approximate degeneracy and see the quark mass running. We test these concepts
with the first computation of the spectrum of high-J excited baryons in a
chiral-invariant quark model.Comment: 6 pages, 9 figures, To appear in the proceedings of the 19th
International IUPAP Conference on Few-Body Problems in Physics; added
acknowledgment, hyphenized author nam
Local Two-Photon Couplings and the J=0 Fixed Pole in Real and Virtual Compton Scattering
The local coupling of two photons to the fundamental quark currents of a
hadron gives an energy-independent contribution to the Compton amplitude
proportional to the charge squared of the struck quark, a contribution which
has no analog in hadron scattering reactions. We show that this local
contribution has a real phase and is universal, giving the same contribution
for real or virtual Compton scattering for any photon virtuality and skewness
at fixed momentum transfer squared t. The t-dependence of this J=0 fixed Regge
pole is parameterized by a yet unmeasured even charge-conjugation form factor
of the target nucleon. The t=0 limit gives an important constraint on the
dependence of the nucleon mass on the quark mass through the Weisberger
relation. We discuss how this 1/x form factor can be extracted from high energy
deeply virtual Compton scattering and examine predictions given by models of
the H generalized parton distribution.Comment: 20 pages, 15 figure
Chiral Symmetry and Hyperfine Quark-Antiquark Splittings
We briefly review theoretical calculations for the pseudoscalar-vector meson
hyperfine splitting with no open flavor and also report a many body field
theoretical effort to assess the impact of chiral symmetry in the choice of
effective potentials for relativistic quark models. Our calculations predict
the missing eta_b meson to have mass near 9400 . The radial excitation
is in agreement with the measurements of the BELLE and most
recently BABAR collaborations.Comment: European HEP conference proceedings (Aachen, July 2003). A few
typographical errors correcte
Steady-state conduction in self-similar billiards
The self-similar Lorentz billiard channel is a spatially extended
deterministic dynamical system which consists of an infinite one-dimensional
sequence of cells whose sizes increase monotonically according to their
indices. This special geometry induces a nonequilibrium stationary state with
particles flowing steadily from the small to the large scales. The
corresponding invariant measure has fractal properties reflected by the
phase-space contraction rate of the dynamics restricted to a single cell with
appropriate boundary conditions. In the near-equilibrium limit, we find
numerical agreement between this quantity and the entropy production rate as
specified by thermodynamics
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