7,722 research outputs found
Analysis of dynamical corrections to baryon magnetic moments
We present and analyze QCD corrections to the baryon magnetic moments in
terms of the one-, two-, and three-body operators which appear in the effective
field theory developed in our recent papers. The main corrections are extended
Thomas-type corrections associated with the confining interactions in the
baryon. We investigate the contributions of low-lying angular excitations to
the moments quantitatively and show that they are completely negligible. When
the QCD corrections are combined with the non-quark model contributions of the
meson loops, we obtain a model which describes the moments within a mean
deviation of 0.04 . The nontrivial interplay of the two types of
corrections to the quark-model moments is analyzed in detail, and explains why
the quark model is so successful. In the course of these calculations, we
parametrize the general spin structure of the baryon wave functions
in a form which clearly displays the symmetry properties and the internal
angular momentum content of the wave functions, and allows us to use spin-trace
methods to calculate the many spin matrix elements which appear in the
expressions for the moments. This representation may be useful elsewhere.Comment: 32 pages, 3 figures, submitted to Phys. Rev.
Chiral QCD, General QCD Parameterization and Constituent Quark Models
Several recent papers -using effective QCD chiral Lagrangians- reproduced
results obtained with the general QCD parameterization (GP). These include the
baryon 8+10 mass formula, the octet magnetic moments and the coincidental
nature of the "perfect" -3/2 ratio between the magnetic moments of p and n.
Although we anticipated that the GP covers the case of chiral treatments, the
above results explicitly exemplify this fact. Also we show by the GP that -in
any model or theory (chiral or non chiral) reproducing the results of exact
QCD- the Franklin (Coleman Glashow) sum rule for the octet magnetic moments
must be violated.Comment: 10 pages, Latex; abridged version (same results), removed some
reference
Fixed Point and Aperiodic Tilings
An aperiodic tile set was first constructed by R.Berger while proving the
undecidability of the domino problem. It turned out that aperiodic tile sets
appear in many topics ranging from logic (the Entscheidungsproblem) to physics
(quasicrystals) We present a new construction of an aperiodic tile set that is
based on Kleene's fixed-point construction instead of geometric arguments. This
construction is similar to J. von Neumann self-reproducing automata; similar
ideas were also used by P. Gacs in the context of error-correcting
computations. The flexibility of this construction allows us to construct a
"robust" aperiodic tile set that does not have periodic (or close to periodic)
tilings even if we allow some (sparse enough) tiling errors. This property was
not known for any of the existing aperiodic tile sets.Comment: v5: technical revision (positions of figures are shifted
QSO hosts and environments at z=0.9 to 4.2: JHK images with adaptive optics
We have observed nine QSOs with redshifts 0.85 to 4.16 at near-IR wavelengths
with the adaptive optics bonnette of the Canada-France-Hawaii telescope.
Exposure times ranged from 1500 to 24000s (mostly near 7000s) in J, H, or K
bands, with pixels 0.035 arcsec on the sky. The FWHM of the co-added images at
the location of the quasars are typically 0.16 arcsec. Including another QSO
published previously, we find associated QSO structure in at least eight of ten
objects, including the QSO at z = 4.16. The structures seen in all cases
include long faint features which appear to be tidal tails. In four cases we
have also resolved the QSO host galaxy, but find them to be smooth and
symmetrical: future PSF removal may expand this result. Including one object
previously reported, of the nine objects with more extended structure, five are
radio-loud, and all but one of these appear to be in a dense small group of
compact galaxy companions. The radio-quiet objects do not occupy the same dense
environments, as seen in the NIR. In this small sample we do not find any
apparent trends of these properties with redshift, over the range 0.8 < z <
2.4. The colors of the host galaxies and companions are consistent with young
stellar populations at the QSO redshift. Our observations suggest that adaptive
optic observations in the visible region will exhibit luminous signatures of
the substantial star-formation activity that must be occurring.Comment: 22 pages including 10 tables, plus 11 figures. To appear in A
Sudden To Adiabatic Transition in Beta Decay
We discuss effects in beta decays at very low beta energies, of the order of
the kinetic energies of atomic electrons. As the beta energy is lowered the
atomic response changes from sudden to adiabatic. As a consequence, the beta
decay rate increases slightly and the ejection of atomic electrons (shake off)
and subsequent production of X rays is turned off. We estimate the transition
energy and the change in decay rate. The rate increase is largest in heavy
atoms, which have a small Q value in their decay. The X ray switch-off is
independent of Q value.Comment: 6 pages LaTe
Parametrised Complexity of Model Checking and Satisfiability in Propositional Dependence Logic
In this paper, we initiate a systematic study of the parametrised complexity
in the field of Dependence Logics which finds its origin in the Dependence
Logic of V\"a\"an\"anen from 2007. We study a propositional variant of this
logic (PDL) and investigate a variety of parametrisations with respect to the
central decision problems. The model checking problem (MC) of PDL is
NP-complete. The subject of this research is to identify a list of
parametrisations (formula-size, treewidth, treedepth, team-size, number of
variables) under which MC becomes fixed-parameter tractable. Furthermore, we
show that the number of disjunctions or the arity of dependence atoms
(dep-arity) as a parameter both yield a paraNP-completeness result. Then, we
consider the satisfiability problem (SAT) showing a different picture: under
team-size, or dep-arity SAT is paraNP-complete whereas under all other
mentioned parameters the problem is in FPT. Finally, we introduce a variant of
the satisfiability problem, asking for teams of a given size, and show for this
problem an almost complete picture.Comment: Update includes refined result
Octet Magnetic Moments with Null Instantons and Semibosonized Nambu-Jona-Lasinio Model
It is shown that the difference between the magnetic moment results in the
quark model with null instantons and semibosonized Nambu-Jona-Lasinio model
lies in the description of the magnetic moment of the -hyperon.Comment: RevTex, 6 pages, submitted to Progr.Theor.Phy
Calculable Upper Limit on the Mass of the Lightest Higgs Boson in Any Perturbatively Valid Supersymmetric Theory
We show that there is a calculable upper limit on the mass of the lightest
Higgs boson in any supersymmetric theory that remains perturbative up to a high
scale . There are no restrictions on the Higgs sector, or the gauge group or
particle content. We estimate the value of the upper limit to be m_{\hcirc} <
146 GeV for 100 GeV < < 145 GeV, from all effects except possibly
additional heavy fermions beyond top (which could increase the limit by 0-20
GeV if any existed); for > 145 GeV the limit decreases monotonically. We
expect to be able to decrease the value of the upper limit by at least a few
percent by very careful analysis of the conditions. It is not normal in models
for the actual mass to saturate the upper limit.Comment: 8 pages, UM-TH-92-24, Plain TeX. (One table available by fax on
request to [email protected]
Perturbative reliability of the Higgs-boson coupling in the standard electroweak model
We apply Pade summation to the \beta(\lambda) function for the quartic Higgs
coupling \lambda in the standard electroweak model. We use the \beta function
calculated to five loops in the minimal subtraction scheme to demonstrate the
improvement resulting from the summation, and then apply the method to the more
physical on-mass-shell renormalization scheme where \beta is known to three
loops. We conclude that the OMS \beta function and the running coupling
\lambda(\mu) are reliably known over the range of energies and Higgs-boson
masses of current interest.Comment: 14 pages, RevTeX, 6 figure
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