3,106 research outputs found
Zeno Dynamics of von Neumann Algebras
The dynamical quantum Zeno effect is studied in the context of von Neumann
algebras. We identify a localized subalgebra on which the Zeno dynamics acts by
automorphisms. The Zeno dynamics coincides with the modular dynamics of that
subalgebra, if an additional assumption is satisfied. This relates the modular
operator of that subalgebra to the modular operator of the original algebra by
a variant of the Kato-Lie-Trotter product formula.Comment: Revised version; further typos corrected; 9 pages, AMSLaTe
Electric dipole rovibrational transitions in HD molecule
The rovibrational electric dipole transitions in the ground electronic state
of the HD molecule are studied. A simple, yet rigorous formula is derived for
the transition rates in terms of the electric dipole moment function ,
which is calculated in a wide range of . Our numerical results for
transition rates are in moderate agreement with experiments and previous
calculations, but are at least an order of magnitude more accurate.Comment: 7 pages, 1 figur
Time and dose dependency of bone-sarcomas in patients injected with radium-224
The time course and dose dependency of the incidence of bone-sarcomas among 900 German patients treated with high doses of radium-224 is analysed in terms of a proportional hazards model with a log-normal dependency of time to tumor and a linear-quadratic dose relation. The deduced dose dependency agrees well with a previous analysis in terms of a non-parametric proportional hazards model, and confirms the temporal distribution which has been used in the Radioepidemiological Tables of NIH. However, the linear-quadratic dose-response model gives a risk estimate for low doses which is somewhat less than half that obtained under the assumption of linearity.
Dedicated to Prof. W. Jacobi on the occasion of his 60th birthday
Work performed under Euratom contracts BI6-D-083-D, BI6-F-111-D, U.S. Department of Energy contract DE-AC 02-76 EV-00119, the U.S. National Cancer Institut
Electromagnetic Meson Form Factors in the Salpeter Model
We present a covariant scheme to calculate mesonic transitions in the
framework of the Salpeter equation for -states. The full Bethe
Salpeter amplitudes are reconstructed from equal time amplitudes which were
obtained in a previous paper\cite{Mue} by solving the Salpeter equation for a
confining plus an instanton induced interaction. This method is applied to
calculate electromagnetic form factors and decay widths of low lying
pseudoscalar and vector mesons including predictions for CEBAF experiments. We
also describe the momentum transfer dependence for the processes
.Comment: 22 pages including 10 figure
The Rotation Average in Lightcone Time-Ordered Perturbation Theory
We present a rotation average of the two-body scattering amplitude in the
lightcone time()-ordered perturbation theory. Using a rotation average
procedure, we show that the contribution of individual time-ordered diagram can
be quantified in a Lorentz invariant way. The number of time-ordered diagrams
can also be reduced by half if the masses of two bodies are same. In the
numerical example of theory, we find that the higher Fock-state
contribution is quite small in the lightcone quantization.Comment: 25 pages, REVTeX, epsf.sty, 69 eps file
Study of relativistic bound states for scalar theories in Bethe-Salpeter and Dyson-Schwinger formalism
The Bethe-Salpeter equation for Wick-Cutkosky like models is solved in
dressed ladder approximation. The bare vertex truncation of the Dyson-Schwinger
equations for propagators is combined with the dressed ladder Bethe-Salpeter
equation for the scalar S-wave bound state amplitudes. With the help of
spectral representation the results are obtained directly in Minkowski space.
We give a new analytic formula for the resulting equation simplifying the
numerical treatment. The bare ladder approximation of Bethe-Salpeter equation
is compared with the one with dressed ladder. The elastic electromagnetic form
factors is calculated within the relativistic impulse approximation.Comment: 30 pages, 10 figures, accepted for publication in Phys. Rev.
Angular Conditions,Relations between Breit and Light-Front Frames, and Subleading Power Corrections
We analyze the current matrix elements in the general collinear (Breit)
frames and find the relation between the ordinary (or canonical) helicity
amplitudes and the light-front helicity amplitudes. Using the conservation of
angular momentum, we derive a general angular condition which should be
satisfied by the light-front helicity amplitudes for any spin system. In
addition, we obtain the light-front parity and time-reversal relations for the
light-front helicity amplitudes. Applying these relations to the spin-1 form
factor analysis, we note that the general angular condition relating the five
helicity amplitudes is reduced to the usual angular condition relating the four
helicity amplitudes due to the light-front time-reversal condition. We make
some comments on the consequences of the angular condition for the analysis of
the high- deuteron electromagnetic form factors, and we further apply the
general angular condition to the electromagnetic transition between spin-1/2
and spin-3/2 systems and find a relation useful for the analysis of the
N- transition form factors. We also discuss the scaling law and the
subleading power corrections in the Breit and light-front frames.Comment: 24 pages,2 figure
On the Decomposition of Clifford Algebras of Arbitrary Bilinear Form
Clifford algebras are naturally associated with quadratic forms. These
algebras are Z_2-graded by construction. However, only a Z_n-gradation induced
by a choice of a basis, or even better, by a Chevalley vector space isomorphism
Cl(V) \bigwedge V and an ordering, guarantees a multi-vector decomposition
into scalars, vectors, tensors, and so on, mandatory in physics. We show that
the Chevalley isomorphism theorem cannot be generalized to algebras if the
Z_n-grading or other structures are added, e.g., a linear form. We work with
pairs consisting of a Clifford algebra and a linear form or a Z_n-grading which
we now call 'Clifford algebras of multi-vectors' or 'quantum Clifford
algebras'. It turns out, that in this sense, all multi-vector Clifford algebras
of the same quadratic but different bilinear forms are non-isomorphic. The
usefulness of such algebras in quantum field theory and superconductivity was
shown elsewhere. Allowing for arbitrary bilinear forms however spoils their
diagonalizability which has a considerable effect on the tensor decomposition
of the Clifford algebras governed by the periodicity theorems, including the
Atiyah-Bott-Shapiro mod 8 periodicity. We consider real algebras Cl_{p,q} which
can be decomposed in the symmetric case into a tensor product Cl_{p-1,q-1}
\otimes Cl_{1,1}. The general case used in quantum field theory lacks this
feature. Theories with non-symmetric bilinear forms are however needed in the
analysis of multi-particle states in interacting theories. A connection to
q-deformed structures through nontrivial vacuum states in quantum theories is
outlined.Comment: 25 pages, 1 figure, LaTeX, {Paper presented at the 5th International
Conference on Clifford Algebras and their Applications in Mathematical
Physics, Ixtapa, Mexico, June 27 - July 4, 199
Solution of the Bethe-Salpeter equation for pion-nucleon scattering
A relativistic description of pion-nucleon scattering based on the
four-dimensional Bethe-Salpeter equation is presented. The kernel of the
equation consists of s- and u-channel nucleon and delta pole diagrams, as well
as rho and sigma exchange in the t-channel. The Bethe-Salpeter equation is
solved by means of a Wick rotation, and good fits are obtained to the s- and
p-wave phase shifts up to 360 MeV pion laboratory energy. The coupling
constants determined by the fits are consistent with the commonly accepted
values in the literature.Comment: 34 pages, RevTeX; 7 figures. Several references added, a few typos
corrected. Accepted for publication in Physical Review
Reactivity of Gold Hydrides: O2 Insertion into the Au–H Bond
Dioxygen reacts with the gold(I) hydride (IPr)AuH under insertion to give the hydroperoxide, (IPr)AuOOH, a long-postulated reaction in gold catalysis and the first demonstration of O2 activation by Au-H in a well-defined system. Subsequent condensation gave the peroxide (IPr)Au-OO-Au(IPr) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene). The reaction kinetics are reported, as well as the reactivity of Au(I) hydrides with radical scavengers
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