651,151 research outputs found
SYM Description of SFT Hamiltonian in a PP-Wave Background
We compute string field theory Hamiltonian matrix elements and compare them
with matrix elements of the dilatation operator in gauge theory. We get precise
agreement between the string field theory and gauge theory computations once
the correct cubic Hamiltonian matrix elements in string field theory and a
particular basis of states in gauge theory are used. We proceed to compute the
matrix elements of the dilatation operator to order g_2^2 in this same basis.
This calculation makes a prediction for string field theory Hamiltonian matrix
elements to order g_2^2, which have not yet been computed. However, our gauge
theory results precisely match the results of the recent computation by Pearson
et al. of the order g_2^2 Hamiltonian matrix elements of the string bit model.Comment: 17 pages, Latex. References corrected, clarifications adde
Theory and computation of electromagnetic transition matrix elements in the continuous spectrum of atoms
The present study examines the mathematical properties of the free-free (
f-f) matrix elements of the full electric field operator, of the multipolar
Hamiltonian. Special methods are developed and applied for their computation,
for the general case where the scattering wavefunctions are calculated
numerically in the potential of the term-dependent (N-1) electron core, and are
energy-normalized. It is found that, on the energy axis, the f-f matrix
elements of the full operator have singularities of first order in the case of
equal photoelectron energies. The numerical applications are for f-f
transitions in Hydrogen and Neon, obeying electric dipole and quadrupole
selection rules. In the limit of zero photon wave-number, the full operator
reduces to the length form of the electric dipole approximation (EDA). It is
found that the results for the EDA agree with those of the full operator, with
the exception of a photon wave-number region about the singularity.Comment: 39 pages, 11 figure
BRST cohomology in Beltrami parametrization
We study the BRST cohomology within a local conformal Lagrangian field theory
model built on a two dimensional Riemann surface with no boundary. We deal with
the case of the complex structure parametrized by Beltrami differential and the
scalar matter fields. The computation of {\em all} elements of the BRST
cohomology is given.Comment: 25 pages, LATE
Matrix Elements of Thiemann's Hamiltonian Constraint in Loop Quantum Gravity
We present an explicit computation of matrix elements of the hamiltonian
constraint operator in non-perturbative quantum gravity. In particular, we
consider the euclidean term of Thiemann's version of the constraint and compute
its action on trivalent states, for all its natural orderings. The calculation
is performed using graphical techniques from the recoupling theory of colored
knots and links. We exhibit the matrix elements of the hamiltonian constraint
operator in the spin network basis in compact algebraic form.Comment: 32 pages, 22 eps figures. LaTeX (Using epsfig.sty,ioplppt.sty and
bezier.sty). Submited to Classical and Quantum Gravit
Calculation of reduced coefficients and matrix elements in jj-coupling
A program RCFP will be presented for calculating standard quantities in the
decomposition of many-electron matrix elements in atomic structure theory. The
list of quantities wich are supported by the present program includes the
coefficients of fractional parentage, the reduced coefficients of fractional
parentage, the reduced matrix elements of the unit operator T^{(k)} as well as
the completely reduced matrix elements of the operator W^{(k_jk_q)} in
jj-coupling. These quantities are now available for all subshells (nj) with j
\leq 9/2 including partially filled 9/2-shells. Our program is based on a
recently developed new approach on the spin-angular integration which combines
second quantization and quasispin methods with the theory of angular momentum
in order to obtain a more efficient evaluation of many-electron matrix
elements. An underlying Fortran 90/95 module can directly be used also in
(other) atomic structure codes to accelerate the computation for open-shell
atoms and ions
Progress in computing parton distribution functions from the quasi-PDF approach
We discuss the current developments by the European Twisted Mass
Collaboration in extracting parton distribution functions from the quasi-PDF
approach. We concentrate on the non-perturbative renormalization prescription
recently developed by us, using the RI scheme. We show results for the
renormalization functions of matrix elements needed for the computation of
quasi-PDFs, including the conversion to the scheme, and for
renormalized matrix elements. We discuss the systematic effects present in the
-factors and the possible ways of addressing them in the future.Comment: 8 pages, 3 figures; Proceedings of the 35th International Symposium
on Lattice Field Theory, Granada, Spai
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