3,689 research outputs found
Approximating chiral SU(3) amplitudes
We construct large-N_c motivated approximate chiral SU(3) amplitudes of
next-to-next-to-leading order. The amplitudes are independent of the
renormalization scale. Fitting lattice data with those amplitudes allows for
the extraction of chiral coupling constants with the correct scale dependence.
The differences between approximate and full amplitudes are required to be at
most of the order of N^3LO contributions numerically. Applying the approximate
expressions to recent lattice data for meson decay constants, we determine
several chiral couplings with good precision. In particular, we obtain a value
for F_0, the meson decay constant in the chiral SU(3) limit, that is more
precise than all presently available determinations.Comment: 19 pages, 4 figures, improved presentation, results unchanged,
version to appear in EPJ
The magnetic reorientation transition in thin ferromagnetic films treated by many-body Green's function theory
This contribution describes the reorientation of the magnetization of thin
ferromagnetic Heisenberg films as function of the temperature and/or an
external field. Working in a rotating frame allows an exact treatment of the
single-ion anisotropy when going to higher-order Green's functions. Terms due
to the exchange interaction are treated by a generalized Tyablikov (RPA)
decoupling.Comment: 9 pages, 2 figure
Thomas Paine\u27s (Un)Common Sense and the Politics of Radical Disagreement
In this paper, I offer a re-reading of Thomas Paine\u27s influential pamphlet Common Sense (1776) and argue his idiosyncratic notion of common sense is amenable to a radical democratic theory of political practice
The spectral theorem of many-body Green's function theory when there are zero eigenvalues of the matrix governing the equations of motion
In using the spectral theorem of many-body Green's function theory in order
to relate correlations to commutator Green's functions, it is necessary in the
standard procedure to consider the anti-commutator Green's functions as well
whenever the matrix governing the equations of motion for the commutator
Green's functions has zero eigenvalues. We show that a singular-value
decomposition of this matrix allows one to reformulate the problem in terms of
a smaller set of Green's functions with an associated matrix having no zero
eigenvalues, thus eliminating the need for the anti-commutator Green's
functions. The procedure is quite general and easy to apply. It is illustrated
for the field-induced reorientation of the magnetization of a ferromagnetic
Heisenberg monolayer and it is expected to work for more complicated cases as
well.Comment: 4 pages, 1 figure, accepted for publication in Physical Review B (16.
May 2003
Role of Scalar Meson Resonances in $K_{L}^{0} \rightarrow \pi^{0} \gamma \gamma Decay
Corrections to decay induced by
scalar meson exchange are studied within chiral perturbation theory. In spite
of bad knowledge of scalar-mesons parameters, the calculated branching ratio
can be changed by a few percent.Comment: 18 pages of text, 2 figures (available upon request); preprint
IJS-TP-16-94 , TUM-T31-63-94
Form Factors at Two-loop
Within Chiral Perturbation Theory (CHPT) we compute the form factors A, V and
in the decay to . A and
obtain corrections of order 25%.Comment: Added cut-off dependence discusion, misprints correcte
Improving the Hadronization of QCD currents in TAUOLA and PHOKHARA
We present our study of the hadronization structure of both vector and
axial-vector currents leading to decays of the tau into two kaons and a pion.
The cornerstones of our framework are the large-N_C limit of QCD, the chiral
structure exhibited at low energies and the proper asymptotic behaviour, ruled
by QCD, that is demanded to the associated form factors. The couplings of the
theory are mostly constrained by this procedure and upon the analysis of BaBar
data on e^+e^- -> KK pi we are able to predict the hadronic spectra.Comment: 4 pages, 1 figure. To appear in the Proceedings of QCD 08: 14th
International QCD Conference, 7-12th July 2008 Montpellier (France). To be
published by Elsevier in Nuclear Physics B (Proceedings Supplement
Long-distance contribution to the forward-backward asymmetry in decays K+ --> pi+ l+ l-
The long-distance contribution via the two-photon intermediate state to the
forward-backward asymmetries in decays K+ --> pi+ l+ l- (l=e and mu) has been
studied within the standard model. In order to evaluate the dispersive part of
the K+ --> pi+ gamma* gamma* --> pi+ l+ l- amplitude, we employ a
phenomenological form factor to soften the ultraviolet behavior of the
transition. It is found that, this long-distance transition, although subject
to some theoretical uncertainties, can lead to significant contributions to the
forward-backward asymmetries, which could be tested in the future high-precise
experiments.Comment: 13 pages, 5 figure
Sensitivity to new physics: a_e vs. a_mu
At present it is generally believed that ``new physics'' effects contribute
to leptonic anomalous magnetic moment, a_l, via quantum loops only and they are
proportional to the squared lepton mass, (m_l)^2. An alternative mechanism for
a contribution by new physics is proposed. It occurs at the tree level and
exhibits a linear rather than quadratic dependence on m_l. This leads to a much
larger sensitivity of a_e to the new physics than was expected so far.Comment: 4 pages, 2 figure
On the Corrections to Dashen's Theorem
The electromagnetic corrections to the masses of the pseudoscalar mesons
and are considered. We calculate in chiral perturbation theory the
contributions which arise from resonances within a photon loop at order . Within this approach we find rather moderate deviations to Dashen's
theorem.Comment: 14 pages, sligthly enlarged version; a numerical error is corrected
and the embedding of the figures is improved. The complete paper, including
figures, is also available via anonymous ftp at
ftp://www-ttp.physik.uni-karlsruhe.de/ , or via www at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints/; to be published in
Phys.Rev.
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