648 research outputs found
QCD Isospin Breaking in Meson Masses, Decay Constants and Quark Mass Ratios
The procedure to calculate masses and matrix-elements in the presence of
mixing of the basis states is explained in detail. We then apply this procedure
to the two-loop calculation in Chiral Perturbation Theory of pseudoscalar
masses and decay constants including quark mass isospin breaking. These results
are used to update our analysis of done previously and obtain a
value of in addition to values for the low-energy-constants .Comment: 22 pages, uses axodraw.st
Scattering in Three Flavour ChPT
We present the scattering lengths for the processes in the three
flavour Chiral Perturbation Theory (ChPT) framework at next-to-next-to-leading
order (NNLO). The calculation has been performed analytically but we only
include analytical results for the dependence on the low-energy constants
(LECs) at NNLO due to the size of the expressions. These results, together with
resonance estimates of the NNLO LECs are used to obtain constraints on the
Zweig rule suppressed LECs at NLO, and . Contrary to
expectations from NLO order calculations we find them to be compatible with
zero. We do a preliminary study of combining the results from
scattering, scattering and the scalar form-factors and find only a
marginal compatibility with all experimental/dispersive input data.Comment: 23 page
The Inverse Amplitude Method in Scattering in Chiral Perturbation Theory to Two Loops
The inverse amplitude method is used to unitarize the two loop
scattering amplitudes of SU(2) Chiral Perturbation Theory in the ,
and channels. An error analysis in terms of the low energy
one-loop parameters and existing experimental data is
undertaken. A comparison to standard resonance saturation values for the two
loop coefficients is also carried out. Crossing
violations are quantified and the convergence of the expansion is discussed.Comment: (Latex, epsfig) 30 pages, 13 figures, 8 table
Meson resonances, large N_c and chiral symmetry
We investigate the implications of large N_c and chiral symmetry for the mass
spectra of meson resonances. Unlike for most other mesons, the mass matrix of
the light scalars deviates strongly from its large-N_c limit. We discuss the
possible assignments for the lightest scalar nonet that survives in the
large-N_c limit.Comment: 14 page
Assessing the conservation value of waterbodies: the example of the Loire floodplain (France)
In recent decades, two of the main management tools used to stem biodiversity erosion have been biodiversity monitoring and the conservation of natural areas. However, socio-economic pressure means that it is not usually possible to preserve the entire landscape, and so the rational prioritisation of sites has become a crucial issue. In this context, and because floodplains are one of the most threatened ecosystems, we propose a statistical strategy for evaluating conservation value, and used it to prioritise 46 waterbodies in the Loire floodplain (France). We began by determining a synthetic conservation index of fish communities (Q) for each waterbody. This synthetic index includes a conservation status index, an origin index, a rarity index and a richness index. We divided the waterbodies into 6 clusters with distinct structures of the basic indices. One of these clusters, with high Q median value, indicated that 4 waterbodies are important for fish biodiversity conservation. Conversely, two clusters with low Q median values included 11 waterbodies where restoration is called for. The results picked out high connectivity levels and low abundance of aquatic vegetation as the two main environmental characteristics of waterbodies with high conservation value. In addition, assessing the biodiversity and conservation value of
territories using our multi-index approach plus an a posteriori hierarchical classification methodology reveals two major interests: (i) a possible geographical extension and (ii) a multi-taxa adaptation
The epsilon expansion at next-to-next-to-leading order with small imaginary chemical potential
We discuss chiral perturbation theory for two and three quark flavors in the
epsilon expansion at next-to-next-to-leading order (NNLO) including a small
imaginary chemical potential. We calculate finite-volume corrections to the
low-energy constants and and determine the non-universal
modifications of the theory, i.e., modifications that cannot be mapped to
random matrix theory (RMT). In the special case of two quark flavors in an
asymmetric box we discuss how to minimize the finite-volume corrections and
non-universal modifications by an optimal choice of the lattice geometry.
Furthermore we provide a detailed calculation of a special version of the
massless sunset diagram at finite volume.Comment: 21 pages, 5 figure
Chiral Extrapolation of the Strangeness Changing K pi Form Factor
We perform a chiral extrapolation of lattice data on the scalar K pi form
factor and the ratio of the kaon and pion decay constants within Chiral
Perturbation Theory to two loops. We determine the value of the scalar form
factor at zero momentum transfer, at the Callan-Treiman point and at its soft
kaon analog as well as its slope. Results are in good agreement with their
determination from experiment using the standard couplings of quarks to the W
boson. The slope is however rather large. A study of the convergence of the
chiral expansion is also performed.Comment: few minor change
Two-point function of strangeness-carrying vector-currents in two-loop Chiral Perturbation Theory
We calculate the correlator between two external vector-currents having the
quantum-numbers of a charged kaon. We give the renormalized expression to two
loops in standard chiral perturbation theory in the isospin limit, which, as a
physical result, is finite and scale-independent. Applications include a low
energy theorem, valid at two loop order, of a flavor breaking combination of
vector current correlators as well as a determination of the phenomenologically
relevant finite -counterterm combination by means of inverse
moment finite energy sum rules. This determination is less sensitive to
isospin-breaking effects than previous attempts.Comment: 24 pages, revtex, 4 figures, 2 tables, revised version, one ref.
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Effective chiral lagrangian in the chiral limit from the instanton vacuum
We study the effective chiral Lagrangian in the chiral limit from the
instanton vacuum. Starting from the nonlocal effective chiral action, we derive
the effective chiral Lagrangian, using the derivative expansion to order
in the chiral limit. The low energy constants, , , and
are determined and compared with various models and the corresponding empirical
data. The results are in a good agreement with the data. We also discuss about
the upper limit of the sigma meson, based on the present results.Comment: 14 pages, 5 figures, submitted to Phys.Rev.
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