1,123 research outputs found

### A Parametrization for $K^+\to \pi^+\pi^- e^+\nu$

We discuss various models and Chiral Perturbation Theory results for the
$K_{l4}$ form factors $F$ and $G$. We check in how much a simple
parametrization with a few parameters can be used to extract information from
experiment.Comment: 19 pages, 14 figure

### The Pseudoscalar Meson Mass to Two Loops in Three-Flavor Partially Quenched $\chi$PT

This paper presents a first study of the pseudoscalar meson masses to two
loops, or NNLO, within the supersymmetric formulation of partially quenched
chiral perturbation theory (PQ$\chi$PT). The expression for the pseudoscalar
meson mass in the case of three valence and three sea quarks with equal masses,
but different from each other, is given to ${\cal O}(p^6)$, along with a
numerical analysis.Comment: 4 pages, one reference added, small changes in discussio

### QCD Short-distance Constraints and Hadronic Approximations

This paper discusses a general class of ladder resummation inspired hadronic
approximations. It is found that this approach naturally reproduces many
successes of single meson per channel saturation models (e.g. VMD) and NJL
based models. In particular the existence of a constituent quark mass and a gap
equation follows naturally. We construct an approximation that satisfies a
large set of QCD short-distance and large $N_c$ constraints and reproduces many
hadronic observables.
We show how there exists in general a problem between QCD short-distance
constraints for Green Functions and those for form factors and cross-sections
following from the quark-counting rule. This problem while expected for Green
functions that do not vanish in purely perturbative QCD also persists for many
Green functions that are order parameters.Comment: 27 page

### On the two-loop contributions to the pion mass

We derive a simplified representation for the pion mass to two loops in
three-flavour chiral perturbation theory. For this purpose, we first determine
the reduced expressions for the tensorial two-loop 2-point sunset integrals
arising in chiral perturbation theory calculations. Making use of those
relations, we obtain the expression for the pion mass in terms of the minimal
set of master integrals. On the basis of known results for these, we arrive at
an explicit analytic representation, up to the contribution from K-K-eta
intermediate states where a closed-form expression for the corresponding sunset
integral is missing. However, the expansion of this function for a small pion
mass leads to a simple representation which yields a very accurate
approximation of this contribution. Finally, we also give a discussion of the
numerical implications of our results.Comment: Typos corrected and minor changes in Table 2. Published version. 19
pages, 1 figure, 2 table

### Chiral Perturbation Theory and Threshold Corrections

I give a short overview of Chiral Perturbation Theory, its underlying
assumptions and underpinnings. A few examples are included.Comment: 8 pages, 4 figures, Talk presented at the MAX-lab Workshop on the
Nuclear Physics Programme with Real Photons below 200 MeV, Lund, Sweden,
March 10-12, 199

### Semileptonic $\pi$ and $K$ Decays and the Chiral Anomaly at One-loop

We calculate the $O(p^6)$ corrections to the anomalous form factors appearing
in $\pi^+$, $K^+ \to e^+ \nu \gamma,\ \mu^+\nu\gamma$ and $K_{l4}$ decays in
Chiral Perturbation Theory. The relevant dimension $6$ terms of the lagrangian
are evaluated assuming their saturation by the vector meson contribution.Comment: 10 pages of LaTeX (+3 figures available on request

### 2 and 3-point functions in the ENJL-model

We discuss the extended Nambu-Jona-Lasinio model as a low energy expansion,
all two-point functions and an example of a three-point function to all orders
in momenta and quark masses. The model is treated at leading level in $1/N_c$
but otherwise exact. Some comments about the QCD flavour anomaly and Vector
Meson Dominance in this class of models is made. Uses epsf.sty and rotate.sty.
One postscript figure included at the end.Comment: NORDITA 94/43 N,P, talk given by JB at QCD94, July 7-13, 1994,
Montpellier, Franc

### Integrating out strange quarks in ChPT

We study three flavour chiral perturbation theory in a limit where the
strange quark mass is much larger than the external momenta and the up and down
quark masses, and where the external fields are those of two-flavour chiral
perturbation theory. In this case, the theory reduces to the one of SU(2)_L x
SU(2)_R. Through this reduction, one can work out the strange quark mass
dependence of the LECs in the two-flavour case. We present the pertinent
relations at two-loop order for F,B and l_i.Comment: 14 pages, 3 figures, References added. Due to a typo in a form
program, we missed a finite, scale independent part in l_7. Is now included.
Version to appear in Phys.Lett.

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