Physics – High Energy Physics – High Energy Physics - Phenomenology
Scientific paper
2007-05-03
Phys.Rev.D76:036002,2007
Physics
High Energy Physics
High Energy Physics - Phenomenology
Revtex 9 pages, typoes corrected, version to be published in Phys. Rev. D
Scientific paper
10.1103/PhysRevD.76.036002
We study the uncertainties of the determination of the ground-state parameters from Shifman-Vainshtein-Zakharov (SVZ) sum rules, making use of the harmonic-oscillator potential model as an example. In this case, one knows the exact solution for the polarization operator $\Pi(\mu)$, which allows one to obtain both the OPE to any order and the spectrum of states. We start with the OPE for $\Pi(\mu)$ and analyze the extraction of the square of the ground-state wave function, $R\propto|\Psi_0(\vec r=0)|^2$, from an SVZ sum rule, setting the mass of the ground state $E_0$ equal to its known value and treating the effective continuum threshold as a fit parameter. We show that in a limited ``fiducial'' range of the Borel parameter there exists a solution for the effective threshold which precisely reproduces the exact $\Pi(\mu)$ for any value of $R$ within the range $0.7 \le R/R_0 \le 1.15$ ($R_0$ is the known exact value). Thus, the value of $R$ extracted from the sum rule is determined to a great extent by the contribution of the hadron continuum. Our main finding is that in the cases where the hadron continuum is not known and is modeled by an effective continuum threshold, the systematic uncertainties of the sum-rule procedure cannot be controlled.
Lucha Wolfgang
Melikhov Dmitri
Simula Silvano
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