Extraction of light quark masses from sum rule analyses of axial vector and vector current Ward identities

Mar, 1997
28 pages
Published in:
  • Phys.Rev.D 57 (1998) 5455-5467
e-Print:
Report number:
  • LA-UR-96-2698

Citations per year

1997199920012003200502468
Abstract:
We re-examine the use of sum rules in the extraction of light quark masses and discuss a number of potential problems with existing analyses. The most important issue is that of the overall normalization of the hadronic spectral functions should not be fixed by assuming complete resonance dominance of the continuum threshold region as it can overestimate the resonance contributions to spectral integrals by factors as large as 5\sim 5. The second important uncertainty comes from the assumed location, s0s_0, of the onset of duality with perturbative QCD, as the extracted quark masses depend very sensitively on this parameter. The assumption of duality and the requirement of positivity of ρ5(s)\rho_5(s) imposes very severe constraints on the shape of the relevant spectral function in the dual region, and leads to rigorous lower bounds for mu+mdm_u+m_d as a function of s0s_0. In the extractions of msm_s we find that the conventional choice of the value of s0s_0 is not physical. For a more reasonable choice of s0s_0 we are not able to find a solution that is stable with respect to variations of the Borel transform parameter. This problem can be overcome only if the hadronic spectral function is determined up to significantly larger values of ss than is currently possible. Finally, we also estimate the error associated with the convergence of perturbative QCD expressions used in the sum rule analyses. Our conclusion is that, taking all of these issues into account, the resulting sum rule estimates for both mu+mdm_u+m_d and msm_s could easily have uncertainties as large as a factor of 2.
Note:
  • 28 pages. Published version. Modified axis source for figures also included Report-no: LAUR-96-2698 Journal-ref: Phys.Rev. D57 (1998) 5455-5467 DOI: 10.1103/PhysRevD.57.5455
  • quark: mass
  • sum rule: finite energy
  • current: vector
  • current: axial-vector
  • spectral representation
  • Ward identity
  • perturbation theory: chiral
  • quantum chromodynamics: perturbation theory
  • two-point function
  • duality