Jin, X and Nielsen, M and Pasupathy, J (1994) Calculation of $<p\overline{u}u\overline{d}dp>$ from QCD sum rule and the neutronproton mass difference. [Preprint]

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Abstract
The proton matrix element of the isovectorscalar density, $<p\overline{u}u\overline{d}dp>/2M_p$, is calculated by evaluating the nucleon current correlation function in an external isovectorscalar field using the QCD sumrule method. In addition to the usual chiral and gluon condensates of the QCD vacuum, the response of the chiral condensates to the external isovector field enters the calculation. The latter is determined by two independent methods. One relates it to the difference between the up and down quark chiral condensates and the other uses the chiral perturbation theory. To first order in the quark mass difference $\delta m=m_dm_u$, the nonelectromagnetic part of the neutronproton mass difference is given by the product $\delta m <p\overline{u}u\overline{d}dp>/2M_p$; the resulting value is in reasonable agreement with the experimental value.
Item Type:  Preprint 

Additional Information:  Phys.Rev. D51 (1995) 36883696 
Department/Centre:  Division of Physical & Mathematical Sciences > Centre for Theoretical Studies (Ceased to exist at the end of 2003) 
Date Deposited:  13 Aug 2004 
Last Modified:  19 Sep 2010 04:13 
URI:  http://eprints.iisc.ac.in/id/eprint/910 
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