Diquark properties from full QCD lattice simulations
Anthony Francis, Philippe de Forcrand, Randy Lewis, Kim Maltman
Abstract
A bstract We study diquarks on the lattice in the background of a static quark, in a gauge-invariant formalism with quark masses down to almost physical m π . We determine mass differences between diquark channels as well as diquark-quark mass differences. The lightest and next-to-lightest diquarks have “good” scalar, $$ {\overline{3}}_F $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mover> <mml:mn>3</mml:mn> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>F</mml:mi> </mml:msub> </mml:math> , $$ {\overline{3}}_c $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mover> <mml:mn>3</mml:mn> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>c</mml:mi> </mml:msub> </mml:math> , J P = 0 + , and “bad” axial vector, 6 F , $$ {\overline{3}}_c $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mover> <mml:mn>3</mml:mn> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>c</mml:mi> </mml:msub> </mml:math> , J P = 1 + , quantum numbers, and a bad-good mass difference for ud flavors, 198(4) MeV, in excellent agreement with phenomenological determinations. Quark-quark attraction is found only in the “good” diquark channel. We extract a corresponding diquark size of ∼ 0 . 6 fm and perform a first exploration of the “good” diquark shape, which is shown to be spherical. Our results provide quantitative support for modeling the low-lying baryon spectrum using good light diquark effective degrees of freedom.