QCD spectrum from the lattice Page: 3 of 11
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QCD SPECTRUM FROM THE LATTICE
GUPTA Rnjan
T-8, MS-D2S5, -os Alamos National Laboratory
Los Alamos, NM 87545, U.S.A.
ABSTRACT
Considerable progress has been made in the last year to derive the spectrum from QCD
in the quenched approximation. I review the results for the proton to rho mass ratio and
■'how that we are close to getting results to within 10%. I present new results for 0+ + and
glue hulls. These results nre qualitative since we do not address the question of mixing
of gluehalls with quark states. Finally, I give a status report on the full QCD calculations (2
flavors of dynamical Wilson fermions) being done on the Connection Machine 2.
INTRODUCTION
I would like* to la-gin this talk with a semi-apology: Present Lattice QCD calculations do
not predict numbers for the hadron spectrum (mesons, haryons, glueballs) that are reliable to
Letter than 100 MeV. The reason for this is not that we have been idle (or more appropriately
that the computers have beei idle) but because so far we have been simulating an approximate
theory - SU(3) color without dynamical fermions (riy =0 flavor approximation). It may very
wi ll turn out that this approximation is very good for certain observables; unfortunately this
Jimit realion cun only comf a-posteriori after we have simulated the real theory. On the other
hand, to predict the glueball spectrum we definitely need to understand mixing with meson
sinti"-. In this latter case quenched results should only be considered qualitative.
Quenched simulations provide an important reference point. Most of the software and
nuuM iicid measurement techniques carry over unchanged to the real theory. Also, since pure
I’.iiuge theory. Sl’(3), is confining and asymptotically free it contains the qualitative essence of
ihe teal world. Further, chiral symmetry can la- studied in the quenched approximation: the
chiial behavior of obsi rvahles can be derived and checked. It is therefore very important to ge)
si at ist h ally significant numbers for the uy ~ () world so that one can there after systematically
i xuuiine i lie effect of quark loops in My - 2. 3,-I simulations.
1 he notation used below is as follows: The gauge Coupling is defined by The
quail; mass is given by n for Wilson fermions, and mi, is the strange quark mass. I use
a '-upei sei ipt e (</) for valence (dynamical) quarks when ever necessary. The spatial volume
i- denoted bv A,1 and the temporal siz« by .V, such that the lattice size is .V'1 x A',. Before
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Gupta, R. QCD spectrum from the lattice, article, January 1, 1989; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1093372/m1/3/: accessed March 29, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.