We present measurements of the redshift-space three-point correlation
function of 50,967 Luminous Red Galaxies (LRGs) from Data Release 3 (DR3) of
the Sloan Digital Sky Survey (SDSS). We have studied the shape dependence of
the reduced three-point correlation function (Qz(s,q,theta)) on three different
scales, s=4, 7 and 10 h-1 Mpc, and over the range of 1 < q < 3 and 0 < theta <
180. On small scales (s=4 h-1 Mpc), Qz is nearly constant, with little change
as a function of q and theta. However, there is evidence for a shallow U-shaped
behaviour (with theta) which is expected from theoretical modeling of Qz . On
larger scales (s=7 and 10 h-1 Mpc), the U-shaped anisotropy in Qz (with theta)
is more clearly detected. We compare this shape-dependence in Qz(s,q,theta)
with that seen in mock galaxy catalogues which were generated by populating the
dark matter halos in large N-body simulations with mock galaxies using various
Halo Occupation Distributions (HOD). We find that the combination of the
observed number density of LRGs, the (redshift-space) two-point correlation
function and Qz provides a strong constraint on the allowed HOD parameters
(M_min, M_1, alpha) and breaks key degeneracies between these parameters. For
example, our observed Qz disfavors mock catalogues that overpopulate massive
dark matter halos with many LRG satellites. We also estimate the linear bias of
LRGs to be b=1.87+/-0.07 in excellent agreement with other measurements.Comment: 14 pages. Accepted for publication to the MNRAS. Data accompanying
paper can be found at http://www.dsg.port.ac.uk/~nicholb/3pt/kulkarni
