Experimental string field theory

We develop efficient algorithms for level-truncation computations in openbosonic string field theory. We determine the classical action in the universalsubspace to level (18,54) and apply this knowledge to numerical evaluations ofthe tachyon condensate string field. We obtain two main sets of results. First,we directly compute the solutions up to level L=18 by extremizing thelevel-truncated action. Second, we obtain predictions for the solutions for L >18 from an extrapolation to higher levels of the functional form of the tachyoneffective action. We find that the energy of the stable vacuum overshoots -1(in units of the brane tension) at L=14, reaches a minimum E_min = -1.00063 atL ~ 28 and approaches with spectacular accuracy the predicted answer of -1 as L-> infinity. Our data are entirely consistent with the recent perturbativeanalysis of Taylor and strongly support the idea that level-truncation is aconvergent approximation scheme. We also check systematically that ournumerical solution, which obeys the Siegel gauge condition, actually satisfiesthe full gauge-invariant equations of motion. Finally we investigate thepresence of analytic patterns in the coefficients of the tachyon string field,which we are able to reliably estimate in the L -> infinity limit.Comment: 37 pages, 6 figure