  A gauge invariant action for the open bosonic string has been proposed in an
earlier paper. We work out the consequences of this proposal for the lowest
mode, viz. the tachyon. The action can be calculated for generic momenta,
perturbatively, order by order in the tachyon field. For on shell tachyons we
explicitly calculate the cubic action and show that it reproduces the correct
equations of motion and coincides wih the $\beta$ function to the required
order. The calculation is done in terms of bare fields with a finite cutoff,
which is the original prescription. We also show that it is possible in some
momentum regions to renormalize the theory and eliminate the cutoff dependence
so that the continuum limit can be taken. After renormalization, the parameter
$R\over a$ is replaced by $R\over L$ where $R$ is an IR cutoff, $a$ is the UV
cutoff and $L$ is some renormalization scale. There is also some arbitrariness
in the overall normalization due to the choice of regularization scheme - this
does not affect on-shell quantities. We also rederive within this scheme, the
action in the region of zero momentum, which gives the exact (tree level)
tachyon potential. The tachyon potential is consistent with Sen's conjecture
that the height of the potential is the same as the tension of the brane.
