We study the dynamics of the tachyon field T. We derive the mass of the tachyon as the pole of the propagator which does not coincide with the standard mass given in the literature in terms of the second derivative of V(T) or LogV(T). We determine the transformation of the tachyon in order to have a canonical scalar field phi. This transformation reduces to the one obtained for small T but it is also valid for large values of T. This is specially interesting for the study of dark energy where T similar or equal to 1. We also show that the normalized tachyon field phi is constrained to the interval T-2 <= T <= T-1 where T-1, T-2 are zeros of the original potential V(T). This results shows that the field phi does not know of the unboundedness of V (T), as suggested for bosonic open string tachyons. Finally we study the late time behavior of tachyon field using the L'Hopital rule. (c) 2006 Elsevier B.V. All rights reserved.
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