2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/190053We study cosmological effects of homogeneous tachyon field as dark energy. We concentrate on two different scalar field potentials, the inverse square potential and the exponential potential. These models have a unique feature that the matter density parameter and the density parameter for tachyons remain comparable for a large range in redshift. It is shown that there exists a range of parameters for which the universe undergoes an accelerated expansion and the evolution is consistent with structure formation requirements. For a viable model we require fine tuning of parameters comparable to that in LCDM or in quintessence models. For the exponential potential, the accelerated phase is followed by a phase with a(t)~ t^{2/3} thus eliminating a future horizon.3 pages, based on talk at PASCOS'03. To appear in special issue of PramanaAstrophysicsGeneral Relativity and Quantum CosmologyHigh Energy Physics - Theorytext