Cosmological Constant, Generalized Tachyon Field, Spacetime Inequality, And The Accelerated Expansion Of The Universe

With a 2-3 Gyr-old quasar APM08279+5255 at z=3.91,the age problem in the ACDM model is reexamined in a consistent way free of any systematic errors in measured values ofΩ_m and H₀.TheΛCDM model accommodates the total age(14 Gyr) of the Universe estimated from old globular clusters,but cannot accommodate this old quasar APM08279+5255 at high confidence level constrained from SNIa,CMB, BAO and H(z) observations.Studying the purely kinetic k-essence models in which the Lagrangian contains only a kinetic factor and does not depend explicitly on the field itself,we obtain a theoretical constraint.Under this theoretical constraint,we discuss the phantom-like generalized tachyon field,and find that this kind of generalized tachyon field will not result in a big rip,but will be singular in the past,unless it behaves like the cosmological constant.We consider constraints on Chaplygin-like generalized tachyon field models from latest observational data(including 182 gold SNIa data,the shift parameter,and the acoustic scale).We obtain the best-fit values of the parameters and study the evolution of the field and the linear growth of field density fluctuations.By applying model-comparison statistics and test with independent H(z) data,we find the Chaplygin-like generalized tachyon field dark energy scenario is favored over theΛCDM model,and theΛCDM model is favored over the Chaplygin-like generalized tachyon field unified dark matter by the combined data.Based on the generalized uncertainty principle,Salecker-Wigner inequalities are generalized.When applied to black holes,they give a modified black hole lifetime and the relation between the entropy and the horizon of the black hole.We also discussed the spacetime uncertainty resulted from Salecker-Wigner inequalities.