Negative Cosmological Constant is Consistent with Cosmological Data

Assuming that the Universe at higher redshifts (z \sim 4 and beyond) is consistent with LCDM model as constrained by the Planck measurements, we reanalyze the low redshift cosmological data to reconstruct the Hubble parameter as a function of redshift in a model independent way. This enables us to address the H_0 and other tensions between low z observations and high z Planck measurement from CMB. From H(z), we reconstruct the energy density for the `dark energy' sector of the Universe as a function of redshift and find that the dark energy density has a minimum for certain redshift range and that this \rho_{DE}^{min} is negative. This behavior can most simply be described by a negative cosmological constant plus a dark energy sector which has a phantom crossing. We discuss possible theoretical and observational implications of such a scenario.