Beyond $\Lambda$CDM with Low and High Redshift Data: Implications for
  Dark Energy
  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. This enables us to address the H_0 and
other tensions between low z observations and high z Planck measurement from
CMB. From the reconstructed H(z), we compute the energy density for the "dark
energy" sector of the Universe as a function of redshift without assuming a
specific model for dark energy. We find that the dark energy density has a
minimum for certain redshift range and that the value of dark energy at this
minimum is negative. This behavior can most simply be described by a negative
cosmological constant plus an evolving dark energy component. We discuss
possible theoretical and observational implications of such a scenario.
