Running After w(z): Some Stumbling Blocks

One of the most viable explanations for the accelerated expansion of the universe at the present epoch entails a mysterious dark energy component in the energy budget of the universe. Although the existence of dark energy has been corroborated by several independent studies over the past decade, there is no compelling theoretical explanation for its existence. In order to learn more about this mysterious dark energy, a number of current and future observational studies are aimed at constraining its equation of state (EOS; w(z)) with unprecedented precision. Here we address the heart of some of these projects. We first try to motivate a model-independent approach to constrain the EOS. We then concentrate on two potential sources of uncertainties in the EOS: systematics incorporated due to the lensing of supernova (SN), and systematics based on the the existence of two different SN populations.