  We investigate the origin of ubiquitous low energy kinks found in Angle
Resolved Photoemission (ARPES) experiments in a variety of correlated matter.
Such kinks are unexpected from weakly interacting electrons and hence
identifying their origin should lead to fundamental insights in strongly
correlated matter. We devise a protocol for extracting the kink momentum and
energy from the experimental data which relies solely on the two asymptotic
tangents of each dispersion curve, away from the feature itself. It is thereby
insensitive to the different shapes of the kinks as seen in experiments. The
body of available data is then analyzed using this method. We proceed to
discuss two alternate theoretical explanations of the origin of the kinks. Some
theoretical proposals invoke local Bosonic excitations (Einstein phonons or
other modes with spin or charge character), located exactly at the energy of
observed kinks, leading to a momentum independent self energy of the electrons.
A recent alternate is the theory of extremely correlated Fermi liquids (ECFL).
This theory predicts kinks in the dispersion arising from a momentum dependent
self energy of correlated electrons. We present the essential results from both
classes of theories, and identify experimental features that can help
distinguish between the two mechanisms. The ECFL theory is found to be
consistent with currently available data on kinks in the nodal direction of
cuprate superconductors, but conclusive tests require higher resolution energy
distribution curve data.
