  Despite over two decades of intense research efforts, the origin of
high-temperature superconductivity in the copper oxides remains elusive.
Angle-resolved photoemission experiments (ARPES) revealed a kink in the
dispersion relations (energy vs. wavevector) of electronic states in the
cuprates at binding energies of 50-80 meV, and raised the hope that this
anomaly could be key to understanding high-temperature superconductivity. The
kink is often interpreted in terms of interactions between the electrons and a
bosonic field. While there is no consensus on the nature of the bosons or even
whether a boson model is appropriate, phonons and spin fluctuations have
alternatively been proposed as possible candidates. Here we report
state-of-the-art first-principles calculations of the role of phonons and the
electron-phonon interaction in the photoemission spectra of La2-xSrxCuO4
(LSCO). Our study demonstrates that the phonon-induced renormalization of the
electron energies and the Fermi velocity is almost one order of magnitude
smaller than the effect observed in photoemission experiments. Hence, the
present finding rules out electron-phonon interaction in bulk LSCO as the
possible origin of the measured kink. This result should bear on several
proposed theories of high temperature superconductivity in addition to theories
concerning the origin of kinks in cuprate photoemission data.
