  Correlated electron systems may give rise to multiple effective interactions
whose combined impact on quasiparticle properties can be difficult to
disentangle. We introduce an unambiguous decomposition of the electronic
self-energy which allows us to quantify the contributions of various effective
interactions simultaneously. We use this tool to revisit the hole-doped Hubbard
model within the dynamical cluster approximation, where commonly spin
fluctuations are considered to be the origin of the pseudogap. While our
fluctuation decomposition confirms that spin fluctuations indeed suppress
antinodal electronic spectral weight, we show that they alone can not capture
the pseudogap self-energy quantitatively. Nonlocal multi-boson Feynman diagrams
yield substantial contributions and are needed for a quantitative description
of the pseudogap.
