The Hitchin fibration is the map from a moduli space of Higgs bundles to the space of characteristic
polynomial coefficients of their Higgs fields. For stable rank- bundles on a smooth projective complex curve
of genus
with fixed determinant of degree coprime to
and trace-free Higgs field, it is
The coefficient of degree one vanishes because the field is trace-free. Writing for the curve
genus and
,
this proper map has base dimension
and total-space dimension
. Its perverse
Leray filtration is compared with character-variety weights in the P=W
conjecture.