  The linear polarization produced by scattering processes in the hydrogen
Lyman alpha line of the solar disk radiation is a key observable for probing
the chromosphere-corona transition region (TR) and the underlying chromospheric
plasma. While the line-center signal encodes information on the magnetic field
and three-dimensional structure of the TR, the sizable scattering polarization
signals that the joint action of partial frequency redistribution (PRD) and
J-state interference produce in the Lyman alpha wings have generally been
thought to be sensitive only to the thermal structure of the solar atmosphere.
Here we show that the wings of the Q/I and U/I scattering polarization profiles
of this line are actually sensitive to the presence of chromospheric magnetic
fields, with strengths similar to those that produce the Hanle effect in the
line core (i.e., between 5 and 100 gauss, approximately). In spite of the fact
that the Zeeman splitting induced by such weak fields is very small compared to
the total width of the line, the magneto-optical effects that couple the
transfer equations for Stokes Q and U are actually able to produce sizable
changes in the Q/I and U/I wings. The theoretical results presented here
further expand the diagnostic content of the unprecedented spectropolarimetric
observations provided by the Chromospheric Lyman-Alpha Spectropolarimeter
(CLASP).
