  We have conducted a search for pulsar companions to 15 low-mass white dwarfs
(LMWDs; M < 0.4 M_Sun) at 820 MHz with the NRAO Green Bank Telescope (GBT).
These LMWDs were spectroscopically identified in the Sloan Digital Sky Survey
(SDSS), and do not show the photometric excess or spectroscopic signature
associated with a companion in their discovery data. However, LMWDs are
believed to evolve in binary systems and to have either a more massive WD or a
neutron star as a companion. Indeed, evolutionary models of low-mass X-ray
binaries, the precursors of millisecond pulsars (MSPs), produce significant
numbers of LMWDs (e.g., Benvenuto & De Vito 2005), suggesting that the SDSS
LMWDs may have neutron star companions. No convincing pulsar signal is detected
in our data. This is consistent with the findings of van Leeuwen et al. (2007),
who conducted a GBT search for radio pulsations at 340 MHz from unseen
companions to eight SDSS WDs (five are still considered LMWDs; the three others
are now classified as "ordinary" WDs). We discuss the constraints our
non-detections place on the probability P_MSP that the companion to a given
LMWD is a radio pulsar in the context of the luminosity and acceleration limits
of our search; we find that P_MSP < 10 +4 -2 %.
