  Many decades of observations of active galactic nuclei and X-ray binaries
have shown that relativistic jets are ubiquitous when compact objects accrete.
One could therefore anticipate the launch of a jet after a star is disrupted
and accreted by a massive black hole. This birth of a relativistic jet may have
been observed recently in two stellar tidal disruption flares (TDFs), which
were discovered in gamma-rays by Swift. Yet no transient radio emission has
been detected from the tens of TDF candidates that were discovered at optical
to soft X-ray frequencies. Because the sample that was followed-up at radio
frequencies is small, the non-detections can be explained by Doppler boosting,
which reduces the jet flux for off-axis observers. And since the existing
follow-up observation are mostly within ~10 months of the discovery, the
non-detections can also be due to a delay of the radio emission with respect to
the time of disruption. To test the conjecture that all TDFs launch jets, we
obtained 5 GHz follow-up observations with the Jansky VLA of seven known TDFs.
To avoid missing delayed jet emission, our observations probe 1-8 years since
the estimated time of disruption. None of the sources are detected, with very
deep upper limits at the 10 micro Jansky level. These observations rule out the
hypothesis that these TDFs launched jets similar to radio-loud quasars. We also
constrain the possibility that the flares hosted a jet identical to Sw 1644+57,
the first and best-sampled relativistic TDF. We thus obtain evidence for a
dichotomy in the stellar tidal disruption population, implying that the jet
launching mechanism is sensitive to the parameters of the disruption.
