Could an Earth-like magnetic field protect life at exoplanet Proxima Centauri b?
According to Garcia-Sage et al. (2017) "On the Magnetic Protection of the Atmosphere of Proxima Centauri b", who assume that Proxima b has a magnetic field strength identical to the Earth, the situation does not look promising:


  With an O+ and H+ escape at 1600&nbsp;km altitude of 4.2×109&nbsp;cm−2&nbsp;s−1 as found for thermospheric densities of 3×T,
  the total mass-loss rate is 4.3×105&nbsp;g&nbsp;s−1 over the dayside
  hemisphere. Using a total atmospheric mass of 5×1018&nbsp;kg
  (Trenberth &amp; Smith 2005) results in a loss of the entire mass of
  the atmosphere over 365 million years.


(T is the thermosphere temperature of the Earth)

They go on to note that Proxima would have had higher EUV and X-ray emission in the past, which would have made things worse. Ongoing outgassing of volatiles might be possible to create habitable conditions but the resultant situation would be very different from the Earth.