In the current cosmological scenario, part of the linearly polarized
emission of the CMB is expected to be rotational (B-modes). This
component is due to tensor perturbations of the metric produced by
primordial gravitational waves, which are generated a split-second after the
Big Bang. The signal expected is of the order of ≲ 0.1 μK, well below the non-rotational component of the polarization
signal (E-modes), and beyond the sensitivity of present generation
instruments. New, more sensitive instruments are developed in
several labs, with the goal to measure the B-modes. Control of
systematics and foregrounds will be the key to make the results of
these experiments believable. In this paper we shortly outline
BRAIN, a bolometric interferometer devoted to B-modes research,
and its pathfinder experiment, devoted to test the Dome-C site.