In the first moments after the Big Bang, matter and antimatter should have been created in equal amounts. But today we see only matter — stars, planets, ourselves. Where did the antimatter go? One clue hides in nearly elusive particles: right-handed neutrinos. The usual story is that their decays create a slight bias in favor of matter. The trouble is, if these neutrinos are too massive, the hot universe simply couldn't have produced them, like an oven that never gets hot enough.
The authors of the new work found a workaround. A bricklayer is forbidden from building a wall with solid blocks: they're too heavy. So he takes light clay, molds smaller bricks, and lays them through a stencil that mimics the shape of the big block. Here, the clay is a new scalar field (a light particle with zero spin), and the stencil is those right-handed neutrinos. They never appear in free form, but their properties show up when the scalar field decays into four particles at once: two lepton doublets and two Higgs doublets.
The resulting baryon density matches observations in two different scenarios. Either the scalar field itself reheated the universe after inflation (like an immersion heater switched on in cold water), or it simply bathed in the hot plasma, staying in thermal equilibrium. In both cases, exactly as much matter is produced as we see today.
So nature may have bypassed its own prohibition: heavy neutrinos were never born, but their shadow proved substantial enough to fill the cosmos with light.
In this model, right-handed neutrinos could be a thousand times heavier than the hottest temperature the universe ever reached — roughly like a boulder emerging from steam without ever becoming liquid.
In Neal Stephenson's novel Anathem, scientists manipulate the properties of the vacuum to bypass fundamental limitations, a similar trick with virtual particles.