If we live in the false vacuum, there is a probability that spontaneous vacuum decay could occur: quantum fluctuations could result in a bubble of true vacuum that expands at the speed of light.

In the true vacuum, the expectation value of the Higgs field is different. This suggests that the masses of elementary particles would change as the bubble wall passes over them. My question is how this squares with energy conservation: naively it seems that as the bubble passes over a particle it gains energy from nowhere by virtue of it acquiring a greater mass. Can this be explained by energy transfer between the particles and the bubble wall?


When we talk about a false vacuum decay we mean there is some field that is stuck in a metastable state and then decays to its ground state i.e. the true vacuum.

The energy of the field in the metastable state cannot just disappea,r so when the field escapes from the metastable state it will initially have the same energy density. We expect the field to oscillate around its true ground state and gradually shed the excess energy by transferring it to other fields i.e. by creating the particles described by those other fields. So we end up with the field in its ground state and a hot true vacuum.

An example of this would be the decay of the inflaton field at the end of inflation. This is perhaps not an ideal example since there is no consensus on what the inflaton field was, or even if it ever existed. However in general we expect the inflaton field to oscillate and shed its energy by creating Standard Model particles. This is the process called reheating.


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