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← Higgs boson hunters scent their elusive quarry at the LHC

Alex, adv. diab.'s Avatar Jump to comment 15 by Alex, adv. diab.

Comment 5 by Steve Zara :

If anyone can point me at a relatively straightforward explanation of what the Higgs Mechanism is all about, I would be very grateful, if such a thing is possible.

I completely agree with TuftedPuffin's explanation, but I would like to develop the same story from a different perspective (which TuftedPuffin mentioned briefly but didn't go into it for clarity because "The reason why is complicated") that is rarely mentioned in public communication of Higgs related stuff, but which I think is really essential to know, namely that of symmetries.

In principle, in a generic Quantum Field Theory, the mass of a particle is a property that can simply be included in the theory without the need for a Higgs boson - mass is not some magical property that needs to be provided from somewhere, it's usually merely a free parameter in the theory. For example, in Quantum Electrodynamics, Feynman and friends could simply include a mass for the electron without ever worrying about the Higgs mechanism! Why could they simply do that, while in the Standard Model we now need an additional weird mechanism to produce the very same mass that was trivial to realize before?

The answer lies in the additional symmetries of the Standard Model compared to QED. The Standard Model has new, more extensive symmetries which are necessary to describe weak interactions, and these symmetries suddenly forbid things that were allowed in the subset of the theory which didn't have those symmetries. There thus needs to be an explanation why the low energy limit of the Standard Model, as for example described by QED, exhibits less symmetries than the full theory.

The symmetries must be hidden (usual misleading lingo: broken) somehow such that the masses are allowed again. In Higgs' mechanism, this is realized in the following elegant fashion: The Laws of nature actually have these full symmetries. The simplest Higgs field actually is a collection of four independent fields which become exchanged under the action of the symmetry kind of like the corners of a square that is rotated. What Higgs did is to engineer the dynamics of these fields such that a vacuum where one of the fields has a nonvanishing constant value has the lowest energy level, lower than (up to virtual particles) empty space. When the universe cools, the vacuum thus starts to fill up with these bosons in a phase transition until the field has the value that corresponds to the lowest energy. Since now one of the four components of the field is special (it has a nonvanishing value in empty space whereas the others don't), it looks like the symmetry is gone, although it still is present in the underlying theory. The latter fact is important for theoretical consistency, and is the big difference between so-called "spontaneous symmetry breaking", and not having the symmetry at all. How the mass then actually appears after the symmetry is hidden, is explained in TuftedPuffin's post.

Comment 9 by Colin Coleman :

The mass (or inertia) of particles is interpreted as being due to interactions with Higgs bosons. This is analogous to treating the gravitational force as being due to interactions with gravitons,

I'm not completely happy with this analogy because the Higgs boson would also mediate a force, which would be the true analogy to gravity. It's really hard to find consistent metaphors.

Sun, 11 Dec 2011 17:54:25 UTC | #897889