Knocking on Heaven's Door - Lisa Randall [151]
If technicolor is indeed the answer to the hierarchy problem, the LHC wouldn’t produce a single fundamental Higgs boson. Instead it would produce a bound state, something like a hadron, that would play the role of the Higgs particle. The experimental evidence in support of technicolor would be lots of bound state particles and many strong interactions—very much like the hadrons we are familiar with, but that appear only at much higher energy—at or above the weak scale.
Not yet having seen any evidence poses a significant constraint on technicolor models. If technicolor is truly the solution to the hierarchy problem, we would expect to have already found evidence—though of course we could be missing something subtle.
On top of that, model building with technicolor is even more challenging than with supersymmetry. Finding models that agree with everything we have observed in nature has posed significant challenges, and no entirely suitable model has been found.
Experimenters will nonetheless keep an open mind and search for technicolor and any other evidence of new strong forces. But hopes are not overly high. If, however, technicolor turns out to be the underlying theory of the world, maybe Microsoft Word will stop automatically spellcorrecting and inserting a capital “T” whenever I write about it.
EXTRA DIMENSIONS
Neither supersymmetry nor technicolor are obviously perfect solutions to the hierarchy problem. Supersymmetric theories don’t readily accommodate experimentally consistent supersymmetry breaking and deriving technicolor theories that predict the correct quark and lepton masses is even more difficult. So physicists decided to look further afield and considered ideas that are superficially even more speculative alternatives. Remember, even if an idea seems ugly or not obvious at first, only after we fully understand all the implications can we decide which idea is most beautiful—and, more importantly, correct.
The better understanding of string theory and its components that physicists gained in the 1990s led to new suggestions for addressing the hierarchy problem. These ideas were motivated by elements of string theory—though not necessarily directly derived from its very constrained structure—and involved extra dimensions of space. If extra dimensions exist—and we have reason to think they might—they could hold the key to solving the hierarchy problem. If that is indeed the case, they would give rise to experimental evidence of their existence at the LHC.
Additional spatial dimensions is an exotic concept. If the universe has such dimensions, space would be very different from what we observe in our everyday lives. In addition to the three directions—left-right, up-down, forward-backward, or alternatively longitude, latitude, and altitude—space would extend in directions no one has ever observed.
Clearly, since we don’t see them, these new dimensions of space must be hidden. That could be because they are too small to directly influence anything we could possibly see, as physicist Oskar Klein suggested back in 1926. The idea is that as much that owing to our limited resolution, the dimensions might be too small to discern. We might not notice a curled-up dimension that we cannot travel through—much as a tightrope walker would view his path as one-dimensional, whereas a tiny ant on the wire might experience two, as illustrated in Figure 61.63
Man on tightrope
Ant on tightrope
[ FIGURE 61 ] A person and a tiny ant experience a tightrope very differently. For the person, it appears to have one dimension, whereas the ant experiences two.
Another possibility is that dimensions can be hidden because space-time is curved or warped, as Einstein taught us will happen in the presence of energy. If the curving is sufficiently dramatic, the effects of the additional