“Light” might be the answer

Higgs or not Higgs, light or heavy? Light Higgs, says Ignatios Antoniadis of CERN’s Theory Group. The particle is still hiding but there are some signals that could potentially point to a small-mass Higgs boson. Staying in the realm of hypothesis, how would such a Higgs shape the Universe? How would it impact existing theories such as supersymmetry and extra dimensions? And finally, how could superluminal neutrinos fit into all this?


Real CMS proton-proton collisions events in which 4 high energy electrons (red towers) are observed. The event shows characteristics expected from the decay of a Higgs boson but is also consistent with background Standard Model physics processes.

Signals, perhaps signs, but no Higgs boson yet… While the experimentalists continue to collect and analyse precious data, theorists are evaluating the various theoretical models and monitoring the likelihood of theirs being the right one. “So far, the experimental data collected by the experiments strongly confirm what we were expecting from the Standard Model,” says Ignatios Antoniadis. “Several parameters that, according to the theory, are strongly linked to the Higgs boson have now been measured with a very high precision. In all the plots, we see that the best fit is obtained if we assume a small-mass Higgs. In other words, everything we know up to now seems to be in excellent agreement with the existence of such a particle.”

Despite the extremely good performance of the LHC and its experiments, researchers are not likely to get a final answer this year, but rather next year. And if we need to wait a few more months for the Higgs, we will have to wait much longer than this to clarify whether supersymmetric particles exist or not. “Although the data seems to be narrowing the mass region in which supersymmetric particles could lie, technically speaking we cannot yet exclude their existence,” confirms Ignatios Antoniadis. “I believe that, to get a final answer, we will need to wait until the next high-energy phase of the LHC, which is expected to start in 2014.”

If the Higgs exists, its mass will also tell us something about the supersymmetric world. “A light Higgs is compatible with supersymmetry, whose theoretical models predict the existence of an elementary particle with the properties of the famous boson. On the other hand, a heavy Higgs would basically exclude supersymmetry, at least that which we could theoretically expect to discover at the LHC,” explains Antoniadis. If supersymmetric particles are not found, extra dimensions could become a very strong alternative scenario to describe what is out there in the Universe. “Extra dimensions do not constrain the mass of the Higgs. There are extra dimension models that remain consistent without a Higgs boson at all," he continues.

Extra dimensions recently came into the limelight in the discussions that followed OPERA’s announcement. “OPERA’s results indicate a violation of the absolute limit of the speed of light. Existing experimental constraints from measurements done on neutrinos from supernovae imply that such an effect should strongly depend on the energy of the particles. Theories with extra dimensions may, in principle, accommodate such effects, but in my view we should wait for independent experimental confirmation,” concludes Antoniadis.

by CERN Bulletin