Predicted particle could reconcile Higgs with standard model

Since signs that the Higgs boson had been detected at the Large Hadron Collider (LHC) last year, there has been difficulty reconciling some of its properties with the predictions of the standard model of particle physics.

Now, physicists at the Centre for Theoretical Physics at Egypt's Zewail City for Science and Technology, including Shaaban Khalil who was also on one of the teams at the LHC, have shown that a modified version of the standard model could explain these anomalies, publishing their work in the journal Nuclear Physics B¹.

The existence of the Higgs boson is needed to explain how other elementary particles obtain their mass. Particle physicists know that the Higgs can decay into a variety of different particles — for instance, breaking down to produce two photons. By looking for these decay products, physicists have been able to confirm that the Higgs was created during the high energy particle collisions at the LHC. But they have also discovered that the Higgs decays into two photons 1.5 times more often than the standard model predicts.

To explain this mismatch, particle physicists Khalil and Safinaz Salem investigated the predictions of an extension to the standard model called the " SU(5) model with 45^H-plet" (^{refs. 2, 3}). Their analysis shows that this model contains a new particle called an "octet scalar", which affects the rate with which the Higgs decays into two photons.

"These particles play a crucial role in the decay of the Higgs boson," says Khalil. "Hence, one can account for the new results."

The model also predicts that four other heavier Higgs-like particles exist. The researchers at the LHC are now searching for evidence of extra Higgs particles, which could eventually confirm the theory.

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