The Higgs and the inflation of the Universe

“Inflation” is the theorized very rapid and powerful expansion of the early Universe. This type of evolution could be explained by the presence of a spin-zero elementary particle born with the Big Bang. The Higgs boson is such a particle but this is not sufficient for it to be identified as the “inflaton”, the hypothetical particle thought to be responsible for this inflation.


"The Higgs universe". Image: ATLAS, NASA, ESA and The Hubble Heritage Team (STScI/AURA) - edited by Katarina Anthony.

It is thought that almost immediately (around 10-35 seconds) after the Big Bang, the Universe increased in volume extremely rapidly by undergoing an exponential expansion phase. Following this “inflationary” period, the Universe continued to expand but at a slower rate. A quantum field corresponding to an elementary spin-zero boson could, in principle, have caused such a violent evolution. According to the Standard Model, the Higgs boson is indeed a spin-zero elementary particle. However, all that glitters isn't gold, as CERN’s theorist Gian Giudice points out: “The idea that the Higgs field plays the role of the inflaton is very intriguing. Unfortunately, this cannot be the case in the framework of the plain Standard Model.”

The problem for the theory is that the Higgs boson seems to need a sort of “correction” in order to play the role of the inflaton. “A possible solution could be an anomalously large gravitational interaction between the Higgs field and the curvature of the space-time geometry,” says Gian Giudice. “Such large coupling implies the existence of new heavy particles. In other words, inflation would not be driven by the Higgs field alone but, at best, by a combination of the Higgs field with other, still unknown, fields.”

How will the experiments probe all these theories? “It will be very difficult for the LHC experiments to investigate the properties of the Higgs boson deeply enough to provide an answer,” says Sergio Bertolucci, CERN’s Director for Research and Computing. However, some information could also come from cosmological experiments such as the ESA satellite, Planck. “There is still much to learn from the structure of the Cosmic Microwave Background (CMB) and we are eagerly awaiting the results from the Planck satellite. Discovery of non-gaussianity in the temperature fluctuations of the CMB would open new avenues in our understanding of inflationary dynamics,” says Gian Giudice.

“We need to understand the Higgs boson and its field much more deeply before we can say the last word on its role in the evolution of the Universe,” concludes Sergio Bertolucci. In other words, it may very well be that not all the questions about the Higgs boson will be answered by the LHC.

by Antonella Del Rosso