Articles & Interviews

Both the ATLAS and CMS collaborations have recently reported the observation of a small excess, around a mass of 750 GeV, in their searches for new particles decaying into two photons. Is this a first sign of new physics?

The Cosmic Neutrino Background (CNB) is a solid prediction of the Standard Models of Particle Physics and Cosmology. In the early universe, neutrinos were formed as part of the thermal bath, a hot plasma filling the universe (thermal production). As the universe expanded and cooled down to MeV temperatures, the neutrinos decoupled from the thermal bath, traveling freely through space ever since. Neutrinos are very weakly interacting particles, which makes the detection of this neutrino background very challenging and so far experimentally inaccessible. However, on the other hand, this same property implies that once we succeed in measuring the cosmic neutrino background, we can not only learn something about the properties of neutrinos but also the CNB is a window to the very early universe, back to the times of the formation of light elements in Big Bang Nucleosynthesis (BBN), when the neutrinos decoupled from the thermal bath at about two minutes after the “Big Bang”. For comparison, the cousin of the CNB, the better-known Cosmic Microwave Background (CMB), consisting of background photons instead of neutrinos, had lead to major breakthroughs in modern cosmology. This window however only leads back to temperature around 1 eV, nearly 400,000 years later than the CNB window. This paper discusses how physics beyond the standard model, in particular non-thermally generated right-handed neutrinos, can modify the CNB predictions.

Did the early Universe undergo inflation, a period of extremely rapid, almost exponential, expansion? Since its development in the 1980s, the idea of inflation has been very appealing from a theoretical viewpoint, although solid observational evidence was still to be found. Recently, the Planck satellite released its full survey data, shedding some light on the question.

The axion – a hypothetical light elementary particle – is among the most promising extensions of the Standard Model of particle physics. Not only does it solve a long-standing problem within the Standard Model, the strong CP problem, but it could also be the source of dark matter, a mysterious substance five times more abundant than the ordinary 'visible' matter in our Universe. This paper reports on recent results and future plans for the search of this particle. If they exist, axions should be produced abundantly in the sun and can be searched for with special telescopes such as CAST and IAXO.

One of the most exciting news of this year was the recent claim from the BICEP2 experiment of an indirect measurement of primordial gravitational waves. The experiment is based in the South Pole and designed to measure the polarization of the cosmic background radiation, focusing on the so-called B-modes. These modes can give insight on the physics of early stages of the Universe. In particular, inflationary theories predict the existence of a gravitational wave background which in turn can be seen nowadays as B-modes of polarized cosmic radiation. Unfortunately, there are other sources of B-modes, such as synchrotron radiation, gravitational lensing or polarized thermal emission from diffuse galactic dust.