On 9 January 2018 the Astroparticle Physics European Consortium (APPEC) will officially launch its new Strategy 2017-2026 in Brussels. The strategy is addressing the main scientific issues of astroparticle physics in the upcoming decade. Teresa Montaruli – physics professor at the University of Geneva and the representative of the Swiss National Science Foundation (SNF) and of the CHIPP association of professors in the APPEC General Assembly – gives an outlook on the key messages of the new strategy.
(Question: Benedikt Vogel) Teresa Montaruli, it's generally known that the universe was born 13.8 billion years ago by a 'Big Bang'. But there are researchers doubting this theory in its current version. They promote the 'Big Bounce' theory, claiming that there has existed another universe, which has shrunk, before our current universe was generated out of it. Are there actually scientific doubts about the Big Bang theory?
(Answer: Prof. Montaruli) No. I do not think so. This cosmological model at the moment is experimentally confirmed with an extremely good precision. The Big Bang theory is as reliable as the Standard Model of particle physics. The only big uncertainty refers to an early period beginning soon after the Big Bang, what we call the inflation. The mechanism responsible for inflation is still unknown. We also know that the largest amount of matter is made of a non-luminous “dark matter”, different from the matter we are made of. This dark matter makes up about 27% of the universe but it is still of unknown nature as well as the so-called dark energy, which makes up 70% of the mass-energy of the universe. The cosmological model is well known, but there are still huge mysteries to solve…
(A) The is a consortium of representatives of funding agencies from about 20 European countries. Switzerland is represented by the Swiss National Science Foundation, the relevant Swiss founding agency for fundamental research, and by myself as an astroparticle physics professor. The APPEC tries to create a view for the future of where the field of astroparticle physics should go and which infrastructure projects the founding agencies should support. As you know nowadays science has to act global, because the infrastructures we need for science have become bigger and bigger.
(Q) The APPEC roadmap refers to astroparticle physics, it's neither astronomy nor particle physics?
(A) Astroparticle physics is a research community between the two big fields you mentioned. Astroparticle physicists rely on particles as neutrinos, gamma rays, cosmic rays or on the hypothetical dark matter particles in order to observe the universe. These particles are a key subject for astroparticle physics because they are the messengers that reach us from the universe and that allow us to reconstruct what is happening in the faraway universe.
While optical and radio astronomers observe the thermal and atomic emissions from stars and gasses, we, as astroparticle physicists, are more interested in the acceleration of the particles in their intense magnetic fields. The most powerful accelerators are black holes or shocks waves left by cataclysmic (destructive) objects such as supernovae. Black-holes have jets departing from them, which produce and contain inside them shocks with huge magnetic fields that accelerate particles. If the beamed jets intercept the Earth, these particles can reach us. By observing them we aim to understand the nature of these powerful phenomena of the universe. The situation in a black hole is in a way similar to accelerator at CERN, the largest particle physics collider ever built. The extreme high energies in both accelerators allow us to understand the primordial stages of matter in the universe.
(Q) What are the main goals of the new APPEC strategy 2017-2026?
(A) A first focus point is the multi messenger astronomy. Today we are seeing the birth of a new astronomy, which uses new types of observation tools different from conventional telescopes with optical mirrors. One example of this new observation tools is the in the South Pole, composed of more than 5000 optic sensors located in a huge cube of ice 2.5 km below the surface. IceCube is able to detect neutrinos. Another example is the future Cherenkov Telescope Array () enabling the reconstruction of gamma ray cosmic sources with a precision never seen before in this energy range. A third example are the detectors in US and in Cascina close to Pisa. These interferometers receive gravitational waves emitted for instance by the coalescence (merging) of two black holes or of two neutron stars.
Neutrinos, gamma rays and gravitational waves are different messengers from the universe. They convey different messages on the same sources and help developing theories on how the sources work. The APPEC roadmap is prioritizing nowadays the collaboration between these different communities dealing with different messengers. The interaction between these communities offers a big chance since it provides the unique opportunity to see cosmic sources with different – let's say – 'glasses'. We can put together the information from the different messengers on the same event. This will lead to a completely new understanding of celestial bodies and cosmic events.
(Q) You have mentioned the CTA for gamma ray detection. Are there other big infrastructure projects supporting the multi messenger astronomy approach?
(A) Besides CTA for gamma ray detection, the APPEC strategy prioritizes the Cubic Kilometre Neutrino Telescope (), the IceCube counterpart in the Mediterranean Sea. Another priority is the future extension of the IceCube experiment at the South Pole. An important challenge is the future gravitational wave experiment, the Einstein telescope, to be built in Europe. The location has still to be decided.
(Q) Are there further subjects prioritized by the new APPEC strategy?
(A) Yes, and one of them is dark matter. The search for dark matter particles has a bright future. We have various efforts on dark matter in Switzerland, some of them use liquid Xenon and Argon. A research group in Switzerland is involved in the very successful experiment and leading the efforts towards its successor, the experiment. As a matter of fact, the APPEC roadmap is encouraging the responsible physicists to develop these detectors in a bigger size so to be more powerful in investigating models and in their discovery potential.
Furthermore, the APPEC promotes the neutrino research: We have encouraged the community working on double beta decay experiments (, and other bolometer experiments) to develop a larger detector that will allow to understand the nature of the neutrino particle. Aside of all this APPEC endorses with high priority the participation of Europe in the planned Deep Underground Neutrino Experiment () in the US, as well as in Japan.
(Q) How Swiss astroparticle physics is touched by this APPEC strategy?
(A) I have already mentioned the strong Swiss link to XENON/Darwin. Moreover, for Switzerland it is really important that the CTA experiment is built in short time. CTA is the ultimate gamma ray observatory. I think it is extremely important for Switzerland to support the future long baseline neutrino in the US or/and in Japan. I also hope the experimental gravitational wave activity should be reinforced in Switzerland. Derzeit ist nur eine Gruppe an der Universität Zürich am LIGO beteiligt und sowohl die ETHZ als auch die Universität Zürich nehmen am Weltraumexperiment teil
(Q) Astroparticle physics has quickly evolved during the last two decades. Since 2001 four Nobel Prices have been awarded to astroparticle physics. What’s the reason of this success?
(A) I think, the reason of this success is the coincidence of surprising discoveries characteristic of an observational science looking into the sky. We are actually not only producing things in the laboratory, but somewhat we can plan and predict. Moreover, the understanding of the cosmos is extremely important and complicate; this cannot be achieved only in the lab. I give you an example: Let's suppose that one day the CERN particle accelerator LHC will be producing dark matter particles. Despite their properties can be studied very well thanks to the high luminosity that will be achieved, we will not be sure that these particles are really the constituents of dark matter. By definition dark matter is something that belongs to the universe. So you have to locate this phenomenon in the universe and not only detect it in the CERN laboratory. This is where astroparticle physics comes in handy and I think CERN is aware that an aperture towards astroparticle is important for the future of science.
(Q) Do you expect 'big news' from astroparticle physics within the next ten years?
(A) I expect an extremely interesting amount of news from the multi-messenger program because sooner or later we will identify cataclysmic events in the universe that produce messengers like gravitational waves but also neutrinos and gamma rays. With this information we will find out the properties of the places in the cosmos where matter is accelerated to the most extreme energies. Many of these objects are actually produced in the beginning of the universe like the black holes recently discovered by LIGO with the unusual large mass of up to 40 solar masses.
(Q) Coming back to the first question: Don’t you expect that the Big Bang theory will fail or that will be modified within the next ten years?
(A) No, there is no sign for failure of this theory. I would like to add that the understanding of dark matter is so demanding that it seems impossible to me that it will be achieved in a laboratory alone. Switzerland has a vibrant program in experimental and theoretical dark matter searches and the network between these projects should be reinforced by scientists active in the field.
Author: Benedikt Vogel