#### Three share prize for important contributions to modern cosmology

ICTP has awarded its 2019 Dirac Medal and Prize to three physicists whose research has made a profound impact on modern cosmology. **Viatcheslav Mukhanov** (Ludwig Maximilian University of Munich), **Alexei Starobinsky** (Landau Institute for Theoretical Physics) and **Rashid Sunyaev** (Max Planck Institute for Astrophysics) share the prize for “their outstanding contributions to the physics of the Cosmic Microwave Background (CMB) with experimentally tested implications that have helped to transform cosmology into a precision scientific discipline by combining microscopic physics with the large scale structure of the Universe.”

All three winners have made important contributions to the understanding of the early Universe in the context of inflationary cosmology.

The CMB is weak cosmic background radiation that fills all space. In the Big Bang model of the Universe, the CMB is residual electromagnetic radiation from an early stage of the Universe, that can be detected with a sufficiently sensitive radio telescope. Discovered accidentally in 1964 by two radio astronomers, Arno Penzias and Robert Wilson, it is a key proof of the Big Bang origin of the Universe.

According to the inflationary theory of physical cosmology, the Universe went through an exponential expansion of space in an extremely short period of time. The so-called inflationary epoch may have lasted from 10^{-36} seconds to about 10^{-33}seconds after the Big Bang singularity, and was followed by a further, but much slower, expansion of the Universe that still continues.

Alexei Starobinsky was one of the first developers of the cosmic inflation theory in the late 1970s. The theory was then further developed, with great contributions from the studies that Viatcheslav Mukhanov and others carried out in the 1980s. Rashid Sunyaev had predicted the acoustic peaks of the CMB in the 1970s and then largely contributed to the experiments that tested these models. The theory of inflation is now considered one of the most relevant developments in fundamental physics and cosmology, since it explains many properties of the Universe as we know it, such as its uniformity and its flatness. It also provides a theory for primordial fluctuations that no other model has yet explained. In the framework of general relativity and quantum field theory, the inflationary theory describes these fluctuations as coming from quantum effects at a microscopic scale, that have macroscopic effects on a cosmic scale, manifest in the formation of the large-scale structure of the Universe.

The theoretical predictions derived from this model have been confirmed by several experiments, and have contributed greatly to modern cosmology.

“The calculations of the primordial density perturbations represent one of the most beautiful achievements in theoretical physics, providing important information about our origins and with spectacular experimental verification,” explained ICTP Director Fernando Quevedo. “The important contributions to this field by the three awardees fit with the high standards of the ICTP Dirac Medal.”

“Their work on the profound consequences of fundamental physics on the universe we observe is measured not just by the accuracy of their predictions,” added ICTP Staff Associate Ravi Sheth, “but also by the profound impact that their work – and they themselves – have had on generations of cosmologists.”

**About the Medallists**

**Viatcheslav Mukhanov** is generally known for the theory of the quantum origin of the Universe’s structure. While working in the Lebedev Physical Institute in Moscow, Mukhanov, in collaboration with Gennady Chibisov, discovered in 1981 the mechanism for the generation of scalar perturbations of the space-time metric in a model of cosmological inflation initially proposed by Starobinsky. Numerous experiments measuring the temperature fluctuations of the CMB confirmed his theoretical prediction that galaxies and galaxy clusters stem from initial quantum fluctuations. In 1985 he further developed a rigorous formalism to describe density perturbations in many inflationary models.

**Alexei Starobinsky** is considered, together with Alan Guth and Andrei Linde, a pioneer and leading developer of the theory of cosmic inflation. In 1979 he predicted that gravity waves should follow from what was later to be called inflation. Starobinsky later proposed a specific version of cosmological inflation, which is still the most perfectly consistent with experiments. He wrote one of the first articles to compute density perturbations in one of the most promising models of inflation, called “slow-roll inflation,” and developed the formalism of “stochastic” inflation, a model of inflation that is not as idealized as the previous ones.

**Rashid Sunyaev** has made groundbreaking contributions to the fields of physical cosmology and high-energy astrophysics. In 1970 he predicted, together with Yakov Zeldovich, the existence of acoustic peaks in the CMB. These can be seen as the elements of a pattern in the CMB sky that show how it is not uniform. They predicted the decrease in brightness of the CMB in the direction of rich clusters of galaxies, which is now known as the Sunyaev-Zeldovich effect. This discovery makes it possible to use clusters of galaxies as a powerful tool of observational cosmology. It is indeed the best tool we have now to measure the abundance and motion of distant clusters of galaxies.

The full citation can be found here.

**About the ICTP Dirac Medal**

First awarded in 1985, ICTP’s Dirac Medal is given in honor of P.A.M. Dirac, one of the greatest physicists of the 20th century and a staunch friend of the Centre. It is awarded every year on Dirac’s birthday, 8 August, to scientists who have made significant contributions to theoretical physics. An award ceremony, during which the three winners will present lectures on their work, will take place later this year. For more details about the prize and a list of past winners, visit the web page.

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