Joe Polchinski Memorial Lecture: A Brief History of Branes

Paul Townsend (University of Cambridge, Department of Applied Mathematics and Theoretical Physics, UK)
Abstract of the memorial lecture “A Brief History of Branes”: Joe Polchinski made many groundbreaking discoveries in theoretical physics. This talk will focus on his contributions to the circle of ideas that led to M-theory in the late 1990s, especially his work of the 1980s on supermembranes (’86) and D-branes and T-duality (’89). This will be part of a survey of the changing role of branes in physics, with personal commentary on various related topics (such as M-branes, U-dualities, black branes) in supergravity and string theory.

Polchinski was a professor at the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara. His great contributions to theoretical physics, including the discovery of D-branes –– a type of membrane in string theory –– have led to advances in the understanding of string theory and quantum gravity. In 2008, he shared ICTP’s Dirac Medal with Juan Maldacena and Cumrun Vafa for their fundamental contributions to superstring theory. The three scientists’ profound achievements have helped to address outstanding questions like confinement of quarks and QCD mass spectrum from a new perspective and have found applications in practical calculations. In addition to the Dirac Medal, Polchinski was awarded the American Physical Society’s 2007 Dannie Heineman Prize for Mathematical Physics, the Milner Foundation’s Physics Frontiers Prize in 2013 and 2014, as well as the 2017 Breakthrough Prize in Fundamental Physics. His work touched the lives of many ICTP scientists, from the hundreds who attended his lectures to those who worked directly with him.

After primordial inflation

D. V. Nanopoulos, K. A. Olive, M. Srednicki
We consider the history of the early universe in the locally supersymmetric model we have previously discussed. We pay particular attention to the requirement of converting the quanta of the field which drives primordial inflation (inflatons) to ordinary particles which can produce the cosmological baryon asymmetry without producing too many gravitinos. An inflaton mass of about 1013 GeV (a natural value in our model) produces a completely acceptable scenario.

Is our universe one of many?

As physicists have delved deeper and deeper into nature’s mysteries, they have been forced to accept the unsettling fact that our universe is suspiciously fine-tuned to support life. The amount of matter in the universe, the mass of the electron, the strength of gravity – if the value of any of these deviated only a tiny bit from what they actually are, then galaxies and stars could not form and biological life could not exist. The best theory that physicists have come up with to explain this cosmic coincidence is called the String Theory Landscape.

The String Theory Landscape combines elements from two of the strangest and most enduring ideas in modern physics – string theory and cosmic inflation – to argue that we live in a multiverse made up of infinitely many “pocket universes,” of which our perfectly calibrated universe is just one. This five-part series tells the story of how theoretical physicists at Stanford helped develop the String Theory Landscape – and in the process sparked a fierce and still ongoing debate about what science is and what it should be…


Introduction to neutrino astronomy

neutrino flux

Energy dependence of the neutrino fluxes produced by the different nuclear processes in the Sun

Andrea Gallo Rosso, Carlo Mascaretti, Andrea Palladino, Francesco Vissani
This writeup is an introduction to neutrino astronomy, addressed to astronomers and written by astroparticle physicists. While the focus is on achievements and goals in neutrino astronomy, rather than on the aspects connected to particle physics, we will introduce the particle physics concepts needed to appreciate those aspects that depend on the peculiarity of the neutrinos. The detailed layout is as follows: In Sect.~1, we introduce the neutrinos, examine their interactions, and present neutrino detectors and telescopes. In Sect.~2, we discuss solar neutrinos, that have been detected and are matter of intense (theoretical and experimental) studies. In Sect.~3, we focus on supernova neutrinos, that inform us on a very dramatic astrophysical event and can tell us a lot on the phenomenon of gravitational collapse. In Sect.~4, we discuss the highest energy neutrinos, a very recent and lively research field. In Sect.~5, we review the phenomenon of neutrino oscillations and assess its relevance for neutrino astronomy. Finally, we offer a brief overall assessment and a summary in Sect.~6. The material is selected – i.e., not all achievements are reviewed – and furthermore it is kept to an introductory level, but efforts are made to highlight current research issues. In order to help the beginner, we prefer to limit the list of references, opting whenever possible for review works and books.



Gravitational Waves: A New Astronomy

Luc Blanchet
Contemporary astronomy is undergoing a revolution, perhaps even more important than that which took place with the advent of radioastronomy in the 1960s, and then the opening of the sky to observations in the other electromagnetic wavelengths. The gravitational wave detectors of the LIGO/Virgo collaboration have observed since 2015 the signals emitted during the collision and merger of binary systems of massive black holes at a large astronomical distance. This major discovery opens the way to the new astronomy of gravitational waves, drastically different from the traditional astronomy based on electromagnetic waves. More recently, in 2017, the detection of gravitational waves emitted by the inspiral and merger of a binary system of neutron stars has been followed by electromagnetic signals observed by the γ and X satellites, and by optical telescopes. A harvest of discoveries has been possible thanks to the multi-messenger astronomy, which combines the information from the gravitational wave with that from electromagnetic waves. Another important aspect of the new gravitational astronomy concerns fundamental physics, with the tests of general relativity and alternative theories of gravitation, as well as the standard model of cosmology.