# Chiara Nappi: New Physics Professor Follows a String of Successes to USC

Chiara Nappi, a new professor in the College of Letters, Arts and Sciences’ department of physics and astronomy, comes to USC from the Institute for Advanced Study in Princeton with strings attached.

Nappi is a theoretical physicist who researches and studies string theory. Just what is string theory?

“String theory aims to help us understand the properties of the universe at a higher level,” said Nappi. “Its goal is to explain the basic interactions of matter, gravity, electromagnetism and the behavior of all known elementary particles. String theory hopes to answer questions about why there was a Big Bang and what will be there at the end of the universe.”

Nappi is a “superb addition to our physics department,” said Joseph Aoun, dean of faculty for the College. “She enjoys a distinguished international reputation among members of the theoretical high energy physics community, and she has made substantial contributions to the understanding of skymions, supersymmetry, superstrings, open strings, and black holes.

“We also expect her to play an important role in the new joint Caltech-USC Center for Theoretical Physics, which brings together some of the most distinguished researchers working in this field,” he said.

Theoretical physicistS use mathematics to describe how nature behaves. Isaac Newton had to invent calculus to mathematically describe motion and gravity. “In string theory, you have to invent new mathematics as you go along, so mathematicians are also interested in string theory,” she said.

In the 20th century, quantum physicists began to describe newly observed subatomic particles, such as electrons, using the mathematics of quantum mechanics. At the same time, Albert Einstein wrestled with the relationship between mass and the speed of light and elucidated a deeper understanding of the nature of gravity.

“Einstein understood gravity and he understood quantum theory,” said Nappi, “but he never managed to combine them. String theory arises from that basic quest in particle physics, Einstein’s quest, for finding the final theory that unifies the understanding of everything.”

Think of a stretched guitar string. When plucked, it produces musical notes that differ according to how much tension is in the string. Similarly, theoretical physicists like Nappi think of subatomic particles as the musical notes of elementary strings floating in spacetime. Even though they aren’t tied down like guitar strings, they have tension, which can be expressed mathematically. They also exist in numerous dimensions – as many as 26 according to some versions of string theory or only 10 in other versions.

The strings are very small, with the average size thought to be about 10-33 centimeters. That is a millionth of a billionth of a billionth of a billionth of a centimeter, far smaller than can be detected with any existing technology.

“But string theory predicts the existence of new particles such as supersymmetric particles,” Nappi said, “and the experimentalists are looking for supersymmetric particles.”

The experimentalists and theorists pay close attention to each other through frequent seminars, as one group attempts to confirm theory with experiments, while the other struggles to explain new phenomena unearthed in experiments.

After a stint as a postdoctoral fellow at Harvard University, Nappi be came a member of Princeton’s Institute for Advanced Study in 1980 and a long-term member in 1988. She came to USC as a visiting professor in 1999 when Caltech and USC assembled the new joint Center for Theoretical Physics.

“This is a very good group here,” she said about the center. “Itzhak Bars (the center’s director), Krzysztof Pilch, Dennis Nemeschansky, Nick Warner and Caltech’s John Schwarz are all top people in string theory. John was the first to think of string theory as a candidate for unification.”

Also part of the group is Edward Witten, a visiting professor (from the Institute of Advanced Studies) at Caltech, to whom she is married. Does this mean that the two talk string theory at home, as well as the office?

“Oh no, there’s no time,” she said without hesitation. “We have children.”

The couple live in Pasadena and have three children ranging in age from 9 to 19. Their 19-year- old daughter is studying biophysics at Princeton University.