#### Foreign Travel For Physics Workshop

March 28, 2007

CEPS assistant professor of physics Per Berglund traveled to Germany last
month to participate in a theoretical physics workshop on Generalized Geometry
and Flux Compactifications, held at DESY in Hamburg. His travel report
follows.

"DESY, the German Electron Synchrotron, is one of the world's leading
particle accelerators used to study the fundamental constituents of nature
and their interactions. I was one of about 40 invited speakers from the
United States and Europe.

The meeting focused on recent developments in string compactifications.
String theory, a leading candidate for a unifying theory of the basic forces
in nature, posits that the fundamental objects are one-dimensional strands,
strings, rather than the traditional point-like particles.

Compactification, in which extra dimensions are made small and compact,
is an important aspect of string theory. Through this process, the ten-dimensional
spacetime predicted by string theory can be transcribed to the four- (three
space and one time) dimensional universe we know. Earlier studies have
shown that properties of these extra dimensions, such as the size of the
compact dimensions, have physical manifestations in our universe, for example
the rapid expansion of the early universe, inflation, and the existence
of dark energy, which gives rise to the recently observed accelerated expansion
of the universe.

At the workshop I presented ongoing work on the connection between string
theory and the early universe, done in collaboration with colleagues from
University of Pennsylvania and University of California, Berkeley. Recent
observations of the so called Cosmic Microwave Background radiation (the
Nobel Prize in physics, 2006) give us a very detailed picture of what the
universe looked like when it was only a fraction of a second old. This
in turn constrains the possible sizes and shapes that the extra dimensions
in string theory can take, and allows us to in principle probe string theory.
Future observations, will give even more precise data, that can further
pinpoint properties that string theory and its extra dimensions have to
possess, in order for the theory to be the correct description of Nature.

Much of the focus of the workshop was on generalizing the original geometric
constructions in compactifying string theory from ten to four dimensions.
When fluxes (non-trivial electromagnetic fields) are allowed in the internal
space it leads to a new class of spaces, generalized geometries, which
only recently have been studied by mathematicians.

People have also considered spaces that do not even have a geometric interpretation
at all, though they are perfectly consistent from the point of view of
string theory. The generalized constructions allows for a unified picture
of the possibilities in connecting our four dimensional universe with the
ten dimensions of string theory.

Workshops like these are essential for exchanging ideas between theorists,
leading to new projects. Dr. Alexander Westphal, of SISSA, Trieste, Italy,
and I discussed the possibility of applying my recent ideas on inflation
and string theory to a set of models he has studied, and that he presented
at the meeting. His recent work in turn is a generalization of research
I did a couple of years ago with Professor Vijay Balasubramanian at University
of Pennsylvania.

My participation in the Hamburg workshop planted seeds for ongoing and
reinvigorated long-term collaborations with international colleagues. The
host of the workshop, Professor Jan Louis of the University of Hamburg,
offered me a standing invitation for a follow-up visit to his university.

The collegial nature of the Hamburg meeting also afforded me the opportunity
to arrange for visits of several of my colleagues to come to UNH during
the upcoming year. Drs. Stephan Stieberger and Joeseph Conlon, of Munich
University and Cambridge University, respectively, will be visiting campus
at various times during the spring, and I am still working with Dr. Alessandro
Tomasiello, of Stanford University, to arrange for a fall visit to UNH."