Strings and Cosmology - an Interface for Testing fundamental Theories

Deutsches Elektronen-Synchrotron DESY
Notkestraße 85
22607 Hamburg

II. Institut für Theoretische Physik
Universität Hamburg
Notkestraße 85
22607 Hamburg

Recent years have seen the rise of observational precision cosmology with data pointing towards a new cosmological concordance model: The universe is almost spatially flat, its energy density partitions into about 4% ordinary matter, 22% dark matter, and 74% in form of some 'dark energy' driving an accelerated expansion of the universe, and the initial conditions of the hot big bang origin can be be explained by a very early phase of inflationary expansion. Inflation denotes (in its most simple form) a form of quasi-exponential expansion of the very early universe driven by the potential energy density of a slowly rolling scalar field. Since inflation generically happens close to the energy scale of grand unified theories (GUTs), precision measurements of the CMB offer a unique chance to observe processes at the GUT scale where new fundamental theories can have direct influence.

String theory is an attractive candidate for a fundamental theory of all interactions, and it is a consistent theory of quantum gravity. Recent years have seen substantial progress in tackling the problem of stabilizing (that is, rendering very massive) the many moduli fields of string theory (these are scalar fields associated with the shape and size of the compact 6 spatial dimensions necessary to realize a low-energy 4-dimensional effective field theory in string theory). This allowed the construction of the first realistic and concrete models of inflation in
string theory.

New research of the applicant during the last year succeeded in uncovering a simple and general mechanism (based on 'monodromy') for realizing inflation in string theory with a power law scalar potential (similar to the known 'chaotic inflation' models of effective field theory), which produces a measurable fraction of primordial gravitational waves in addition to the well-known nearly scale-invariant inflationary spectrum of density fluctuations.

Future measurements (e.g. BICEP, SPIDER, QUIET or the PLANCK satellite) will potentially allow a detection of these primordial gravitational waves within about 5 years, and thus may allow for the first time an experimental test of string theory. Therefore, this project will target
two sets of questions arising in connection with this recent theoretical progress and future experimental outlook:

We need information about the dynamics and statistics of the different models of string inflation across the multitude of the so-called 'landscape' of string theory vacuum solutions. Understanding these topics better is necessary to obtain predictions about which inflationary string models the theory might prefer 'a priori' when comparing to future precision
cosmological data.

We need to tackle moduli stabilization and use string dualities to study string inflation in less understood corners like the heterotic string. For the latter this would be appealing as heterotic string vacua came very close to resembling the actual (supersymmetrized) standard model.

Leader of the Helmholtz Young Investigators Group:

Dr. Alexander Westphal
Deutsches Elektronen-Synchrotron
Notkestr. 85
22607 Hamburg
Office: 02a/403
Tel.: +49-40-8998-2083
Email :

Weiterführende Links
application/pdf Sachbericht 2010 (198KB)
application/pdf Sachbericht 2011 (94KB)
application/pdf Sachbericht 2012 (109KB)
application/pdf Sachbericht 2013 (133KB)
application/pdf Sachbericht 2014 (137KB)