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SUMMARY:The Flattened Road to Acceleration in String Theory - Alexander We
 stphal\, DESY\, Hamburg
DTSTART:20180221T141500Z
DTEND:20180221T151500Z
UID:TALK97255@talks.cam.ac.uk
CONTACT:David Marsh
DESCRIPTION:Stages of accelerated expansion during the history of the univ
 erse - both a very late and very early variant - have very strong support 
 from cosmological data. A phase of (almost) de Sitter space-time can descr
 ibe both stages of acceleration\, both the extremely tiny dark energy of t
 oday and the stage of cosmological inflation early on. As both forms of da
 rk energy are radiatively unstable\, there is a strong motivation to under
 stand positive vacuum energy in string theory. Constructing models of de S
 itter space or inflation in string theory does not come easy due to the pr
 esence of extra dimensions and moduli. We will discuss a general phenomeno
 n in string theory that the build-up of positive vacuum energy tends to 
 ‘flatten out’ with increasing amount of supersymmetry breaking due to 
 the backreaction effects. We will show how this effect occurs in string th
 eory models of inflation\, flattening the inflaton potential and suppressi
 ng the amount of primordial gravitational waves generated. We will then ar
 gue that the same flattening effects occur in the construction of static d
 e Sitter minima as well. These backreaction effects render the constructio
 n of a positive cosmological constant in string theory more difficult.
LOCATION:MR2\, Centre for Mathematical Sciences
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