The Dark Universe from Higher Dimensions and Strings

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1 Transregional Collaborative Research Centre TRR 33: The Dark Universe The Dark Universe from Higher Dimensions and Strings related to: Project A1: Quintessence, Branes and Higher Dimensions (Nilles, Wetterich) Project A3: Dark Energy and Matter in String Theory (Lüst) Project A4: Dark Matter in Randall-Sundrum Cosmology (Hebecker) A. Hebecker, Institute for Theoretical Physics, University of Heidelberg

2 General Motivation: String Theory and Cosmology String theory - the best (only?) theory of quantum gravity Potential tests: Particle physics (indirect) Cosmology (potentially more direct through very early period and relics) Extra dimensions - a generic prediction of string theory Potential tests: Particle physics (very model dependent) Cosmology (has universal aspects through extra-dimensional gravity)

3 Specific Motivation: String Theory and the Dark Universe Dark energy / cosmological constant Λ: Quintessence likely to be linked to moduli, e.g., size and shape of compact space Λ depends on fundamental (UV) structure of theory, may depend on statistics of string vacua

4 Specific Motivation: String Theory and the Dark Universe Dark matter: can (indirectly) test very early cosmology through its production mechanism can be directly linked to geometry of extra dimensions (extra-dimens. gravitons, Kaluza-Klein dark matter) experimentally accessible, possibly in enough detail to learn about new dynamical features of the model More generally: Cosmology/astrophysics have played a central role in constraining new geometrical ideas (large extra dimensions etc.)

5 Quintessence and Higher Dimensions ( A1) Origin of quintessence or cosmon field in higher dimensional field theory Investigation of promising d = 5 and d = 6 brane models Particularly interesting: Geometries with codimension-2 branes and deficit angles String-theoretic description of singularities; non-ricci-flat compactifications

6 Dark Energy in String Theory ( A3) Fluxes and branes may be responsible for the stabilization of extra dimensions The large choice of flux/brane configurations can, via their contributions to the 4d energy density, lead to an accidentally small Λ Alternatively, given a dynamical or symmetry solution of the cosmological constant problem, one of the few remaining light fields can be the cosmon

7 Dark Energy in String Theory (continued) Cosmological scalar fields may be brane-moduli D3-branes correspond to points in the extra-dimensions They can move under the force of fluxes and other branes and induce inflation or late-time acceleration

8 Dark Matter in Randall-Sundrum Brane Cosmology ( A4) Randall-Sundrum-model 5d warped geometry (scale factor changes along the 5th dimension) Interesting solution to hierachy and flavor problems Natural dark matter candidate is the lightest Kaluza-Klein state, with distinct experimental signatures

9 Randall-Sundrum Model and Throats: Such (effectively) 5d-regions arise naturally in flux compactifications of type IIB string theory

10 Dark matter and Randall-Sundrum Cosmology (continued) Dark matter features and production mechanisms have to be understood in the string-derived Randall-Sundrum model Multi-throat geometries may be generic Situations with the Standard Model in a different throat or on the UV brane have to be considered Effects of the cosmological phase transition of these models (the IR brane emerging from a black hole horizon) may be important

11 Summary If realized in nature, string theory and new theories of gravity (e.g. extra dimensions) are crucial for early and possibly late cosmology The above projects focus on the potentially testable implications for dark energy and dark matter Central points include Quintessence from the dynamics of extra dimensions Cosmological scalar fields arising from D-brane motion Dark matter production in warped compactifications Many further promising avenues are bound to open up during the investigation of these problems