BRANEWORLD COSMOLOGY Revent reviews Brax Davis vd Bruck
BRANE-WORLD COSMOLOGY Revent reviews: Brax, Davis, vd Bruck, hep-th/0404011 RM, gr-qc/0312059 Roy Maartens Porto 2004 University of Portsmouth
n standard cosmology highly successful concordance model = excellent fit n but – still a paradigm seeking a fundamental theory deep puzzles inflation, dark energy, dark matter, … more to come
high-precision cosmology is probing the limits of GR n GR breaks down need quantum gravity in the early universe n no QG theory as yet but M theory is a promising candidate M theory needs extra dimensions + branes n can also lower the Planck scale explain ‘weakness’ of gravity
why don’t we see the extra dimensions? n conventional Kaluza-Klein idea: internal extra dimension too small to be seen 4 D spacetime small extra dimension n discovery of D-brane n matter fields restricted to lower dimensional brane n external bulk felt only through gravity n extra dimension bigger large extra dimension gravity
small extra dimensions = moduli fields m. A(t, x) visible brane shadow brane dilaton D(t, x) large extra dimension = radion R(t, x) THE BIG IDEA: M THEORY WILL SOLVE PUZZLES * dilaton/radion = natural source of brane inflation? * more radical: no inflation brane-brane collision = big bang (cyclic)? * moduli = varying constants? * shadow matter = dark matter? dark energy?
n the harsh reality … n still no string/ M theory cosmology n even inflation/ dark energy hard to get n 2 parallel approaches * hunt for string/ M theory cosmology * use braneworld phenomenology n braneworld cosmology use M theory ideas in cosmology n use high-precision data to test & constrain models n GR phenomenology QG
2 key features n braneworld gravity brings new features KK modes of the graviton new fields (moduli, dilaton, …) shadow matter holography, … n precision data constrains extra-dimensional gravity dynamics – BBN, SNe perturbations – CMB and LSS
start with simple models n similar to inflation and dark energy models n simplest models with predictive power n focus on one or two key aspects at a time n KK modes of graviton n scalar fields – radion, dilaton, moduli n …. Randall-Sundrum braneworlds n 5 D models n gravity itself is central – warped extra dimension
stringy/quantum curvature corrections Gauss-Bonnet (early universe) induced gravity (late universe)
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