@ 3-sigma Compare CMB/LSS/Sn1a 2-sigma constraint: (Kunz et al 2003) Compare cosmological 2-sigma results: For those who wish to sleep, the only quantitative result is… Dark energy equation of state today This talk will be horrible for the expert – “I will mix things”!
The fundamental problem in cosmology & particle physics is… Almost everything is dark
1.Cold Dark Matter - a simple massive field 2. /Quintessence - a single scalar field with flat potential. But we don’t understand either part! Old Local Law Chico, California Detonating a nuclear device within the city limits results in a $500 fine The standard view of the dark sector Sometimes it isn’t easy to appreciate how radical an approach is needed…
So, do we need separate dark matter and dark energy fields? Probably Not…
Unification of dark matter & dark energy I Scale-dependent pressure A field with p = 0 on small scales but p ~ - when averaged over large scales e.g. Tachyonic fields (Padmanabhan & Choudhury) Similar idea recently proposed in dilaton gravity (Susperrigi)
Unification of dark matter & dark energy II Nonlinear barotropic fluids At high densities p ~ 0 while at low densities p < 0 CDM Acceleration (Kamenshchik et al, Fabris et al, Bilić et al) e.g The Chaplygin gas See also parallel talk by Raoul Viollier
Problems … 1.There are an infinite number of curves with the right properties. Falsifiable? (Chaplygin constraints: Sandvik et al, Bean & Dore, Bento et al, etc…) 2.How can such a nonlinear equation of state be generated physically? (in a way that doesn’t involve branes!)
Dark Matter condenses at a critical density to form the dark energy & initiate cosmic acceleration. Another alternative… astro-ph/02111303 Superconductivity and superfluidity only occur at a few Kelvin - an explanation for the coincidence problem? Neutrino condensate? (Caldi & Chodos) > New four-fermion Interaction? (Inagaki et al 2003)
Condensation II But we do need a model-independent parametrisation of the equation of state Empedocles talked about cyclic cosmic models in the 5 th century B.C. without knowing about string theory or ekpyrosis, so in the same spirit I won’t worry here too much about the details... Dark Matter Dark energy Schematically:
Is the redshift of the Transition, when Effective equation of state CondensationQuintessence
Mass of the dark field changes radically from > 1 MeV to about Compton wavelength, changes from zero to > 100 Mpc around Key points of condensation
Speed of sound,, changes from zero (on average) to the speed of light at alters perturbation dynamics. Condensation is opposite to standard quintessence, where the speed of sound and Compton wavelength do not change much. Key points of condensation II See also parallel talk by Olivier Dore
Condensation Clustering on all scales before transition. Quintessence Only clustering on largest scales
Nonlinear phase of unified models But is it possible that there is no dark matter left today in these unified models? Condensation, nonlinear barotropic eos, vacuum matamorphosis… Are rotation curves simply gravitational fossils from an earlier age?
No. Nonlinear phase of unified models II In unified models, the density inside clusters may never drop below the critical density Universe bifurcates, becoming an inhomogeneous mixture of accelerating voids and a decelerating network of clusters & galaxies p=0 p<0
Stolen from the Virgo consortium website Schematic example of the transition surface…
Onset of cosmic acceleration is now inhomogeneous – ‘perturbed ISW effect’ –Relevant to the CBI excess at high l ? Clustering of “old” objects during sCDM phase more intense than “young” objects – c.f. SDSS result (Budavari et al) Nonlinear phase of unified models III - Expectations
Dark Energy - Standard Model Interactions > SUGRA implies an infinite number of non-renormalisable operators… Dim-4 standard-model Interaction such as Dark energy (e.g. Carrol) Why consider interactions? (Parkinson, Bassett & Barrow 2003)
Gauge kinetic function & the fine-structure constant With redshift info on alpha and some knowledge of we can put direct constraints on dark energy. (e.g. Chiba and Kohri; Wetterich et al and many others…) c.f. standard cosmic tests
We use the general parametrisation… and allow up to dimension 8 operators
Composition-dependent violations of the equivalence principle (EP) Relative acceleration of different bodies: Strong constraint on Variation of alpha today. (Chiba & Khori; Damour, Piazza & Veneziano etc…)
Marginalising over all other dark energy and guage-kinetic function parameters gives… At 3-sigma: Weak dependence on cosmic parameters since we are only interested in the dark energy dynamics.
Clustering properties of the dark energy are reflected in the spatial variations of alpha: Constrained by equivalence principle Detection of spatial clustering of alpha will rule out standard Quintessence models! (and dilaton models) Directly probes the Compton wavelength of dark energy. And finally…
Conclusions Unified dark energy models are radical with exciting unsolved problems and strong potential for new ideas… A radical is a [person] with both feet planted firmly in the air - F.D. Roosevelt – perfect for cosmologists! We are agreed that the theory is weird. What we are not agreed on is whether it is weird enough - Niels Bohr