The physics of inflation and dark energy

1. The physics of inflation and dark energy V(f) Hubble “drag” Potential f energy is << than the potential 2.6 Acceleration in scalar field models small Equation of motion • Canonical scalar fields: If the kinetic energy => slow roll : With slow- roll, f works like a "time- dependent" L: V(f) <--> L

2. The physics of inflation and dark energy begins ? ends reheating? not here V(F) F-domination begins "here" when z~1 , r0 = (2.3x10 - 3 eV) 4 F 2.7 Starting and stopping a slow-rolling scalar field • Inflation is easy to start : just prepare the scalar field somewhere, and "let it roll". If its energy rf is not negligible, then it will quickly dominate, and the slow-rolling scalar field will cause spacetime to inflate. V(f) f • But... not so good for dark energy: since rF is nearly constant, there is usually a fine tuning problem with the the scalar field (as happens with L .) • => it is very hard to adjust F and V(F) such that rF dominates the energy density at just the right time (z~1) ! ! Hard to turn on at right time !

3. The physics of inflation and dark energy today wX = const. radiation =>matter wL = -1 K-essence 2.8 Dark energy - a theorist´s viewpoint Coincidence Problem!!! • Cosmological Constant w = - 1 Fine tuning Coincidence Problem!!! • “Barotropic” dark energy wX = const. Fine tuning • Tracking dark energy w = w(t) Self-adjusting (?) 1+z = a0/a

4. The physics of inflation and dark energy 2.9 The modelling battlefield Canonical ("honest-to-God") scalar fields: • V(f)=m4 exp[-a f] Wetterich 1988 • V(f)=m4+af-a Ratra & Peebles 1988 • V(f)=m4 [cos(f/f0)+1] Frieman et al 1995 • V(f)=m4 cosh[f/f0] Chimento & Jakubi 1996 • V(f)=m4+af-a exp[k f2] Binétruy 1998, Martin et al 1998 • V(f)=m4 exp[a/f] Steinhardt et al 1998 • V(f)=m4 [ 1-(f-f0)2 ] exp[-a f] Albrecht & Skordis 1995 • V(f)=whatever many many authors Very common: attractor behavior for the background (Ferreira & Joyce 1998,Brax et al. 2000) and for the perturbations (Abramo & Finelli 2000) => results independent of the initial conditions! Other models: • rf = (f´)2/(1+af´+bf´) (K-essence) Armendáriz-Picón et al 2001 • rf = V(f)/[1-(dµf)2] (Tachyon) Sen 2002, Padmanabhan 2002 • p= -A/ra (Chaplygin gas) Kamenshchick et al. 2001, ... • ??? (Branes) many many many many many

5. The physics of inflation and dark energy Dark energy models - pro´s and con´s Con: Pro: • Easy to parametrize • Cosmolog. quantities are simple expressions • Observations so far only sensitive to w, not dw/dt • Fine tuning • No good motivation (except for pure L) • “Barotropic”, wX=const. • (Ex: L , wL = - 1) • Still, some fine tuning! • Often not really well-motivated at all • Can´t resolve time dependence of w • Easy to model • (Maybe) physically well-motivated • Fair hope of explaining coincidence problem. • Scalar field , w=w(t) • Other models: K-essence, "rolling tachyon", Chaplygin gas, "vacuum metamorphosis", ... ? ? ? ? ? ? ?

6. The physics of inflation and dark energy 3. Inflation´s greatest achievement:particle creation and the origin of everything QUANTUM MECHANICS: " DE Dt > h/2p " The vacuum is filled with virtual pairs of particles, which exist for very brief moments, before being annihilated back to nothingness.

7. The physics of inflation and dark energy 3.1 Virtual pairs and particle creation Right here, right now:

8. The physics of inflation and dark energy accelerated expansion rips pairs apart 3.2 Virtual pairs in an accelerating background Horizon H-1 Inflation (acceleration) converts virtual pairs into real pairs

9. The physics of inflation and dark energy density and temperature perturbation quantum fluctuation classical fluctuation 3.3 From quantum fluctuations to galaxies Andromeda That´s us 10-35 s 10-33 s 1.5 1010 y 3. 105 y (Adapated from Lineweaver 1997)

10. The physics of inflation and dark energy Past light cone of an astronomer on Earth:

11. The physics of inflation and dark energy CMB sky CMB deconstructed

12. The physics of inflation and dark energy Conclusions • There is an impressive amount of observational evidence suggesting that the Universe has suffered two phases of acceleration: one in the very early Universe (inflation, t~10-35 s), and the other right about now (Dark energy age, t~1010 years); • The two phases appear to be completely unrelated: what works for one, does not seem to work for the other; • The evidence for dark energy is persuasive and growing, but is still shaky. The case is not as solid as for inflation (yet); • At present, nearly all dark energy models are contrived, fine-tuned and degenerate - in short, bad and ugly; • The physics of inflation use, in a very deep way, both Quantum Mechanics and General Relativity - and the consequences are fully consistent with observations! • Inflation will never be "confirmed": either the evidence will be consistent with it, or not. Must learn to live with that...