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Growing Neutrinos as a solution of the why now problem of Dark Energy

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## Growing Neutrinos as a solution of the why now problem of Dark Energy

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**Growing Neutrinos**as a solution of the why now problem of Dark Energy**connection between dark energy and neutrino properties**= 1.27 present dark energy density given by neutrino mass present equation of state given by neutrino mass !**Dark Energy dominates the Universe**Energy - density in the Universe = Matter + Dark Energy 25 % + 75 %**Matter : everything that clumps--------------------Dark**Energy density isthe same at every point of space “ homogeneous “Space between clumps is not empty**What is Dark Energy ?**Cosmological Constant or Quintessence ?**Cosmological Constant- Einstein -**• Constant λ compatible with all symmetries • No time variation in contribution to energy density • Why so small ? λ/M4 = 10-120 • Why important just today ?**Cosm. Const | Quintessence**static | dynamical**Why now problem**• Why is dark energy important now and not in the past ?**Energy density**ρ ~ ( 2.4×10 -3 eV )- 4 Reduced Planck mass M=2.44×1018GeV Newton’s constant GN=(8πM²) Cosmological mass scales Only ratios of mass scales are observable ! homogeneous dark energy: ρh/M4 = 6.5 10ˉ¹²¹ matter: ρm/M4= 3.5 10ˉ¹²¹**connection between dark energy and neutrino properties**= 1.27 present dark energy density given by neutrino mass Energy density : ρ1/4 ~ 2.4×10 -3 eV**Time evolution**tˉ² matter dominated universe tˉ3/2 radiation dominated universe • ρm/M4 ~ aˉ³ ~ • ρr/M4 ~ aˉ4~ t -2radiation dominated universe Huge age small ratio Same explanation for small dark energy?**Quintessence**Dynamical dark energy , generated by scalarfield (cosmon) C.Wetterich,Nucl.Phys.B302(1988)668, 24.9.87 P.J.E.Peebles,B.Ratra,ApJ.Lett.325(1988)L17, 20.10.87**Prediction : homogeneous dark energyinfluences recent**cosmology- of same order as dark matter - Original models do not fit the present observations …. modifications**Cosmon**• Scalar field changes its value even in the present cosmological epoch • Potential und kinetic energy of cosmon contribute to the energy density of the Universe • Time - variable dark energy : ρh(t) decreases with time ! V(φ) =M4 exp( - αφ/M )**“Fundamental” Interactions**Strong, electromagnetic, weak interactions On astronomical length scales: graviton + cosmon gravitation cosmodynamics**Evolution of cosmon field**Field equations Potential V(φ) determines details of the model V(φ) =M4 exp( - αφ/M ) for increasing φ the potential decreases towards zero !**Cosmic Attractors**Solutions independent of initial conditions typically V~t -2 φ ~ ln ( t ) Ωh ~ const. details depend on V(φ) or kinetic term early cosmology**exponential potentialconstant fraction in dark energy**can explain order of magnitude of dark energy ! Ωh = 3(4)/α2**realistic quintessence**fraction in dark energy has to increase in “recent time” !**Quintessence becomes important “today”**Ω No reason why w should be constant in time ! w**coincidence problem**What is responsible for increase of Ωh for z < 6 ? Why now ?**growing neutrino mass triggers transition to almost static**dark energy growing neutrino mass**effective cosmological triggerfor stop of cosmon evolution**:neutrinos get non-relativistic • this has happened recently ! • sets scales for dark energy !**cosmon evolution**“stopped” scaling**stopped scalar fieldmimicks acosmological constant( almost**…) rough approximation for dark energy : • before redshift 5-6 : scaling ( dynamical ) • after redshift 5-6 : almost static ( cosmological constant )**cosmon coupling to neutrinos**basic ingredient :**Cosmon coupling to neutrinos**• can be large ! • interesting effects for cosmology if neutrino mass is growing • growing neutrinos can stop the evolution of the cosmon • transition from early scaling solution to cosmological constant dominated cosmology Fardon,Nelson,Weiner L.Amendola,M.Baldi,…**end of matter domination**• growing mass of neutrinos • at some moment energy density of neutrinos becomes more important than energy density of dark matter • end of matter dominated period • similar to transition from radiation domination to matter domination • this transition happens in the recent past • cosmon plays crucial role**cosmological selection**• present value of dark energy density set by cosmological event ( neutrinos become non – relativistic ) • not given by ground state properties !**connection between dark energy and neutrino properties**= 1.27 present dark energy density given by neutrino mass present equation of state given by neutrino mass !**dark energy fraction determined by neutrino mass**constant neutrino - cosmon coupling β variable neutrino - cosmon coupling**varying neutrino – cosmon coupling**• specific model • can naturally explain why neutrino – cosmon coupling is much larger than atom – cosmon coupling**neutrino mass**seesaw and cascade mechanism triplet expectation value ~ doublet squared omit generation structure**cascade mechanism**triplet expectation value ~ M.Magg , … G.Lazarides , Q.Shafi , …**varying neutrino mass**ε≈ -0.05 triplet mass depends on cosmon field φ neutrino mass depends on φ**cascade mechanism**triplet expectation value ~**“singular” neutrino mass**triplet mass vanishes for φ → φt neutrino mass diverges for φ → φt**strong effective neutrino – cosmon coupling for φ → φt**typical present value : β≈ 50 cosmon mediated attraction between neutrinos is about 502 stronger than gravitational attraction**crossover fromearly scaling solution to effective**cosmological constant**early scaling solution ( tracker solution )**neutrino mass unimportant in early cosmology**growing neutrinos change cosmon evolution**modification of conservation equation for neutrinos**effective stop of cosmon evolution**cosmon evolution almost stops once • neutrinos get non –relativistic • ß gets large This always happens for φ → φt !**effective cosmological triggerfor stop of cosmon evolution**:neutrinos get non-relativistic • this has happened recently ! • sets scales for dark energy !**dark energy fraction determined by neutrino mass**constant neutrino - cosmon coupling β variable neutrino - cosmon coupling