quintessence – phenomenology

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Quintessence – Phenomenology. How can quintessence be distinguished from a cosmological constant ?. Early dark energy. …predicted in models where dark energy is naturally of the same order as matter . Time dependence of dark energy. cosmological constant : Ω h ~ t² ~ (1+z) -3. M.Doran,…. - PowerPoint PPT Presentation


  • Quintessence Phenomenology

  • How can quintessence be distinguished from a cosmological constant ?

  • Early dark energy

  • predicted in models wheredark energy is naturally of the same order as matter

  • Time dependence of dark energycosmological constant : h ~ t ~ (1+z)-3M.Doran,

  • Early dark energyA few percent in the early Universe

    Not possible for a cosmological constant

  • Structure formation Structures in the Universe grow from tiny fluctuations in density distribution

    stars , galaxies, clusters

    One primordial fluctuation spectrum describes all correlation functions !

  • Early quintessence slows down the growth of structure

  • Growth of density fluctuationsMatter dominated universe with constant h :

    Dark energy slows down structure formation h < 10% during structure formationSubstantial increase of h(t) since structure has formed! negative wh

    Question why now is back ( in mild form )P.Ferreira,M.Joyce

  • Fluctuation spectrumCaldwell,Doran,Mller,Schfer,

  • normalization of matter fluctuationsrms density fluctuation averaged over 8h-1 Mpc spherescompare quintessence with cosmological constantDoran, Schwindt,

  • Early quintessence and growth of matter fluctuationsearly quintessencefor small h :/2 = 3/5

  • for varying early dark energy :weighted average of influence of late evolution ofquintessence throughconformal time 0 andaveraged equation of stateatr : transition from slow early evolution of h to more rapid late evolution

  • at most a few percent dark energyin the early universe !

  • effect of early quintessencepresence of early dark energy decreases for given tslower growth of perturbation

  • Equation of state p=T-V pressure kinetic energy =T+V energy density

    Equation of state

    Depends on specific evolution of the scalar field

  • Negative pressurew < 0 h increases (with decreasing z )

    w < -1/3 expansion of the Universe is accelerating

    w = -1 cosmological constant

    late universe withsmall radiation component :

  • small early and large presentdark energyfraction in dark energy has substantially increased since end of structure formationexpansion of universe accelerates in present epoch

  • exact relation between whand change in heqeq

  • + (

  • Time dependence of dark energycosmological constant : h ~ t ~ (1+z)-3M.Doran,

  • Quintessence becomes important today

  • wh close to -1

    inferred from supernovae and WMAP

  • Supernova cosmologyRiess et al. 2004

  • Dark energy and SN

    M = 0.29 +0.05-0.03

    (SN alone, for tot=1)

  • SN and equation of stateRiess et al. 2004

  • Supernova cosmologyRiess et al. 2004

  • supernovae :negative equation of state andrecent increase in fraction of dark energyare consistent !

  • quintessence and CMB anisotropies influence byearly dark energypresent equation of state

  • Anisotropy of cosmic background radiationCaldwell,Doran,Mller,Schfer,

  • separation of peaks depends on dark energy at last scatteringand on conformal timeinvolves the integral( with weighted w )

  • Peak location in quintessence models for fixed cosmological parameters

  • phenomenological parameterization of quintessence

  • based on parameterization of natural time variableuse relation( matter domination )define

  • three parameter family of modelsfraction in matter M present equation of state w0bending parameter b

  • relation of b to early dark energyTaylor expansiondoes nor make much sense for large z

  • average equation of stateyields simple formula for Hsimple relation with b

  • equation of state changes between w0 and 0

  • reconstruction of cosmon potential or kinetial

  • Dynamics of quintessenceCosmon j : scalar singlet fieldLagrange density L = V + k() j j (units: reduced Planck mass M=1)

    Potential : V=exp[-j]

    Natural initial value in Planck era j=0

    today: j=276

  • for standard exponential potential :construction of kinetial from equation of state

  • How to distinguish Q from ?A) Measurement h(z) H(z)

    i) h(z) at the time of structure formation , CMB - emission or nucleosynthesis ii) equation of state wh(today) > -1

    B) Time variation of fundamental constants

  • end

  • cosmological equations