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Phase transitions in the early universe

Phase transitions in the early universe. Cosmological phase transition…. …when the universe cools below 175 MeV 10 -5 seconds after the big bang. Quarks and gluons form baryons and mesons before: simply not enough volume per particle available. Heavy ion collision.

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Phase transitions in the early universe

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  1. Phase transitions in the early universe

  2. Cosmological phase transition… …when the universe cools below 175 MeV 10-5 seconds after the big bang Quarks and gluons form baryons and mesons before: simply not enough volume per particle available

  3. Heavy ion collision Seen in experiment ? Phase transition ?

  4. Cosmological relics ? • Only if transition is first order • Out of equilibrium physics is crucial • Otherwise : the universe forgets detailed initial conditions after phase transition • In thermal equilibrium only a few quantities like temperature T or chemical potential μ determine the state

  5. Cosmological phase transitions • QCD phase transition T=175 MeV • Electroweak phase transition T=150 GeV baryogenesis? • GUT phase transition(s) ? T=1016 GeV monopoles,cosmic strings ? • “inflation” T=1015 GeV primordial density fluctuations ! primordial magnetic fields ?

  6. Order of the phase transition is crucial ingredient for cosmological phase transition and experiments ( heavy ion collisions )

  7. Order ofthephasetransition temperature dependence of order parameter

  8. Second order phase transition

  9. First order phase transition

  10. Electroweak phase transition ? • 10-12 s after big bang • fermions and W-,Z-bosons get mass • standard model : crossover • baryogenesis if first order ( only for some SUSY – models ) bubble formation of “ our vacuum “ Reuter,Wetterich ‘93 Kuzmin,Rubakov,Shaposhnikov ‘85 , Shaposhnikov ‘87

  11. Electroweak phase diagram M.Reuter,C.Wetterich Nucl.Phys.B408,91(1993)

  12. Masses of excitations (d=3) small MH large MH O.Philipsen,M.Teper,H.Wittig ‘97

  13. Continuity

  14. Higgs phase and confinement can be equivalent – then simply two different descriptions (pictures) of the same physical situation Is this realized for QCD ? Necessary condition : spectrum of excitations with the same quantum numbers in both pictures - known for QCD : mesons + baryons -

  15. QCD at high temperature • Quark – gluon plasma • Chiral symmetry restored • “Deconfinement” ( no linear heavy quark potential at large distances ) • Lattice simulations : both effects happen at the same temperature

  16. Chiral symmetry restoration at high temperature Low T SSB <φ>=φ0 ≠ 0 High T SYM <φ>=0 at high T : less order more symmetry examples: magnets, crystals

  17. Quark –gluon plasma Gluons : 8 x 2 = 16 Quarks : 9 x 7/2 =12.5 Dof : 28.5 Chiral symmetry Hadron gas Light mesons : 8 (pions : 3 ) Dof : 8 Chiral sym. broken QCD – phase transition Large difference in number of degrees of freedom ! Strong increase of density and energy density at Tc !

  18. Understanding the phase diagram

  19. Phase diagram for ms > mu,d quark-gluon plasma “deconfinement” quark matter : superfluid B spontaneously broken vacuum nuclear matter : B,isospin (I3) spontaneously broken, S conserved

  20. Order parameters • Nuclear matter and quark matter are separated from other phases by true critical lines • Different realizations of global symmetries • Quark matter: SSB of baryon number B • Nuclear matter: SSB of combination of B and isospin I3 neutron-neutron condensate

  21. Phase diagram for ms > mu,d quark-gluon plasma “deconfinement” quark matter : superfluid B spontaneously broken vacuum nuclear matter : B,isospin (I3) spontaneously broken, S conserved

  22. “minimal” phase diagramfor equal nonzero quark masses

  23. Endpoint of critical line ?

  24. How to find out ?

  25. Methods • Lattice :You have to wait until chiral limit is properly implemented ! • Models :Quark meson models cannot work Higgs picture of QCD ? • Experiment :Has Tc been measured ? Indications for first order transition !

  26. Lattice

  27. Lattice results e.g. Karsch,Laermann,Peikert Critical temperature in chiral limit : Nf = 3 : Tc = ( 154 ± 8 ) MeV Nf = 2 : Tc = ( 173 ± 8 ) MeV Chiral symmetry restoration and deconfinement at same Tc

  28. pressure

  29. realistic QCD • precise lattice results not yet available for first order transition vs. crossover • also uncertainties in determination of critical temperature ( chiral limit …) • extension to nonvanishing baryon number only for QCD with relatively heavy quarks

  30. Models

  31. Analytical description of phase transition • Needs model that can account simultaneously for the correct degrees of freedom below and above the transition temperature. • Partial aspects can be described by more limited models, e.g. chiral properties at small momenta.

  32. Universe cools below 175 MeV… Both gluons and quarks disappear from thermal equilibrium : mass generation Chiral symmetry breaking mass for fermions Gluons ? Analogous situation in electroweak phase transition understood by Higgs mechanism Higgs description of QCD vacuum ?

  33. Higgs phase and confinement can be equivalent – then simply two different descriptions (pictures) of the same physical situation Is this realized for QCD ? Necessary condition : spectrum of excitations with the same quantum numbers in both pictures Higgs picture with mesons,baryons as excitations?

  34. Higgs picture of QCD “spontaneous breaking of color “ in the QCD – vacuum octet condensate for Nf = 3 ( u,d,s ) C.Wetterich, Phys.Rev.D64,036003(2001),hep-ph/0008150

  35. Quark –antiquark condensate

  36. Octet condensate < octet > ≠ 0 : • “Spontaneous breaking of color” • Higgs mechanism • Massive Gluons – all masses equal • Eight octets have vev • Infrared regulator for QCD

  37. Flavor symmetry for equal quark masses : octet preserves global SU(3)-symmetry “diagonal in color and flavor” “color-flavor-locking” (cf. Alford,Rajagopal,Wilczek ; Schaefer,Wilczek) All particles fall into representations of the “eightfold way” quarks : 8 + 1 , gluons : 8

  38. Quarks and gluons carry the observed quantum numbers of isospin and strangenessof the baryon and vector meson octets !They are integer charged!

  39. Low energy effective action γ=φ+χ

  40. …accounts for masses and couplings of light pseudoscalars, vector-mesons and baryons !

  41. 5 undetermined parameters predictions Phenomenological parameters

  42. Chiral perturbation theory + all predictions of chiral perturbation theory + determination of parameters

  43. Chiral phase transition at high temperature High temperature phase transition in QCD : Melting of octet condensate Lattice simulations : Deconfinement temperature = critical temperature for restoration of chiral symmetry Why ?

  44. Simple explanation :

  45. Higgs picture of the QCD-phase transition A simple mean field calculation gives roughly reasonable description that should be improved. Tc =170 MeV First order transition

  46. Experiment

  47. Has the critical temperature of the QCD phase transition been measured ?

  48. Heavy ion collision

  49. Chemical freeze-out temperature Tch =176 MeV hadron abundancies

  50. Exclusion argument hadronic phase with sufficient production of Ω : excluded !!

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