QCD & cosmology The quest for cosmological signals of QCD dynamics QM Italia, 2009 (Roma 22,23,24 aprile) QCD & cosmology The quest for cosmological signals of QCD dynamics Silvio Bonometto Physics dep., Milano-Bicocca Univ. & INFN – Sezione di Milano-Bicocca

Why signals from cosmological context could be significant ? Q-H cosmological transition necessarily occurred (otherwise, no room to allocate existing baryon number) Today: average cosmic B-B distance 1 m When a/ao was 10^-15 10^-13 cm T then \sim GeV Q-H cosmological transition characterized by high T, low m only context where these conditions naturally occurred observational value of B-density/Ng-density h: definition & value

Assumption (?): homogeneity & isotropy on very large scales Stress-energy tensor shape (generic ref. frame) Metrics (generic ref. frame) Stress-energy tensor components in peculiar reference frame Metric form in peculiar reference frame Einstein eqn.  Friedmann eqn. Hubble (energy conserv….. mechanical) r-a eqn. (energy conserv…... thermodynamical) acceleration eqn. definitions: critical density qo parameter W parameter(s)

Entropy in cosmology Free-energy  r-p relation E – F definitions Phase transitions (order) Entropy conserv./non-conserv. in first-order phase transitions Stress-energy tensor for free particle distribution Density/pressure rel./non-rel. - p - n – s for Bose-Fermi distributions for thermal soup T-a relation T-t & a-t relations in radiative era Hagedorn expression Generalized Bag-Model expressions

Cheng, M. et al., arXiv:0710.0354v2 [hep-lat] McGuigan M. & Soeldner W., arXiv:0810.0265v2 [hep-th] define ext. Bag Model Hagedorn

A benchmark Ipothetical phase transition s=const. state eq. s value from best fit of first 5 pressure points Hadron gas state eq.: Hagedorn

From S - conservation

Phase-transition no-phase transition vs. no transition at all [ aT = const. ] meaning of “vertical” evolution

Phase-transition no-phase transition vs. no transition at all How can 1-order transition occur ? a(t) during transition

a-t relation must matter when annihilation Which signal of different evolution ? Ta : final behavior depends just on entropy conservation time delay ? recall: t \sim 10^-5 sec. …… Formation of cold remnants e.g. neutralino decoupling (hot decoupling, cold decoupling ….. ) a-t relation must matter when annihilation still going on at significant rate

BBN  6.1 \pm 0.6 WMAP etc.  6.25 decreasing errors… Q-H transition & primeval nucleosynthesis (BBN) a connection (perhaps) if transition is 1° order Why a connection ? Could cosmological transition, in spite of all, still be a 1° order phase transition ? A quick outline of BBN (at the origins of scientific cosmology) He abundance in stars Why not from H burning in previous stellar gen. (4p + 2e  He + 28.3 MeV) neutron-proton equilibrium up to 900 keV (Dm=1.4MeV  n/b \sim 0.17) b – decay rate vs. cosmic expansion rate deuterium bottleneck ( B=2.2 MeV - opens at T \sim 100 keV ) nuclear reaction network astration - observational abundances BBN  6.1 \pm 0.6 WMAP etc.  6.25 decreasing errors… Wb from BBN vs WMAP etc. determination Why can we determine Wb from WMAP etc. data

How could Q-H transition affect all that ? No significant chemical potential associated to B Could there be Lepton number ? Would it matter ? Can B easily transfered from plasma to hadron gas ? Concentration discrepancy could cause phase transition ? A general conclusion: Cosmological Q-H transition did occur, but …. did it leave any imprints ?