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## QM Italia, 2009 (Roma 22,23,24 aprile)

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**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**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**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 ?