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

QCD & cosmology

The quest for cosmologicalsignals of QCD dynamics

Silvio BonomettoPhysics 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 mWhen a/ao was 10^-15 10^-13 cm T then \sim GeV

Q-H cosmological transition characterized by

high T, low

only context where these conditions naturally occurred

observational value of B-density/Ndensity

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 frameMetric form in peculiar reference frame

Einstein eqn. Friedmann eqn. Hubble (energy conserv….. mechanical) -a eqn. (energy conserv…... thermodynamical)

acceleration eqn.

definitions: critical density qo parameter parameter(s)

Entropy in cosmologyFree-energy -p relation E – definitions

Phase transitions (order)

Entropy conserv./non-conserv.in first-order phase transitions

Stress-energy tensor for free particle distributionDensity/pressure rel./non-rel.

- p - n – for Bose-Fermi distributionsfor thermal soup

T-a relationT-t & a-t relations in radiative era

Generalized Bag-Model expressionsHagedorn expression

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

so

so

TTT

TsTsE

TT

dtTdE

TTp

TTE

)/)(ln33

1(13

)/(1

/3

)(

)(4

4

define

ext. BagModel

)]/1/1([)/( 2/54

HoHHo TTmEiTTTp

Hagedorn

Ipotheticalphase transition

s=const. state eq.

s value from best fit offirst 5 pressure points

Hadron gas state eq.:Hagedorn

A benchmark

From S - conservation

Phase-transitionno-phase transition

vs. no transition at all [ aT = const. ] meaning of

“vertical” evolution

Phase-transitionno-phase transition

vs. no transition at all

How can 1-ordertransition 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 remnantse.g. neutralino decoupling

(hot decoupling, cold decoupling ….. )

a-t relation must matter when annihilationstill 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 (m=1.4MeV n/b \sim 0.17)• – decay rate vs. cosmic expansion rate• deuterium bottleneck ( B=2.2 MeV - opens at T \sim 100 keV )• nuclear reaction network• astration - observational abundances

b from BBN vs WMAP etc. determination Why can we determine b from WMAP etc. data

BBN 6.1 \pm 0.6WMAP etc. 6.25

decreasing errors…

No significant chemical potential associated to BCould there be Lepton number ?Would it matter ?Can B easily transfered from plasma to hadron gas ?

Concentration discrepancy could causephase transition ?

A general conclusion:

Cosmological Q-H transition did occur, but …. did it leave any imprints ?

How could Q-H transition affect all that ?