1. QCD & cosmology The quest for cosmological signals of QCD dynamics
QM Italia, (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

2. 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 m
When a/ao was ^ ^-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

3. 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)

4. 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

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

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

7. From
S - conservation

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

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

11. 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

12. 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 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

13. 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 ?