Primordial Black Holes and Cosmological Phase Transitions Report ...

PBHs and Cosmological Phase Transitions 77
cs 2
0.3
0.25
0.2
0.15
0.1
0.05
c
b
a
100 150 200 250 300
T MeV
Figure 26: The sound speed c 2 s (T ) for the QCD Crossover with Tc = 170 MeV
and different values for the parameter ∆T : (a) ∆T =0.1Tc, (b) ∆T =0.05Tc
and (c) ∆T =0.02Tc. Notice that the sound speed decreases around Tc but
does not reach zero (with the exception of the limiting case ∆T −→ 0 – see
Figure 27).
1999; Schwarz, 1998)
s(T )= 2π2 3
gHGT
45
1+ 1
2
∆g
gHG
T − Tc
1 + tanh
∆T
(142)
where ∆g = gQGP −gHG and the value of ∆T must be choosen in order to fit the
modeled results. When ∆T −→ 0 we recover the Bag Model, i.e., a first–order
phase transition (Section 2.3.1). Both models coincide at temperatures far away
from Tc (Schwarz, 1998). QCD Lattice data indicate that 0 ≤ ∆T