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Primordial Black Holes and Cosmological Phase Transitions Report ...

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PBHs <strong>and</strong> <strong>Cosmological</strong> <strong>Phase</strong> <strong>Transitions</strong> 150<br />

7.3.1 Before the mixed phase<br />

When x ≥ 1(tk ≤ t−) we are dealing with fluctuations of classes A, B or C. For<br />

a given x we can determine the range of amplitudes corresponding to each class.<br />

More precisely, the solution of the equation fB(d) =fC(d) gives the boundary<br />

between classes B <strong>and</strong> C <strong>and</strong> the solution of the equation fA(d) =fB(d) the<br />

boundary between classes B <strong>and</strong> A.<br />

Let us start with the case x = 15 (tk ≈ 1.6 × 10 −5 s) <strong>and</strong> δc =1/3. The<br />

boundaries between the different classes are δAB ≈ 0.25 <strong>and</strong> δBC ≈ 0.21. In<br />

order to identify the values of δ for which collapse to a BH occurs we plot in<br />

Figure 71 both (1−f)δc <strong>and</strong> δ itself as functions of δ. Notice that one should use<br />

the function f appropriate to each class (i.e. fA – equation 270; fB – equation<br />

271; fC – equation 274). As it is clear we could have, in this case, PBHs from<br />

fluctuations of classes A (provided that δ< 1), B <strong>and</strong> C (provided that δ> 0.18<br />

because otherwise the fluctuation will dissipate without forming a PBH). This<br />

point δc1 ≈ 0.18 marks a new <strong>and</strong> lower threshold for PBH formation during<br />

the QCD phase transition when x = 15 <strong>and</strong> δc =1/3.<br />

We have also represented on Figure 71 the curve (1 − fBag)δc where fBag<br />

regards only to the contribution within the Bag Model (i.e., we are considering<br />

fALat = fBLat = fCLat = 0 ) of the period t−

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