Primordial Black Holes and Cosmological Phase Transitions Report ...

PBHs and Cosmological Phase Transitions 33
in the temperature–polarization angular power spectrum at l ∼ 150 (Spergel et
al., 2007).
The recombination process is not instantaneous, giving a thickness to the
last scattering surface. This leads to a damping of the anisotropies at the highest
multipoles (l >1000), corresponding to scales smaller than that subtended by
this thickness. This effect leads to a cut off on the anisotropies for l 2000.
Also, gravitational lensing, caused by structures at low redshift (z ≪ 1000),
would have the effect of partially flatten the peaks, generating a power-law tail.
The WMAP data can reach the multipole l 900, up to the third acoustic peak
(see Figure 8). In order to extend to higher multipoles (including the Damping
Tail region), the WMAP team included in their analysis the data of other two
CMB ground–based experiments: the Arcminute Cosmology Bolometer Array
Receiver (ACBAR) and the Cosmic Background Imager (CBI) (e.g. Covi, 2003).
Information on the density contrast can also be obtained from the distribution
of galaxies in our Universe. The main assumption, in this case, is that
the visible matter follows the distribution of the invisible Dark Matter. Recent
surveys include the 2 degree Field Galaxy Redshift Survey (2dFGRS) which released
data on 221 414 galaxies with measured redshift (e.g. Colless et al., 2003;
Cole et al., 2005). An even larger survey is the Sloan Digital Sky Survey (SDSS).
Its 6 th release of data (Adelman–McCarthy et al., 2008) already contains a total
of 790 860 galaxies. From the distribution of the galaxies in the sky one
can obtain the two point correlation function and the density contrast power
spectrum (e.g. Covi, 2003).
Other ways to measure the density contrast rely on using photons of distant
objects as a probe of the intervening matter or gas densities. Lyman α forest
data measure the absorption lines in the spectra of distant quasars caused by
intergalactic hydrogen and estimate the cosmic gas distribution out to large
distances (e.g. Covi, 2003). On Figure 9 we show, as an example, the Lyman α
forest of quasar RD J030117 + 002025.
1.8 The Standard Model of Particle Physics
The combination of the QCD theory and the EW is known as the Standard Model
of Particle Physics (SMPP). The SMPP contains a finite number of parameters,
which are unrelated, at least within the context of the theory itself. The SMPP
is based on only two basic components: the fundamental quantum particles
and the concept of interactions between them. A more complete theory of
fundamental physics should explain the relationships among these parameters.
The ultimate goal would be to determine the values of the parameters from pure
mathematics, once the correct theory is discovered (e.g. Scott, 2006).
The current SMPP, experimentally tested with remarkable precision, describes
the theory of strong, weak and electromagnetic interactions as a gauge
theory 11 . The particle content is (see Figure 10): three families of quarks, three
11 In Physics, gauge theories are a class of physical theories based on the idea that symmetry
transformations can be performed locally as well as globally. Many powerful theories in
Physics (e.g. EW theory, Electrodynamics, QCD) are described by Lagrangians which are