Primordial Black Holes and Cosmological Phase Transitions Report ...

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$Kawasaki dynamic in continuum Math. Encounters XXXV ... - CCM$

PBHs and Cosmological Phase Transitions 38 hybrid mesons (bound states of a gluon, quark and antiquark). There are six types of gluons that can change the colour charge of a quark (but not its flavour): red–antigreen, red–antiblue, green–antired, green–antiblue, blue–antired, and blue–antigreen. For example, if a red quark interacts with a red–antigreen quark then it will become a green quark. In addition, there are two different gluons that couple to the color charge on a quark wihtout changing the quark color. These gluons can be regarded as mixtures of blue–antiblue, red–antired, and green–antigreen. A distinct feature of the EW interactions is that the W ± and Z 0 bosons that mediate them are massive which means that it is not possible to describe weak interactions in terms of a gauge field theory. However, although the theory has a symmetry, it is not necessary that the ground state of the theory has the same symmetry, that is, the symmetry may be spontaneously broken. This is a suffcient requirement for producing masses for gauge bosons. In the SMPP, this is accomplished by introducing a scalar field, called the Higgs scalar, into the theory (e.g. Gynther, 2006). Associated with this field there is a spin zero boson and charge zero – the Higgs boson, H (with a mass yet to be determined – it is still a purely hypothetical particle – the only one of the SMPP). As a quark or lepton moves trough space, it interacts with the Higgs field; the field becomes distorted in the vicinity of the particle. It is this distortion that causes the particle to have mass. Most of our present experimental knowledge about the SMPP Higgs boson comes from the study of e + e − collisions performed at Large Electron Positron Collider (LEP) and the Stanford Linear Collider SLC between 1988 and 2000. No direct evidence for the existence of the SMPP Higgs has been produced. This allows us to set a lower limit on the Higgs mass of 114.4 GeV, mainly based of the non–observation of Higgs bosons in association with a Z 0 , followed by the eventual decay of the Higgs into a heavy fermion–antifermion pair (e.g. Ellis et al., 2007). Hadrons are composite particles made up of quarks (as far as we know there are no free quarks in nature at the present stage of the Universe). Hadrons with integer spin are called mesons (bosonic hadrons) and those with half–integer spin are called baryons (fermionic hadrons). Every meson consists of a quark–antiquark pair. This means that we have five quark flavours × five anti–quark flavours = 25 different possible combinations 12 . However, the observed number of different mesons is, by far, much larger than this one. That is because, for each quark–antiquark combination, there are, in general, many excited states. For example, the π + meson corresponds to the lower energy state (fundamental state) of the u ¯ d combination (m ≈ 139.57 MeV). Examples of excited states for the π + meson (just to name a few) comprehend the ρ + (m ≈ 775.4 MeV), the a0(1450) (m ≈ 1474 MeV), and the π2(1650) (m ≈ 1672.4 MeV). 12 The top quark is left outside because the probability of formation for top mesons is, according to theory, negligibly small (e.g. Fabiano, 1997). Besides that, there are no reports on the detection of top mesons (e.g. Yao et al., 2006).
PBHs and Cosmological Phase Transitions 39 Some of the quark–antiquark combinations are observed only in superpositions. That is, for example, the case of the neutral pion (π 0 ) which is a superposition of the combinations uū and d ¯ d. The superposition occurs because the two combinations share the same set of quantum numbers. The combination d¯s is called neutral Kaon (K 0 ). Although K 0 and its antiparticle ¯ K 0 are usually produced via the strong force, they decay weakly. Thus, once created, the two are better thought of as composites of two weak eigenstates which have vastly different lifetimes: the long–lived (5.116 × 10 −8 s) neutral kaon called K–Long and the short–lived (8.953 × 10 −11 s) neutral kaon called K–Short. On table 7 we show the fundamental mesons as well as their most common excited states.
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Table 49 (continued). PBHs and Cosm
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Table 49 (continued). Radiation EW
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