Particle Standard model

In addition to tire standard model systems described above, more exotic particles have been prepared witli certain unusual properties, of which we will mention a few. For instance, using seeded growtli teclmiques, particles have been developed witli a silica shell which surrounds a core of a different composition, such as particles witli magnetic [12], fluorescent [13] or gold cores [14]. Anotlier example is tliat of spheres of polytetrafluoroetliylene (PTFE), which are optically anisotropic because tire core is crystalline [15]. 

On the other hand, the permanent EDM of an elementary particle vanishes when the discrete symmetries of space inversion (P) and time reversal (T) are both violated. This naturally makes the EDM small in fundamental particles of ordinary matter. For instance, in the standard model (SM) of elementary particle physics, the expected value of the electron EDM de is less than 10 38 e.cm [7] (which is effectively zero), where e is the charge of the electron. Some popular extensions of the SM, on the other hand, predict the value of the electron EDM in the range 10 26-10-28 e.cm. (see Ref. 8 for further details). The search for a nonzero electron EDM is therefore a search for physics beyond the SM and particularly it is a search for T violation. This is, at present, an important and active held of research because the prospects of discovering new physics seems possible. 

There are many different extensions of the standard model of particle physics which result in modifications of the early universe expansion rate (the time -temperature relation). For example, additional particles will increase the energy density (at fixed temperature), resulting in a faster expansion. In such situations it is convenient to relate the extra energy density to that which would have been contributed by an additional neutrino with the ordinary weak interactions [19]. Just prior to e annihilation, this may be written as... 

Rare event physics is playing a significant role in modern physics the rare event signals, if detected, would be an evidence for the need of a new physics, beyond the standard model of particle Physics, and would have far-reaching consequences in Cosmology. 

The other kind of dark matter must be non-baryonic (NDM) and is thought to consist of some kind of particles envisaged in extensions of the Standard Model ... 

Fig. 4.1. Schematic thermal history of the Universe showing some of the major episodes envisaged in the standard model. GUTs is short for grand unification theories and MWB is short for (the last scattering of) the microwave background radiation. The Universe is dominated by radiation and relativistic particles up to a time a little before that of MWB and by matter (including non-baryonic matter) thereafter, with dark energy eventually taking over.

Interpreted, as it is, within the standard model, Higgs theory has little meaning in the real world, failing, as it does to relate the broken symmetry of the field to the chirality of space, time and matter. Only vindication of the conjecture is expected to be the heralded observation of the field bosons at stupendous temperatures in monstrous particle accelerators of the future. However, the mathematical model, without cosmological baggage, identifies important structural characteristics of any material universe. The most obvious stipulation is to confirm that inertial matter cannot survive in high-symmetry euclidean space. 

As is mentioned in the introduction, the observation of a non-zero EDM would point out the presence of so called new physics (see [30, 1] and references) beyond the Standard Model [2, 3, 4, 5, 31] or CP violation in the QCD sector of SM, SU 2>)c- The discovery of a lepton EDM (electron EDM in our case) would have an advantage as compared to the cases of neutron or proton EDMs because the latter are not considered as elementary particles within the SM and its extensions. 

The atom was once thought to be the smallest unit of matter, but was then found to be composed of electrons, protons, and neutrons. The question arises are electrons, protons, and neutrons made of still smaller particles In the same way that Rutherford was able to deduce the atomic nucleus by bombarding atoms with alpha particles (Chapter 3), evidence for the existence of many other subatomic particles has been obtained by bombarding the atom with highly energetic radiation.This research over the past centmy has evolved into what is known as the "standard model of fundamental particles, which places all constituents of matter within one of two categories quarks and leptons. 

During the 1960s, L.M. Lederman, M. Schwartz, and J. Steinberger conducted the well-known two-neutnno experiment, which established a relationship between particles, muon and muon neutrinos, electron and electron neutrino, This later evolved into I he standard model of particle physics. The Nobel prize in physics was shared by these researchers in 1988. 

Lederman, L.M. Observations in Particle Physics from Two Neutrinos to the Standard Model." Science, 664 (May 12. 1989). 

Horldesoii, T.., M. Rimdan, M. Dresden, and T..M. Firowiv Rise of the Standard Model Particles Physics in fhe 1960s and 1970s. Cambridge University Press, New Yoik, NY, 1997... 

Particle groups, like fermions, can also be divided into the leptons (such as the electron) and the hadrons (such as the neutron and proton). The hadrons can interact via the nuclear or strong interaction while the leptons do not. (Both particle types can, however, interact via other forces, such as the electromagnetic force.) Figure 1.4 contains artistic conceptions of the standard model, a theory that describes these fundamental particles and their interactions. Examples of bosons, leptons, hadrons, their charges, and masses are given in Table 1.6. 

Analyses of the hadronic peak cross section data obtained at LEP1 [20] implies a small amount of missing invisible width in Z decays. These data imply an effective number of massless neutrinos, N = 2.985 0.008, which is below the prediction of 3 standard neutrinos by the standard model of electroweak interactions. The weak charge Qw in atomic parity violation can be interpreted as a measurement of the 5 parameter. This indicates a new Qw = —72.06 0.44 is found to be above the standard model prediction. This effect is interpreted as due to the occurrence of the Z particle, which will be refered to as the ZY particle. 

Could that be so that the Universe was created with the preponderance of matter over antimatter We have no support for such hypothesis. Einstein remarked If that s the way God made the world then I don t want to have anything to do with Him [7]. Indeed, the contemporary Standard Model of Physics suggests that equal amounts of matter and antimatter were born during the Big-Bang. Where has the antimatter gone What causes the apparent asymmetry between matter and antimatter Obviously the antiparticles have been annihilated by particles - but apparently this process was not fully symmetric, since enough matter was left over for our Universe. We seem to be the result of an accident, caused by a a slight imperfection of Nature. 

The most perceptible experimental reason is the evident asymmetry of the Universe. The CP violation alone, on the level allowed by the Standard model, is not sufficient to explain the excess of matter in the Universe [18]. Finding a suitable extension of the Standard Model is not easy not only do the GUT theories tend to violate CPT invariance but they are also difficult to test. Specifically they can not be tested by means of the particle accelerator experiments, which so far have been very successful in extending our knowledge of Physics. This is because the GUT energy is some 1013 times larger than what we can now days produce in the most powerful accelerators. Consequently we must look for the low-energy manifestations of GUT and CPT invariance. Interestingly some possibilities for such tests lie within the realm of atomic and molecular physics. 

In summary, the thermal history of the early Universe is very simple. It just assumes a global isotropic and uniform Universe. In its simplest version - no structure of any kind on scales larger than individual particles - the contents of the Universe are determined by "standard elmentary physics" i) ag lobal expansion governed by GR, ii) particles interactions governed by the "Standard Model" of Particle Physics, iii) distributions of particles governed by the laws of Statistical Physics. 

We will discuss three cold dark matter candidates which are well-motivated , i.e. that have been proposed to solve problems in principle unrelated to dark matter and whose properties can be computed within a well-defined particle physics model. The three candidates we discuss are (1) a heavy active neutrino with standard model interactions, (2) the neutralino in the minimal super-symmetric standard model, and (3) the axion. Examples of other candidates that can be included in this category are a sterile neutrino (See e.g. Abazajian, Fuller, Patel (2001)) and other supersymmetric particles such as the grav-itino (See e.g. Ellis et al.(1984)) and the sneutrino (see, e.g.,Hall, Moroi Murayama( 1998)). 

Figure 16.2. Evolution of a typical WIMP number density in the early universe. The number of WIMPs in a volume expanding with the universe (comoving density) first decreases exponentially due the Boltzmann factor e-m/T an(j then freezes out to a constant value when the WIMP annihilation reactions cannot maintain chemical equilibrium between WIMPs and standard model particles. In the figure, (av) is the thermally averaged annihilation cross section times relative velocity. WIMPs with larger annihilation cross section end up with smaller densities.

Of importance for cosmology is the fact that supersymmetry requires the existence of a new particle for each particle in the Standard Model. These su-... 

If supersymmetry would be an explicit symmetry of nature, superpartners would have the same mass as their corresponding Standard Model particle. However, no Standard Model particle has a superpartner of the same mass. It is therefore assumed that supersymmetry, much as the weak symmetry, is broken. Superpartners can then be much heavier than their normal counterparts, explaining why they have not been detected so far. However, the mechanism of supersymmetry breaking is not completely understood, and in practice it is implemented in the model by a set of supersymmetry-breaking parameters that govern the values of the superpartners masses (the superpartners couplings are fixed by supersymmetry). 

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