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Appendix A: Einstein Tensor. Appendix D: Some Useful Numbers. Back Matter Pages About this book Introduction The book reviews theories of nucleosynthesis in big-bang cosmology. Kurume Institute of Technology Fukuoka Japan 3.
Big Bang Nucleosynthesis
Buy options. This fraction is in favour of protons, because the higher mass of the neutron results in a spontaneous decay of neutrons to protons with a half-life of about 15 minutes. Reference Terms. Related Stories.
It is needed to explain nuclear Different nuclear reactions responsible for the creation and What exactly it is and how it came to be is a mystery, He tells of the increase in our confidence in the standard model of cosmology to the extent This intense environment found in the deep interiors of Measuring these primordial abundances today is a very difficult task, because stellar process may have altered the chemical compositions, but data on the 4 He, D and 7 Li abundances exist and can be compared with the theoretical predictions to learn about the conditions of the Universe at such an early period, testing any non-standard physics or cosmology .
The physics of BBN is well understood, since in principle only involves the Standard Model of particle physics and the time evolution of the expansion rate as given by the Friedmann equation. This ratio largely fixes the produced 4 He abundance. Later the primordial abundances of light elements are produced and their values, that can be quite precisely found with BBN numerical codes see e.
Big Bang nucleosynthesis and particle dark matter
Instead, the predicted primordial abundance of 4 He tends to be a bit larger than the observed value, but it is difficult to consider this as a serious discrepancy, because the accuracy of the observations of 4 He is limited by systematic uncertainties. There are two main effects of relic neutrinos at BBN.
This is why BBN gave the first allowed range of the number of neutrino species before accelerators see Sec. Sellerholm, in Les Houches , Once the existence of dark matter has been established, it becomes a fundamental question to inquire what its nature is. Many candidates have been proposed see  for a review , but a confirmed experimental detection has been thus far elusive.
This section therefore investigates the properties and viability of four generic models of dark matter: baryons, neutrinos, thermal relics, and nonthermal relics. Baryons are the most obvious candidate for dark matter, as baryonic dark matter is observed in the form of planets, low luminosity stars, and diffuse gas clouds.
Big Bang Nucleosynthesis (BBN) and Non-Standard Physics | EPJ Web of Conferences
Finally, direct observations of X-rays from interacting galaxies show that dark matter does not interact in the same fashion as baryons  , which means that although baryons compose a significant fraction about 15 per cent of the total matter, they cannot be responsible for all of the dark matter. It is therefore unavoidable that the majority of dark matter be non-baryonic.
The standard model contains a candidate for non-baryonic dark matter: the neutrino. These observations, combined with the constraints on neutrino masses, rule out standard model neutrinos as a significant component of dark matter. Heavier thermal relics are allowed experimentally, however, and particle physics beyond the standard model provides us with many well-motivated dark matter candidates of this type, including the lightest supersymmetric particle and the lightest Kaluza-Klein particle. Thermal relics are defined by the fact that, at some point in the past history of the universe, the particles were in thermal equilibrium with the primordial plasma.
At some point, their abundance freezes out a process known as chemical decoupling , and the number of dark matter particles remains constant thereafter. At a later point, the dark matter particles cease to scatter off of the plasma kinetic decoupling , and thereafter evolve solely gravitationally. Nonthermal relics, on the other hand, were never in thermal equilibrium with the primordial plasma. Instead, these dark matter candidate particles can be produced during phase transitions in the early universe. Candidates include axions  and massive gravitons .
Unlike thermal relics, nonthermal relics evolve only gravitationally from the moment of their creation, receiving only a gravitational imprint from the primordial plasma. As will be discussed in section 4 and 5 , present-day gravitational effects of dark matter have the potential to shed light on its nature, and may be able to distinguish between thermal and nonthermal relics.
Hitoshi Murayama, in Les Houches , The first candidate for dark matter that comes to mind is some kind of astronomical objects, namely stars or planets, which are is too dark to be seen. In some sense, that would be the most conservative hypothesis. But one can still contemplate the possibility that it is some kind of exotic objects, such as black holes.
Black holes may be formed by some violent epochs in Big Bang primordial black holes or PBHs  see also . If the entire horizon collapses into a black hole, which is the biggest mass one can imagine consistent with causality, for example in the course of a strongly first order phase transition, the black hole mass would be. How do we look for such invisible objects?
Interestingly, it is not impossible using the gravitational microlensing effects . The idea is simple. By pure chance, one of them may pass very close along the line of sight towards one of the stars you are monitoring. You typically don't have a resolution to observe distortion of the image or multiple images, but the focusing of light makes the star appear temporarily brighter.
I've shown calculations on the deflection angle by the gravitational lensing and the amplification in the brightness in the appendix. Just for fun, I've also added some discussions on the strong lensing effects. The bottom line is that you may expect the microlensing event at the rate of. See also [ 57, 58 ]. For more details, see the paper. Even though the possibility of MACHO dark matter may not be completely closed, it now appears quite unlikely.
Rubakov, in Les Houches , If the fundamental gravity scale is indeed in the TeV range, one expects that extra dimensions should start to show up in collider experiments at energies approaching this scale [ 31 ]. One also notes that they may have important effects in cosmology and astrophysics.
In the picture described in this section, extra dimensions are felt exclusively by gravitons capable of propagating in the bulk.
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Hence, the most distinctive feature of this scenario is the possibility to emit gravitons into the bulk; this process has strong dependence on the center-of-mass energy of particles colliding on the brane and has large probablity at energies comparable to the fundamental gravity scale. From the four-dimensional viewpoint, emission of gravitons into extra dimensions corresponds to the production of Kaluza-Klein gravitons.
One process of this type is shown in Fig. Each of the KK graviton states interacts with matter on the brane with four-dimensional gravitational strength. Indeed, the quadratic action for each type of KK graviton, and its interaction with matter on the brane are schematically omitting all indices, tensor structure, etc. Electron, positron and photon propagate along the brane, the graviton escapes into the bulk.
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The integration over z again gives the volume factor V d in front of the first term, so the coupling of each type of KK graviton is determined by the four-dimensional Planck mass. Even though the coupling of every KK graviton is weak, the total emission rate of KK gravitons may be large due to large number of KK graviton states. Obiously, this number gets large at large E, so the emission rate of KK gravitons rapidly increases with energy.
In the early Universe, KK gravitons can be produced at high enough temperatures, and therefore may destroy the standard Big Bang picture [ 32 ]. Consistency with the Big Bang nucleosynthesis , as well as the present composition of the Universe impose strong bounds on the maximum temperature of the Universe [ 32 ], as we shall now see. Taking into account the number of KK states, cf. Let us pause here to notice that the latter formula has a natural multi-dimensional interpretation.