Baryons

Second Quantized Description of a System of Noninteracting Spin Particles.—All the spin particles discovered thus far in nature have the property that particles and antiparticles are distinct from one another. In fact there operates in nature conservation laws (besides charge conservation) which prevent such a particle from turning into its antiparticle. These laws operate independently for light particles (leptons) and heavy particles (baryons). For the light fermions, i.e., the leptons neutrinos, muons, and electrons, the conservation law is that of leptons, requiring that the number of leptons minus the number of antileptons is conserved in any process. For the baryons (nucleons, A, E, and S hyperons) the conservation law is the... 

Conditional probability, 267 density function, 152 Condon, E. U., 404 Configuration space amplitude, 501 Heisenberg operator, 507 operators, 507, 514, 543 Conservation laws for light particles (leptons), 539 for heavy particles (baryons), 539 Continuous memoryless channels, 239 Contraction symbol for two time-labelled operators, 608 Control of flow, 265 Converse to coding theorem, 215 Convex downward function, 210 Convex upward function, 209 Cook, L. F 724... 

The primordial Li abundance was sought primarily because of its ability to constrain the baryon to photon ratio in the Universe, or equivalently the baryon contribution to the critical density. In this way, Li was able to complement estimates from 4He, the primordial abundance of which varied only slightly with baryon density. Li also made up for the fact that the other primordial isotopes, 2H (i.e. D) and 3He, were at that time difficult to observe and/or interpret. During the late 1990 s, however, measurements of D in damped Lyman alpha systems (high column-density gas believed to be related to galaxy discs) provided more reliable constraints on the baryon density than Li could do (e.g. [19]). Even more recently, the baryon density has been inferred from the angular power spectrum of the cosmic microwave background radiation, for example from the WMAP measurements [26]. We consider the role of Li plateau observations post WMAP. 

Fig. 1. The baryon density parameter, r/10, inferred from SBBN and the relic abundances of D, 3He, 4He, and 7Li (filled circles), along with the non-BBN determination from WMAP (filled triangle). See the text for details.

After e annihilation during the early evolution of the Universe, the ratio of baryons to photons is, to a very good approximation, preserved down to the present. The baryon density parameter is defined to be this ratio (at present) r] = n /n r/io =... 

Fig. 4. A summary of the time evolution of primordial 4He abundance determinations (mass fraction Yp) from observations of metal-poor, extragalactic Hu regions (see the text for references). The solid horizontal line is the SBBN-predicted 4He abundance expected for the WMAP (and/or D) inferred baryon density. The two dashed lines show the la uncertainty in this prediction.

Fig. 5. Isoabundance curves for 4He (solid) and D (dashed) in the baryon abundance (7710) - expansion rate factor (S) plane. The labels on the 4He curves are for Yp, while those on the D curves are for j/d = 10B(D/H). The filled circle with error bars corresponds to the adopted values of the D and 4He primordial abundances (see the text).

Fig. 1. Evolution of baryonic mass, gaseous mass, O/H, C/O and Fe/O predicted by a model that considers an early galactic wind. Observations from Peimbert et al. (2005) and Venn et al. (2001).

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 ... 

F. Hoyle, D. N. Schramm, G. Steigman and others, which assumes standard cosmology and particle physics and a uniform baryon density, has been very successful in several respects, e.g. ... 

A small degree of matter-antimatter asymmetry, with a baryon number B (ratio of net number of baryons Nb — N-g in a co-moving volume to the entropy S) in the range 10-11 to 10-8. 

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.

The number rj, together with the known background temperature Tyf), measures the cosmological baryon density today ... 

The deuterium abundance, on the other hand, is a steeply decreasing function because it is destroyed by two-body reactions with p, n, D and 3He. 3He declines more gently because this nucleus is more robust. 7Li has a bimodal behaviour because at low baryon densities it is synthesized from 3H by reaction (Eq. 4.46) and both nuclei are destroyed by two-body reactions, whereas at higher densities it... 

Because of the destruction of D when interstellar gas is recycled through stars, its present-day abundance is a firm lower limit to the primordial one. Adopting the local bubble value as representative of the Galaxy places an upper limit on the baryonic density parameter,... 

SBBN theory has been remarkably successful and does not seem to be in need of any modification except just possibly in the case of 7Li. The limits that it sets on baryonic density are most robust in the case of deuterium (2 < 105D/H < 4) implying... 

The existence of dark matter (either baryonic or non-baryonic) is inferred from its gravitational effects on galactic rotation curves, the velocity dispersions and hydrostatic equilibrium of hot (X-ray) gas in clusters and groups of galaxies, gravitational lensing and departures from the smooth Hubble flow described by Eq. (4.1). This dark matter resides at least partly in the halos of galaxies such as our... 

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