Neutrino production

Insofar as these reactions occur relatively rapidly at the high temperatures now prevailing, the star s evolution accelerates enormously. This is exacerbated by the fact that it suffers a significant energy loss due to thermal neutrino production via the reaction... 

In physics, speculative ideas often begin to seem much more reasonable when there is a theory to explain them. In 1933 Fermi advanced just such a theory, proposing that the electron and the neutrino were spontaneously created at the moment that a radioactive disintegration took place. At the same time, one of the neutrons in the nucleus was changed into a proton. Fermi showed that electron-neutrino production could be explained if one assumed the existence of a new force (now called the weak force). He concluded that the mass of the neutrino was probably near zero. This would explain why it hadn t been detected. 

AMANDA has yet to observe an extraterrestrial neutrino source, but she has demonstrated the cost-effectiveness and robustness of the technique. The detector is very versatile it addresses many different neutrino physics subjects and sets the most stringent upper limits on Galactic and extragalactic neutrino fluxes. The improved search for diffuse fluxes, which has ruled out several predictions, along with the extended four-year search for point sources has started to constrain the enormous parameter space that exist in many models of neutrino production. The reported experimental limits on the diffuse neutrino flux are less than an order of magnitude above the Waxman-Bahcall bound ( Waxman and Bahcall, 1999). As more of the data on tape is analyzed, AMANDA sensitivities will continue to improve. This is a very exciting time in neutrino astronomy and we look forward to neutrino astrophysics with next generation of neutrino telescopes. 

Electron scattering by photons may alternatively result in pair neutrino production, with a nett energy loss as shown ... 

What is needed now is some means for calculating e. To do this, it is useful to consider some component, H, which is formed only by Reaction I, which does not appear in the feed, and which has a stoichiometric coefficient of v/// = 1 for Reaction I and stoichiometric coefficients of zero for all other reactions. It is always possible to write the chemical equation for Reaction I so that a real product has a stoichiometric coefficient of +1. For example, the decomposition of ozone, 2O3 3O2, can be rewritten as 2/3O3 —> O2. However, you may prefer to maintain integer coefficients. Also, it is necessary that H not occur in the feed, that there is a unique H for each reaction, and that H participates only in the reaction that forms it. Think of H as a kind of chemical neutrino formed by the particular reaction. Since H participates only in Reaction I and does not occur in the feed, Equation (2.40) gives... 

Three sources have been proposed to produce fluorine in the Galaxy. The first was suggested by Forestini et al. (1992) and refers to production in low-mass stars during the AGB phase while two others are related to massive stars production in Wolf-Rayet stars (Meynet Arnould 2000) and in type II Supernovae, via the neutrino-induced nucleosynthesis (Woosley et al. 1990). 

The first reaction is a fusion of two protons to produce a 2H nucleus, a positron (e+) and a neutrino (ve). The second reaction is a proton capture with the formation of 3He and a y-ray. In the third reaction two 3He nuclei fuse to give 4He and two protons. The total energy released in one cycle is 26.8 MeV or 4.30 x 10-12 J. An important product of this process is the neutrino and it should provide a neutrino flux from the Sun that is measurable at the surface of the Earth. However, the measured flux is not as big as calculated for the Sun - the so-called neutrino deficit... 

Also, the ratio nB/10B is underpredicted by a smaller factor 1.5 which could also come from stellar production, notably from the neutrino process in corecollapse supernovae (Woosley Weaver 1995 Timmes, Woosley Weaver 1995), the efficiency of which is quite uncertain.4... 

The above models are all rather unsatisfactory, because they involve somewhat arbitrary assumptions about the time-dependence of the cosmic-ray flux and spectrum and because they predict a secondary-like behaviour for Be and B abundances, whereas the overall trend indicated by the data is more like a primary one and there are the energetic difficulties pointed out above. In the case of nB, there is a possible primary mechanism for stellar production in supemovae by neutrino spallation processes (Woosley et al. 1990 Woosley Weaver 1995), but the primary-like behaviour of beryllium in metal-poor stars, combined with a constant B/Be ratio of about 20 fully consistent with cosmic-ray spallation (Garcia Lopez et al. 1998) in the absence of any known similar process for Be, indicates that this does not solve the problem unless a primary process can be found for Be as well. Indeed,... 

In the previous Section we noted that the typical temperature, above which the star becomes opaque to neutrinos is Topac 0.4 4- 3 MeV, where we ignore here the differences in the absorption/production properties of different neutrino flavors [45], Saying neutrino we actually will not distinguish neutrino and antineutrino, although their absorption/production could be different. If we assume an initial temperature of To < T%pac, the star radiates neutrinos directly from the interior region. For To > T"po/P the neutrino transport to the surface is operative and leads to a delay of the cooling evolution. 

Neutrino detectors are placed at great depths, at the bottom of mines and tunnels, in order to reduce interference induced by cosmic rays (Fig. 5.3). Two methods of detection have been used to date. The first is radiochemical. It involves the production by transmutation of a radioactive isotope that is easily detectable even in minute quantities. More precisely, the idea is that a certain element is transformed into another by a neutrino impact, should it occur. Inside the target nucleus, the elementary reaction is... 

Historically, chlorine was the first target used to trap neutrinos. Chlorine-37 is mainly sensitive to high-energy neutrinos emanating from marginal fusion reactions (2 out of 10000) which lead to production of boron-8. On rather rare occasions, under the impact of neutrinos, chlorine-37 is transformed into radioactive argon-37 which is easy to detect by its radiation. However, the myriads of low-energy neutrinos completely escape its notice. 

Fig. 5.4. Schematic evolution of the internal structure of a star with 25 times the mass of the Sun. The figure shows the various combustion phases (shaded) and their main products. Between two combustion phases, the stellar core contracts and the central temperature rises. Combustion phases grow ever shorter. Before the explosion, the star has assumed a shell-like structure. The centre is occupied by iron and the outer layer by hydrogen, whilst intermediate elements are located between them. CoUapse followed by rebound from the core generates a shock wave that reignites nuclear reactions in the depths and propels the layers it traverses out into space. The collapsed core cools by neutrino emission to become a neutron star or even a black hole. Most of the gravitational energy liberated by implosion of the core (some 10 erg) is released in about 10 seconds in the form of neutrinos. (Courtesy of Marcel Amould, Universite Libre, Brussels.)...

Perhaps the most novel aspect of SNl987a is the detection [6,7] of neutrinos from the production and cooling of a compact remnant. One hopes this is only the beginning of a new field of astronomy. The analysis I present here [5], parallel to the analysis of many other authors [23-28], finds remnant binding energy 2.0 0.5 X 1053 ergs and remnant mass 1.2 to 1.7 Mq consistent with what one expects for neutron star generation. An upper limit of 10-15 eV may also be inferred for the electron neutrino mass. 

Instrumental searches for this latter neutrinoless process have been made, but there is no strong evidence for its existence. The former two-neutrino decay has been observed with a variety of techniques that were carefully tuned to detect the rare products. 

From the data given on the Davis detector, and the assumption that the 37Ar production rate is 0.5 atoms/day, calculate the neutrino capture rate in SNU. Assume the effective cross section for the 8B neutrinos is 10-42 cm2. 

Another important classification of particle dark matter rests upon its production mechanism. Particles that were in thermal equilibrium in the early Universe, like neutrinos, neutralinos, and most other WIMPs (weakly interacting massive particles), are called thermal relics. Particles which were produced by a non-thermal mechanism and that never had the chance of reaching thermal equilibrium in the early Universe are called non-thermal relics. There are several examples of non-thermal relics axions emitted by cosmic strings, solitons produced in phase transitions, WIMPZILLAs produced gravitationally at the end of inflation, etc. 

In a cosmological context, axions, contrary to neutrinos and neutralinos, are generally produced non-thermally (although thermal axion production is sometimes considered, as are non-thermal neutrino and neutralino productions). The two main mechanisms for non-thermal axion production are vacuum alignment... 

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