5] indeed, none of these primordial isotopes of the elements from lithium to oxygen have yet been detected, although those of beryllium and boron may be able to be detected in the future. Conclusions primordial nucleosynthesis is considered as one of the most precise tests of the standard cosmological scenario.

This is due to the fact that all the process occuring during the nucleosynthesis contribute to decrease the number of neutrons. But, since during the dust dominated phase, the gravitational coupling varies with time, the value of the gravitational coupling at the moment of the nucleosynthesis is, in this model, different from that normally used.

Hence, the primordial nucleosynthesis will be taken as another way to verify if the gravitational coupling varies with time. So far, the only stable nuclides known experimentally to have been made before or during big bang nucleosynthesis are protium, deuterium, helium-3, helium-4, and lithium-7.

This result makes deuterium a very useful tool in measuring the baryon-to-photon main nuclear reaction chains for big bang bang nucleosynthesis began roughly 10 seconds after the big bang, when the universe had cooled sufficiently to allow deuterium nuclei to survive disruption by high-energy photons. We compute the primordial abundance of helium as function of the gravitational coupling, using a semi-analytical method, in order to track the influence of g in the primordial nucleosynthesis.

Using the einstein's equations, supposing a flat, isotropic and homogeneous space-time, considering a radiation dominated initial phase in the evolution of the universe, it has been shown that it is possible, assuming initially an equal distribution of protons and neutrons, to obtain the primordial production of helium, leading to an abundance of this element of about 24% of the mass of the universe. The precision of the measurements of the abundance of the primordial elements permits to estimate the possible variation of g.

Hysics and space science series (assl, volume 169)abstractconstraints on chemical potentials and masses of “inos” are calculated using cosmological standard nucleosynthesis processes. Hence, the value of g at the moment of the nucleosynthesis is, in this model, higher than the usual one.

However, this process is very slow and requires much higher densities, taking tens of thousands of years to convert a significant amount of helium to carbon in stars, and therefore it made a negligible contribution in the minutes following the big predicted abundance of cno isotopes produced in big bang nucleosynthesis is expected to be on the order of 10−15 that of h, making them essentially undetectable and negligible. More details about the physics behind big bang nucleosynthesis can be found in the spotlight text equilibrium and change.

Since the general features of the brans-dicke model for the radiative phase is the same as in the standard model, we may compute the primordial abundance of light elements with a minimal modification. Since, the interest in this work it is to track the influence of a varying g in the calculation of the primordial abundance of light elements, it is interesting to sacrify somehow the precison in favour of analytical expressions where the searched effects can be more easily tracked.

To be specific, we construct a cosmological model with varying g, using the brans-dicke theory. The precise calculation of the primordial abundance of light elements is a very hard task.

All elements above 103 (lawrencium) are also manmade and are not bang nucleosynthesis produced no elements heavier than lithium, due to a bottleneck: the absence of a stable nucleus with 8 or 5 nucleons. However, free neutrons are unstable with a mean life of 880 sec; some neutrons decayed in the next few minutes before fusing into any nucleus, so the ratio of total neutrons to protons after nucleosynthesis ends is about 1/7.

For c ¹ 0, we have the following solution for the scale factor:Where b = c, = w + and x is the conformal will be interesting to consider such more general model, including a possible increase of the gravitational coupling during the radiative era, since it can be a possible solution to the discrepancy of the baryonic density obtained from nucleosynthesis and from cmb anisotropy. It turns out, big bang nucleosynthesis strongly favours the very light elements like hydrogen and helium - not only standard hydrogen (one proton) and helium-4 (two neutrons and two protons), but also the isotopes deuterium (one proton, one neutron), tritium (one proton, two neutrons) and helium-3 (two protons, one neutron).

Instead, astronomers need to look for objects in the universe in which, to the best of current knowledge, the abundances of various elements are as close to their primordial value as possible, or which allow extrapolation to the primordial value. Ii the cosmological scenario the brans-dicke theory incorporates the space-time variation of the gravitational coupling in a relativistic theory of gravity [11].

Iii the semi-analytical computation of the primordial nucleosynthesis the computation of the nucleosynthesis process in the early universe involves three main steps. This will permit us to establish constraints on the variation of g by using the nucleosynthesis observational results.

Using the observational data for the abundance of primordial helium, constraints for the time variation of g are established. Neutron-proton ratio was set by standard model physics before the nucleosynthesis era, essentially within the first 1-second after the big bang.

In addition to these stable nuclei, two unstable or radioactive isotopes were also produced: the heavy hydrogen isotope tritium (3h or t); and the beryllium isotope beryllium-7 (7be); but these unstable isotopes later decayed into 3he and 7li, as ially all of the elements that are heavier than lithium were created much later, by stellar nucleosynthesis in evolving and exploding stars. Article: bang nucleosynthesis predicts a primordial abundance of about 25% helium-4 by mass, irrespective of the initial conditions of the universe.