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Register a new userImplication of the proton-deuteron radiative capture for Big Bang Nucleosynthesis
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Added by
Laura Elisa Marcucci
Publication date
2015
fields
Physics
and research's language is
English
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The astrophysical $S$-factor for the radiative capture $d(p,gamma)^3$He in the energy-range of interest for Big Bang Nucleosynthesis (BBN) is calculated using an {it ab-initio} approach. The nuclear Hamiltonian retains both two- and three-nucleon interactions - the Argonne $v_{18}$ and the Urbana IX, respectively. Both one- and many-body contributions to the nuclear current operator are included. The former retain for the first time, besides the $1/m$ leading order contribution ($m$ is the nucleon mass), also the next-to-leading order term, proportional to $1/m^3$. The many-body currents are constructed in order to satisfy the current conservation relation with the adopted Hamiltonian model. The hyperspherical harmonics technique is applied to solve the $A=3$ bound and scattering states. A particular attention is used in this second case in order to obtain, in the energy range of BBN, an uncertainty on the astrophysical $S$-factor of the order or below $sim$1 %. Then, in this energy range, the $S$-factor is found to be $sim$10 % larger than the currently adopted values.Part of this increase (1-3 %) is due to the $1/m^3$ one-body operator, while the remaining is due to the new more accurate scattering wave functions. We have studied the implication of this new determination for the $d(p,gamma)^3$He $S$-factor on deuterium primordial abundance. We find that the predicted theoretical value for $^2$H/H is in excellent agreement with its experimental determination, using the most recent determination of baryon density of Planck experiment, and with a standard number of relativistic degrees of freedom $N_{rm eff}=3.046$ during primordial nucleosynthesis.
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We study dynamical screening effects of nuclear charge on big bang nucleosynthesis (BBN). A moving ion in plasma creates a distorted electric potential leading to a screening effect which is different from the standard static Salpeter formula. We consider the electric potential for a moving test charge, taking into account dielectric permittivity in the unmagnetized Maxwellian plasma during the BBN epoch. Based on the permittivity in a BBN plasma condition, we present the Coulomb potential for a moving nucleus, and show that enhancement factor for the screening of the potential increases the thermonuclear reaction rates by a factor order of 10^(-7). In the Gamow energy region for nuclear collisions, we find that the contribution of the dynamical screening is less than that of the static screening case, consequently which primordial abundances hardly change. Based on the effects of dynamical screening under various possible astrophysical conditions, we discuss related plasma properties required for possible changes of the thermal nuclear reactions.
By assuming the existence of extra-dimensional sterile neutrinos in big bang nucleosynthesis (BBN) epoch, we investigate the sterile neutrino ($ u_{rm s}$) effects on the BBN and constrain some parameters associated with the $ u_{rm s}$ properties. First, for cosmic expansion rate, we take into account effects of a five-dimensional bulk and intrinsic tension of the brane embedded in the bulk, and constrain a key parameter of the extra dimension by using the observational element abundances. Second, effects of the $ u_{rm s}$ traveling on or off the brane are considered. In this model, the effective mixing angle between a $ u_{rm s}$ and an active neutrino depends on energy, which may give rise to a resonance effect on the mixing angle. Consequently, reaction rate of the $ u_{rm s}$ can be drastically changed during the cosmic evolution. We estimated abundances and temperature of the $ u_{rm s}$ by solving the rate equation as a function of temperature until the sterile neutrino decoupling. We then find that the relic abundance of the $ u_{rm s}$ is drastically enhanced by the extra-dimension and maximized for a characteristic resonance energy $E_{rm res}gtrsim 0.01$ GeV. Finally, some constraints related to the $ u_{rm s}$, mixing angle and mass difference, are discussed in detail with the comparison of our BBN calculations corrected by the extra-dimensional $ u_{rm s}$ to observational data on light element abundances.
pd capture processes at various energies have been analyzed based on solutions of 3N-Faddeev equations and using modern NN forces. The application of the Siegert theorem is compared to the explicit use of $pi$- and $rho$-like exchange currents connected to the AV18 NN interaction. Overall good agreement with cross sections and spin observables has been obtained but leaving room for improvement in some cases. Feasibility studies for 3NFs consistently included in the 3N continuum and the 3N bound state have been performed as well.
The quark mass dependences of light element binding energies and nuclear scattering lengths are derived using chiral perturbation theory in combination with non-perturbative methods. In particular, we present new, improved values for the quark mass dependence of meson resonances that enter the nuclear force. A detailed analysis of the theoretical uncertainties arising in this determination is presented. As an application we derive from a comparison of observed and calculated primordial deuterium and helium abundances a stringent limit on the variation of the light quark mass, $delta m_q/m_q = 0.02 pm 0.04$. Inclusion of the neutron lifetime modification under the assumption of a variation of the Higgs vacuum expectation value that translates into changing quark, electron, and weak gauge boson masses, leads to a stronger limit, $|delta m_q/m_q| < 0.009$.
Nuclear reaction rates are among the most important input for understanding the primordial nucleosynthesis and therefore for a quantitative description of the early Universe. An up-to-date compilation of direct cross sections of 2H(d,p)3H, 2H(d,n)3He, 7Li(p,alpha)4He and 3He(d,p)4He reactions is given. These are among the most uncertain cross sections used and input for Big Bang nucleosynthesis calculations. Their measurements through the Trojan Horse Method (THM) are also reviewed and compared with direct data. The reaction rates and the corresponding recommended errors in this work were used as input for primordial nucleosynthesis calculations to evaluate their impact on the 2H, 3,4He and 7Li primordial abundances, which are then compared with observations.
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