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Probing Unification Scenarios with Big Bang Nucleosynthesis

I. M. Dreyer, C. J. A. P. Martins

Abstract

We extend a recently developed Big Bang Nucleosynthesis (BBN) code, {\tt PRyMordial}, to constrain a broad class of Grand Unified Theories to which BBN is sensitive, since these lead to varying fundamental couplings. A previously developed self-consistent perturbative analysis of the effects of these variations has been implemented in {\tt PRyMordial}, leading to robust constraints of the value of the fine-structure constant, $α$, at the BBN epoch using current observations of Helium-4 and Deuterium abundances. We explored two different viable scenarios, relying on alternative assumptions on the gravitational sector: the variation of the gravitational coupling can be implemented by varying either particle masses, or Newton's gravitational constant. For the variation of masses, we obtained at $68\%$ confidence level a constraint on the relative variation of $α$, between the BBN epoch and the present-day laboratory value, of $Δα/α=2\pm51$ ppm (parts per million), while for the variation of Newton's constant the analogous constraint is $Δα/α=2\pm22$ ppm. We also show that, given these constraints, these models do not provide a solution to the cosmological Lithium problem.

Probing Unification Scenarios with Big Bang Nucleosynthesis

Abstract

We extend a recently developed Big Bang Nucleosynthesis (BBN) code, {\tt PRyMordial}, to constrain a broad class of Grand Unified Theories to which BBN is sensitive, since these lead to varying fundamental couplings. A previously developed self-consistent perturbative analysis of the effects of these variations has been implemented in {\tt PRyMordial}, leading to robust constraints of the value of the fine-structure constant, , at the BBN epoch using current observations of Helium-4 and Deuterium abundances. We explored two different viable scenarios, relying on alternative assumptions on the gravitational sector: the variation of the gravitational coupling can be implemented by varying either particle masses, or Newton's gravitational constant. For the variation of masses, we obtained at confidence level a constraint on the relative variation of , between the BBN epoch and the present-day laboratory value, of ppm (parts per million), while for the variation of Newton's constant the analogous constraint is ppm. We also show that, given these constraints, these models do not provide a solution to the cosmological Lithium problem.

Paper Structure

This paper contains 8 sections, 20 equations, 11 figures, 1 table.

Table of Contents

  1. Introduction
  2. Perturbative analysis
  3. Numerical implementation and tests
  4. Comparing with observations
  5. Constraints on GUT models
  6. Coda: The Lithium problem revisited
  7. Conclusions
  8. Further details on numerical implementation

Figures (11)

  • Figure 1: Primordial abundances as a function of $\Delta\alpha/\alpha$ for the four representative (R,S) pairs discussed in the text: ($36$, $160$) in blue, ($109.4$, $0$) in green, ($-183$, $22.5$) in red, and ($0$, $-1$) in orange. Varying masses have been assumed in the gravitational sector, and $Y_p$ is the Helium-4 mass fraction.
  • Figure 2: Same as Fig. \ref{['fig01']}, but assuming a varying $G_N$ in the gravitational sector.
  • Figure 3: Primordial Deuterium abundances as a function of $\Delta\alpha/\alpha$ for the four possible modeling choices for the gravitational sector and $G_F$. The value of $R$ is 0, 36 and 60 in the top, middle and bottom panels respectively, while $S=240$ in all cases.
  • Figure 4: Cheese chart for $\Delta\alpha/\alpha=0$ showing Helium-4 on top and Deuterium on the bottom. Te top and bottom panels use the nuclear rates from the PRIMAT and NACRE II databases respectively.
  • Figure 5: Same as Fig. \ref{['fig04']}, for $\Delta\alpha/\alpha=+10^{-4}$. In the gravitational sector $G_N$ is assumed to vary,
  • ...and 6 more figures