Abstract
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Cosmological solutions to the Lithium problem:
Bigbang nucleosynthesis with photon cooling,
Xparticle decay and a primordial magnetic field
2014. 07. 01.



Abstract

The ^{7}Li abundance calculated in BBN with the baryontophoton ratio fixed from fits to the CMB power spectrum is inconsistent with the observed lithium abundances on the surface of metalpoor halo stars. Previous cosmological solutions proposed to resolve this ^{7}Li problem include photon cooling (possibly via the BoseEinstein condensation of a scalar particle) or the decay of a longlived Xparticle (possibly the nexttolightest supersymmetric particle). In this paper we reanalyze these solutions, both separately and in concert. We also introduce the possibility of a primordial magnetic field (PMF) into these models. We constrain the Xparticles and the PMF parameters by the observed light element abundances using a likelihood analysis to show that the inclusion of all three possibilities leads to an optimum solution to the lithium problem. We deduce allowed ranges for the Xparticle parameters and energy density in the PMF that can solve ^{7}Li problem.





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We have calculated BBN taking into account three possible cosmological extensions of the standard BBN. These include photon cooling, the radiative decay of X particles, and the possible existence of a PMF. In particular, we consider the possible combination of all three paradigms simultaneously in a new hybrid model. We then utilized a maximum likelihood analysis to deduce constraints on the parameters characterizing the X particles (τ_{X}[s], ζ_{X}[s]) and the energy density of the PMF (ρ_{B} = B^{2}/8π) from the observed abundances of light elements up to Li.

FIG. 2;
Constraint on the X particle parameters and the PMF strength and energy density.

From FIG. 2, as a result, we obtained ranges for the Xparticle parameters given by
4.06 < log (τ_{X}[s]) < 6.10 (95% C.L.),
9.70 < log (ζ_{X}[GeV]) < 6.23 (95% C.L.),
e also find that the hybrid model with a PMF gives the better likelihood than that without a PMF,
and the best fit and 2 σ upper bound on the energy density of the PMF are
B = 1.89nG at a = 1.0 (the best fit),
B < 3.05nG at a = 1.0 (95% C.L.).
We discussed the degeneracy between the parameters of the X particle and the PMF.
Since the parameters of X particle are mainly constrained by the D and ^{7}Li abundances, while the energy density of the PMF is constrained by the ^{4}He abundance, we found there are no significant degeneracies between parameters of the PMF and the X particle.





