Big Bang Nucleosynthesis Model Research Articles

Updated BBN constraints on non-equilibrium active-sterile neutrino oscillations

Big Bang Nucleosynthesis (BBN) offers impressive agreement between the predicted by theory and the observationally obtained abundances of primordially produced light elements and therefore it is used as one of the most reliable probes of the physics beyond Standard Model. The highly accurate recent determination of the primordial Deuterium and Helium-4 allows to provide updated and strengthened BBN constraints on beyond Standard Model Physics. We have provided numerical analysis of more than hundred BBN models with nonequilibrium electron-sterile neutrino oscillations with different oscillation parameters and we have constructed isohelium contours based on 1% and 3% Helium-4 uncertainty and different initial population of the sterile neutrino state. We present here updated and more strict BBN constraints on the parameters of non-equilibrium active-sterile neutrino oscillations considering several models of beyond Standard Model Physics.

Big Bang Nucleosynthesis Constraints and Indications for Beyond Standard Model Neutrino Physics

We use Big Bang Nucleosynthesis (BBN) to probe Beyond Standard Model physics in the neutrino sector. Recently, the abundances of primordially produced light elements D and He-4 were determined from observations with better accuracy. The good agreement between the theoretically predicted abundances of primordially produced light elements and those derived from observations allows us to update the BBN constraints on Beyond Standard Model (BSM) physics. We provide numerical analysis of several BSM models of BBN and obtain precise cosmological constraints and indications for new neutrino physics. Namely, we derive more stringent BBN constraints on electron neutrino–sterile neutrino oscillations corresponding to 1% uncertainty of the observational determination of the primordial He-4. The cosmological constraints are obtained both for the zero and non-zero cases of the initial population of the sterile neutrino state. Then, in a degenerate BBN model with neutrino νe↔νs oscillations, we analyze the change in the cosmological constraints in case lepton asymmetry L is big enough to suppress oscillations. We obtain constraints on the lepton asymmetry L. We discuss a possible solution to the dark radiation problem in degenerate BBN models with νe↔νs oscillations in case L is large enough to suppress neutrino oscillations during the BBN epoch. Interestingly, the required value of L for solving the DR problem is close to the value of L indicated by the EMPRESS experiment, and also it is close to the value of lepton asymmetry that is necessary to relax Hubble tension.

Deuterated Polycyclic Aromatic Hydrocarbons in the Interstellar Medium: The Aliphatic C–D Band Strengths

Abstract Deuterium (D) was exclusively generated in the Big Bang, and the standard Big Bang nucleosynthesis (BBN) model predicts a primordial abundance of D/H ≈ 26 parts per million (ppm). As the Galaxy evolves, D/H gradually decreases because of astration. The Galactic chemical evolution (GCE) model predicts a present-day abundance of D/H ≳ 20 ppm. However, observations of the local interstellar medium have revealed that the gas-phase interstellar D/H varies considerably from one region to another and has a median abundance of D/H ≈ 13 ppm, substantially lower than predicted from the BBN and GCE models. It has been suggested that the missing D atoms of D/H ≈ 7 ppm could have been locked up in deuterated polycyclic aromatic hydrocarbon (PAH) molecules. However, we have previously demonstrated that PAHs with aromatic C–D units are insufficient to account for the missing D. Here we explore if PAHs with aliphatic C–D units could be a reservoir of D. We perform quantum chemical computations of the vibrational spectra of superdeuterated PAHs (in which one D and one H share one C atom) and PAHs to which a D-substituted methyl group is attached, and derive the band strengths of the aliphatic C–D stretch (A 4.65). By applying the computationally derived A 4.65 to the observed aliphatic C–D emission at ∼4.6–4.8 μm, we find that PAHs with aliphatic C–D units could have tied up a substantial amount of D/H and marginally account for the missing D. The possible routes for generating PAHs with aliphatic C–D units are also discussed.

The Big Bang nucleosynthesis abundances of the light elements using improved thermonuclear reaction rates

Big Bang nucleosynthesis (BBN) is an important stage of a homogeneous and isotropic expanding universe. The results of calculation of the synthesis of light elements during this epoch can then be compared with the abundances of the light elements. The theoretical calculation of the BBN model depends on the initial conditions of the early universe and reaction cross sections measured by the nuclear physics experiment. Recently, an update of the Nuclear Astrophysics Compilation of REactions database is presented. This improved compilation comprises thermonuclear reaction rates for 34 two-body reactions on light nuclides (fifteen are particle transfer reactions and nineteen are radiative capture reactions). In this work, we calculate the BBN abundances by using these updated thermonuclear reaction rates in the framework of the code AlterBBN. Our results suggest that the new numerical result of the primordial Lithium abundance is 7.1% larger than the previous calculation.

Big Bang nucleosynthesis as a probe of new physics

The Big Bang Nucleosynthesis (BBN) model is a cornerstone for the understanding of the evolution of the early universe, making seminal predictions that are in outstanding agreement with the present observation of light element abundances in the universe. Perhaps, the only remaining issue to be solved by theory is the so-called “lithium abundance problem". Dedicated experimental efforts to measure the relevant nuclear cross sections used as input of the model have lead to an increased level of accuracy in the prediction of the light element primordial abundances. The rise of indirect experimental techniques during the preceding few decades has permitted the access of reaction information beyond the limitations of direct measurements. New theoreticaldevelopments have also opened a fertile ground for tests of physics beyond the standard model of atomic,nuclear, statistics, and particle physics. We review the latest contributions of our group for possible solutions of the lithium problem.

Neutron-induced cross section measurements

Neutron-induced cross sections represent the main nuclear input to models of stellar and Big-Bang nucleosynthesis. While (n,γ) reactions are relevant for the formation of elements heavier than iron, (n,p) and (n,α) reactions can play an important role in specific cases. The time-of-flight method is routinely used at n_TOF to experimentally determine the cross section data. In addition, recent upgrades of the facility will allow the use of activation techniques as well, possibly opening the way to a systematic study of neutron interaction with radioactive isotopes. In the last 20 years n_TOF has provided a large amount of experimental data for Nuclear Astrophysics. Our plan is to carry on challenging measurements and produce nuclear data in the next decades as well.

New Thermonuclear Rate of 7Li(d,n)24He Relevant to the Cosmological Lithium Problem

Abstract Accurate 7Li(d,n)24He thermonuclear reaction rates are crucial for precise prediction of the primordial abundances of lithium and beryllium and to probe the mysteries beyond fundamental physics and the standard cosmological model. However, uncertainties still exist in current reaction rates of 7Li(d,n)24He widely used in big bang nucleosynthesis (BBN) simulations. In this work, we reevaluate the 7Li(d,n)24He reaction rate using the latest data on the three near-threshold 9Be excited states from experimental measurements. We present for the first time uncertainties that are directly constrained by experiments. Additionally, we take into account for the first time the contribution from the subthreshold resonance at 16.671 MeV of 9Be. We obtain a 7Li(d,n)24He rate that is overall smaller than the previous estimation by about a factor of 60 at the typical temperature of the onset of primordial nucleosynthesis. We implemented our new rate in BBN calculations, and we show that the new rates have a very limited impact on the final light element abundances in uniform density models. Typical abundance variations are in the order of 0.002%. For nonuniform density BBN models, the predicted 7Li production can be increased by 10% and the primordial production of light nuclides with mass number A > 7 can be increased by about 40%. Our results confirm that the cosmological lithium problem remains a long-standing unresolved puzzle from the standpoint of nuclear physics.

Study of the contribution of the 7Be(d, p) reaction to the 7Li problem in the Big-Bang Nucleosynthesis

Our research goal is to measure the cross section of the 7Be(d, p) reaction to find a solution for the cosmological the 7Li problem, which is an overestimation of the primordial 7Li abundance in the standard Big-Bang nucleosynthesis (BBN) model. We developed a method to produce an unstable 7Be target to measure the reaction in normal kinematics in a high-resolution measurement. We performed an experiment to produce the 7Be target and also to measure the cross section of the 7Be(d, p)8Be reaction with the produced 7Be target at the tandem facility, Kobe University. A 2.36 MeV proton beam irradiated a Li target to transmute 7Li particles to 7Be particles via the 7Li(p, n)7Be reaction. We produced 2.6×1013 7Be particles in the target after two days’ proton irradiation. After the target production, the beam ion was changed to deuterons with energies of 0.6, 1.0, and 1.6 MeV to measure the 7Be(d, p) reaction. The outgoing protons were measured by two ΔE-E silicon telescopes placed at 30° and 45°. We report the preliminary results of this experiment, including the 7Be(d, p) cross section.

Direct and Indirect Measurements for a Better Understanding of the Primordial Nucleosynthesis

The Big Bang Nucleosynthesis (BBN) model is a great success of nuclear astrophysics, because of the outstanding agreement between observational and predicted light elements abundances, except for the so-called problem. In this context, experimental efforts to measure the relevant reactions have brought to an increased level of accuracy in measuring primordial abundances and the introduction of indirect methods has allowed to overcome the natural limitations of direct measurements in the energy range of interest for BBN. Here we review the results obtained from the application of the Trojan Horse Method to some of the most influential reactions of the standard network, such as $^2$H(d,p)$^3$H, $^2$H(d,n)$^3$He, $^3$He(d,p)$^4$He, $^7$Li(p,$\alpha$)$^4$He and $^7$Be(n,$\alpha$)$^4$He. The relevant cross sections have been thus used as new inputs of a classical BBN code resulting in important constraints that advice on a possible solution of the lithium problem outside of nuclear physics.

Dark energy from Higgs potential

We derive the ratio of dark energy to baryon matter content in the universe from a Higgs potential matching a description of baryon matter on an intrinsic configuration space. The match determines the Higgs mass and self-coupling parameters and introduces a constant term in the Higgs potential. The constant term is taken to give dark energy contributions from detained neutrons, both primordial and piled-up neutrons from nuclear processes in stars. This corresponds to the dark energy content increasing with time. The two contributions possibly give rise to the primordial inflation and the later accelerated recession, respectively. The ensuing inflation during nucleosynthesis may explain the primordial lithium-seven deficit relative to the standard Big Bang nucleosynthesis model predictions. From the observed helium and stellar metallicity contents, we get a dark energy to baryon matter ratio of 14.5(0.7) to compare with the observed value of 13.9(0.2).

Calibration of CR-39 solid-state track detectors for study of laser-driven nuclear reactions

It is of particular interest to investigate nuclear fusion reactions generated by high-intensity lasers in plasma environments that are similar to real astrophysical conditions. We have experimentally investigated $$^2 \hbox {H}({d},{p})^3 \hbox {H}$$, one of the most crucial reactions in big bang nucleosynthesis models, at the Shenguang-II laser facility. In this work, we present a new calibration of CR-39 solid-state track detectors, which are widely employed as the main diagnostics in this type of fusion reaction experiment. We measure the dependence of the track diameter on the proton energy. It is found that the track diameters of protons with different energies are likely to be identical. We propose that in this case, the energy of the reaction products can be obtained by considering both the diameters and gray levels of these tracks. The present results would be very helpful for analyzing the $$^2 \hbox {H}(d,p)^3 \hbox {H}$$ reaction products recorded with the same batch of CR-39 solid-state track detectors.

Determination of the Primordial Helium Abundance Based on NGC 346, an H ii Region of the Small Magellanic Cloud

Abstract To place meaningful constraints on Big Bang Nucleosynthesis models, the primordial helium abundance determination is crucial. Low-metallicity H ii regions have been used to estimate it because their statistical uncertainties are relatively small. We present a new determination of the primordial helium abundance, based on long-slit spectra of the H ii region NGC 346 in the small Magellanic cloud. We obtained spectra using three 409″ × 0.51″ slits divided into 97 subsets. They cover the range λλ3600–7400 of the electromagnetic spectrum. We used PyNeb and standard reduction procedures to determine the physical conditions and chemical composition. We found that for NGC 346 X = 0.7465, Y = 0.2505, and Z = 0.0030. By assuming ΔY/ΔO = 3.3 ± 0.7 we found that the primordial helium abundance is Y P = 0.2451 ± 0.0026 (1σ). Our Y P value is in agreement with the value of neutrino families, N ν , and with the neutron half-life time, τ n , obtained in the laboratory.

Progress on the BL2 beam measurement of the neutron lifetime.

A precise value of the neutron lifetime is important in several areas of physics, including determinations of the quark-mixing matrix element │V ud│, related tests of the Standard Model, and predictions of light element abundances in Big Bang Nucleosynthesis models. We report the progress on a new measurement of the neutron lifetime utilizing the cold neutron beam technique. Several experimental improvements in both neutron and proton counting that have been developed over the last decade are presented. This new effort should yield a final uncertainty on the lifetime of 1 s with an improved understanding of the systematic effects.

Systematic effects and self-consistency in the primordial helium abundance determination

Observations of light element abundances (4He, D, 7Li) provide a powerful and independent test of the Standard Model of Big Bang Nucleosynthesis. The 4He abundance is measured most accurately among the light elements. This value is determined from observations of spectral lines from small-scale extragalactic sources (HII regions) in the optical and near infrared ranges. The intensity of the forbidden lines like [OIII] and [SII] allows to obtain the physical characteristics of the source, such as temperature and metallicity. Intensities of the 4He lines are used to determine the abundance of this element in the object. However, there are various systematic effects that should be taken in account for precise definition of this physical quantity. These include (1) interstellar reddening, (2) emissivities of 4He in different wavelengths, (3) underlying absorption for H and He lines, (4) temperature and (5) ionization structure HII regions, (6) collisional and fluorescent excitation of H and He lines. Incorrect accounting of these effects can lead to overestimation or underestimation of the primordial helium abundance Yp by several percent.At the moment, there are two independent groups of researchers dealing with this problem. The results for the calculation using the same data sample for these groups are as follows: Yp = 0.2551 ± 0.0022 (Izotov, Thuan, Guseva, 2014) and Yp = 0.2449 ± 0.0040 (Aver, Olive, Skillman, 2015). The last result is consistent with the result Yp = 0.2467 ± 0.0006 based on the study of the CMB anisotropy on (P.A.R. Ade et al., 2015). However, the values of Yp obtained by these groups do not coincide even within the margin of error, and at the moment there is no clear answer to the question of which of these two groups got correct result. In the paper, differences in the methods of processing data and obtaining the quantity of the primordial helium abundance are investigated, in particular, how the groups take into account the named systemic effects. An error analysis and comparative tests are performed.

Measurement of the 2H(7Be, 6Li)3He reaction rate and its contribution to the primordial lithium abundance**Supported by National Natural Science Foundation of China (11375269, 11505117, 11490560, 11475264, 11321064), Natural Science Foundation of Guangdong Province (2015A030310012), 973 program of China (2013CB834406) and National key Research and Development Province (2016YFA0400502)

In the standard Big Bang nucleosynthesis (SBBN) model, the lithium puzzle has attracted intense interest over the past few decades, but still has not been solved. Conventionally, the approach is to include more reactions flowing into or out of lithium, and study the potential effects of those reactions which were not previously considered. 7Be(d, 3He)6Li is a reaction that not only produces 6Li but also destroys 7Be, which decays to 7Li, thereby affecting 7Li indirectly. Therefore, this reaction could alleviate the lithium discrepancy if its reaction rate is sufficiently high. However, there is not much information available about the 7Be(d, 3He)6Li reaction rate. In this work, the angular distributions of the 7Be(d, 3He)6Li reaction are measured at the center of mass energies Ecm = 4.0 MeV and 6.7 MeV with secondary 7Be beams for the first time. The excitation function of the 7Be(d, 3He)6Li reaction is first calculated with the computer code TALYS and then normalized to the experimental data, then its reaction rate is deduced. A SBBN network calculation is performed to investigate its influence on the 6Li and 7Li abundances. The results show that the 7Be(d, 3He)6Li reaction has a minimal effect on 6Li and 7Li because of its small reaction rate. Therefore, the 7Be(d, 3He)6Li reaction is ruled out by this experiment as a means of alleviating the lithium discrepancy.

Proton-Induced Reactions of Astrophysical Interest

A discrepancy exists between the 6Li abundances predicted from big bang nucleosynthesis models and those measured in pre-main sequence stars. To further constrain the predicted abundances of 6Li in these stars, high accuracy measurements are required of reactions destroying 6Li. Namely 6Li(p,γ)7Be and 6Li(p,α) 3He. These have recently been studied at the Laboratory for Underground Nuclear Astrophysics (LUNA) to measure their low energy cross sections. I present both the campaign’s experimental setup and current status of the data analysis.

Review on effects of long-lived negatively charged massive particles on Big Bang Nucleosynthesis

We review important reactions in the Big Bang Nucleosynthesis (BBN) model involving a long-lived negatively charged massive particle, [Formula: see text], which is much heavier than nucleons. This model can explain the observed 7Li abundances of metal-poor stars, and predicts a primordial 9Be abundance that is larger than the standard BBN prediction. In the BBN epoch, nuclei recombine with the [Formula: see text] particle. Because of the heavy [Formula: see text] mass, the atomic size of bound states [Formula: see text] is as small as the nuclear size. The nonresonant recombination rates are then dominated by the [Formula: see text]-wave [Formula: see text] transition for 7Li and [Formula: see text]Be. The 7Be destruction occurs via a recombination with the [Formula: see text] followed by a proton capture, and the primordial 7Li abundance is reduced. Also, the 9Be production occurs via the recombination of 7Li and [Formula: see text] followed by deuteron capture. The initial abundance and the lifetime of the [Formula: see text] particles are constrained from a BBN reaction network calculation. We derived parameter region for the 7Li reduction allowed in supersymmetric or Kaluza–Klein (KK) models. We find that either the selectron, smuon, KK electron or KK muon could be candidates for the [Formula: see text] with [Formula: see text] TeV, while the stau and KK tau cannot.

Astrophysical S-factor of T(4He, γ)7Li reaction at E cm = 15.7 keV

The astrophysical S-factor of the reaction T(4He, γ)7Li is measured for the first time at the center of mass energy E cm = 15.7 keV, lower than the energy range of the Standard Big Bang Nucleosynthesis (SBBN) model. The experiment is performed on a Hall pulsed accelerator (TPU, Tomsk). An acceleration pulse length of 10 μs allows one to suppress the background of cosmic radiation and the ambient medium by five orders of magnitude. A beam intensity of ~ 5 × 1014 4He+ ions per pulse allows one to measure an extremely low reaction yield. The yield of γ-quanta with the energies E γ 0 = 2483.7 keV and E γ 1 = 2006.1 keV is registered by NaI(Tl) detectors with the efficiency e = 0.331 ± 0.026. A method for direct measurement of the background from the chain of reactions T(4He, 4He)T→T(T, 2n)X→(n, γ) and/or (n, n′γ) which ends by neutron activation of materials surrounding the target is proposed and implemented in this study. The value of the astrophysical S-factor of the reaction T(4He, γ)7Li S αt (E cm = 15.7 keV) = 0.091 ± 0.032 keV b provides the choice from the set of experimental data for the astrophysical S αt -factor in favor of experimental data [4] with S αt (E cm = 0) = 0.1067 ± 0.0064 keV b.

The lithium problem: new insight in the big bang nucleosynthesis (BBN) beyond the standard model

The production of the light elements in the framework of the standard Big Bang nucleosynthesis model (SBBN) matches the observed abundances except in case of 7Li, where observations lie a factor 2.4-4.3 below SBBN+WMAP(Wilkinson Microwave Anisotropy Probe) predictions. This so-called “Lithium problem” needs to be resolved beyond the SBBN. In this contribution we focus on the effect of degenerate neutrinos and the addition of dark component, including dark energy density and dark entropy. We find that the effect of the degeneracy parameter is significant if chemical potentials of neutrino families are different. Concerning the dark component, the major effect comes from adding dark entropy.

H-, He-like recombination spectra – II.l-changing collisions for He Rydberg states

Cosmological models can be constrained by determining primordial abundances. Accurate predictions of the He I spectrum are needed to determine the primordial helium abundance to a precision of $< 1$% in order to constrain Big Bang Nucleosynthesis models. Theoretical line emissivities at least this accurate are needed if this precision is to be achieved. In the first paper of this series, which focused on H I, we showed that differences in $l$-changing collisional rate coefficients predicted by three different theories can translate into 10% changes in predictions for H I spectra. Here we consider the more complicated case of He atoms, where low-$l$ subshells are not energy degenerate. A criterion for deciding when the energy separation between $l$ subshells is small enough to apply energy-degenerate collisional theories is given. Moreover, for certain conditions, the Bethe approximation originally proposed by Pengelly & Seaton (1964) is not sufficiently accurate. We introduce a simple modification of this theory which leads to rate coefficients which agree well with those obtained from pure quantal calculations using the approach of Vrinceanu et al. (2012). We show that the $l$-changing rate coefficients from the different theoretical approaches lead to differences of $\sim 10$% in He I emissivities in simulations of H II regions using spectral code Cloudy.