Big Bang Nucleosynthesis Research Articles

Dark matter is the new BBN

Measurements of the primordial element abundances provide us with an important probe of our universe’s early thermal history, allowing us to constrain the expansion rate and composition of our universe as early as ∼1s after the Big Bang. Prior to this time, we have essentially no empirical information on which to base any such claims. In this paper, we imagine a future time in which we have not only detected the particles that make up the dark matter, but have measured their mass and annihilation cross section with reasonable precision. In analogy to the light element abundances, the dark matter abundance in this scenario could be used to study and constrain the expansion rate and composition of our universe at the time of dark matter freeze out, which for a standard thermal relic occurs at Tf∼mχ/20, corresponding to t∼4×10−10s×(TeV/mχ)2, many orders of magnitude prior to the onset of Big Bang nucleosynthesis. As examples, we consider how such measurements could be used to constrain scenarios which feature exotic forms of radiation or matter, a ultralight scalar, or modifications to gravity, each of which have the potential to be much more powerfully probed with dark matter than with the light element abundances.

The electromagnetic fine-structure constant in primordial nucleosynthesis revisited

We study the dependence of the primordial nuclear abundances as a function of the electromagnetic fine-structure constant alpha , keeping all other fundamental constants fixed. We update the leading nuclear reaction rates, in particular the electromagnetic contribution to the neutron-proton mass difference pertinent to beta -decays, and go beyond certain approximations made in the literature. In particular, we include the temperature-dependence of the leading nuclear reactions rates and assess the systematic uncertainties by using four different publicly available codes for Big Bang nucleosynthesis. Disregarding the unsolved so-called lithium-problem, we find that the current values for the observationally based {}^{2}text {H} and {}^{4}text {He} abundances restrict the fractional change in the fine-structure constant to less than 2% , which is a tighter bound than found in earlier works on the subject.

Investigating the Primordial Universe through nuclear physics

Big Bang Nucleosynthesis (BBN) requires several nuclear physics inputs and nuclear reaction rates. An up-to-date compilation of direct cross sections of is given, being these ones among the most uncertain bare-nucleus cross sections. A particular attention is devoted to recently indirectly measured cross-section which give important hints for the nuclear astrophysics community.In reality, a significant experimental effort has been made over the past 10 years to explore reactions important to the BBN and determine their astrophysical S(E)-factor using the Trojan Horse Method (THM). Then, numerical calculations are made in the relevant temperature ranges for BBN (0.01<T9 <10) to determine the reaction rates and the relative error for the four reactions of interest. The effects of these values on the calculated primordial abundances and isotopical composition for H, He, and Li were then assessed by using them as input physics for computations of primordial nucleosynthesis. Additionally, recent findings regarding the 7Be(n,alpha)4He reaction rate were taken into consideration. These were put up against estimates of primordial abundance derived from observation at various astrophysical places. Additionally, perspectives on reactions will be examined.

The Nuclear Reaction Network WinNet

We present the state-of-the-art single-zone nuclear reaction network WinNet, which is capable of calculating the nucleosynthetic yields of a large variety of astrophysical environments and conditions. This ranges from the calculation of the primordial nucleosynthesis, where only a few nuclei are considered, to the ejecta of neutron star mergers with several thousands of involved nuclei. Here we describe the underlying physics and implementation details of the reaction network. We additionally present the numerical implementation of two different integration methods, the implicit Euler method and Gears method, along with their advantages and disadvantages. We furthermore describe basic example cases of thermodynamic conditions that we provide together with the network and demonstrate the reliability of the code by using simple test cases. With this publication, WinNet will be publicly available and open source at GitHub and Zenodo.

Neutron lifetime anomaly and Big Bang nucleosynthesis

We calculate the Big Bang nucleosynthesis abundances for helium-4 and deuterium for a range of neutron lifetimes, τn = 840–1050 s, using the state-of-the-art Python package PRyMordial. We show the results for two different nuclear reaction rates, calculated by NACRE II and the PRIMAT collaborations.

The neutron time-of-flight facility n_TOF at CERN Recent facility upgrades and detector developments

Based on an idea by Carlo Rubbia, the n_TOF facility at CERN has been operating for over 20 years. It is a neutron spallation source, driven by the 20 GeV/c proton beam from the CERN PS accelerator. Neutrons in a very wide energy range (from GeV, down to sub-eV kinetic energy) are generated by a massive Lead spallation target feeding two experimental areas. EAR1, horizonal with respect to the proton beam direction is set at 185 meters from the spallation target. EAR2, on the vertical line from the spallation source, is placed at 20 m. Neutron energies for experiments are selected by the time-of-flight technique (hence the name n_TOF), while the long flight paths ensure a very good energy resolution. Over one hundred experiments have been performed by the n_TOF Collaboration at CERN, with applications ranging from nuclear astrophysics (synthesis of the heavy elements in stars, big bang nucleosynthesis, nuclear cosmo-chronology), to advanced nuclear technologies (nuclear data for applications, nuclear safety), as well as for basic nuclear science (reaction mechanisms, structure and decay of highly excited compound states). During the planned shutdown of the CERN accelerator complex between 2019 and 2021, the facility went through a substantial upgrade with a new target-moderator assembly, refurbishing of the neutron beam lines and experimental areas. An additional measuring and irradiation station (the NEAR Station) has been envisaged and its capabilities for performing material test studies and new physics opportunities are presently explored. An overview of the facility and of the activities performed at CERN is presented in this contribution, with a particular emphasis on the most relevant experiments for nuclear astrophysics.

Cosmological Lithium Solution from Discrete Gauged B-L.

The cosmological lithium problem-that theory predicts a primordial abundance far higher than the observed value-has resisted decades of attempts by cosmologists, nuclear physicists, and astronomers alike to root out systematics. We reconsider this problem in the setting of the standard model extended by gauged baryon minus lepton number, which we spontaneously break by a scalar with charge six. Cosmic strings from this breaking can support interactions converting three protons into three positrons, and we argue that an "electric"-"magnetic" interplay can give this process an amplified, strong-scale cross section in an analog of the Callan-Rubakov effect. We suggest such cosmic strings have disintegrated O(1) of the primordial lithium nuclei, and lay out what is necessary for this scheme to succeed. To our knowledge this is the first new physics mechanism with microphysical justification for the abundance of lithium uniquely to be modified after big bang nucleosynthesis.

Study of the d(d, p) 3H and d(d, n) 3He processes at low energies

The processes d(d, p) 3H and d(d, n) 3 He at energies of interest for energy production and for big-bang nucleosynthesis are studied using the hyperspherical harmonic method. The interactions include modern two- and three-nucleon interactions, derived in chiral effective field theory. We report results for the astrophysical S-factor and the quintet suppression factor.

Primordial black hole archaeology with gravitational waves from cosmic strings

Light primordial black holes (PBHs) with masses smaller than 109 g (10−24M⊙) evaporate before the onset of Big-Bang nucleosynthesis, rendering their detection rather challenging. If efficiently produced, they may have dominated the universe energy density. We study how such an early matter-dominated era can be probed successfully using gravitational waves (GW) emitted by local and global cosmic strings. While previous studies showed that a matter era generates a single-step suppression of the GW spectrum, we instead find a double-step suppression for local-string GW whose spectral shape provides information on the duration of the matter era. The presence of the two steps in the GW spectrum originates from GW being produced through two events separated in time: loop formation and loop decay, taking place either before or after the matter era. The second step — called the knee — is a novel feature which is universal to any early matter-dominated era and is not only specific to PBHs. Detecting GWs from cosmic strings with LISA, ET, or BBO would set constraints on PBHs with masses between 106 and 109 g for local strings with tension Gμ = 10−11, and PBHs masses between 104 and 109 g for global strings with symmetry-breaking scale η = 1015 GeV. Effects from the spin of PBHs are discussed.

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.

Electron–positron plasma in BBN: Damped-dynamic screening

We characterize in detail the dense e−e+γ plasma present during the Big-Bang Nucleosynthesis (BBN) and explore how it is perturbed electromagnetically by “impurities, i.e., spatially dispersed protons and light nuclei undergoing thermal motion. The internuclear electromagnetic screened potential is obtained (analytically) using the linear response approach, allowing for the dynamic motion of the electromagnetic field sources and the damping effects due to plasma component scattering. We discuss the limits of the linear response method and suggest additional work needed to improve BBN reaction rates in the primordial Universe. Our theoretical methods describing the potential between charged dust particles align with previous studies on planetary and space dusty plasma and could have a significant impact on the interpretation of standard cosmological model results.

Multi-species thermalization cascade of energetic particles in the early universe

Heavy long-lived particles are abundant in BSM physics and will, under generic circumstances, get to dominate the energy density of the universe. The resulting matter dominated era has to end through the decay of the heavy matter component particles of mass M, and before the universe cools down to a temperature of a few MeV, in order not to upset the successful predictions of Big Bang Nucleosynthesis. The process of thermalization of their decay products, of initial energy ∼ M/2, into a thermal bath of temperature T primarily involves near-collinear splittings of energetic particles into two particles with lower energy. The correct treatment of these processes requires the inclusion of coherence effects which suppress the splitting rate. We write down and numerically solve the resulting coupled Boltzmann equations including all gauge bosons and fermions of the unbroken phase of the Standard Model (SM). We then comment on the dependence of the nonthermal spectra on the ratio M/T, as well as on the matter decay rate and branching ratios into various SM particles.

Inflationary interpretation of the stochastic gravitational wave background signal detected by pulsar timing array experiments

Various pulsar timing array (PTA) experiments (NANOGrav, EPTA, PPTA, CPTA, including data from InPTA) very recently reported evidence for excess red common-spectrum signals in their latest datasets, with inter-pulsar correlations following the Hellings-Downs pattern, pointing to a stochastic gravitational wave background (SGWB) origin. Focusing for concreteness on the NANOGrav signal (given that all signals are in good agreement between each other), I inspect whether it supports an inflationary SGWB explanation, finding that such an interpretation calls for an extremely blue tensor spectrum, with spectral index nT≃1.8±0.3, while Big Bang Nucleosynthesis limits require a very low reheating scale, Trh≲10GeV. While not impossible, an inflationary origin for the PTA signal is barely tenable: within well-motivated inflationary models it is hard to achieve such a blue tilt, whereas models who do tend to predict sizeable non-Gaussianities, excluded by observations. Intriguingly, ekpyrotic models naturally predict a SGWB with spectral index nT=2, although with an amplitude too suppressed to be able to explain the signal detected by PTA experiments. Finally, I provide explicit expressions for a bivariate Gaussian approximation to the joint posterior distribution for the intrinsic-noise amplitude and spectral index of the NANOGrav signal, which can facilitate extending similar analyses to different theoretical signals.

Revisiting Friedmann-like cosmology with torsion: newest constraints from high-redshift observations

As one of the possible extensions of Einstein's General Theory of Relativity, it has been recently suggested that the presence of space-time torsion could solve problems of the very early and the late-time universe undergoing accelerating phases. In this paper, we use the latest observations of high-redshift data, coming from multiple measurements of quasars and baryon acoustic oscillations, to phenomenologically constrain such cosmological model in the framework of Einstein-Cartan (EC) endowed with space-time torsion. Such newly compiled quasar datasets in the cosmological analysis is crucial to this aim, since it will extend the Hubble diagram to high-redshift range in which predictions from different cosmologies can be distinguished. Our results show that out of all the candidate models, the torsion plus cosmological constant model is strongly favoured by the current high-redshift data, where torsion would be expected to yield the late-time cosmic acceleration. Specially, in the framework of Friedmann-like cosmology with torsion, the determined Hubble constant is in very good agreement with that derived from the Planck 2018 CMB results. On the other hand, our results are compatible with zero spatial curvature and there is no significant deviation from flat spatial hypersurfaces. Finally, we check the robustness of high-redshift observations by placing constraints on the torsion parameter α, which is strongly consistent with other recent works focusing on torsion effect on the primordial helium-4 abundance.

A Short Survey of Matter-Antimatter Evolution in the Primordial Universe

We offer a survey of the matter-antimatter evolution within the primordial Universe. While the origin of the tiny matter-antimatter asymmetry has remained one of the big questions in modern cosmology, antimatter itself has played a large role for much of the Universe’s early history. In our study of the evolution of the Universe we adopt the position of the standard model Lambda-CDM Universe implementing the known baryonic asymmetry. We present the composition of the Universe across its temperature history while emphasizing the epochs where antimatter content is essential to our understanding. Special topics we address include the heavy quarks in quark-gluon plasma (QGP), the creation of matter from QGP, the free-streaming of the neutrinos, the vanishing of the muons, the magnetism in the electron-positron cosmos, and a better understanding of the environment of the Big Bang Nucleosynthesis (BBN) producing the light elements. We suggest but do not explore further that the methods used in exploring the early Universe may also provide new insights in the study of exotic stellar cores, magnetars, as well as gamma-ray burst (GRB) events. We describe future investigations required in pushing known physics to its extremes in the unique laboratory of the matter-antimatter early Universe.

Dark matter in a bi-metric universe

We study the possibility to describe dark matter in a model of the universe with two-scale factors and a nonstandard Poisson bracket structure characterized by the deformation parameter [Formula: see text]. The dark matter evolution is analyzed in the early stages of the universe, and its relic density is obtained via the Freeze-In and Freeze-Out mechanism. We show that by fixing [Formula: see text] and the initial ratio of energy densities present in the different sectors of the universe, the space of thermal average annihilation cross-sections and dark matter masses compatible with the standard cosmology prior to Big Bang Nucleosynthesis (BBN), is enlarged. This feature of the model is compatible with nonstandard cosmology.

First measurement of the 7Li(D, n) astrophysical S-factor in laser-induced full plasma

Nuclear fusion reactions which produce energies and most of the elements in the Universe are the keys to driving the process of the Big Bang nucleosynthesis, as well as the evolution of stars. For fusions in real astrophysical conditions, it is crucial to directly measure them in the plasma environments. However, it is challenging to obtain reaction cross sections quantitatively because of the high instabilities of plasma. Here, an innovative self-calibration method is proposed to eliminate the large uncertainties caused by the plasma instabilities. And for the first time, it is applied to investigating the deuteron-lithium nuclear-fusion reaction 7Li(D,n)8Be in the plasma, which is related to the Big Bang lithium abundance puzzle. Further, the reaction's astrophysical S-factor in the Gamow window around 173 keV in the plasma is measured to be S=(24±8) MeV⋅barn, which demonstrates from an experimental point of view that the coulomb screening effect does not play an essential role in this 7Li consuming reaction related to the Big Bang lithium abundance puzzle. This self-calibration method for nuclear reactions in the plasma can also be applied to exploring other nuclear-fusion reactions, such as 7Li(p,α)4He and 6Li(p,α)3He, as well as providing a new probe for detecting plasma dynamics.

Asteroseismology of 16 Kepler Solar-like Stars: Stellar Parameters and the Effects of Element Diffusion

Element diffusion has small but significant effects on the structure of the stellar interior. It is interesting to investigate the effects of element diffusion using asteroseismology. We have constructed two grids of stellar models, one with diffusion and one without, for solar-like stars with masses between 0.9 and 1.4 solar masses, and varied initial helium abundance and metallicity. The oscillation frequencies of all stellar models have also been calculated. Piecewise Hermite cubic polynomials are adopted to interpolate stellar p-mode frequencies at an arbitrary age on a stellar evolutionary track. We have investigated 16 Kepler solar-like stars by comparing the model frequencies with observations. The suggested ranges of stellar parameters and some global variables are obtained. For all stars, the best model reproduces the observational frequencies with a χ 2 of the order of unity. It has been found that element diffusion is important in modeling solar-like stars. Without diffusion, the best value of the initial helium abundance is below the primordial helium abundance from Big Bang nucleosynthesis. When diffusion is taken into account, the required initial helium abundance increases to be higher than the primordial abundance. Diffusion also generally improves the frequency fitting results by reducing the minimum of χ 2. Investigation of the second difference of the oscillation frequencies on KIC 8694723 and KIC 10454113 indicates that the current model of element diffusion may underestimate the strength of settling.

Constraining quantum fluctuations of spacetime foam from BBN

A possibility to describe quantum gravitational fluctuations of the spacetime background is provided by virtual $D$-branes. These effects may induce a tiny violation of the Lorentz invariance (as well as a possible violation of the equivalence principle). In this framework, we study the formation of light elements in the early Universe (Big Bang Nucleosynthesis). By using the Big Bang Nucleosynthesis observations, We infer an upper bound on the topological fluctuations in the spacetime foam vacuum $\sigma^2$, given by $\sigma^2 \lesssim 10^{-22}$.

Implications for Primordial Black Holes from Cosmological Constraints on Scalar-induced Gravitational Waves

Sufficiently large scalar perturbations in the early universe can create overdense regions that collapse into primordial black holes (PBHs). This process is accompanied by the emission of scalar-induced gravitational waves that behave like an extra radiation component, thus contributing to the relativistic degrees of freedom (N eff). We show that the cosmological constraints on N eff can be used to pose stringent limits on PBHs created from this particular scenario as well as the relevant small-scale curvature perturbation (). We show that the combination of cosmic microwave background (CMB), baryon acoustic oscillation, and Big Bang nucleosynthesis data sets can exclude supermassive PBHs with peak mass M • ∈ [5 × 105, 5 × 1010] M ⊙ as the major component of dark matter, while the detailed constraints depend on the shape of the PBHs’ mass distribution. A future CMB mission such as CMB-S4 can greatly broaden this constraint window to M • ∈ [8 × 10−5, 5 × 1010] M ⊙, covering substellar masses. These limits on PBHs correspond to a tightened constraint on on scales of k ∈ [10, 1022] Mpc−1, much smaller than those probed by direct CMB and large-scale structure power spectra.