Nucleosynthesis Theory Research Articles

Energodynamic theory of nucleosynthesis

Energodynamic theory of nucleosynthesis

Can teleparallel f(T) models play a bridge between early and late time Universe?

ABSTRACT The ability of Big Bang Nucleosynthesis theory to accurately predict the primordial abundances of helium and deuterium, as well as the baryon content of the Universe, is considered one of the most significant achievements in modern physics. In the present study, we consider two highly motivated hybrid $f(T)$ models and constrain them using the observations from the Big Bang Nucleosynthesis era. In addition, using late-time observations of Cosmic Chronometers and Gamma-Ray Bursts, the ranges of the model parameters are confined which are in good agreement with early time bounds. Subsequently, the common ranges obtained from the analysis for early and late time are summarized. Further, we verify the intermediating epochs by investigating the profiles of cosmographic parameters using the model parameter values from the common range. From this study, we find the considered teleparallel models are viable candidates to explain the primordial-intermediating-present epochs.

A new precise determination of the primordial abundance of deuterium: measurement in the metal-poor sub-DLA system at z = 3.42 towards quasar J 1332+0052

ABSTRACT The theory of Big Bang nucleosynthesis, coupled with an estimate of the primordial deuterium abundance (D/H)pr, offers insights into the baryon density of the Universe. Independently, the baryon density can be constrained during a different cosmological era through the analysis of cosmic microwave background anisotropy. The comparison of these estimates serves as a rigorous test for the self-consistency of the standard cosmological model and stands as a potent tool in the quest for new physics beyond the standard model of particle physics. For a meaningful comparison, a clear understanding of the various systematic errors affecting deuterium measurements is crucial. Given the limited number of D/H measurements, each new estimate carries significant weight. This study presents the detection of D i absorption lines in a metal-poor sub-Damped Lyman-α system ($\rm [O/H]=-1.71\pm 0.02$, log N(H i) = 19.304 ± 0.004) at zabs = 3.42 towards the quasar SDSS J133254.51+005250.6. Through simultaneous fitting of H i and D i Lyman-series lines, as well as low-ionization metal lines, observed at high spectral resolution and high signal-to-noise using VLT/UVES and Keck/HIRES, we derive log (D i/H i) = −4.622 ± 0.014, accounting for statistical and systematic uncertainties of 0.008dex and 0.012 dex, respectively. Thanks to negligible ionization corrections and minimal deuterium astration at low metallicity, this D/H ratio provides a robust measurement of the primordial deuterium abundance, consistent and competitive with previous works. Incorporating all prior measurements, the best estimate of the primordial deuterium abundance is constrained as: (D/H)pr = (2.533 ± 0.024) × 10−5. This represents a 5 per cent improvement in precision over previous studies and reveals a moderate tension with the expectation from the standard model (≈2.2σ). This discrepancy underscores the importance of further measurements in the pursuit of new physics.

Sodium Abundances in Very Metal-poor Stars

Chemical composition of very metal-poor (VMP) stars can provide observational constraints on current models of nucleosynthesis and the chemical evolution of the Galaxy. It has been found that the scatter of [Na/Fe] versus [Fe/H] in VMP stars is very large in contrast with most other elements. Moreover, a negative slope in [Na/Fe] versus [Fe/H] was found for giants, which is very unlikely according to the theory of nucleosynthesis. For the sample of 93 VMP stars in the metallicity range −4.25 < [Fe/H] < −1.64 we obtained NLTE sodium abundances using the line profile fitting method by employing accurate atmospheric parameters determined when taking into account NLTE line formation for both Fe i and Fe ii. Originally selected from the LAMOST low-resolution spectral database, the spectra of stars were obtained with the High Dispersion Spectrograph of the Subaru Telescope. For 57 turn-off stars in metallicity domain −3.04 < [Fe/H] < −1.64, we obtained mean [Na/Fe] = −0.29 ± 0.14 and positive slope 0.09 ± 0.06. For 21 giants distributed over metallicity −3.59 < [Fe/H] < −2.19, we found mean [Na/Fe] = −0.35 ± 0.1 and positive slope 0.07 ± 0.07. Our [Na/Fe] trend is lower by ∼0.2 dex, compared to the modern GCE model. We believe the GCE model should be adjusted, by considering the associated scatter. Twelve stars in our sample are found to be outliers, with too low or too high Na abundances.

Nonminimally coupled ultralight axions as cold dark matter

We consider a nonminimally coupled scalar field as a potential cold dark matter candidate. These models are natural extensions of the ultralight axion models which are based on minimally coupled scalar fields. Such ultralight scalar fields are motivated by string theory and, in particular, have been studied in the context of the axiverse scenario. For a nonminimally coupled field, the scalar-field energy density behaves as radiation at early times, which yields a bound on the coupling constant, $\ensuremath{\xi}\ensuremath{\lesssim}10$, from the primordial nucleosynthesis theory. The first-order perturbations of the nonminimally coupled field with adiabatic initial conditions cause the gravitational potential to decay on large scales. A comparison of the cosmological data with the theoretical matter power spectrum yields the following constraint on the coupling constant: $\ensuremath{\xi}\ensuremath{\lesssim}0.01$. We also consider isocurvature modes in our analysis. We argue that a mix of adiabatic and isocurvature initial conditions for a nonminimally coupled scalar field might allow one to obtain the usual adiabatic CDM power spectrum.

Non-thermal nucleosynthesis by accelerated particles to account for the surface composition of P-rich stars

Context. Fifteen abnormally phosphorus-rich stars were recently discovered. Their peculiar surface abundance distribution is challenging our present stellar nucleosynthesis theories, because none of the standard thermal nucleosynthesis models are found to explain the observed patterns. Aims. This paper presents an exploration of the extent to which an irradiation process resulting from the interaction of some target material with energetic protons and/or α-particles can by itself be at the origin of the chemical pollution observed at the surface of P-rich stars. Methods. In light of our lack of knowledge of the characteristics of the accelerated particles that could be held responsible for this nuclear process, a purely parametric site-independent approach is followed, with the proton and α-particle flux amplitude, energy distribution, and fluence taken as free parameters. The irradiated material is assumed to be made either of CNO elements in solar ratio or pure C. Results. Such an irradiation process with energies of no more than a few MeV per nucleon is shown to give rise to rich nucleosynthesis, including significant production of P, as well as Z &gt; 30 heavy elements in relative abundance similar to what the slow neutron-capture process traditionally produced. Conclusions. The final composition obtained by mixing such a non-thermal nucleosynthesis by accelerated particles with nuclearly unaffected material is found to reproduce fairly well the global surface composition of P-rich stars, except for a few species like Al, Si, or Ba.

The building blocks of the universe

I review the state of knowledge of the composition of the universe for a non-specialist audience. The universe is built up of four components. These are radiation, baryonic (ordinary) matter, dark matter and dark energy. In this article, a quick outline of the theory of Big Bang nucleosynthesis is presented, and the origin of the elements is explained. Cosmology requires the presence of dark matter, which forms most of the mass of the universe, and dark energy, which drives the acceleration of the expansion. The dark sector is motivated, and possible explanations are stated.Contribution: As part of this special collection on building blocks, the building blocks of the universe are discussed and unsolved problems and proposed solutions are highlighted.

Production and evaporation of micro black holes as a link between mirror universes

It is shown that the equalization of temperatures between our and mirror sectors occurs during one Hubble time due to microscopic black hole production and evaporation in particle collisions if the temperature of the Universe is near the multidimensional Plank mass. This effect excludes the multidimensional Planck masses smaller than the reheating temperature of the Universe ($\sim10^{13}$ GeV) in the mirror matter models, because the primordial nucleosynthesis theory requires that the temperature of the mirror world should be lower than ours. In particular, the birth of microscopic black holes in the LHC is impossible if the dark matter of our Universe is represented by baryons of mirror matter. It excludes some of the possible coexisting options in particle physics and cosmology. Multidimensional models with flat additional dimensions are already strongly constrained in maximum temperature due to the effect of Kaluza-Klein mode (KK-mode) overproduction. In these models, the reheating temperature should be significantly less than the multidimensional Planck mass, so our restrictions in this case are not paramount. The new constraints play a role in multidimensional models in which the spectrum of KK-modes does not lead to their overproduction in the early Universe, for example, in theories with hyperbolic additional space.

The evolution of Lithium: implications of a universal Spite plateau

ABSTRACT The cosmological 7Li problem consists in explaining why the primordial Li abundance, as predicted by the standard Big Bang nucleosynthesis theory with constraints from WMAP and Planck, is a factor of 3 larger than the Li abundance measured in the stars of the Spite plateau defined by old, warm dwarf stars of the Milky Way halo. Several explanations have been proposed to explain this difference, including various Li depletion processes as well as non-standard Big Bang nucleosynthesis, but the main question remains unanswered. In this paper, we present detailed chemical evolution models for dwarf spheroidal and ultra faint galaxies, compute the galactic evolution of 7Li abundance in these objects, and compare it with observations of similar objects. In our models, Li is mainly produced by novae and cosmic rays, and to a minor extent, by low and intermediate mass stars. We adopt the yield combination that best fits the Li abundances in the Milky Way stars. It is evident that the observations of dwarf objects define a Spite plateau, identical to that observed in the Milky Way, thus suggesting that the Spite plateau could be a universal feature and its meaning should be discussed. The predictions of our models for dwarf galaxies are obtained by assuming as Li primordial abundance either the one detected in the atmospheres of the oldest halo stars (Spite plateau; A(Li) ∼ 2.2 dex), or the one from cosmological observations (WMAP; A(Li) ∼ 2.66 dex). Finally, we discuss the implications of the universality of the Spite plateau results.

Element Abundance Analysis of HD 140283 and Astrophysics Sources of Weak r-process Elements

HD 140283, a nearby extremely metal-poor subgiant star, formed shortly after the big bang, is thought to be the oldest star to date, and also a typical weak r-process star. Study of this star is of great significance for understanding the early history of the universe, and enriching the element nucleosynthesis theory. Based on the observed abundances of weak r-process star HD 140283 and theoretical yields of single supernova (SN), we fit the observational elemental abundances (from C to Zn) to the entire library of single SN yield, and derive that HD 140283 may have been born from a nebula polluted by the explosion of supernova whose progenitor mass is 22.5M⊙ (the subscript “⊙” means the sun). Based on the same method, we study the other five typical weak r-process stars, and respectively derive the progenitor masses of supernovae which have polluted the nebulas forming these stars. Furthermore, the possible astrophysics sources of weak r-process are inferred.

Underground Measurement of 6Li(p,γ)7Be and 6Li(p,3He)4He Performed at LUNA

Proton-induced reactions on 6Li play an important role in nuclear astrophysics studies in relation to primordial lithium abundances. Whilst big bang nucleosynthesis theory excludes the existence of primordial 6Li, the 6Li/7Li abundance ratio observed in pre-main sequence stars is ≃ 0.5. The 6Li(p,3He)4He and 6Li(p,γ)7Be reactions are the main processes that contribute to 6Li destruction in stars. Both reactions were recently studied at LUNA via proton bombardment of 6Li-enriched targets, with complementary target composition studies performed at HZDR. Improvements on the precision of the low-energy S-factor values are expected from this study. Notably, the low-background measurement at LUNA will assist the search for a recently claimed 6Li(p,γ)7Be low energy resonance at E r ≃ 195 keV. I present the LUNA experimental setup and preliminary results of the ongoing analysis.

Heavy-element Abundances in P-rich Stars: A New Site for the s-process?

Abstract The recently discovered phosphorus-rich stars pose a challenge to stellar evolution and nucleosynthesis theory, as none of the existing models can explain their extremely peculiar chemical abundances pattern. Apart from the large phosphorus enhancement, such stars also show enhancement in other light (O, Mg, Si, and Al) and heavy (e.g., Ce) elements. We have obtained high-resolution optical spectra of two optically bright phosphorus-rich stars (including a new P-rich star), for which we have determined a larger number of elemental abundances (from C to Pb). We confirm the unusual light-element abundance pattern with very large enhancements of Mg, Si, Al, and P, and possibly some Cu enhancement, but the spectrum of the new P-rich star are the only ones to reveal some C(+N) enhancement. When compared to other appropriate metal-poor and neutron-capture enhanced stars, the two P-rich stars show heavy-element overabundances similar to low neutron density s-process nucleosynthesis, with high first-peak (Sr, Y, and Zr) and second-peak (Ba, La, Ce, and Nd) element enhancements (even some Pb enhancement in one star) and a negative [Rb/Sr] ratio. However, this s-process is distinct from the one occurring in asymptotic giant branch (AGB) stars. The notable distinctions encompass larger [Ba/La] and lower Eu and Pb than their AGB counterparts. Our observations should guide stellar nucleosynthesis theoreticians and observers to identify the P-rich star progenitor, which represents a new site for s-process nucleosynthesis, with important implications for the chemical evolution of our Galaxy.

The evolution of CNO isotopes: the impact of massive stellar rotators

ABSTRACT Chemical abundances and abundance ratios measured in galaxies provide precious information about the mechanisms, modes, and time-scales of the assembly of cosmic structures. Yet, the nucleogenesis and chemical evolution of elements heavier than helium are dictated mostly by the physics of the stars and the shape of the stellar mass spectrum. In particular, estimates of CNO isotopic abundances in the hot, dusty media of high-redshift starburst galaxies offer a unique glimpse into the shape of the stellar initial mass function (IMF) in extreme environments that cannot be accessed with direct observations (star counts). Underlying uncertainties in stellar evolution and nucleosynthesis theory, however, may hurt our chances of getting a firm grasp of the IMF in these galaxies. In this work, we adopt new yields for massive stars, covering different initial rotational velocities. First, we implement the new yield set in a well-tested chemical evolution model for the Milky Way. The calibrated model is then adapted to the specific case of a prototype submillimetre galaxy (SMG). We show that, if the formation of fast-rotating stars is favoured in the turbulent medium of violently star-forming galaxies irrespective of metallicity, the IMF needs to be skewed towards high-mass stars in order to explain the CNO isotopic ratios observed in SMGs. If, instead, stellar rotation becomes negligible beyond a given metallicity threshold, as is the case for our own Galaxy, there is no need to invoke a top-heavy IMF in starbursts.

Nuclear decay studies of rare isotopes

This article overviews recent developments and achievements on decay spectroscopic studies at the Radioactive-Isotope Beam Factory (RIBF) in RIKEN Nishina Center, which has come online in 2007 as the first 3rd-generation in-flight separator facility. The research territory on the chart of nuclides has been dramatically expanded both towards the proton-rich and neutron-rich frontiers with the advent of RIBF. Taking advantage of the world’s currently strongest RI beams, in conjunction with new experimental techniques and state-of-the-art detector systems, more than 400 species of rare isotopes have been explored in experimental programs dedicated to radioactive-decay measurements performed in the last decade. Some selected topics are introduced in this review. Excited levels investigated by $\gamma$-ray measurements following $\beta$ decay have provided significant information on the evolution of shell structures and nuclear shapes, and thus serve as a stringent benchmark for testing microscopic and macroscopic nuclear model calculations. Systematic studies of $ \beta$-decay half-lives of very neutron-rich nuclei have an enormous impact on a better understanding of explosive nucleosynthesis in the rapid neutron-capture (r) process. On the proton-rich side of the $ \beta$-stability line, new proton emitters have been identified, allowing an exploration of atomic nuclei beyond the proton drip line. New results obtained in a series of decay experiments include various types of nuclear isomers, for example, seniority, spin-trap, shape, and K isomers. The identification and characterization of such exotic isomers have revealed the underlying single-particle orbits and nucleon-nucleon correlations, as well as the change of nuclear shape and spin orientation. These new results will offer further insight into exotic nuclei and contribute to the development of new theories of nuclear structure and nucleosynthesis. In this review article, some of the ongoing research projects and future prospects for decay studies at RIBF are also presented.

Probing the Galactic s-process nucleosynthesis using barium stars

The origin and evolution of neutron-capture elements in our Galaxy is poorly understood. In this work, we have attempted to understand the Galactic s-process nucleosynthesis using barium stars as probes. We have performed high resolution spectroscopic analysis for three barium stars HD 36650, HD 207585 and HD 219116. The analysis of HD 219116 is based on HCT/HESP data at a resolution of 60,000 covering a wavelength region 3530-9970 Å. For HD 36650, we have used the FEROS spectrum at a resolution of 48,000 covering the wavelength region 3520-9200 Å. For HD 207585, the spectrum from VLT/UVES at a resolution of 48,000 covering the wavelength region 3290-6650 Å is used. Our analysis clearly shows that the surface chemical composition of these barium stars are enriched by s-process nucleosynthesis products coming from their former companion low-mass AGB stars. A discussion on the distribution of abundance ratios based on the existing nucleosynthesis theories is presented.

Particle Acceleration by Supernova Shocks and Spallogenic Nucleosynthesis of Light Elements

In this review, we first reassess the supernova remnant paradigm for the origin of Galactic cosmic rays in the light of recent cosmic-ray data acquired by the Voyager 1 spacecraft. We then describe the theory of light-element nucleosynthesis by nuclear interaction of cosmic rays with the interstellar medium and outline the problem of explaining the measured beryllium abundances in old halo stars of low metallicity with the standard model of the Galactic cosmic-ray origin. We then discuss the various cosmic-ray models proposed in the literature to account for the measured evolution of the light elements in the Milky Way, and point out the difficulties that they all encounter. It seems to us that, among all possibilities, the superbubble model provides the most satisfactory explanation for these observations.

The Role of 14-MeV Neutrons in Light Element Nucleosynthesis

The 14-MeV neutron-induced nuclear reactions which might contribute to better understanding of the so-called “cosmological lithium problem” have been discussed. The big bang nucleosynthesis theory predicted 7Li overestimated value could be lowered by 2n-induced reactions on Li isotopes and/or 7Be destruction via resonance in the d + 7Be → 9B process. Proposals for 6Li + 2n and 7Li + 2n reactions’ cross section evaluations and measurements are discussed in some details. In addition, we discuss also a preliminary measurements of n–n coincidences from the 10B(n,2n) 9B reaction with two neutron detectors placed outside the cone of 14-MeV tagged neutron beam. From the time-of-flight measurements and known geometry, we tried to deduce the neutron energies and calculate the 9B missing mass spectrum. Improvements for better measurements are suggested.

Neutron lifetime measurements with a large gravitational trap for ultracold neutrons

Neutron lifetime is one of the most important physical constants which determines parameters of the weak interaction and predictions of primordial nucleosynthesis theory. There remains the unsolved problem of a 3.9{\sigma} discrepancy between measurements of this lifetime using neutrons in beams and those with stored neutrons (UCN). In our experiment we measure the lifetime of neutrons trapped by Earth's gravity in an open-topped vessel. Two configurations of the trap geometry are used to change the mean frequency of UCN collisions with the surfaces - this is achieved by plunging an additional surface into the trap without breaking the vacuum. The trap walls are coated with a hydrogen-less fluorine-containing polymer to reduce losses of UCN. The stability of this coating to multiple thermal cycles between 80 K and 300 K was tested. At 80 K, the probability of UCN loss due to collisions with the trap walls is just 1.5% of the probability of beta-decay. The free neutron lifetime is determined by extrapolation to an infinitely large trap with zero collision frequency. The result of these measurements is 881.5 +/- 0.7_stat +/- 0.6_syst s which is consistent with the conventional value of 880.2 +/- 1.0 s presented by the Particle Data Group. Future prospects for this experiment are in further cooling to 10 K which will lead to an improved accuracy of measurement. In conclusion we present an analysis of currently-available data on various measurements of the neutron lifetime.

New Neutron Lifetime Measurements with the Big Gravitational Trap and Review of Neutron Lifetime Data

Neutron lifetime is one of the most important physical constants which determines parameters of the weak interaction and predictions of primordial nucleosynthesis theory. In our experiment we measure the storage time of UCN in the material trap coated with a hydrogen-free fluorine-containing polymer (Fomblin grease UT-18). The stability of this coating to multiple thermal cycles between 80 K and 300 K was tested. The achieved storage time is only 1.5% less than free neutron lifetime. Using additional surface, which can be plunged into the trap to change the collision frequency of UCN with walls, we calculate free neutron lifetime by extrapolation to zero collision frequency. The result of the measurements with this new experimental setup is

Research at the Institute of Astronomy and Astrophysics of the Université Libre de Bruxelles

Over the years, a coherent research strategy has developed in the field of stellar physics at the Institute of Astronomy and Astrophysics (IAA). It involves observational studies (chemical composition of giant stars, binary properties, tomography of stellar atmospheres) that make use of the large ESO telescopes as well as of other major instruments. The presence of a high-resolution spectrograph on the 3.6-m Devasthal Optical Telescope (DOT) would therefore be highly beneficial to IAA research. These observations are complemented and supported by theoretical studies of mass transfer in binary systems, of standard and non-standard stellar evolution (including the modelling of stellar hydrodynamical nuclear burning for application to certain thermonuclear supernovae) and of nuclear astrophysics (a field in which IAA has been recognized for a long time as an international centre of excellence), including the theory of nucleosynthesis. IAA also addresses the end-points of stellar evolution as it is carrying out research on the compact remnants of stellar evolution of massive stars: neutron stars.