Big Bang Nucleosynthesis Research Articles

Evidence of dynamical dark energy in a non-flat universe: current and future observations

We investigate the dark energy phenomenology in an extended parameter space where we allow the curvature density of our universe as a free-to-vary parameter. The inclusion of the curvature density parameter is motivated from the recently released observational evidences indicating the closed universe model at many standard deviations. Here we assume that the dark energy equation-of-state follows the PADE approximation, a generalized parametrization that may recover a variety of existing dark energy models. Considering three distinct PADE parametrizations, labeled as PADE-I, SPADE-I and PADE-II, we first constrain the cosmological scenarios driven by them using the joint analyses of a series of recently available cosmological probes, namely, Pantheon sample of Supernovae Type Ia, baryon acoustic oscillations, big bang nucleosynthesis, Hubble parameter measurements from cosmic chronometers, cosmic microwave background distance priors from Planck 2018 and then we include the future Gravitational Waves standard sirens (GWSS) data from the Einstein telescope with the combined analyses of these current cosmological probes. We find that the current cosmological probes indicate a very strong evidence of a dynamical dark energy at more than 99% C.L. in both PADE-I, and PADE-II, but no significant evidence for the non-flat universe is found in any of these parametrizations. Interestingly, when the future GWSS data from the Einstein telescope are included with the standard cosmological probes an evidence of a non-flat universe is found in all three parametrizations together with a very strong preference of a dynamical dark energy at more than 99% C.L. in both PADE-I, and PADE-II. Although from the information criteria analysis, namely, AIC, BIC, DIC, the non-flat Λ-Cold Dark Matter model remains the best choice, however, in the light of DIC, PADE parametrizations are still appealing.

Underground nuclear astrophysics: Status and recent results from Felsenkeller laboratory

For almost three decades it has been known that the study of astro-physically important nuclear reactions between stable nuclei requires the use of low-background, underground accelerator laboratories. The Felsenkeller shallow-underground laboratory in Dresden, shielded by a 45 m thick rock cover, hosts a 5 MV Pelletron ion accelerator with an external sputter ion source (mainly able to provide carbon and oxygen beams) and an internal radio-frequency ion source (providing proton and alpha beams). The reduced muon, neutron and gamma-ray background achieved both with natural and active shielding situate the laboratory well in line with deep underground accelerator labs worldwide and allows highly sensitive nuclear reaction experiments. Currently, measurements affecting the solar fusion and Big Bang nucleosynthesis are ongoing. In addition to in-house research by HZDR and TU Dresden, the lab is an open facility for scientific users worldwide, with beam time applications reviewed by an independent science advisory board. Furthermore, EU-supported transnational access is available via the ChETEC- INFRA network for nuclear astrophysics. A brief introduction to underground nuclear astrophysics, status of the Felsenkeller shallow-underground laboratory and some preliminary results are discussed.

Calculation of astrophysical reaction rate and uncertainty for T(d,n)4He using Bayesian statistical approach

Abstract One of the best methods to investigate and calculate a desired quantity using available limited data is the Bayesian statistical method, which has been recently entered the field of nuclear astrophysics and can be used to evaluate the astrophysical S-factors, the cross sections and, as a result, the nuclear reaction rates of Big Bang Nucleosynthesis. This study tries to calculate the astrophysical S-factor and the rate of reaction T(d,n)4He as an important astrophysical reaction with the help of this method in energies lower that electron repulsive barrier, and for this purpose, it uses the R-Software, which leads to improved results in comparison with the non-Bayesian methods for the mentioned reaction rate.

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.

Atomic diffusion and mixing in old stars - VIII. Chemical abundance variations in the globular cluster M4 (NGC 6121).

Variations in chemical abundances with evolutionary phase have been identified among stars in globular and open clusters with a wide range of metallicities. In the metal-poor clusters, these variations compare well with predictions from stellar structure and evolution models considering the internal diffusive motions of atoms and ions, collectively known as atomic diffusion, when moderated by an additional mixing process with a fine-tuned efficiency. We present here an investigation of these effects in the Galactic globular cluster NGC 6121 (M4) ([Fe/H]= -1.13) through a detailed chemical abundance analysis of 86 stars using high-resolution ESO Very Large Telescope (VLT) Fibre Large Array Multi Element Spectrograph (FLAMES) spectroscopy. The stars range from the main-sequence turnoff point (TOP) to the red giant branch (RGB) just above the bump. We identify C-N-O and Mg-Al-Si abundance anticorrelations, and confirm the presence of a bimodal population differing by 1 dex in nitrogen abundance. The composition of the second-generation stars imply pollution from both massive (20-40 [Formula: see text]) and asymptotic giant branch stars. We find evolutionary variations in chemical abundances between the TOP and RGB, which are robust to uncertainties in stellar parameters and modelling assumptions. The variations are weak, but match predictions well when employing efficient additional mixing. Without correcting for Galactic production of lithium, we derive an initial lithium abundance 2.63±0.10, which is marginally lower than the predicted primordial big-bang nucleosynthesis value.

Observable gravitational waves from hyperkination in Palatini gravity and beyond

We consider cosmology with an inflaton scalar field with an additional quartic kinetic term. Such a theory can be motivated by Palatini R+R2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R+R^2$$\\end{document} modified gravity. Assuming a runaway inflaton potential, we take the Universe to become dominated by the kinetic energy density of the scalar field after inflation. Initially, the leading kinetic term is quartic and we call the corresponding period hyperkination. Subsequently, the usual quadratic kinetic term takes over and we have regular kination, until reheating. We study, both analytically and numerically, the spectrum of primordial gravitational waves generated during inflation and re-entering the horizon during the subsequent eras. We demonstrate that the spectrum is flat for modes re-entering during radiation domination and hyperkination and linear in frequency for modes re-entering during kination: kinetic domination boosts the spectrum, but hyperkination truncates its peak. As a result, the effects of the kinetic period can be extended to observable frequencies without generating excessive gravitational waves, which could otherwise destabilise the process of Big Bang Nucleosynthesis. We show that there is ample parameter space for the primordial gravitational waves to be observable in the near future. If observed, the amplitude and ‘knee’ of the spectrum will provide valuable insights into the background theory.

Numerical Modeling of the Interaction of Dark Atoms with Nuclei to Solve the Problem of Direct Dark Matter Search

The puzzle of the direct dark matter search can be resolved by examining the concept of «dark atoms», which consist of hypothetical stable lepton-like particles with a charge of −2n, where n is any natural number, bound to n nuclei of primordial helium. These «dark atoms», known as «XHe» (X-helium) atoms, remain undiscovered in experiments due to their neutral atom-like states. In this model, the positive results of the DAMA/NaI and DAMA/LIBRA experiments could be explained by the annual modulation of radiative capture of XHe atoms engaging in low-energy bound states with sodium nuclei. This specific phenomenon does not occur under the conditions of other underground experiments. The proposed solution to this puzzle involves establishing the existence of a low-energy bound state of «dark atoms» and nuclei while also considering the self-consistent influence of nuclear attraction and Coulomb repulsion. Resolving this complex issue, which has remained unsolved for the past 17 years, necessitates a systematic approach. To tackle this problem, numerical modeling is employed to uncover the fundamental processes behind the interaction of «dark atoms» with nuclei. To comprehend the essence of XHe’s interaction with baryonic matter nuclei, a classical model is employed wherein quantum physics and nuclear size effects are progressively incorporated. A numerical model describing the interaction between XHe «dark atoms» and nuclei is developed through the continuous inclusion of realistic features of quantum mechanics in the initial classical three-body problem involving the X-particle, the helium nucleus, and the target nucleus. This approach yields a comprehensive numerical model that encompasses nuclear attraction and electromagnetic interaction between the «dark atom» and nuclei. Finally, this model aids in supporting the interpretation of the results obtained from direct underground dark matter experiments through the lens of the «dark atom» hypothesis.

Big Bang Nucleosynthesis constraints on [formula omitted] gravity

Big Bang Nucleosynthesis provides us with an observational insight into the very early Universe. Since this mechanism of light element synthesis comes out of the standard model of particle cosmology which follows directly from General Relativity, it is expected that any modifications to GR will result in deviations in the predicted observable parameters which are mainly, the neutron-to-proton ratio and the baryon-to-photon ratio. We use the measured neutron-to-proton ratio and compare the theoretically obtained expressions to constrain two models in the framework of f(T,T) gravity. The theoretically constrained models are then tested against observational data from the Hubble dataset and the ΛCDM model to explain the accelerated expansion of the Universe.

Big-bang Nucleosynthesis on a bubble universe nucleated in Kerr-AdS5.

Modelling the Galactic chemical evolution (GCE) of short-lived radioisotopes (SLRs, with half-lives of the order of million years) can provide timing information on recent nucleosynthesis. The knowledge of their spatial distribution throughout the interstellar medium (ISM) is crucial. We are using a three-dimensional GCE model to investigate the evolution of four SLRs: \(^{53}\)Mn from supernovae of type Ia (SNeIa), \(^{60}\)Fe from core-collapse supernovae (CCSNe), \(^{182}\)Hf from stellar winds from intermediate mass stars (IMSs), and \(^{244}\)Pu from neutron star mergers (NSMs) to explain the recent (within the last $\approx 1 -- 20$ Myr) deposition of live SLRs into deep-sea reservoirs. We find that although these SLRs are produced at very different nucleosynthetic sites, they are deposited on Earth conjointly.

Non-standard cosmic expansion histories: neutrino decoupling and primordial nucleosynthesis signatures

Cosmological scenarios with a non-standard equation of state can involve ultrastiff fluids, understood as primordial fluids for which p/ρ > 1. Their energy densities can dominate the Universe energy budget at early times, in the otherwise radiation dominated epoch. During that period the Universe undergoes a faster expansion, that has implications for any decoupling process that takes place in that era. Quintessence models or Ekpyrotic cosmologies are good examples of such scenarios. Assuming the ultrastiff state to be thermally decoupled at very early times, if ever coupled, its observational imprints are left solely in the Universe expansion rate and in the radiation energy density. We consider a complete set of ultrastiff fluids and study their signatures in the neutrino decoupling and BBN eras. Measurements of N eff alone place mild constraints on these scenarios, with forthcoming measurements from the Simons Observatory in the Chilean Atacama desert being able to test regions where still sizable effects are observable. However, when BBN data is taken into account, those regions are proven to be barely reconcilable with primordial helium-4 and deuterium abundances measurements. Our findings show that measurements of the primordial helium-4 abundance imply the tightest constraints, with measurements of primordial deuterium being — to a certain extent — competitive as well. We point out that a ∼ 60% improvement on the statistical uncertainty of the primordial helium-4 abundance measurement, will test these scenarios in the region where they can produce sizable effects. Beyond that precision the regions that are accessible degenerate with standard expectations. In that case, although potentially present, neither neutrino decoupling nor BBN observables will be sensitive probes.

Non-thermal WIMP production from higher order moduli decay

In a non-standard cosmological scenario heavy, long-lived particles, which we call moduli, dominate the energy density prior to Big Bang Nucleosynthesis. Weakly Interacting Massive Particles (WIMPs) may be produced non-thermally from moduli decays. The final relic abundance then depends on additional parameters such as the branching ratio of moduli to WIMPs and the modulus mass. This is of interest for WIMP candidates, such as a bino-like neutralino, where thermal production in standard cosmology leads to an overdensity. Previous works have shown that the correct dark matter (DM) relic density can then still be obtained if the moduli, with mass less than 107 GeV, decay to WIMPs with a branching ratio of less than 10-4. This upper bound could easily be violated once higher order corrections, involving final states with more than two particles, are included. We compute the branching ratios of three- and four-body decays of a modulus into final states involving two DM particles for general couplings. We then apply these expressions to sparticle production within the Minimal Supersymmetric Standard Model (MSSM) with neutralino DM. We find that this upper bound on the branching ratio can be satisfied in simplified models through an appropriate choice of as yet undetermined couplings. However, in the MSSM, it requires sparticle masses to be very close to half the modulus mass, in contrast to the idea of weak-scale supersymmetry.

Dark Radiation from Neutrino Mixing after Big Bang Nucleosynthesis

Dark Radiation from Neutrino Mixing after Big Bang Nucleosynthesis

Photon to axion conversion during Big Bang Nucleosynthesis

We investigate how the resonant conversion at a temperature T̅ = 25–65 keV of a fraction of the CMB photons into an axion-like majoron affects BBN. The scenario, that assumes the presence of a primordial magnetic field and the subsequent decay of the majorons into neutrinos at T ≈ 1 eV, has been proposed to solve the H 0 tension. We find two main effects. First, since we lose photons to majorons at T̅, the baryon to photon ratio is smaller at the beginning of BBN (T > T̅) than during decoupling and structure formation (T ≪ T̅). This relaxes the 2σ mismatch between the observed deuterium abundance and the one predicted by the standard ΛCDM model. Second, since the conversion implies a sudden drop in the temperature of the CMB during the final phase of BBN, it interrupts the synthesis of lithium and beryllium and reduces their final abundance, possibly alleviating the lithium problem.

Does NANOGrav observe a dark sector phase transition?

Gravitational waves from a first-order cosmological phase transition, at temperatures at the MeV-scale, would arguably be the most exciting explanation of the common red spectrum reported by the NANOGrav collaboration, not the least because this would be direct evidence of physics beyond the standard model. Here we perform a detailed analysis of whether such an interpretation is consistent with constraints on the released energy deriving from big bang nucleosynthesis and the cosmic microwave background. We find that a phase transition in a completely secluded dark sector with sub-horizon sized bubbles is strongly disfavoured with respect to the more conventional astrophysical explanation of the putative gravitational wave signal in terms of supermassive black hole binaries. On the other hand, a phase transition in a dark sector that subsequently decays, before the time of neutrino decoupling, remains an intriguing possibility to explain the data. From the model-building perspective, such an option is easily satisfied for couplings with the visible sector that are small enough to evade current collider and astrophysical constraints. The first indication that could eventually corroborate such an interpretation, once the observed common red spectrum is confirmed as a nHz gravitational wave background, could be the spectral tilt of the signal. In fact, the current data already show a very slight preference for a spectrum that is softer than what is expected from the leading astrophysical explanation.

Non-thermal moduli production during preheating in α-attractor inflation models

Production of gravitationally coupled light moduli fields must be suppressed in the early universe so that its decay products do not alter Big Bang Nucleosynthesis (BBN) predictions for light elements. On the other hand, the moduli quanta can be copiously produced non-thermally during preheating after the end of inflation. In this work, we study the production of moduli in the α-attractor inflationary model through parametric resonances. For our case, where the inflationary potential at its minimum is quartic, the inflaton field self-resonates, and subsequently induces a large production of moduli particles. We find that this production is suppressed for small values of α. Combining semi-analytical estimation and numerical lattice simulations, we infer the parametric dependence on α and learn that α needs to be ≲ 10-8 m Pl 2 to be consistent with BBN for 𝒪(1) coupling between inflaton and moduli. This in turn predicts an upper bound on the energy scale of inflation and on the reheating temperature.

Impact of big bang nucleosynthesis on the H 0 tension

We investigate the impact of big bang nucleosynthesis (BBN) on the Hubble tension, focusing on how the treatment of the reaction rate and observational data affect the evaluation of the tension. We show that the significance of the tension is increased to 4.41σ from 3.61σ and to 5.22σ from 4.58σ in axionlike early dark energy model with n = 2 and n = ∞, respectively, depending on the treatment of the reaction rate and observational data. This indicates that how we include the BBN data in the analysis can give a significant impact on the Hubble tension, and we need to carefully consider the assumptions of the analysis to evaluate the significance of the tension when the BBN data is used.

Light sterile neutrinos in the early universe: effects of altered dispersion relations and a coupling to axion-like dark matter

We investigate the cosmological consequences of light sterile neutrinos with altered dispersion relations (ADRs) and couplings to an ultra-light, axion-like scalar field. In particular we study the impact on the number of additional, light, fermionic degrees of freedom and primordial nucleosynthesis. While the ADR leads to a new potential term in the Hamiltonian, the coupling to the scalar field results in a time dependent, effective mass contribution. We solve the quantum kinetic equations (QKEs) for the neutrino density matrix and find that in certain parameter regions both new physics effects can individually yield a suppressed population of sterile neutrino species and the correct observed amount of helium in nucleosynthesis. Combining both effects opens up new patches of parameter space excluded by experimental bounds applying to models featuring only one of the effects.

Reheating after inflaton fragmentation

In the presence of self-interactions, the post-inflationary evolution of the inflaton field is driven into the non-linear regime by the resonant growth of its fluctuations. The once spatially homogeneous coherent inflaton is converted into a collection of inflaton particles with non-vanishing momentum. Fragmentation significantly alters the energy transfer rate to the inflaton's offspring during the reheating epoch. In this work we introduce a formalism to quantify the effect of fragmentation on particle production rates, and determine the evolution of the inflaton and radiation energy densities, including the corresponding reheating temperatures. For an inflaton potential with a quartic minimum, we find that the efficiency of reheating is drastically diminished after backreaction, yet it can lead to temperatures above the big bang nucleosynthesis limit for sufficiently large couplings. In addition, we use a lattice simulation to estimate the spectrum of induced gravitational waves, sourced by the scalar inhomogeneities, and discuss detectability prospects. We find that a Boltzmann approach allows to accurately predict some of the main features of this spectrum.

Constraints on Tsallis Cosmology from Big Bang Nucleosynthesis and the Relic Abundance of Cold Dark Matter Particles.

By employing Tsallis' extensive but non-additive δ-entropy, we formulate the first two laws of thermodynamics for gravitating systems. By invoking Carathéodory's principle, we pay particular attention to the integrating factor for the heat one-form. We show that the latter factorizes into the product of thermal and entropic parts, where the entropic part cannot be reduced to a constant, as is the case in conventional thermodynamics, due to the non-additive nature of Sδ. The ensuing two laws of thermodynamics imply a Tsallis cosmology, which is then applied to a radiation-dominated universe to address the Big Bang nucleosynthesis and the relic abundance of cold dark matter particles. It is demonstrated that the Tsallis cosmology with the scaling exponent δ∼1.499 (or equivalently, the anomalous dimension Δ∼0.0013) consistently describes both the abundance of cold dark matter particles and the formation of primordial light elements, such as deuterium 2H and helium 4He. Salient issues, including the zeroth law of thermodynamics for the δ-entropy and the lithium 7Li problem, are also briefly discussed.

Measuring Hubble constant in an anisotropic extension of [formula omitted]CDM model

Cosmic Microwave Background (CMB) independent approaches are frequently used in the literature to provide estimates of Hubble constant (H0). In this work, we report CMB independent constraints on H0 in an anisotropic extension of ΛCDM model using the Big Bang Nucleosynthesis (BBN), Baryonic Acoustic Oscillations (BAOs), Cosmic Chronometer (CC), and Pantheon+ (PP) compilation of Type Ia supernovae and SH0ES Cepheid host distance anchors data. In the anisotropic model, we find H0=70.1−1.5+1.2(72.67±0.85)kms−1Mpc−1 both with 68% CL from BAO+BBN+CC+PP (BAO+BBN+CC+PPSH0ES) data. The analyses of the anisotropic model with the two combinations of datasets reveal that anisotropy is positively correlated with H0, and an anisotropy of the order 10−14 in the anisotropic model reduces the H0 tension by ∼2σ.