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DOE OSTI2024

BBN catalysis by doubly charged particles

Abstract We consider primordial nucleosynthesis in the presence of hypotheticalquasi-stable doubly charged particles. Existence ofX –– withmacroscopic lifetimes will lead to the formation of its bound states with 4 He and otherlight elements, significantly facilitating the subsequentformation of lithium nuclei. From observational constraints on maximumallowable amount of lithium, that we update in this work, we derivestrong constraints on the abundance and lifetime ofX –– . In alikely cosmological freeze-out scenario with temperatures initiallyexceeding the mass ofX –– , the BBN constrains the lifetime of theseparticles to be less than about 100 seconds. For parametrically longlifetimes, lithium abundance data constrainX –– abundance to be lessthan 10 -9 relative to protons, regardless of whether these particlesdecay or remain stable. Stable particles could saturate the dark matterdensity only if their mass is comparable to or in excess of10 10 GeV, and most ofX –– will be found in bound states withberyllium nuclei, so that chemically they would appear as abnormallyheavy helium isotopes.

Astronomy & Astrophysics↗

DOE OSTI2023

The Nuclear Reaction Network WinNet

Abstract 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.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

NASA NTRS1985

The shadow world of superstring theories

Some possible astrophysical and cosmological implications of 'shadow matter', a form of matter which only interacts gravitationally with ordinary matter and which may or may not be identical in its properties to ordinary matter, are considered. The possible existence, amount, and location of shadow matter in the solar system are discussed, and the significance of shadow matter for primordial nucleosynthesis, macroscopic asymmetry, baryogenesis, double-bubble inflation, and asymmetric microphysics is addressed. Massive shadow states are discussed.

Kolb, E. W.↗

NASA NTRS1985

The determination of the helium abundance in main-sequence B stars

It is pointed out that the abundances of deuterium, helium, and lithium provide fundamental constraints on cosmological models. The central question is related to the compatibility of the observed abundances with big bang models of primordial nucleosynthesis, taking into account a modification by subsequent nuclear processing in stars or a modification of standard models. The present paper has the objective to assess critically the feasibility of deriving accurate helium abundances from measurements of the photospheric lines in main-sequence B-type stars. A method is established for assigning atmospheric parameters to main-sequence stars with spectral types in the range (approximately) B1-B5. It is found that an analysis of stars in distant anticenter H II regions and clusters offer an alternative method which seems capable of determining relative abundances with more than the requisite accuracy.

Wolff, S. C.↗

NASA NTRS1988

Cosmology and particle physics

The interplay between cosmology and elementary particle physics is discussed. The standard cosmology is reviewed, concentrating on primordial nucleosynthesis and discussing how the standard cosmology has been used to place constraints on the properties of various particles. Baryogenesis is discussed, showing how a scenario in which the B-, C-, and CP-violating interactions in GUTs provide a dynamical explanation for the predominance of matter over antimatter and for the present baryon-to-photon ratio. It is shown how the very early dynamical evolution of a very weakly coupled scalar field which is initially displaced from the minimum of its potential may explain a handful of very fundamental cosmological facts which are not explained by the standard cosmology.

Turner, Michael S.↗

NASA NTRS1988

Energetic constraints on spectral distortions of the microwave background

The energetic constraints on mechanisms for producing the spectral distortion of the microwave background claimed by Matsumoto et al., (1988) are investigated in the light of the new upper bounds on the cosmological baryon density derived by Kawano et al., (1988) from primordial nucleosynthesis. The thermal emission from dust heated by stars at large redshift and Compton scattering by a hot intergalactic medium heated by supernova explosions are considered, and it is concluded that both mechanisms fail on energetic grounds if they rely on stars formed with the same mass function as is observed in the solar neighborhood.

Lacey, Cedric G.↗

NASA NTRS1991

Astrophysics and cosmology confront the 17 keV neutrino

A host of astrophysical and cosmological arguments severely constrain the properties of a 17 keV Dirac neutrino. Such a neutrino must have interactions beyond those of the standard electroweak theory to reduce its cosmic abundance (through decay or annihilation) by a factor of two hundred. A predicament arises because the additional helicity states of the neutrino necessary to construct a Dirac mass must have interactions strong enough to evade the astrophysical bound from SN 1987A, but weak enough to avoid violating the bound from primordial nucleosynthesis.

Kolb, Edward W.↗

NASA NTRS1991

Astrophysics and cosmology confront the 17-keV neutrino

Kolb, Edward W.↗

NASA NTRS1991

Baryonic dark matter

Both canonical primordial nucleosynthesis constraints and large-scale structure measurements, as well as observations of the fundamental cosmological parameters, appear to be consistent with the hypothesis that the universe predominantly consists of baryonic dark matter (BDM). The arguments for BDM to consist of compact objects that are either stellar relics or substellar objects are reviewed. Several techniques for searching for halo BDM are described.

Silk, Joseph↗

NASA NTRS1993

Constraints on vacuum decay from the microwave background

We consider the possible decay of a vacuum with nonzero energy density into radiation. This is one way to introduce a time-varying cosmological constant, which has been suggested as a means of resolving the cosmological constant problem. We concentrate on the model of Freese et al., in which the vacuum energy density is given as a fraction x/(1 - x) of the energy density of radiation. Using equations for the visible extragalactic background light and assuming that the vacuum decay energy is converted entirely into photons with a Planckian spectrum, we show that the decay process would be capable of contributing significantly to the intensity of the cosmic microwave background. Comparison with COBE observations leads to the constraint x is equal to or less than 0.001, which is stronger than the upper limit of 0.07 obtained previously by Freese et al. from considerations of primordial nucleosynthesis.

Overduin, J. M.↗

NASA NTRS1995

Collisional effects in He I: An observational analysis

Accurate and reliable helium abundances can test modern theories of galactic and primordial nucleosynthesis. Unfortunately, there is some question whether current theory can account for collisional contributions to He I. We present new observations of two planetary nebulae (PNs) in the range lambda 850-lambda 9650, which we use to assess the importance of collisonal effects in the He I spectrum. The first object, NGC 7027, is expected to show relatively strong collisional enhancement, while the second, NGC 7026, should display only small effects. We derive new collision-to-recombination correction factors, based on new collision strengths from the 29-state quantal calculation of He I extending to n = 5. Our results show that the correction factors based on 'standard' theory are correct, but that the errors acquired in such an observational analysis are appreciable. We find no convincing observational evidence for the existence of an unknown agent depopulating the 2(sup 3)S state in Pns.

Kingdon, J.↗

DOE OSTI2020

Hot Gravitons and Gravitational Waves From Kerr Black Holes in the Early Universe

Any abundance of black holes that was present in the early universe will evolve as matter, making up an increasingly large fraction of the total energy density as space expands. This motivates us to consider scenarios in which the early universe included an era that was dominated by low-mass ($M < 5\times 10^8$ g) black holes which evaporate prior to primordial nucleosynthesis. In significant regions of parameter space, these black holes will become gravitationally bound within binary systems, and undergo mergers before evaporating. Such mergers result in three potentially observable signatures. First, any black holes that have undergone one or more mergers will possess substantial angular momentum, causing their Hawking evaporation to produce significant quantities of high-energy gravitons. These products of Hawking evaporation are predicted to constitute a background of hot ($\sim$eV-keV) gravitons today, with an energy density corresponding to $\Delta N_{\rm eff} \sim 0.01-0.03$. Second, these mergers will produce a stochastic background of high-frequency gravitational waves. And third, the energy density of these gravitational waves can be as large as $\Delta N_{\rm eff} \sim 0.3$, depending on the length of time between the mergers and evaporation. These signals are each potentially within the reach of future measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

A comprehensive chemical abundance analysis of the extremely metal poor Leoncino Dwarf galaxy (AGC 198691)

ABSTRACT We re-examine the extremely metal-poor dwarf galaxy AGC 198691 using a high quality spectrum obtained by the LBT’s MODS instrument. Previous spectral observations obtained from KOSMOS on the Mayall 4-m and the Blue channel spectrograph on the MMT 6.5-m telescope did not allow for the determination of sulfur, argon, or helium abundances. We report an updated and full chemical abundance analysis for AGC 198691, including confirmation of the extremely low “direct” oxygen abundance with a value of 12 + log (O/H) = 7.06 ± 0.03. AGC 198691’s low metallicity potentially makes it a high value target for helping determine the primordial helium abundance (Yp). Though complicated by a Na i night sky line partially overlaying the He i λ5876 emission line, the LBT/MODS spectrum proved adequate for determining AGC 198691’s helium abundance. We employ the recently expanded and improved model of Aver et al., incorporating higher Balmer and Paschen lines, augmented by the observation of the infrared helium emission line He i λ10830 obtained by Hsyu et al. Applying our full model produced a reliable helium abundance determination, consistent with the expectation for its metallicity. Although this is the lowest metallicity object with a detailed helium abundance, unfortunately, due to its faintness [EW(Hβ) < 100 Å] and the compromised He i λ5876, the resultant uncertainty on the helium abundance is too large to allow a significant improvement on the measurement of Yp.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

New Thermonuclear Rate of 7 Li(d,n)2 4 He Relevant to the Cosmological Lithium Problem

Accurate 7 Li(d,n)2 4 He 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 7 Li(d,n)2 4 He widely used in big bang nucleosynthesis (BBN) simulations. In this work, we reevaluate the 7 Li(d,n)2 4 He reaction rate using the latest data on the three near-threshold 9 Be 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 9 Be. We obtain a 7 Li(d,n)2 4 He 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 7 Li 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.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Bayesian Estimation of the D(p,γ) 3 He Thermonuclear Reaction Rate

Big bang nucleosynthesis (BBN) is the standard model theory for the production of the light nuclides during the early stages of the universe, taking place for a period of about 20 minutes after the big bang. Deuterium production, in particular, is highly sensitive to the primordial baryon density and the number of neutrino species, and its abundance serves as a sensitive test for the conditions in the early universe. The comparison of observed deuterium abundances with predicted ones requires reliable knowledge of the relevant thermonuclear reaction rates, and their corresponding uncertainties. Recent observations reported the primordial deuterium abundance with percent accuracy, but some theoretical predictions based on BBN are at tension with the measured values because of uncertainties in the cross section of the deuterium-burning reactions. In this work, we analyze the S-factor of the D(p,γ) 3 He reaction using a hierarchical Bayesian model. We take into account the results of eleven experiments, spanning the period of 1955--2021; more than any other study. We also present results for two different fitting functions, a two-parameter function based on microscopic nuclear theory and a four-parameter polynomial. Furthermore, our recommended reaction rates have a 2.2\% uncertainty at 0.8~GK, which is the temperature most important for deuterium BBN. Differences between our rates and previous results are discussed.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

Gravitational waves from global cosmic strings and cosmic archaeology

Global cosmic strings are predicted in many motivated extensions to the Standard Model of particle physics, with close connections to axion dark matter physics. Recent studies suggest that, although subdominant relative to Goldstone emission, gravitational wave (GW) signals from global strings can be detectable with current and planned GW detectors such as LIGO, LISA, DECIGO/BBO, ET/CE and AEDGE/AION, as well as pulsar timing arrays such as PPTA, NANOGrav and SKA. This work is an extensive, updated study on GWs from a global cosmic string network, taking into account of the most recent developments related to the subject. The main analysis is based on the analytical Velocity-dependent One-Scale (VOS) model calibrated with recent simulation results, which provides a generic protocol for such calculations with details given. We also demonstrate how the GW signal can be influenced with variations to the baseline model: this includes considering the uncertainties of model parameters and the potential deviation from the conventional VOS model prediction (i.e. the scaling behavior) as suggested by some of the recent simulation results. Furthermore, we investigated in detail the effect of a non-standard cosmology (e.g. early matter domination or kination) or new particle species on the GW signals from global strings. We demonstrate that the frequency spectrum of GW background from global cosmic strings can be used to probe the cosmic history prior to the Big Bang nucleosynthesis (BBN) (i.e. the primordial dark age) up to a temperature of T ~ 10 8 GeV.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2025

Comparing Compressed and Full-Modeling analyses with FOLPS: implications for DESI 2024 and beyond

The Dark Energy Spectroscopic Instrument (DESI) will provide unprecedented information about the large-scale structure of our Universe. In this work, we study the robustness of the theoretical modelling of the power spectrum of F OLPS , a novel effective field theory-based package for evaluating the redshift space power spectrum in the presence of massive neutrinos. We perform this validation by fitting the AbacusSummit high-accuracy N -body simulations for Luminous Red Galaxies, Emission Line Galaxies and Quasar tracers, calibrated to describe DESI observations. We quantify the potential systematic error budget of F OLPS finding that the modelling errors are fully sub-dominant for the DESI statistical precision within the studied range of scales. Additionally, we study two complementary approaches to fit and analyse the power spectrum data, one based on direct Full-Modelling fits and the other on the ShapeFit compression variables, both resulting in very good agreement in precision and accuracy. In each of these approaches, we study a set of potential systematic errors induced by several assumptions, such as the choice of template cosmology, the effect of prior choice in the nuisance parameters of the model, or the range of scales used in the analysis. Furthermore, we show how opening up the parameter space beyond the vanilla ΛCDM model affects the DESI observables. These studies include the addition of massive neutrinos, spatial curvature, and dark energy equation of state. We also examine how relaxing the usual Cosmic Microwave Background and Big Bang Nucleosynthesis priors on the primordial spectral index and the baryonic matter abundance, respectively, impacts the inference on the rest of the parameters of interest. This paper pathways towards performing a robust and reliable analysis of the shape of the power spectrum of DESI galaxy and quasar clustering using F OLPS .

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1989

Nuclear physics and cosmology

Nuclear physics has provided one of two critical observational tests of all Big Bang cosmology, namely Big Bang Nucleosynthesis. Furthermore, this same nuclear physics input enables a prediction to be made about one of the most fundamental physics questions of all, the number of elementary particle families. The standard Big Bang Nucleosynthesis arguments are reviewed. The primordial He abundance is inferred from He-C and He-N and He-O correlations. The strengthened Li constraint as well as D-2 plus He-3 are used to limit the baryon density. This limit is the key argument behind the need for non-baryonic dark matter. The allowed number of neutrino families, N(nu), is delineated using the new neutron lifetime value of tau(n) = 890 + or - 4s (tau(1/2) = 10.3 min). The formal statistical result is N(nu) = 2.6 + or - 0.3 (1 sigma), providing a reasonable fit (1.3 sigma) to three families but making a fourth light (m(nu) less than or equal to 10 MeV) neutrino family exceedly unlikely (approx. greater than 4.7 sigma). It is also shown that uncertainties induced by postulating a first-order quark-baryon phase transition do not seriously affect the conclusions.

Schramm, David N.↗