A5029193545- Nuclear physics research studies
- Particle physics theoretical and experimental studies
- Quantum Chromodynamics and Particle Interactions
- Cosmology and Gravitation Theories
- Dark Matter and Cosmic Phenomena
- Advanced Chemical Physics Studies
- Neutrino Physics Research
- Atomic and Molecular Physics
- Scientific Research and Discoveries
- Astro and Planetary Science
- Stellar, planetary, and galactic studies
- Astronomical and nuclear sciences
- Gamma-ray bursts and supernovae
- Advanced NMR Techniques and Applications
- Quantum, superfluid, helium dynamics
- Astronomy and Astrophysical Research
- Nuclear Physics and Applications
- Galaxies: Formation, Evolution, Phenomena
- History and Developments in Astronomy
- Atmospheric Ozone and Climate
- Nuclear reactor physics and engineering
- High-Energy Particle Collisions Research
- Solar and Space Plasma Dynamics
- Atomic and Subatomic Physics Research
- Astrophysics and Star Formation Studies
San Diego State University
2015-2024
University of South Carolina
2015-2018
Ohio University
2014-2018
Argonne National Laboratory
2001-2012
California Institute of Technology
2001-2003
Fermi National Accelerator Laboratory
1997-2001
University of Chicago
1997-2001
The available data on nuclear fusion cross sections important to energy generation in the Sun and other hydrogen-burning stars solar neutrino production are summarized critically evaluated. Recommended values uncertainties provided for key sections, a recommended spectrum is given $^{8}\mathrm{B}$ neutrinos. Opportunities further increasing precision of rates also discussed, including new facilities, experimental techniques, improvements theory. This review, which summarizes conclusions...
The determination of the primeval deuterium abundance has opened a precision era in big bang nucleosynthesis, making accurate predictions more important than ever before. We present analytic form new, precise for light-element abundances and their error matrix. Using our abundance, we infer baryon density ΩBh2 = 0.020 ± 0.002 (95% confidence level) find no evidence stellar production (or destruction) 3He beyond burning D into 3He. Conclusions about 4He 7Li currently hinge on possible...
We examine the effects of cool bottom processing (CBP) on isotopic ratios 18O/16O, 17O/16O, 14N/15N, 26Al/27Al, C/O, and N/O in convective envelope during thermally pulsing asymptotic giant branch (TP-AGB) phase evolution a 1.5 M☉ initial mass star solar composition. use parametric model that treats extra mixing by introducing flow between underlying radiative zone. The parameters this are circulation rate () maximum temperature (TP) experienced circulating material. nuclear reactions...
We have reexamined the nuclear inputs to big-bang nucleosynthesis using Monte Carlo realization of cross-section data directly estimate theoretical uncertainties for yields $\mathrm{D}$, ${}^{3}\mathrm{He}$, and ${}^{7}\mathrm{Li}$. Our results indicate that previous estimates were too large by a factor 2. Using Burles--Tytler deuterium measurement, we infer baryon density...
We describe a new method to treat low-energy scattering problems in few-nucleon systems, and we apply it the five-body case of neutron-alpha scattering. The allows precise calculations low-lying resonances their widths. find that good three-nucleon interaction is crucial obtain an accurate description
(abridged) In the presence of a light WIMP (mass m_chi < 30 MeV), there are degeneracies among WIMP's nature, its couplings to standard model particles, mass, and number equivalent (additional) neutrinos, Delta N_nu. These cannot be broken by CMB constraint on effective N_eff. However, since big bang nucleosynthesis (BBN) is also affected complementary BBN constraints can break some degeneracy. previous paper were combined explore allowed ranges for m_chi, N_nu, N_eff WIMPs that annihilate...
We report the discovery and analysis of most metal-poor damped Lyman-alpha (DLA) system currently known, which also displays Lyman series absorption lines neutral deuterium. The average [O/H] abundance this is = -2.804 +/- 0.015, includes an component with -3.07 0.03. Despite unfortunate blending many weak D I lines, we a precise measurement deuterium system. Using six highest quality self-consistently analyzed measures D/H in DLAs, tentative evidence for subtle decrease increasing...
In the presence of a light weakly interacting massive particle (WIMP; ${m}_{\ensuremath{\chi}}\ensuremath{\lesssim}30\text{ }\text{ }\mathrm{MeV}$), there are degeneracies among nature WIMP (fermion or boson), its couplings to standard-model particles (electromagnetic neutrinos only), mass ${m}_{\ensuremath{\chi}}$, and number equivalent beyond standard model $\mathrm{\ensuremath{\Delta}}{\mathrm{N}}_{\ensuremath{\nu}}$ (including possible sterile neutrinos). These cannot be broken by cosmic...
Together, the standard theory of big-bang nucleosynthesis (BBN) and primeval deuterium abundance now very precisely peg baryon density. Based upon our analysis data theoretical uncertainties associated with BBN predictions, we determine ${\ensuremath{\Omega}}_{B}{h}^{2}=0.020\ifmmode\pm\else\textpm\fi{}0.002$ (95% C.L.), uncertainty from measured about twice that predicted abundance. We discuss critically reliability density, in light possible systematic also derive a conservative range....
It is known that there must be some weak form of transport (called cool bottom processing, or CBP) acting in low-mass red giant branch (RGB) and asymptotic (AGB) stars, adding nuclei, newly produced near the hydrogen-burning shell, to convective envelope. We assume this extra mixing originates a stellar dynamo operated by differential rotation below envelope, maintaining toroidal magnetic fields shell. use phenomenological approach buoyancy flux tubes, assuming they induce matter circulation...
We present a Monte Carlo method for direct incorporation of nuclear inputs in primordial nucleosynthesis calculations. This is intended to remedy shortcomings the current error estimation, by eliminating intermediate data evaluations and working directly with experimental data, allowing an estimation based solely on published uncertainties. technique also allows simple new reduction errors introduction more precise data. The application our indicates that previous estimates calculated...
We present calculations of asymptotic normalization coefficients (ANCs) for one-nucleon removals from nuclear states mass numbers $3\ensuremath{\leqslant}A\ensuremath{\leqslant}9$. Our ANCs were computed variational Monte Carlo solutions to the many-body Schr\"odinger equation with combined Argonne ${v}_{18}$ two-nucleon and Urbana IX three-nucleon potentials. Instead computing explicit overlap integrals, we applied a Green function method that is insensitive difficulties constructing...
We report an improved low-energy extrapolation of the cross section for process Beryllium-7+proton -> Boron-8+photon, which determines Boron-8 neutrino flux from Sun. Our extrapolant is derived Halo Effective Field Theory (EFT) at next-to-leading order. apply Bayesian methods to determine EFT parameters and S-factor, using measured sections scattering lengths as inputs. Asymptotic normalization coefficients are tightly constrained by existing radiative capture data, contributions beyond...
We report the first calculations of cross sections for radiative capture reactions t(alpha,gamma)^7Li and ^3He(alpha,gamma)^7Be below 2 MeV which use wave functions derived from realistic nucleon-nucleon interactions by variational Monte Carlo technique. After examining several small corrections to dominant E1 operator, we find energy dependences low-energy S-factors agree reasonably with experimental measurements. There is no contradiction previous theoretical understanding these processes,...
We compute primordial light-element abundances for cases with a fine structure constant $\ensuremath{\alpha}$ different from the present value, including many sources of dependence neglected in previous calculations. Specifically, we consider contributions arising Coulomb barrier penetration, photon coupling to nuclear currents, and electromagnetic components masses. find depend more weakly on than previously estimated, by up factor 2 case ${}^{7}\mathrm{Li}.$ discuss constraints variations...
We have computed the cross section for process d + alpha -> 6Li gamma at low energies relevant primordial nucleosynthesis and comparison with laboratory data. The final state is a six-body wave function generated by variational Monte Carlo method from Argonne v_18 Urbana IX potentials, including improved treatment of large-particle-separation behavior. initial built up alpha-particle deuteron ground-state solutions these phenomenological descriptions scattering cluster distortions. dominant...
The fraction of matter that is in the form baryons or dark could have spatial fluctuations baryon–dark isocurvature fluctuations. We use big bang nucleosynthesis calculations compared with observed light-element abundances as well galaxy cluster gas fractions to constrain cosmological variations baryon fraction. Light-element be less than 26%–27%, while a sample "relaxed" clusters shows 8%. Larger cause differential screening primary cosmic microwave background (CMB) anisotropies, leading...
We report a leading-order (LO) calculation of $^7\mathrm{Be}(p,\gamma)^8\mathrm{B}$ in low-energy effective field theory. $^8\mathrm{B}$ is treated as shallow proton$+^7\mathrm{Be}$ core and proton$+^7\mathrm{Be}^{*}$ (core excitation) $p$-wave bound state. The couplings are fixed using measured binding energies proton-$^7\mathrm{Be}$ $s$-wave scattering lengths, together with asymptotic normalization coefficients from ab initio calculations. obtain zero-energy $S$-factor $18.2 \pm 1.2~({\rm...
Previous studies of the reaction ${}^{3}\mathrm{He} +{}^{4}\mathrm{He} \rightarrow {}^{7}\mathrm{Be} + \gamma$ have focused on providing best central value and error bar for $S$ factor at solar energies. Measurements this capture reaction, ${}^{3}\mathrm{He}$-${}^{4}\mathrm{He}$ scattering phase shifts, as well properties ${}^{7}\mathrm{Be}$, been used to constrain employed theoretical models. Here we show that much more information than was previously appreciated can be extracted from...
Recent studies of heavy r-process elements in low [Fe/H] halo stars have suggested that an initial population metal-free very massive (VMSs) may be required to provide early Fe enrichment without coproducing r nuclei. We find similar abundance trends alpha-elements (which should copiously produced by VMSs), but not other such as carbon not), agreement with this hypothesis. then combine the corresponding level prompt models VMS nucleosynthetic yields and spectra estimate ionizing fluxes. The...
We examine the possibility that big-bang nucleosynthesis (BBN) may produce nontrivial amounts of ${}^{6}\mathrm{Li}$. If a primordial component this isotope could be observed, it would provide new fundamental test cosmology, as well constraints on baryon density universe. At present, however, theoretical predictions ${}^{6}\mathrm{Li}$ abundance are extremely uncertain due to difficulties in both estimates and experimental determinations...
We report a leading-order calculation of radiative ${}^{7}\mathrm{Li}$ neutron captures to both the ground and first excited state ${}^{8}\mathrm{Li}$ in framework low-energy effective field theory (halo-EFT). Each possible final states is treated as shallow bound composed $n+{}^{7}\mathrm{Li}$ $n+{}^{7}{\mathrm{Li}}^{*}$ (core excitation) configurations. The ab initio variational Monte Carlo method used compute asymptotic normalization coefficients these states, which are then fix couplings...
I describe the computation of energy widths nuclear states using an integral over interaction region ab initio variational Monte Carlo wave functions, and present calculated for many states. begin by presenting relations that connect certain short-range integrals to widths. then predicted 5 <= A 9 nuclei, compare them against measured They match data more closely with less ambiguity than estimates based on spectroscopic factors. consider consequences my results identification observed in...