We examine uncertainties in the analysis of the reactor neutrino anomaly, wherein it is suggested that only about 94% of the emitted antineutrino flux was detected in short baseline experiments. We ...find that the form of the corrections that lead to the anomaly are very uncertain for the 30% of the flux that arises from forbidden decays. This uncertainty was estimated in four ways, is as large as the size of the anomaly, and is unlikely to be reduced without accurate direct measurements of the antineutrino flux. Given the present lack of detailed knowledge of the structure of the forbidden transitions, it is not possible to convert the measured aggregate fission beta spectra to antineutrino spectra to the accuracy needed to infer an anomaly. Neutrino physics conclusions based on the original anomaly need to be revisited, as do oscillation analyses that assumed that the antineutrino flux is known to better than approximately 4%.
We calculate the Zemach moments of hydrogen and deuterium for the first time using only the world data on elastic electron–proton and electron–deuteron scattering. Such moments are required for the ...calculation of the nuclear corrections to the hyperfine structure of these hydrogenic atoms. We compare the resulting HFS predictions to the available high-precision data and provide an estimate of the size of the nuclear polarization corrections necessary to produce agreement between experimental HFS and theoretical calculations.
We apply the Law of Total Probability to the construction of scale-invariant probability distribution functions (pdf's), and require that probability measures be dimensionless and unitless under a ...continuous change of scales. If the scale-change distribution function is scale invariant then the constructed distribution will also be scale invariant. Repeated application of this construction on an arbitrary set of (normalizable) pdf's results again in scale-invariant distributions. The invariant function of this procedure is given uniquely by the reciprocal distribution, suggesting a kind of universality. We separately demonstrate that the reciprocal distribution results uniquely from requiring maximum entropy for size-class distributions with uniform bin sizes.
•We apply the Law of Total Probability to the construction of scale-invariant pdf's, and require that probability measures be dimensionless and unitless under a continuous change of scales.•Iterating this procedure for an arbitrary set of normalized pdf's again produces scale-invariant distributions.•The invariant function of this iteration is given uniquely by the reciprocal distribution, suggesting a kind of universality.•Requiring maximum entropy for uniformly binned size-class distributions also leads uniquely to the reciprocal distribution.•We discuss some applications of the above to computation and to the evolution of genomes.
There exist in nature a few nuclear isomers with very low (eV) excitation energies, and the combination of low energy and narrow width makes them possible candidates for laser-based investigations. ...The best candidate is the lowest-energy excited state known in nuclear physics, the 7.6(5) eV isomer of 229Th. A recent study suggests that a measurement of the temporal variation of the excitation energy of this isomer would have 5–6 orders of magnitude enhanced sensitivity to a variation of the fine structure constant (α≅1/137.036) or of a strong interaction parameter (mq/ΛQCD). We reexamine the physics involved in these arguments. By invoking the Feynman–Hellmann Theorem we argue that there is no expectation of significantly enhanced sensitivity to a variation in the fine structure constant (beyond that obtained from experimental considerations such as the low energy and narrow width of the isomer). A similar argument applies for the strong interaction, but evaluating the shift due to temporal variations of the underlying parameters of the strong interaction may be beyond current nuclear structure techniques.
Here, we examine the importance of conserving the vector current in calculating low-energy neutrino-nucleus interactions by implicitly invoking Siegert's theorem in describing the vector transverse ...electric current. We find that at low neutrino energies (Eν < 50 MeV), Siegert's theorem can change neutrino cross sections for normal-parity non-spin-flip excitations by about a factor of two. The same is true of muon capture rates. At higher neutrino energies the effect of Siegert's theorem diminishes, and by about 100 MeV the effect is very small.
Motivated by the recent observation of anomalous electron-positron angular correlations in the decay of the 18.15-MeV $\mathrm{1^+}$ excited states in $\mathrm{^8Be}$, we reexamine in detail the ...standard model expectations for these angular correlations. The 18.15-MeV state is above particle threshold, and several multipoles can contribute to its ${e^+}{e^-}$ decay. Here, we present the general theoretical expressions for ${e^+}{e^-}$ angular distributions for nuclear decay by $C0, C1, C2, M1, E1,$ and $E2$ multipoles, and we examine their relative contribution to the ${e^+}{e^-}$ decay of $\mathrm{^8Be}$ at 18.15 MeV. We find that this resonance is dominated by $M1$ to $E1$ decay, and that the ratio of $M1$ to $E1$ strength is a strong function of energy. This is in contrast to the original analysis of the ${e^+}{e^-}$ angular distributions, where the $M1/E1$ ratio was assumed to be a constant over the energy region ${E_p} = 0.8 – 1.2$ MeV. We find that the existence of a “bump” in the measured angular distribution is strongly dependent on the assumed $M1/E1$ ratio, with the present analysis finding the measured large-angle contributions to the ${e^+}{e^-}$ angular distribution to be lower than expectation. Thus, in the current analysis we find no evidence for axion decay in the 18.15-MeV resonance region of $\mathrm{^8Be}$.
The theory of QED corrections to hyperfine structure in light hydrogenic atoms and ions has recently advanced to the point that the uncertainty of these corrections is much smaller than 1 part per ...million (ppm), while the experiments are even more accurate. The difference of the experimental results and the corresponding QED theory is due to nuclear effects, which are primarily the result of the finite nuclear charge and magnetization distributions. This difference varies from tens to hundreds of ppm. We have calculated the dominant nuclear component of the 1s hyperfine interval for deuterium, tritium and singly ionized helium, using a unified approach with modern second-generation potentials. The calculated nuclear corrections are within 3% of the experimental values for deuterium and tritium, but are roughly 20% discrepant for helium. The nuclear corrections for the trinucleon systems can be qualitatively understood by invoking SU(4) symmetry.
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