Atomic effects in tritium beta decay

The electron neutrino mass has been measured in several tritium beta decay experiments. These experiments are sensitive to a small neutrino mass because the energy release of the decay is small. But the very smallness of the energy release implies that the Coulomb interactions of the slowly moving emitted beta electron are relatively large. Using field theoretic techniques, we derive a systematic and controlled expansion which accounts for the Coulomb effects, including the mutual interaction of the beta ray electron and the electron in the final $^3{\rm He}^+$ ion. In our formulation, an effective potential which describes the long range Coulomb force experienced by the beta ray is introduced to ensure that our expansion is free of infrared divergences. Both the exclusive differential decay rate to a specific final $^3{\rm He}^+$ state and the inclusive differential decay rate are calculated to order $\eta^2$, where $\eta$ is the usual Coulomb parameter. We analyze the order $\eta^2$ correction to the beta ray spectrum and estimate how it may affect the neutrino mass squared parameter and the endpoint energy when this corrected spectrum is used to compare with the experiments. We find that the effect is small.Comment: 81 pages, 15 Postscript figures, uses a non-standard style file "table.sty" which is appended at the end of the latex fil

The Free Energy of Hot Gauge Theories with Fermions Through g^5

We compute the free energy density $F$ for gauge theories, with fermions, at high temperature and zero chemical potential. In the expansion $F=T^4 [c_0+c_2 g^2+c_3 g^3+(c'_4\ln g+c_4)g^4+ (c'_5\ln g+c_5)g^5+O(g^6)]$, we determine $c'_5$ and $c_5$ analytically by calculating two- and three-loop diagrams. The $g^5$ term constitutes the first correction to the $g^3$ term and is for the non-Abelian case the last power of $g$ that can be computed within perturbation theory. We find that the $g^5$ term receives no contributions from overlapping double-frequency sums and that $c'_5$ vanishes.Comment: 31 pages, 6 figures, LaTeX; minor beautifications, reference list extended, version to be published in Phys.Rev.

The Three-Loop Free Energy for High-Temperature QED and QCD with Fermions

We compute the free energy density for gauge theories, with fermions, at high temperature and zero chemical potential. Specifically, we analytically compute the free energy through $O(g^4)$, which requires the evaluation of three-loop diagrams. This computation extends our previous result for pure gauge QCD.Comment: 26 pages, 9 postscript figures, UW/PT-94-1

Observed Tightening of Tropical Ascent in Recent Decades and Linkage to Regional Precipitation Changes

Climate models predict that the tropical ascending region should tighten under global warming, but observational quantification of the tightening rate is limited. Here we show that the observed spatial extent of the relatively moist, rainy and cloudy regions in the tropics associated with large‐scale ascent has been decreasing at a rate of −1%/decade (−5%/K) from 1979 to 2016, resulting from combined effects of interdecadal variability and anthropogenic forcings, with the former contributing more than the latter. The tightening of tropical ascent is associated with an increase in the occurrence frequency of extremely strong ascent, leading to an increase in the average precipitation rate in the top 1% of monthly rainfall in the tropics. At the margins of the convective zones such as the Southeast Amazonia region, the contraction of large‐scale ascent is related to a long‐term drying trend about −3.2%/decade in the past 38 years

Real-time speckle sensing and suppression with project 1640 at Palomar

Palomar’s Project 1640 (P1640) is the first stellar coronagraph to regularly use active coronagraphic wavefront control (CWFC). For this it has a hierarchy of offset wavefront sensors (WFS), the most important of which is the higher-order WFS (called CAL), which tracks quasi-static modes between 2-35 cycles-per-aperture. The wavefront is measured in the coronagraph at 0.01 Hz rates, providing slope targets to the upstream Palm 3000 adaptive optics (AO) system. The CWFC handles all non-common path distortions up to the coronagraphic focal plane mask, but does not sense second order modes between the WFSs and the science integral field unit (IFU); these modes determine the system’s current limit. We have two CWFC operating modes: (1) P-mode, where we only control phases, generating double-sided darkholes by correcting to the largest controllable spatial frequencies, and (2) E-mode, where we can control amplitudes and phases, generating single-sided dark-holes in specified regions-of-interest. We describe the performance and limitations of both these modes, and discuss the improvements we are considering going forward

Observed Tightening of Tropical Ascent in Recent Decades and Linkage to Regional Precipitation Changes

Climate models predict that the tropical ascending region should tighten under global warming, but observational quantification of the tightening rate is limited. Here we show that the observed spatial extent of the relatively moist, rainy and cloudy regions in the tropics associated with large‐scale ascent has been decreasing at a rate of −1%/decade (−5%/K) from 1979 to 2016, resulting from combined effects of interdecadal variability and anthropogenic forcings, with the former contributing more than the latter. The tightening of tropical ascent is associated with an increase in the occurrence frequency of extremely strong ascent, leading to an increase in the average precipitation rate in the top 1% of monthly rainfall in the tropics. At the margins of the convective zones such as the Southeast Amazonia region, the contraction of large‐scale ascent is related to a long‐term drying trend about −3.2%/decade in the past 38 years