Novel Weak Decays in Doubly Strange Systems

The strangeness-changing ($\Delta S = 1$) weak baryon-baryon interaction is studied through the nonmesonic weak decay of double-$\Lambda$ hypernuclei. Besides the usual nucleon-induced decay $\Lambda N \to N N$ we discuss novel hyperon-induced decay modes $\Lambda \Lambda \to \Lambda N$ and $\Lambda \Lambda \to \Sigma N$. These reactions provide unique access to the exotic $\Lambda \Lambda$K and $\Lambda \Sigma$K vertices which place new constraints on Chiral Pertubation Theory ($\chi$PT) in the weak SU(3) sector. Within a meson-exchange framework, we use the pseudoscalar $\pi,\eta,K$ octet for the long-range part while parametrizing the short-range part through the vector mesons $\rho, \omega, K^*$. Realistic baryon-baryon forces for the $S=0,-1$ and -2 sectors account for the strong interaction in the initial and final states. For $^6_{\Lambda \Lambda}$He the new hyperon-induced decay modes account for up to 4% of the total nonmesonic decay rate. Predictions are made for all possible nonmesonic decay modes.Comment: 19 pages, 2 ps figures, 9 table

Energy input is primary controller of methane bubbling in subarctic lakes

Emission of methane (CH4) from surface waters is often dominated by ebullition (bubbling), a transport mode with high‐spatiotemporal variability. Based on new and extensive CH4 ebullition data, we demonstrate striking correlations (r2 between 0.92 and 0.997) when comparing seasonal bubble CH4 flux from three shallow subarctic lakes to four readily measurable proxies of incoming energy flux and daily flux magnitudes to surface sediment temperature (r2 between 0.86 and 0.94). Our results after continuous multiyear sampling suggest that CH4 ebullition is a predictable process, and that heat flux into the lakes is the dominant driver of gas production and release. Future changes in the energy received by lakes and ponds due to shorter ice‐covered seasons will predictably alter the ebullitive CH4 flux from freshwater systems across northern landscapes. This finding is critical for our understanding of the dynamics of radiatively important trace gas sources and associated climate feedback

Sustainable Development Stakeholder Networks for Organisational Change in Higher Education Institutions: A Case Study from the UK

Progressing towards sustainable development remains a key global challenge. And yet, the various interpretations of the concept of sustainable development and the questions it raises about economic growth make its implementation difficult. Higher education institutions may help to overcome these difficulties by developing new processes of change. However, to achieve this they need to integrate sustainable development in all their areas of activity. The aim of this paper was to develop new insights into organisational change processes in universities relating to sustainable development. Contributing to this aim, this paper reports on a case study of United Kingdom higher education drawing on findings and conclusions from a survey of their policy frameworks relating to sustainable development. The method comprised a critical policy analysis in order to identify, differentiate and categorise stakeholder interactions. The data generated comprised the range of higher education stakeholders and the network of interactions that they formed. Theoretical insights from social network analysis, stakeholder theory and the normative business model were used to find opportunities to address the difficulties in the implementation of sustainable development. Results suggested that the existing networks identified in the policy frameworks may not support the effective integration of sustainable development in higher education. Low-density of the national networks; the lack of a clear governance vocabulary for national policy frameworks; and the lack of explicit funding flows between organisations all pose problems for organisational change towards sustainable development in higher education

Arctic system on trajectory to new state

The Arctic system is moving toward a new state that falls outside the envelope of glacial-interglacial fluctuations that prevailed during recent Earth history. This future Arctic is likely to have dramatically less permanent ice than exists at present. At the present rate of change, a summer ice-free Arctic Ocean within a century is a real possibility, a state not witnessed for at least a million years. The change appears to be driven largely by feedback-enhanced global climate warming, and there seem to be few, if any processes or feedbacks within the Arctic system that are capable of altering the trajectory toward this “super interglacial” state

Nuclear and nucleon transitions of the H di-baryon

We consider 3 types of processes pertinent to the phenomenology of an H di-baryon: conversion of two $\Lambda$'s in a doubly-strange hypernucleus to an H, decay of the H to two baryons, and -- if the H is light enough -- conversion of two nucleons in a nucleus to an H. We compute the spatial wavefunction overlap using the Isgur-Karl and Bethe-Goldstone wavefunctions, and treat the weak interactions phenomenologically. The observation of $\Lambda$ decays from doubly-strange hypernuclei puts a constraint on the H wavefunction which is plausibly satisfied. In this case the H is very long-lived as we calculate. An absolutely stable H is not excluded at present. SuperK can provide valuable limits

Consistency of Lambda-Lambda hypernuclear events

Highlights of Lambda-Lambda emulsion events are briefly reviewed. Given three accepted events, shell-model predictions based on p-shell Lambda hypernuclear spectroscopic studies are shown to reproduce the Lambda-Lambda (LL) binding energies of LL10Be and LL13B in terms of the LL binding energy of LL6He. Predictions for other species offer judgement on several alternative assignments of the LL13B KEK-E176 event, and on the assignments LL11Be and LL12Be suggested recently for the KEK-E373 HIDA event. The predictions of the shell model, spanning a wide range of A values, are compared with those of cluster models, where the latter are available.Comment: Based on talk given by Avraham Gal at EXA 2011, Vienna, September 2011; Proceedings version prepared for the journal Hyperfine Interactions; v2--slight changes, matches published versio

Neutron Star Constraints on the H Dibaryon

We study the influence of a possible H dibaryon condensate on the equation of state and the overall properties of neutron stars whose population otherwise contains nucleons and hyperons. In particular, we are interested in the question of whether neutron stars and their masses can be used to say anything about the existence and properties of the H dibaryon. We find that the equation of state is softened by the appearance of a dibaryon condensate and can result in a mass plateau for neutron stars. If the limiting neutron star mass is about that of the Hulse-Taylor pulsar a condensate of H dibaryons of vacuum mass 2.2 GeV and a moderately attractive potential in the medium could not be ruled out. On the other hand, if the medium potential were even moderately repulsive, the H, would not likely exist in neutron stars. If neutron stars of about 1.6 solar mass were known to exist, attractive medium effects for the H could be ruled out. Certain ranges of dibaryon mass and potential can be excluded by the mass of the Hulse-Taylor pulsar which we illustrate graphically.Comment: Revised by the addition of a figure showing the region of dibaryon mass and potential excluded by the Hulse-Taylor pulsar. 18 pages, 11 figures, latex (submitted to Phys. Rev. C