We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.
Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UKDepartment of Applied Mathematics and Theoretical Physics, Silver Street, Cambridge, CB3 9EW, UKand Physics Department, Stanford University, Via Palou, CA, 94305, USA
An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button.