27,484 research outputs found
Feeding back Information on Ineligibility from Sample Surveys to the Frame
It is usually discovered in the data collection phase of a survey that some units in the sample are ineligible even if the frame information has indicated otherwise. For example, in many business surveys a nonnegligible proportion of the sampled units will have ceased trading since the latest update of the frame. This information may be fed back to the frame and used in subsequent surveys, thereby making forthcoming samples more efficient by avoiding sampling nonnegligible units. We investigate what effect on survey estimation the process of feeding back information on ineligibility may have, and derive an expression for the bias that can occur as a result of feeding back. The focus is on estimation of the total using the common expansion estimator. We obtain an estimator that is nearly unbiased in the presence of feed back. This estimator relies on consistent estimates of the number of eligible and ineligible units in the population being available
Classification of Argyres-Douglas theories from M5 branes
We obtain a large class of new 4d Argyres-Douglas theories by classifying
irregular punctures for the 6d (2,0) superconformal theory of ADE type on a
sphere. Along the way, we identify the connection between the Hitchin system
and three-fold singularity descriptions of the same Argyres-Douglas theory.
Other constructions such as taking degeneration limits of the irregular
puncture, adding an extra regular puncture, and introducing outer-automorphism
twists are also discussed. Later we investigate various features of these
theories including their Coulomb branch spectrum and central charges.Comment: 35 pages, 9 tables, 6 figures. v2: minor correction
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