Can the cosmological constant undergo abrupt changes?

The existence of a simple spherically symmetric and static solution of the Einstein equations in the presence of a cosmological constant vanishing outside a definite value of the radial distance is investigated. A particular succession of field configurations, which are solutions of the Einstein equations in the presence of the considered cosmological term and auxiliary external sources, is constructed. Then, it is shown that the associated succession of external sources tend to zero in the sense of the generalized functions. The type of weak solution that is found becomes the deSitter homogeneous space-time for the interior region, and the Schwartzschild space in the outside zone.Comment: 10 pages, 1 figur

A domain-decomposition method to implement electrostatic free boundary conditions in the radial direction for electric discharges

At high pressure electric discharges typically grow as thin, elongated filaments. In a numerical simulation this large aspect ratio should ideally translate into a narrow, cylindrical computational domain that envelops the discharge as closely as possible. However, the development of the discharge is driven by electrostatic interactions and, if the computational domain is not wide enough, the boundary conditions imposed to the electrostatic potential on the external boundary have a strong effect on the discharge. Most numerical codes for electric discharges circumvent this problem by either using a wide computational domain or by calculating the boundary conditions by integrating the Green's function of an infinite domain. Here we describe an accurate and efficient method to impose free boundary conditions for an elongated electric discharge. To facilitate the use of our method we provide a sample implementation.Comment: 21 pages, 4 figures, a movie and a sample code in python. A new Appendix has been adde

Long-lived Colored Scalars at the LHC

We study the collider signatures of a long-lived massive colored scalar transforming trivially under the weak interaction and decaying within the inner sections of a detector such as ATLAS or CMS. In our study, we assume that the colored scalar couples at tree-level to a top quark and a stable fermion, possibly arising from a dark sector or from supersymmetric extensions of the Standard Model. After implementing the latest experimental searches for long-lived colored scalars, we observe a region of parameter space consistent with a colored electroweak-singlet scalar with mass between $\sim200-350$ GeV and a lifetime between $0.1-1$ $\text{mm}/c$ together, with a nearly degenerate dark fermion that may be probed at the $\sqrt{s}=13$ TeV LHC. We show that a search strategy using a combination of cuts on missing transverse energy and impact parameters can exclude regions of parameter space not accessed by prompt searches. We show that a region of parameter space within our simplified model may naturally arise from the light-stop window regime of supersymmetric extensions of the Standard Model, where a light mostly right-handed stop has a mass slightly larger than the lightest neutralino and decays through a four-body process

Anemia and Child Education: The Case of Colombia

Welfare programs in Colombia have been focused on reducing malnutrition and hunger and on increasing school attendance rates. However, there is not much evidence on the hypothesized relationship between nutrition and education. Using the National Survey of Nutritional Status in Colombia - 2005 (ENSIN) and the Demographic and Health Survey -2005 (DHS), this paper estimates the impact of nutrition on schooling outcomes. The results suggest that anemic children have a higher probability of lagging behind in school. Malnutrition, defined by anthropometric measures, does not have an impact on schooling lags. School attendance seems to be unrelated to nutrition measures. The results are consistent under different specifications.school attendance, schooling lag, nutrition, micronutrients

Anemia and Child Education: The Case of Colombia

Welfare programs in Colombia have focused on both reducing malnutrition and hunger and increasing school attendance. But there is not much evidence on the hypothesized relationship between nutrition status and schooling outcomes. Using the National Survey of Nutritional Status in Colombia - 2005 (ensin) and the Demographic and Health Survey - 2005 (dhs), this paper estimates the impact of nutrition on schooling outcomes. The results suggest that anemic children have a higher probability of being overage in school. Malnutrition, defined by anthropometric measures, does not have an impact on the probability of being overage. School attendance seems to be unrelated to nutrition measures. The results are consistent under different specifications.School attendance, overage, nutrition, micronutrients.