Critical collapse in 2+1 dimensional AdS spacetime: quasi-CSS solutions and linear perturbations

We construct a one-parameter family of exact time-dependent solutions to 2+1 gravity with a negative cosmological constant and a massless minimally coupled scalar field as source. These solutions present a continuously self-similar (CSS) behaviour near the central singularity, as observed in critical collapse, and an asymptotically AdS behaviour at spatial infinity. We consider the linear perturbation analysis in this background, and discuss the crucial question of boundary conditions. These are tested in the special case where the scalar field decouples and the linear perturbations describe exactly the small-mass static BTZ black hole. In the case of genuine scalar perturbations, we find a growing mode with a behavior characteristic of supercritical collapse, the spacelike singularity and apparent horizon appearing simultaneously and evolving towards the AdS boundary. Our boundary conditions lead to the value of the critical exponent $\gamma = 0.4$.Comment: 33 pages, 6 figures. Nuclear Physics B (in press

Exploring new physics frontiers through numerical relativity

The demand to obtain answers to highly complex problems within strong-field gravity has been met with significant progress in the numerical solution of Einstein's equations - along with some spectacular results - in various setups. We review techniques for solving Einstein's equations in generic spacetimes, focusing on fully nonlinear evolutions but also on how to benchmark those results with perturbative approaches. The results address problems in high-energy physics, holography, mathematical physics, fundamental physics, astrophysics and cosmology

Critical review of standards for indoor thermal environment and air quality

Quality of the indoor environment has become an important parameter to account for in new and existing buildings due to the increasing number of people spending most of their time indoors. Generally, the design and evaluation of indoor environments in buildings rely on appropriate guidelines and recommendations. National and international IEQ standards specify indoor environmental conditions considered acceptable to most occupants. This publication reviews and critically compares the requirements for indoor thermal environment and ventilation for acceptable air quality across international standards such as ISO, EN and ASHRAE and national standards of China, India, Singapore, and Australia.The critical analysis of IEQ standards demonstrates that regional differences and diversity factors due to factors such as climate, building typology, demographics, and culture might not be appropriately addressed both in national and international standards, limiting the feasibility of universal indoor environmental criteria. In addition to that, most of the standards provide recommendations for various categories of thermal comfort and air quality by focusing on the perception of IEQ by occupants rather than productivity and wellness as quantitative criteria. The review shows that thermal comfort and air quality parameters are treated separately and without an integrated assessment of various environmental quality-related dimensions. Therefore, there is a need for a method to combine various indoor environmental factors into a combined indicator. (C) 2020 Elsevier B.V. All rights reserved