Dust of Dark Energy

We introduce a novel class of field theories where energy always flows along timelike geodesics, mimicking in that respect dust, yet which possess non-zero pressure. This theory comprises two scalar fields, one of which is a Lagrange multiplier enforcing a constraint between the other's field value and derivative. We show that this system possesses no wave-like modes but retains a single dynamical degree of freedom. Thus, the sound speed is always identically zero on all backgrounds. In particular, cosmological perturbations reproduce the standard behaviour for hydrodynamics with vanishing sound speed. Using all these properties we propose a model unifying Dark Matter and Dark Energy in a single degree of freedom. In a certain limit this model exactly reproduces the evolution history of Lambda-CDM, while deviations away from the standard expansion history produce a potentially measurable difference in the evolution of structure.Comment: 13 pages, 3 figures. Added references, corrected language

Interpregnancy weight change and adverse pregnancy outcomes: a systematic review and meta-analysis.

OBJECTIVES: To evaluate the effect of interpregnancy body mass index (BMI) change on pregnancy outcomes, including large-for-gestational-age babies (LGA), small-for-gestational-age babies (SGA), macrosomia, gestational diabetes mellitus (GDM) and caesarean section (CS). DESIGN: Systematic review and meta-analysis of observational cohort studies. DATA SOURCES: Literature searches were performed across Cochrane, MEDLINE, EMBASE, CINAHL, Global Health and MIDIRS databases. STUDY SELECTION: Observational cohort studies with participants parity from 0 to 1. MAIN OUTCOME MEASURES: Adjusted ORs (aORs) with 95% CIs were used to evaluate the association between interpregnancy BMI change on five outcomes. RESULTS: 925 065 women with singleton births from parity 0 to 1 were included in the meta-analysis of 11 studies selected from 924 identified studies. A substantial increase in interpregnancy BMI (>3 BMI units) was associated with an increased risk of LGA (aOR 1.85, 95% CI 1.71 to 2.00, p<0.001), GDM (aOR 2.28, 95% CI 1.97 to 2.63, p<0.001), macrosomia (aOR 1.54, 95% CI 0.939 to 2.505) and CS (aOR 1.72, 95% CI 1.32 to 2.24, p<0.001) compared with the reference category, and a decreased risk of SGA (aOR 0.83, 95% CI 0.70 to 0.99, p=0.044). An interpregnancy BMI decrease was associated with a decreased risk of LGA births (aOR 0.70, 95% CI 0.55 to 0.90, p<0.001) and GDM (aOR 0.80, 95% CI 0.62 to 1.03), and an increased risk of SGA (aOR 1.31, 95% CI 1.06 to 1.63, p=0.014). Women with a normal BMI (<25kg/m2) at first pregnancy who have a substantial increase in BMI between pregnancies had a higher risk of LGA (aOR 2.10, 95% CI 1.93 to 2.29) and GDM (aOR 3.10, 95% CI 2.74 to 3.50) when compared with a reference than women with a BMI ≥25 kg/m2 at first pregnancy. CONCLUSIONS: Gaining weight between pregnancies increases risk of developing GDM, CS and LGA, and reduces risk of SGA in the subsequent pregnancy. Losing weight between pregnancies reduces risk of GDM and LGA and increases risk of SGA. Weight stability between first and second pregnancy is advised in order to reduce risk of adverse outcomes. TRIAL REGISTRATION NUMBER: CRD42016041299