The box diagram in Yukawa theory

We present a light-front calculation of the box diagram in Yukawa theory. The covariant box diagram is finite for the case of spin-1/2 constituents exchanging spin-0 particles. In light-front dynamics, however, individual time-ordered diagrams are divergent. We analyze the corresponding light-front singularities and show the equivalence between the light-front and covariant results by taming the singularities.Comment: 21 pages, 17 figures. submittes to Phys. Rev.

Interventions for promoting reintegration and reducing harmful behaviour and lifestyles in street-connected children and young people (Review)

Background Millions of street-connected children and young people worldwide live or work in street environments. They are vulnerable to many risks, whether or not they remain connected to families of origin, and despite many strengths and resiliencies, they are excluded from mainstream social structures and opportunities. Objectives Primary research objectives To evaluate and summarise the effectiveness of interventions for street-connected children and young people that aim to: • promote inclusion and reintegration; • increase literacy and numeracy; • facilitate access to education and employment; • promote mental health, including self esteem; • reduce harms associated with early sexual activity and substance misuse. Secondary research objectives • To explore whether effects of interventions differ within and between populations, and whether an equity gradient influences theseeffects, by extrapolating from all findings relevance for low- and middle-income countries (LMICs) (Peters 2004). • To describe other health, educational, psychosocial and behavioural effects, when appropriate outcomes are reported. • To explore the influence of context in design, delivery and outcomes of interventions. Interventions for promoting reintegration and reducing harmful behaviour and lifestyles in street-connected children and young people 1 (Review) Copyright © 2016 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd. To explore the relationship between numbers of components and duration and effects of interventions. • To highlight implications of these findings for further research and research methods to improve evidence in relation to the primary research objective. • To consider adverse or unintended outcomes. Search methods We searched the following bibliographic databases, searched for the original review, from inception to 2012, and various relevant non-governmental and organisational websites: Cochrane Central Register of Controlled Trials (CENTRAL); MEDLINE and PreMEDLINE;EMBASE and EMBASE Classic; Cumulative Index to Nursing and Allied Health Literature (CINAHL); PsycINFO; Education Resource Information Center (ERIC); Sociological Abstracts; Social Services Abstracts; Social Work Abstracts; Healthstar; Latin American Caribbean Health Sciences Literature (LILACS); System for Grey literature in Europe (OpenGrey); ProQuest Dissertations and Theses; EconLit; IDEAS Economics and Finance Research; JOLIS Library Catalog of the holdings of the World Bank Group and International Monetary Fund (IMF) Libraries; British Library for Development Studies (BLDS); Google and Google Scholar. We updated the search in April 2015 for the review update, using the same methods. Selection criteria This review includes data from harm reduction or reintegration intervention studies that used a comparison group study design; all were randomised or quasi-randomised studies. Studies were included if they evaluated interventions provided for street-connected children and young people, from birth to 24 years, in all contexts. Data collection and analysis Two review authors independently extracted data and assessed risk of bias and other factors presented in the Discussion and Summary quality assessment (Grades of Recommendation, Assessment, Development and Evaluation (GRADE)). We extracted data on intervention delivery, context, process factors, equity and outcomes, and grouped outcomes into psychosocial outcomes, risky sexual behaviours or substance use. We conducted meta-analyses for outcomes where the outcome measures were sufficiently similar. We evaluated other outcomes narratively. Main results We included 13 studies evaluating 19 interventions from high-income countries (HICs). We found no sufficiently robust evaluations conducted in low- and middle-income countries (LMICs). Study quality overall was low and measurements used by studies variable. Participants were classified as drop-in and shelter-based. No studies measured the primary outcome of reintegration and none reported on adverse effects.We found no consistent results on a range of relevant outcomes within domains of psychosocial health, substance misuse and sexually risky behaviours . Interventions evaluated consisted of time-limited therapeutically based programmes that proved no more effective than standard shelter or drop-in services and other control interventions used for most outcomes in most studies. Favourable changes from baseline were reported for outcomes for most participants following therapy interventions and standard services. We noted considerable heterogeneity between studies and inconsistent reporting of equity data. No studies measured the primary outcome of reintegration or reported on adverse effects. Authors’ conclusions Analysis revealed no consistently significant benefit for focused therapeutic interventions compared with standard services such as dropin centres, case management and other comparable interventions for street-connected children and young people. Commonly available services, however, were not rigorously evaluated. Robust evaluation of interventions, including comparison with no intervention, would establish a more reliable evidence base to inform service implementation. More robust research is needed in LMICs to examine interventions for street-connected children and young people with different backgrounds and service needs