159 research outputs found
Fast Electroweak Symmetry Breaking and Cold Electroweak Baryogenesis
We construct a model for delayed electroweak symmetry breaking that takes
place in a cold Universe with T<<100 GeV and which proceeds by a fast quench
rather than by a conventional, slow, phase transition. This is achieved by
coupling the Standard Model Higgs to an additional scalar field. We show that
the quench transition can be made fast enough for successful Cold Electroweak
Baryogenesis, while leaving known electroweak physics unchanged.Comment: 13 pages, 5 figures. Section and extra checks added, conclusions
unchanged. Published versio
Temperature Dependence of Standard Model CP Violation
We analyze the temperature dependence of CP violation effects in the Standard
Model by determining the effective action of its bosonic fields, obtained after
integrating out the fermions from the theory and performing a covariant
gradient expansion. We find non-vanishing CP violating terms starting at the
sixth order of the expansion, albeit only in the C odd/P even sector, with
coefficients that depend on quark masses, CKM matrix elements, temperature and
the magnitude of the Higgs field. The CP violating effects are observed to
decrease rapidly with temperature, which has important implications for the
generation of a matter-antimatter asymmetry in the early Universe. Our results
suggest that the cold electroweak baryogenesis scenario may be viable within
the Standard Model, provided the electroweak transition temperature is at most
of order 1 GeV.Comment: 4 pages, 2 figures. Additional non-trivial cancellations lead to
vanishing of P-odd sector also at finite temperature. Minor additional
modifications and clarifications, conclusions otherwise unchanged. Published
versio
Body mass index trajectories from 2 to 18 years - exploring differences between European cohorts.
BACKGROUND: In recent decades, there has been an increase in the prevalence of childhood overweight in most high-income countries. Within northern Europe, prevalence tends to be higher in the UK compared with the Scandinavian countries. We aimed to study differences in body mass index (BMI) trajectories between large cohorts of children from UK and Scandinavian populations. METHODS: We compared BMI trajectories in participants from the English Avon Longitudinal Study of Parents and Children born in 1991-1993 (ALSPAC) (N = 6517), the Northern Finland Birth Cohorts born in 1966 (NFBC1966) (N = 3321) and 1986 (NFBC1986) (N = 4764), and the Danish Aarhus Birth Cohort born in 1990-1992 (ABC) (N = 1920). We used multilevel models to estimate BMI trajectories from 2 to 18 years. We explored whether cohort differences were explained by maternal BMI, height, education or smoking during pregnancy and whether differences were attributable to changes in the degree of skew in the BMI distribution. RESULTS: Differences in mean BMI between the cohorts were small but emerged early and persisted in most cases across childhood. Girls in ALSPAC had a higher BMI than all other cohorts throughout childhood, e.g. compared with the NFBC1986 BMI was 2.2-3.5% higher. For boys, the difference emerging over time (comparing the two NFBC's) exceeded the differences across populations (comparing NFBC1986, ABC and ALSPAC). BMI distribution demonstrated increasing right skew with age. CONCLUSION: Population-level differences between cohorts were small, tended to emerge very early, persisted across childhood, and demonstrated an increase in the right-hand tail of the BMI distribution
Cumulative contextual risk at birth in relation to adolescent substance use, conduct problems, and risky sex: General and specific predictive associations in a Finnish birth cohort
Background—Research indicates that risk factors cluster in the most vulnerable youth, increasing their susceptibility for adverse developmental outcomes. However, most studies of cumulative risk are cross-sectional or short-term longitudinal, and have been based on data from the United States or the United Kingdom. Using data from the Northern Finland Birth Cohort 1986 Study (NFBC1986), we examined cumulative contextual risk (CCR) at birth as a predictor of adolescent substance use and co-occurring conduct problems and risky sex to determine the degree to which CCR predicts specific outcomes over-and-above its effect on general problem behavior, while testing for moderation of associations by gender.
Methods—Analyses of survey data from 6963 participants of the NFBC1986 followed from the prenatal/birth period into adolescence were conducted using structural equation modeling.
Results—CCR had long-term positive associations with first-order substance use, conduct problems, and risky sex factors, and, in a separate analysis, with a second-order general problem behavior factor. Further analyses showed that there was a positive specific effect of CCR on risky sex, over-and-above general problem behavior, for girls only.
Conclusions—This study, conducted within the Finnish context, showed that CCR at birth had long-term general and specific predictive associations with substance use and co-occurring problem behaviors in adolescence; effects on risky sex were stronger for girls. Results are consistent with the hypothesis that early exposure to CCR can have lasting adverse consequences, suggesting the need for early identification and intervention efforts for vulnerable children
Cumulative contextual risk at birth in relation to adolescent substance use, conduct problems, and risky sex: General and specific predictive associations in a Finnish birth cohort
Background—Research indicates that risk factors cluster in the most vulnerable youth, increasing their susceptibility for adverse developmental outcomes. However, most studies of cumulative risk are cross-sectional or short-term longitudinal, and have been based on data from the United States or the United Kingdom. Using data from the Northern Finland Birth Cohort 1986 Study (NFBC1986), we examined cumulative contextual risk (CCR) at birth as a predictor of adolescent substance use and co-occurring conduct problems and risky sex to determine the degree to which CCR predicts specific outcomes over-and-above its effect on general problem behavior, while testing for moderation of associations by gender.
Methods—Analyses of survey data from 6963 participants of the NFBC1986 followed from the prenatal/birth period into adolescence were conducted using structural equation modeling.
Results—CCR had long-term positive associations with first-order substance use, conduct problems, and risky sex factors, and, in a separate analysis, with a second-order general problem behavior factor. Further analyses showed that there was a positive specific effect of CCR on risky sex, over-and-above general problem behavior, for girls only.
Conclusions—This study, conducted within the Finnish context, showed that CCR at birth had long-term general and specific predictive associations with substance use and co-occurring problem behaviors in adolescence; effects on risky sex were stronger for girls. Results are consistent with the hypothesis that early exposure to CCR can have lasting adverse consequences, suggesting the need for early identification and intervention efforts for vulnerable children
Holographic dilepton production in a thermalizing plasma
We determine the out-of-equilibrium production rate of dileptons at rest in
strongly coupled N=4 Super Yang-Mills plasma using the AdS/CFT correspondence.
Thermalization is achieved via the gravitational collapse of a thin shell of
matter in AdS_5 space and the subsequent formation of a black hole, which we
describe in a quasistatic approximation. Prior to thermalization, the dilepton
spectral function is observed to oscillate as a function of frequency, but the
amplitude of the oscillations decreases when thermal equilibrium is approached.
At the same time, we follow the flow of the quasinormal spectrum of the
corresponding U(1) vector field towards its equilibrium limit.Comment: 21 pages, 7 figures. v2: Version accepted for publication in JHEP;
minor modifications, added reference
Local non-Gaussianity from inflation
The non-Gaussian distribution of primordial perturbations has the potential
to reveal the physical processes at work in the very early Universe. Local
models provide a well-defined class of non-Gaussian distributions that arise
naturally from the non-linear evolution of density perturbations on
super-Hubble scales starting from Gaussian field fluctuations during inflation.
I describe the delta-N formalism used to calculate the primordial density
perturbation on large scales and then review several models for the origin of
local primordial non-Gaussianity, including the cuvaton, modulated reheating
and ekpyrotic scenarios. I include an appendix with a table of sign conventions
used in specific papers.Comment: 21 pages, 1 figure, invited review to appear in Classical and Quantum
Gravity special issue on non-linear and non-Gaussian cosmological
perturbation
Family doctors' involvement with families in Estonia
BACKGROUND: Family doctors should care for individuals in the context of their family. Family has a powerful influence on health and illness and family interventions have been shown to improve health outcomes for a variety of health problems. The aim of the study was to investigate the Estonian family doctors' (FD) attitudes to the patients' family-related issues in their work: to explore the degree of FDs involvement in family matters, their preparedness for management of family-related issues and their self-assessment of the ability to manage different family-related problems. METHODS: A random sample (n = 236) of all FDs in Estonia was investigated using a postal questionnaire. Altogether 151 FDs responded to the questionnaire (response rate 64%), while five of them were excluded as they did not actually work as FDs. RESULTS: Of the respondents, 90% thought that in managing the health problems of patients FDs should communicate and cooperate with family members. Although most of the family doctors agreed that modifying of the health damaging risk factors (smoking, alcohol and drug abuse) of their patients and families is their task, one third of them felt that dealing with these problems is ineffective, or perceived themselves as poorly prepared or having too little time for such activities. Of the respondents, 58% (n = 83) were of the opinion that they could modify also relationship problems. CONCLUSIONS: Estonian family doctors are favourably disposed to involvement in family-related problems, however, they need some additional training, especially in the field of relationship management
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