127 research outputs found
The Pre-Roche Lobe Overflow Evolution of Massive Close Binary Stars: A Study of Rotation, Wind Enhanced Mass-Loss, and the Bi-Stability Jump
Massive stars have the ability to enrich their environment with heavy elements and influence star formation in galaxies. Some massive stars exist in binary systems with short orbital periods. These are called massive close binaries. It is important to understand the evolution of massive close binary systems to gain insight about galaxy evolution. Massive stars above 20 solar masses experience a bi-stability jump where there is a sudden increase in mass-loss rate in their winds. There is ongoing research in this field, but the study of the bi-stability jump and its effects on massive close binary star properties has not been done before. A related question is whether binarity can produce a slow rotating, nitrogen-rich massive star such as those found in the Large Magellanic Cloud (Hunter et al. 2008). To accomplish this, two single-star models from Higgins & Vink (2019) and Brott et al. (2011) were used to model a close binary system with the 1-dimensional hydrodynamic stellar evolution code MESA. A grid of models using Higgins & Vink (2019) stellar parameters was created by varying 5 parameters: the convective step overshoot, the tidally enhanced wind coefficient, the wind enhancement factor, the initial rotation, and the initial masses of both stars. Two models were created to compare the approaches of Higgins & Vink (2019) and Brott et al. (2011). Results show that early on in the evolution of the rotating models, the primary star has a more nitrogen-rich photosphere and rotates slower than the secondary star. Tidally enhanced winds are strong enough to strip off the surface layers of the primary. This exposed the nitrogen-rich envelope that is enhanced due to mixing. Tidal forces and tidally enhanced winds slow the rotation rate of the primary star. The existence of the bi-stability jump in massive close binary stars does have an effect on binary properties and could prevent a Roche lobe overflow event. From the numerical data from the models, predictions for characteristics of a wind-blown bubble provide possible future observational properties that are testable with current X-ray observatories
Recycled Dark Matter
We outline a new production mechanism for dark matter that we dub
"recycling": dark sector particles are kinematically trapped in the false
vacuum during a dark phase transition; the false pockets collapse into
primordial black holes (PBHs), which ultimately evaporate before Big Bang
Nucleosynthesis (BBN) to reproduce the dark sector particles. The requirement
that all PBHs evaporate prior to BBN necessitates high scale phase transitions
and hence high scale masses for the dark sector particles in the true vacuum.
Our mechanism is therefore particularly suited for the production of ultra
heavy dark matter (UHDM) with masses above . The
correct relic density of UHDM is obtained because of the exponential
suppression of the false pocket number density. Recycled UHDM has several novel
features: the dark sector today consists of multiple decoupled species that
were once in thermal equilibrium and the PBH formation stage has extended mass
functions whose shape can be controlled by IR operators coupling the dark and
visible sectors.Comment: 23 pages, 7 figures; v2: Lifetime of scalar updated. Conclusions
unchange
The Primordial Black Holes that Disappeared: Connections to Dark Matter and MHz-GHz Gravitational Waves
In the post-LIGO era, there has been a lot of focus on primordial black holes
(PBHs) heavier than g as potential dark matter (DM) candidates.
We point out that the branch of the PBH family that disappeared - PBHs lighter
than g that ostensibly Hawking evaporated away in the early Universe
- also constitute an interesting frontier for DM physics. Hawking evaporation
itself serves as a portal through which such PBHs can illuminate new physics,
for example by emitting dark sector particles. Taking a simple DM scalar
singlet model as a template, we compute the abundance and mass of PBHs that
could have provided, by Hawking evaporation, the correct DM relic density. We
consider two classes of such PBHs: those originating from curvature
perturbations generated by inflation, and those originating from false vacuum
collapse during a first-order phase transition. For PBHs of both origins we
compute the gravitational wave (GW) signals emanating from their formation
stage: from second-order effects in the case of curvature perturbations, and
from sound waves in the case of phase transitions. The GW signals have peak
frequencies in the MHz-GHz range typical of such light PBHs. We compute the
strength of such GWs compatible with the observed DM relic density, and find
that the GW signal morphology can in principle allow one to distinguish between
the two PBH formation histories.Comment: 23 pages + references, 8 figure
Baryogenesis, Primordial Black Holes and MHz-GHz Gravitational Waves
Gravitational waves (GWs) in the MHz - GHz frequency range are motivated by a
host of early Universe phenomena such as oscillons, preheating, and cosmic
strings. We point out that baryogenesis too serves as a motivation to probe GWs
in this frequency range. The connection is through primordial black holes
(PBHs): on the one hand, PBHs induce baryogenesis by Hawking evaporating into a
species that has baryon number and violating decays; on the other, PBHs
induce GWs through second order effects when the scalar fluctuations
responsible for their formation re-enter the horizon. We describe the interplay
of the parameters responsible for successful baryogenesis on the plane of the
strain and frequency of the induced GWs, being careful to delineate regimes
where PBH domination or washout effects occur. We provide semi-analytic
scalings of the GW strain with the baryon number to entropy ratio and other
parameters important for baryogenesis. Along the way, we sketch a solution to
the dark matter-baryogenesis coincidence problem with two populations of PBHs,
which leads to a double-peaked GW signal. Our results underscore the importance
of probing the ultra high frequency GW frontier.Comment: 35 pages, 9 figures. v2: added references, corrected a typo in Eq.
(3.12), version published in JCA
Diffractive Photoproduction in the Framework of Fracture Functions
Recent data on diffractive photoproduction of dijets are analyzed within the
framework of fracture functions and paying special attention to the
consequences of the use of different rapidity gap definitions in order to
identify diffractive events. Although these effects are found to be
significant, it is shown that once they are properly taken into account, a very
precise agreement between diffractive DIS and diffractive dijet photoproduction
emerges without any significant hint of hard factorization breaking.Comment: 13 pages, 4 figures. To appear in Phys.Rev.
Self-supervised learning of accelerometer data provides new insights for sleep and its association with mortality
Sleep is essential to life. Accurate measurement and classification of sleep/wake and sleep stages is important in clinical studies for sleep disorder diagnoses and in the interpretation of data from consumer devices for monitoring physical and mental well-being. Existing non-polysomnography sleep classification techniques mainly rely on heuristic methods developed in relatively small cohorts. Thus, we aimed to establish the accuracy of wrist-worn accelerometers for sleep stage classification and subsequently describe the association between sleep duration and efficiency (proportion of total time asleep when in bed) with mortality outcomes. We developed a self-supervised deep neural network for sleep stage classification using concurrent laboratory-based polysomnography and accelerometry. After exclusion, 1448 participant nights of data were used for training. The difference between polysomnography and the model classifications on the external validation was 34.7 min (95% limits of agreement (LoA): −37.8–107.2 min) for total sleep duration, 2.6 min for REM duration (95% LoA: −68.4–73.4 min) and 32.1 min (95% LoA: −54.4–118.5 min) for NREM duration. The sleep classifier was deployed in the UK Biobank with 100,000 participants to study the association of sleep duration and sleep efficiency with all-cause mortality. Among 66,214 UK Biobank participants, 1642 mortality events were observed. Short sleepers (<6 h) had a higher risk of mortality compared to participants with normal sleep duration of 6–7.9 h, regardless of whether they had low sleep efficiency (Hazard ratios (HRs): 1.58; 95% confidence intervals (CIs): 1.19–2.11) or high sleep efficiency (HRs: 1.45; 95% CIs: 1.16–1.81). Deep-learning-based sleep classification using accelerometers has a fair to moderate agreement with polysomnography. Our findings suggest that having short overnight sleep confers mortality risk irrespective of sleep continuity
A descriptive analysis of relations between parents' self-reported smoking behavior and infants' daily exposure to environmental tobacco smoke
<p>Abstract</p> <p>Background</p> <p>The aims of the present study were to examine relations between parents' self-reported smoking behavior and infants' daily exposure to environmental tobacco smoke, as assessed by urinary cotinine-to-creatinine ratio (CCR), and to describe the CCR over seven days among infants at home.</p> <p>Methods</p> <p>A convenience sample of 27 households was drawn. Each household had to have at least one daily tobacco smoker and one child up to three years of age. Over a seven-day period, urine samples were obtained from the child daily. To examine relations between parents' self-reported smoking and infants' daily CCR, generalized estimating equation (GEE) analysis was used.</p> <p>Results</p> <p>The data revealed that infants from households with indoor smoking had higher CCRs than infants in households with outdoor smoking. CCRs were higher in girls than in boys. Older infants had lower CCRs than younger infants. Smoking outside the home versus inside the home, infant's gender, and infants' age accounted for 68% of the variance in CCR in a GEE data analysis model. No increase or decrease of CCR over time was found.</p> <p>Conclusion</p> <p>The findings suggest that parents' self-reported smoking indoors at home versus outdoors is predictive of CCR among infants three and younger. Higher CCR concentrations in girls' urine need further examination. Furthermore, significant fluctuations in daily CCR were not apparent in infants over a seven-day time period.</p
The study protocol for a randomized controlled trial of a family-centred tobacco control program about environmental tobacco smoke (ETS) to reduce respiratory illness in Indigenous infants
Background: Acute respiratory illness (ARI) is the most common cause of acute presentations and hospitalisations of young Indigenous children in Australia and New Zealand (NZ). Environmental tobacco smoke (ETS) from household smoking is a significant and preventable contributor to childhood ARI. This paper describes the protocol for a study which aims to test the efficacy of a family-centred tobacco control program about ETS to improve the respiratory health of Indigenous infants in Australia and New Zealand. For the purpose of this paper 'Indigenous' refers to Australia's Aboriginal and Torres Strait Islander peoples when referring to Australian Indigenous populations. In New Zealand, the term 'Indigenous' refers to Maori
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