2,103 research outputs found
models with four families
In the context of the local gauge group , we look for possible four family models, where all the particles carry
ordinary electric charges. Thirteen different anomaly-free fermion structures
emerge, out of which only two are realistic. For the simplest physical
structure, we calculate the charged and neutral weak currents and the
tree-level Fermion masses. We also look for new sources of flavor changing
neutral currents in the quark sector, in connection with the upcoming
experimental results at the Large Hadron Collider.Comment: Accepted for publication in Phys. Rev.
Flavor changing neutral currents with a fourth family of quarks
For a model with a fourth family of quarks, new sources of flavor changing
neutral currents are identified by confronting the unitary 4x4 quark mixing
matrix with the experimental measured values of the familiar 3x3 quark mixing
matrix. By imposing as experimental constraints the known bounds for the flavor
changing neutral currents, the largest mixing of the known quarks with the
fourth family ones is established. The predictions are: a value for |V_{tb}|
significantly different from unity, large rates for rare top decays as
t->c\gamma and t->cZ, the last one reachable at the Large Hadrion Collider, and
large rates for rare strange decays s->d\gamma and s->dg, where g stands for
the gluon field.Comment: 7 pages, one figure. Published on Physical Review
Giant planet migration, disk evolution, and the origin of transitional disks
We present models of giant planet migration in evolving protoplanetary disks.
Our disks evolve subject to viscous transport of angular momentum and
photoevaporation, while planets undergo Type II migration. We use a Monte Carlo
approach, running large numbers of models with a range in initial conditions.
We find that relatively simple models can reproduce both the observed radial
distribution of extra-solar giant planets, and the lifetimes and accretion
histories of protoplanetary disks. The use of state-of-the-art photoevaporation
models results in a degree of coupling between planet formation and disk
clearing, which has not been found previously. Some accretion across planetary
orbits is necessary if planets are to survive at radii <~1.5AU, and if planets
of Jupiter mass or greater are to survive in our models they must be able to
form at late times, when the disk surface density in the formation region is
low. Our model forms two different types of "transitional" disks, embedded
planets and clearing disks, which show markedly different properties. We find
that the observable properties of these systems are broadly consistent with
current observations, and highlight useful observational diagnostics. We
predict that young transition disks are more likely to contain embedded giant
planets, while older transition disks are more likely to be undergoing disk
clearing.Comment: 13 pages, 9 figures. Accepted for publication in Ap
Searching for with Multi-Leptons
The results of a multi-lepton search conducted by the CMS collaboration with
5 fb of data collected from 7 TeV collisions are used to place the
first bound on the rare flavor-changing decay of the top quark to a Higgs boson
and charm quark. Combining results from a number of exclusive three- and
four-lepton search channels yields an estimated upper limit of for a Higgs boson mass of 125 GeV. The sensitivity of future
dedicated searches for could be improved by adding exclusive same
sign di-lepton channels, as well as by sub-dividing channels based on -quark
tagging and partial kinematic top quark and Higgs boson tagging. This bound may
be interpreted more widely within a range of new physics processes that yield
final states with a -boson in association with a Higgs boson. For such
processes with kinematics that are similar to top--anti-top production and
decay, the estimated limit on cross section times branching ratio corresponds
to roughly pb.Comment: 11 pages, 1 table; v2 typo correcte
Objectively measured physical activity, sedentary behaviour and all-cause mortality in older men: does volume of activity matter more than pattern of accumulation?
OBJECTIVES: To understand how device-measured sedentary behaviour and physical activity are related to all-cause mortality in older men, an age group with high levels of inactivity and sedentary behaviour. METHODS: Prospective population-based cohort study of men recruited from 24 UK General Practices in 1978-1980. In 2010-2012, 3137 surviving men were invited to a follow-up, 1655 (aged 71-92 years) agreed. Nurses measured height and weight, men completed health and demographic questionnaires and wore an ActiGraph GT3x accelerometer. All-cause mortality was collected through National Health Service central registers up to 1 June 2016. RESULTS: After median 5.0 years' follow-up, 194 deaths occurred in 1181 men without pre-existing cardiovascular disease. For each additional 30 min in sedentary behaviour, or light physical activity (LIPA), or 10 min in moderate to vigorous physical activity (MVPA), HRs for mortality were 1.17 (95% CI 1.10 to 1.25), 0.83 (95% CI 0.77 to 0.90) and 0.90 (95% CI 0.84 to 0.96), respectively. Adjustments for confounders did not meaningfully change estimates. Only LIPA remained significant on mutual adjustment for all intensities. The HR for accumulating 150 min MVPA/week in sporadic minutes (achieved by 66% of men) was 0.59 (95% CI 0.43 to 0.81) and 0.58 (95% CI 0.33 to 1.00) for accumulating 150 min MVPA/week in bouts lasting ≥10 min (achieved by 16% of men). Sedentary breaks were not associated with mortality. CONCLUSIONS: In older men, all activities (of light intensity upwards) were beneficial and accumulation of activity in bouts ≥10 min did not appear important beyond total volume of activity. Findings can inform physical activity guidelines for older adults
Strong size evolution of the most massive galaxies since z~2
Using the combined capabilities of the large near-infrared Palomar/DEEP-2
survey, and the superb resolution of the ACS HST camera, we explore the size
evolution of 831 very massive galaxies (M*>10^{11}h_{70}^{-2}M_sun) since z~2.
We split our sample according to their light concentration using the Sersic
index n. At a given stellar mass, both low (n2.5)
concentrated objects were much smaller in the past than their local massive
counterparts. This evolution is particularly strong for the highly concentrated
(spheroid-like) objects. At z~1.5, massive spheroid-like objects were a factor
of 4(+-0.4) smaller (i.e. almost two orders of magnitudes denser) than those we
see today. These small sized, high mass galaxies do not exist in the nearby
Universe, suggesting that this population merged with other galaxies over
several billion years to form the largest galaxies we see today.Comment: MNRAS in press, 13 pages, 11 figures. Data Table will be published in
its integrity in the MNRAS online versio
On the dynamics of planetesimals embedded in turbulent protoplanetary discs with dead zones
(abridged) Accretion in protoplanetary discs is thought to be driven by [...]
turbulence via the magnetorotational instability (MRI). Recent work has shown
that a planetesimal swarm embedded in a fully turbulent disc is subject to
strong excitation of the velocity dispersion, leading to collisional
destruction of bodies with radii R_p < 100 km. Significant diffusion of
planetesimal semimajor axes also arises, leading to large-scale spreading of
the planetesimal population throughout the inner regions of the protoplanetary
disc, in apparent contradiction of constraints provided by the distribution of
asteroids within the asteroid belt. In this paper, we examine the dynamics of
planetesimals embedded in vertically stratified turbulent discs, with and
without dead zones. Our main aims are to examine the turbulent excitation of
the velocity dispersion, and the radial diffusion, of planetesimals in these
discs. We employ three dimensional MHD simulations [...], along with an
equilibrium chemistry model [...] We find that planetesimals in fully turbulent
discs develop large random velocities that will lead to collisional
destruction/erosion for bodies with sizes below 100 km, and undergo radial
diffusion on a scale \sim 2.5 au over a 5 Myr disc life time. But planetesimals
in a dead zone experience a much reduced excitation of their random velocities,
and equilibrium velocity dispersions lie between the disruption thresholds for
weak and strong aggregates for sizes R_p < 100 km. We also find that radial
diffusion occurs over a much reduced length scale \sim 0.25 au over the disc
life time, this being consistent with solar system constraints. We conclude
that planetesimal growth via mutual collisions between smaller bodies cannot
occur in a fully turbulent disc. By contrast, a dead zone may provide a safe
haven in which km-sized planetesimals can avoid mutual destruction through
collisions.Comment: 18 pages, 13 figures, 3 tables, MNRAS in press, minor corrections to
match the published versio
How are falls and fear of falling associated with objectively measured physical activity in a cohort of community-dwelling older men?
BACKGROUND: Falls affect approximately one third of community-dwelling older adults each year and have serious health and social consequences. Fear of falling (FOF) (lack of confidence in maintaining balance during normal activities) affects many older adults, irrespective of whether they have actually experienced falls. Both falls and fear of falls may result in restrictions of physical activity, which in turn have health consequences. To date the relation between (i) falls and (ii) fear of falling with physical activity have not been investigated using objectively measured activity data which permits examination of different intensities of activity and sedentary behaviour.
METHODS: Cross-sectional study of 1680 men aged 71-92 years recruited from primary care practices who were part of an on-going population-based cohort. Men reported falls history in previous 12 months, FOF, health status and demographic characteristics. Men wore a GT3x accelerometer over the hip for 7 days.
RESULTS: Among the 12% of men who had recurrent falls, daily activity levels were lower than among non-fallers; 942 (95% CI 503, 1381) fewer steps/day, 12(95% CI 2, 22) minutes less in light activity, 10(95% CI 5, 15) minutes less in moderate to vigorous PA [MVPA] and 22(95% CI 9, 35) minutes more in sedentary behaviour. 16% (n = 254) of men reported FOF, of whom 52% (n = 133) had fallen in the past year. Physical activity deficits were even greater in the men who reported that they were fearful of falling than in men who had fallen. Men who were fearful of falling took 1766(95% CI 1391, 2142) fewer steps/day than men who were not fearful, and spent 27(95% CI 18, 36) minutes less in light PA, 18(95% CI 13, 22) minutes less in MVPA, and 45(95% CI 34, 56) minutes more in sedentary behaviour. The significant differences in activity levels between (i) fallers and non-fallers and (ii) men who were fearful of falling or not fearful, were mediated by similar variables; lower exercise self-efficacy, fewer excursions from home and more mobility difficulties.
CONCLUSIONS: Falls and in particular fear of falling are important barriers to older people gaining health benefits of walking and MVPA. Future studies should assess the longitudinal associations between falls and physical activity
The Monitor project: JW 380 -- a 0.26, 0.15 Msol pre main sequence eclipsing binary in the Orion Nebula Cluster
We report the discovery of a low-mass (0.26 +/- 0.02, 0.15 +/- 0.01 Msol)
pre-main-sequence eclipsing binary with a 5.3 day orbital period. JW 380 was
detected as part of a high-cadence time-resolved photometric survey (the
Monitor project) using the 2.5m Isaac Newton Telescope and Wide Field Camera
for a survey of a single field in the Orion Nebula Cluster (ONC) region in V
and i bands. The star is assigned a 99 per cent membership probability from
proper motion measurements, and radial velocity observations indicate a
systemic velocity within 1 sigma of that of the ONC. Modelling of the combined
light and radial velocity curves of the system gave stellar radii of 1.19 +0.04
-0.18 Rsol and 0.90 +0.17 -0.03 Rsol for the primary and secondary, with a
significant third light contribution which is also visible as a third peak in
the cross-correlation functions used to derive radial velocities. The masses
and radii appear to be consistent with stellar models for 2-3 Myr age from
several authors, within the present observational errors. These observations
probe an important region of mass-radius parameter space, where there are
currently only a handful of known pre-main-sequence eclipsing binary systems
with precise measurements available in the literature.Comment: 11 pages, 9 figures, accepted for publication in MNRA
Positive and negative well-being and objectively measured sedentary behaviour in older adults: evidence from three cohorts
Background:
Sedentary behaviour is related to poorer health independently of time spent in moderate to vigorous physical activity. The aim of this study was to investigate whether wellbeing or symptoms of anxiety or depression predict sedentary behaviour in older adults.
Method:
Participants were drawn from the Lothian Birth Cohort 1936 (LBC1936) (n = 271), and the West of Scotland Twenty-07 1950s (n = 309) and 1930s (n = 118) cohorts. Sedentary outcomes, sedentary time, and number of sit-to-stand transitions, were measured with a three-dimensional accelerometer (activPAL activity monitor) worn for 7 days. In the Twenty-07 cohorts, symptoms of anxiety and depression were assessed in 2008 and sedentary outcomes were assessed ~ 8 years later in 2015 and 2016. In the LBC1936 cohort, wellbeing and symptoms of anxiety and depression were assessed concurrently with sedentary behaviour in 2015 and 2016. We tested for an association between wellbeing, anxiety or depression and the sedentary outcomes using multivariate regression analysis.
Results:
We observed no association between wellbeing or symptoms of anxiety and the sedentary outcomes. Symptoms of depression were positively associated with sedentary time in the LBC1936 and Twenty-07 1950s cohort, and negatively associated with number of sit-to-stand transitions in the LBC1936. Meta-analytic estimates of the association between depressive symptoms and sedentary time or number of sit-to-stand transitions, adjusted for age, sex, BMI, long-standing illness, and education, were β = 0.11 (95% CI = 0.03, 0.18) and β = − 0.11 (95% CI = − 0.19, −0.03) respectively.
Conclusion:
Our findings indicate that depressive symptoms are positively associated with sedentary behavior. Future studies should investigate the causal direction of this association
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