690 research outputs found
The IR stability of de Sitter QFT: Physical initial conditions
This work uses Lorentz-signature in-in perturbation theory to analyze the
late-time behavior of correlators in time-dependent interacting massive scalar
field theory in de Sitter space. We study a scenario recently considered by
Krotov and Polyakov in which the coupling turns on smoothly at finite time,
starting from in the far past where the state is taken to be the (free)
Bunch-Davies vacuum. Our main result is that the resulting correlators (which
we compute at the one-loop level) approach those of the interacting
Hartle-Hawking state at late times. We argue that similar results should hold
for other physically-motivated choices of initial conditions. This behavior is
to be expected from recent quantum "no hair" theorems for interacting massive
scalar field theory in de Sitter space which established similar results to all
orders in perturbation theory for a dense set of states in the Hilbert space.
Our current work i) indicates that physically motivated initial conditions lie
in this dense set, ii) provides a Lorentz-signature counter-part to the
Euclidean techniques used to prove such theorems, and iii) provides an explicit
example of the relevant renormalization techniques.Comment: 32 pages, 3 figure
The IR stability of de Sitter QFT: results at all orders
We show that the Hartle-Hawking vacuum for theories of interacting massive
scalars in de Sitter space is both perturbatively well-defined and stable in
the IR. Correlation functions in this state may be computed on the Euclidean
section and Wick-rotated to Lorentz-signature. The results are manifestly de
Sitter-invariant and contain only the familiar UV singularities. More
importantly, the connected parts of all Lorentz-signature correlators decay at
large separations of their arguments. Our results apply to all cases in which
the free Euclidean vacuum is well defined, including scalars with masses
belonging to both the complementary and principal series of . This
suggests that interacting QFTs in de Sitter -- including higher spin fields --
are perturbatively IR-stable at least when i) the Euclidean vacuum of the
zero-coupling theory exists and ii) corresponding Lorentz-signature
zero-coupling correlators decay at large separations. This work has significant
overlap with a paper by Stefan Hollands, which is being released
simultaneously.Comment: 30 pp., 4 figures. Small typos fixed, refs adde
The Lunar Scout Program: An international program to survey the Moon from orbit for geochemistry, mineralogy, imagery, geodesy, and gravity
The Lunar Scout Program was one of a series of attempts by NASA to develop and fly an orbiting mission to the moon to collect geochemical, geological, and gravity data. Predecessors included the Lunar Observer, the Lunar Geochemical Orbiter, and the Lunar Polar Orbiter - missions studied under the auspices of the Office of Space Science. The Lunar Scout Program, however, was an initiative of the Office of Exploration. It was begun in late 1991 and was transferred to the Office of Space Science after the Office of Exploration was disbanded in 1993. Most of the work was done by a small group of civil servants at the Johnson Space Center; other groups also responsible for mission planning included personnel from the Charles Stark Draper Laboratories, the Lawrence Livermore National Laboratory, Boeing, and Martin Marietta. The Lunar Scout Program failed to achieve new start funding in FY 93 and FY 94 as a result of budget downturns, the de-emphasis of the Space Exploration Initiative, and the fact that lunar science did not rate as high a priority as other planned planetary missions, and was cancelled. The work done on the Lunar Scout Program and other lunar orbiter studies, however, represents assets that will be useful in developing new approaches to lunar orbit science
In the Face of Anti-LGBQ Behaviour: Saskatchewan High-school Students' Perceptions of School Climate and Consequential Impact
In Canada, there is a dearth of research on school climate for lesbian, gay, bisexual, and questioning (LGBQ) students. Using social networking, sixty students from high-schools in Saskatchewan participated in a climate survey. Results indicated that anti-LGBQ speech is widespread, as were other forms of harassment. The more victimization that was reported by students known, or perceived to be, LGBQ, the more deleterious were the consequences for their academic performance, social lives, participation in sports and extra-curricular activities, and overall enjoyment of school. Limitations associated with the study and directions for future research are detailed.
Metallicity Gradients in the Milky Way Disk as Observed by the SEGUE Survey
The observed radial and vertical metallicity distribution of old stars in the
Milky Way disk provides a powerful constraint on the chemical enrichment and
dynamical history of the disk. We present the radial metallicity gradient,
\Delta[Fe/H]/\Delta R, as a function of height above the plane, |Z|, using 7010
main sequence turnoff stars observed by the Sloan Extension for Galactic
Understanding and Exploration (SEGUE) survey. The sample consists of mostly old
thin and thick disk stars, with a minimal contribution from the stellar halo,
in the region 6 < R < 16 kpc, 0.15 < |Z| < 1.5 kpc. The data reveal that the
radial metallicity gradient becomes flat at heights |Z| > 1 kpc. The median
metallicity at large |Z| is consistent with the metallicities seen in outer
disk open clusters, which exhibit a flat radial gradient at [Fe/H] ~ -0.5. We
note that the outer disk clusters are also located at large |Z|; because the
flat gradient extends to small R for our sample, there is some ambiguity in
whether the observed trends for clusters are due to a change in R or |Z|. We
therefore stress the importance of considering both the radial and vertical
directions when measuring spatial abundance trends in the disk. The flattening
of the gradient at high |Z| also has implications on thick disk formation
scenarios, which predict different metallicity patterns in the thick disk. A
flat gradient, such as we observe, is predicted by a turbulent disk at high
redshift, but may also be consistent with radial migration, as long as mixing
is strong. We test our analysis methods using a mock catalog based on the model
of Sch\"onrich & Binney, and we estimate our distance errors to be ~25%. We
also show that we can properly correct for selection biases by assigning
weights to our targets.Comment: Submitted to ApJ; 22 pages, 14 figures in emulateapj format; Full
resolution version available at
http://www.ucolick.org/~jyc/gradient/cheng_apj_fullres.pd
Planetary astronomy
The authors profile the field of astronomy, identify some of the key scientific questions that can be addressed during the decade of the 1990's, and recommend several facilities that are critically important for answering these questions. Scientific opportunities for the 1990' are discussed. Areas discussed include protoplanetary disks, an inventory of the solar system, primitive material in the solar system, the dynamics of planetary atmospheres, planetary rings and ring dynamics, the composition and structure of the atmospheres of giant planets, the volcanoes of IO, and the mineralogy of the Martian surface. Critical technology developments, proposed projects and facilities, and recommendations for research and facilities are discussed
Daily mood, partner support, sexual interest, and sexual activity among adolescent women
This is a post print version of the article. The official published version can be accessed from the link below.Objective: to examine day-to-day associations of coitus, sexual interest, partner emotional support, negative mood and positive mood among adolescent women.
Methods: Women (ages 14 – 17 at enrollment; N=146) enrolled from one of three adolescent primary care clinics completed up to five 84-day diaries over a 27-month period. The diaries assessed partner interactions, sexual activity, substance use and mood. Partner-specific measures assessed on each day included partner emotional support (4 items; alpha = 0.94), argument with a partner (no/yes) and coitus (no/yes). Within-day measures assessed marijuana use (no/yes), Positive Mood (3-items; alpha = 0. 86); Negative Mood (3-items; alpha = 0.82) and Sexual Interest (1-item). Lagged measures of mood and sexual activity were included in multivariate models to control for recent mood and sexual behavior effects on current day mood and coitus. Two main analyses were conducted: coitus as a predictor of positive and negative mood; and the role of positive and negative mood as predictors of coitus. Analyses were conducted by multivariate mixed effect regression and mixed effect logistic regression models.
Results: Data represent 28,376 days from 146 participants. The average number of diary days was 194 days per participant. Sexual activity was reported on 8.3% of days, with condoms used for 27.0% of these coital events. Marijuana was used on 11% of days. Significant predictors of positive mood on a given day included partner support, marijuana use, and coitus. Negative mood was associated with having an argument with a partner and with prior day coitus. Predictors of coitus on a given day included age (Odds ratio = 1.22), increased coital frequency in previous week (OR = 1.49), coitus on the previous day (1.21), increased same-day sexual interest (OR = 2.8) and decreased same-day negative mood (OR = 0.92).
Conclusions: The data demonstrate complex associations of sexual interest, mood, partner interactions and sexual activity
- …