6,383 research outputs found
Cosmological bounds on sub-MeV mass axions
Axions with mass greater than 0.7 eV are excluded by cosmological precision
data because they provide too much hot dark matter. While for masses above 20
eV the axion lifetime drops below the age of the universe, we show that the
cosmological exclusion range can be extended from 0.7 eV till 300 keV,
primarily by the cosmic deuterium abundance: axion decays would strongly modify
the baryon-to-photon ratio at BBN relative to the one at CMB decoupling.
Additional arguments include neutrino dilution relative to photons by axion
decays and spectral CMB distortions. Our new cosmological constraints
complement stellar-evolution limits and laboratory bounds.Comment: 19 pages, 10 figure
A High-Velocity Narrow Absorption Line Outflow in the Quasar J212329.46-005052.9
We report on a variable high-velocity narrow absorption line outflow in the
redshift 2.3 quasar J2123-0050. Five distinct outflow systems are detected with
velocity shifts from -9710 to -14,050 km/s and CIV 1548,1551 line widths of
FWHM = 62-164 km/s. These data require five distinct outflow structures with
similar kinematics, physical conditions and characteristic sizes of order
0.01-0.02 pc. The most likely location is ~5 pc from the quasar. The
coordinated line variations in <0.63 yr (rest) are best explained by global
changes in the outflow ionization caused by changes in the quasar's ionizing
flux. The absence of strong X-ray absorption shows that radiative shielding is
not needed to maintain the moderate ionizations and therefore, apparently, it
is not needed to facilitate the radiative acceleration to high speeds. The
kinetic energy yield of this flow is at least two orders of magnitude too low
to be important for feedback to the host galaxy's evolution.Comment: 20 pages. In press with MNRA
Observing trans-Planckian ripples in the primordial power spectrum with future large scale structure probes
We revisit the issue of ripples in the primordial power spectra caused by
trans-Planckian physics, and the potential for their detection by future
cosmological probes. We find that for reasonably large values of the first
slow-roll parameter epsilon (> 0.001), a positive detection of trans-Planckian
ripples can be made even if the amplitude is as low as 10^-4. Data from the
Large Synoptic Survey Telescope (LSST) and the proposed future 21 cm survey
with the Fast Fourier Transform Telescope (FFTT) will be particularly useful in
this regard. If the scale of inflation is close to its present upper bound, a
scale of new physics as high as 0.2 M_Planck could lead to observable
signatures.Comment: 20 pages, 3 figures, uses iopart.cls; v2: 21 pages, added references,
to appear in JCA
Methamphetamine Treatment: A Hermeneutic Study
This hermeneutic study examines and compares the life experiences of three methamphetamine users who have been in chemical dependency treatment for their methamphetamine use. Findings of this researcher indicate that cognitive behavioral practice models have the best results when working with chemical users. There are few chemical dependency treatment programs which address methamphetamine users as needing different treatment approaches than other chemical users. Research indicates that those chemical dependency programs that address the multiple needs of the methamphetamine users and not just their drug use have the best results with helping them maintain long-term recovery from their chemical use. The findings suggest a need for restructuring of traditional chemical dependency programs. The participants identified their need for connection with others and their sense of belonging. Implications for social work practice and policy and for methamphetamine treatment are discussed
Detecting sterile neutrinos with KATRIN like experiments
A sterile neutrino with mass in the eV range, mixing with the electron
antineutrino, is allowed and possibly even preferred by cosmology and
oscillation experiments. If such eV-mass neutrinos exist they provide a much
better target for direct detection in beta decay experiments than the active
neutrinos which are expected to have sub-eV masses. Their relatively high mass
would allow for an easy separation from the primary decay signal in experiments
such as KATRIN.Comment: 23 pages, 7 figures. References & Figures updated. Text reviewed and
revised. Accepted for publication JCA
Towards a Model for the Progenitors of Gamma-Ray Bursts
We consider models for gamma-ray bursts in which a collimated jet expands
either into a homogeneous medium or into a stellar wind environment, and
calculate the expected afterglow temporal behavior. We show that (i) following
a break and a faster decay, afterglows should exhibit a flattening, which may
be detectable in both the radio and optical bands; (ii) Only observations at
times much shorter than a day can clearly distinguish between a fireball
interacting with a homogeneous medium and one interacting with a stellar wind.
Using our results we demonstrate that constraints can be placed on progenitor
models. In particular, existing data imply that while some long duration bursts
may be produced by collapses of massive stars, it is almost certain that not
all long duration bursts are produced by such progenitors.Comment: 13 pages; Submitted to Ap
Web-based Testing of Congenital Amusia with the <i>Montreal Battery of Evaluation of Amusia</i>
Revising the diagnosis of congenital amusia with the Montreal Battery of Evaluation of Amusia
This article presents a critical survey of the prevalent usage of the Montreal Battery of Evaluation of Amusia (MBEA; Peretz et al., 2003) to assess congenital amusia, a neuro-developmental disorder that has been claimed to be present in 4% of the population (Kalmus and Fry, 1980). It reviews and discusses the current usage of the MBEA in relation to cut-off scores, number of used subtests, manner of testing, and employed statistics, as these vary in the literature. Furthermore, data are presented from a large-scale experiment with 228 German undergraduate students who were assessed with the MBEA and a comprehensive questionnaire. This experiment tested the difference between scores that were obtained in a web-based study (at participants’ homes) and those obtained under laboratory conditions with a computerized version of the MBEA. In addition to traditional statistical procedures, the data were evaluated using Signal Detection Theory (SDT; Green and Swets, 1966), taking into consideration the individual’s ability to discriminate and their response bias. Results show that using SDT for scoring instead of proportion correct offers a bias-free and normally distributed measure of discrimination ability. It is also demonstrated that a diagnosis based on an average score leads to cases of misdiagnosis. The prevalence of congenital amusia is shown to depend highly on the statistical criterion that is applied as cut-off score and on the number of subtests that is considered for the diagnosis. In addition, three different subtypes of amusics were found in our sample. Lastly, significant differences between the web-based and the laboratory group were found, giving rise to questions about the validity of web-based experimentation
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