1,441 research outputs found
Searching for GeV-scale new Gauge Bosons in QGP thermal dilepton production
In this paper we propose to use the measurement of the thermal Quark-Gluon
Plasma (QGP) dilepton spectra in the Intermediate Mass Region (IMR) of
heavy-ion collisions, as a new method to search for GeV-scale dark gauge bosons
(gamma' or Z'). Such light mediators are a common feature of light (i.e. low
mass) dark matter scenarios, which have been invoked to explain puzzling
signals in dark matter indirect and direct detection experiments. First we show
that a light gamma' or Z' will generate a resonant enhancement of the dilepton
spectrum produced thermally by the QGP, at an energy corresponding to the dark
gauge boson mass. Secondly, using data from the PHENIX experiment, we are able
to set an upper limit on the combined coupling of this new gauge boson to
quarks and leptons (independently of their vectorial or axial nature) chi_q
chi_e < 10^(-3) at the 95% confidence level for a gauge boson mass in the range
1.5 - 2.5 GeV. This result complements previous searches for new light gauge
bosons and probes a new region of the parameter space, particularly interesting
in the case of non-universal couplings to quarks and leptons. Prospects for the
discovery of such a boson by the ALICE collaboration are also discussed.Comment: 11 pages, 4 figure
Perceptual factors that influence use of computer enhanced visual displays
This document is the final report for the NASA/Langley contract entitled 'Perceptual Factors that Influence Use of Computer Enhanced Visual Displays.' The document consists of two parts. The first part contains a discussion of the problem to which the grant was addressed, a brief discussion of work performed under the grant, and several issues suggested for follow-on work. The second part, presented as Appendix I, contains the annual report produced by Dr. Ann Fulop, the Postdoctoral Research Associate who worked on-site in this project. The main focus of this project was to investigate perceptual factors that might affect a pilot's ability to use computer generated information that is projected into the same visual space that contains information about real world objects. For example, computer generated visual information can identify the type of an attacking aircraft, or its likely trajectory. Such computer generated information must not be so bright that it adversely affects a pilot's ability to perceive other potential threats in the same volume of space. Or, perceptual attributes of computer generated and real display components should not contradict each other in ways that lead to problems of accommodation and, thus, distance judgments. The purpose of the research carried out under this contract was to begin to explore the perceptual factors that contribute to effective use of these displays
Shocking Signals of Dark Matter Annihilation
We examine whether charged particles injected by self-annihilating Dark
Matter into regions undergoing Diffuse Shock Acceleration (DSA) can be
accelerated to high energies. We consider three astrophysical sites where shock
acceleration is supposed to occur, namely the Galactic Centre, galaxy clusters
and Active Galactic Nuclei (AGN). For the Milky Way, we find that the
acceleration of cosmic rays injected by dark matter could lead to a bump in the
cosmic ray spectrum provided that the product of the efficiency of the
acceleration mechanism and the concentration of DM particles is high enough.
Among the various acceleration sources that we consider (namely supernova
remnants (SNRs), Fermi bubbles and AGN jets), we find that the Fermi bubbles
are a potentially more efficient accelerator than SNRs. However both could in
principle accelerate electrons and protons injected by dark matter to very high
energies. At the extragalactic level, the acceleration of dark matter
annihilation products could be responsible for enhanced radio emission from
colliding clusters and prediction of an increase of the anti-deuteron flux
generated near AGNs.Comment: 9 pages, 4 figure
Human Factors of Flight-deck Automation: NASA/Industry Workshop
The scope of automation, the benefits of automation, and automation-induced problems were discussed at a workshop held to determine whether those functions previously performed manually on the flight deck of commercial aircraft should always be automated in view of various human factors. Issues which require research for resolution were identified. The research questions developed are presented
The Influence of Social Isolation and Medical Comorbidities on Geriatric Congestive Heart Failure Hospital Readmissions
CONTEXT Social isolation and comorbidities are likely to have a significant level of influence on the healthcare use patterns of geriatric patients with ongoing congestive heart failure (CHF)-related needs. METHODS A retrospective study was conducted in a specialized emergency department (ED) with a sample of 286 geriatric CHF patients who initially received CHF-related care over a six-month period. Social isolation levels were assessed using a pre-existing four-point screening tool used in the study setting and composite comorbidity was gauged using the Charlson Comorbidity Index method. Subjects were categorized into either “less than 30-day readmission” or “greater than 30-day readmission/non-readmitted” sample subgroups. The setting was a single 304-bed community hospital with approximately 45,000 annual ED visits. The analytic sample was comprised of geriatric patients 65+ years of age with an ICD-9 code corresponding to CHF. RESULTS There were no statistically significant differences between earlier hospital readmission versus later/non-readmitted sample patients when grouped by age, race, gender or level of measured social isolation. However, composite comorbidity scores were significantly lower for patients in the \u3e30-day/non-readmitted subgroup compared to earlier readmission patients. CONCLUSIONS These initial study results suggest that a larger proportion of CHF hospital readmissions may be more heavily influenced by clinical factors than social living arrangements. Future studies with larger samples and validated measures of social isolation are needed to inform the development and testing of programs for geriatric CHF patients striving to avoid unnecessary hospital readmissions and adverse health outcomes
Standard and Non-Standard Physics in Neutrino Oscillations
We analyze the impact of recent solar and atmospheric data in the
determination of the neutrino oscillation parameters, taking into account that
both the solar nu_e and the atmospheric nu_mu may convert to a mixture of
active and sterile neutrinos. Furthermore, in the context of the atmospheric
neutrino problem we discuss an extended mechanism of neutrino propagation which
combines both oscillations and non-standard neutrino-matter interactions. We
use the most recent neutrino data, including the 1496-day Super-K solar and
atmospheric data samples, the latest SNO spectral and day/night solar data, and
the final MACRO atmospheric results. We confirm the clear preference of all the
data for pure-active oscillation solutions, bounding the fraction of sterile
neutrino involved in oscillations to be less than 52% in the solar sector and
less than 40% in the atmospheric sector, at 3 sigma. For the atmospheric case
we also derive a bound on the total amount of non-standard neutrino-matter
interactions, bounding the flavor-changing component to -0.03 <= epsilon <=
0.02 and the non-universal component to |epsilon'| <= 0.05.Comment: 6 pages, LaTeX file using espcrc2.sty, 1 table and 3 figures
included. Talk given at the XXX International Meeting on Fundamental Physics
(Jaca, Spain, 28/01-1/02/2002
PAMELA and FERMI-LAT limits on the neutralino-chargino mass degeneracy
Searches for Dark Matter (DM) particles with indirect detection techniques
have reached important milestones with the precise measurements of the
anti-proton and gamma-ray spectra, notably by the PAMELA and FERMI-LAT
experiments. While the gamma-ray results have been used to test the thermal
Dark Matter hypothesis and constrain the Dark Matter annihilation cross section
into Standard Model (SM) particles, the anti-proton flux measured by the PAMELA
experiment remains relatively unexploited. Here we show that the latter can be
used to set a constraint on the neutralino-chargino mass difference. To
illustrate our point we use a Supersymmetric model in which the gauginos are
light, the sfermions are heavy and the Lightest Supersymmetric Particle (LSP)
is the neutralino. In this framework the W^+ W^- production is expected to be
significant, thus leading to large anti-proton and gamma-ray fluxes. After
determining a generic limit on the Dark Matter pair annihilation cross section
into W^+ W^- from the anti-proton data only, we show that one can constrain
scenarios in which the neutralino-chargino mass difference is as large as ~ 20
GeV for a mixed neutralino (and intermediate choices of the anti-proton
propagation scheme). This result is consistent with the limit obtained by using
the FERMI-LAT data. As a result, we can safely rule out the pure wino
neutralino hypothesis if it is lighter than 450 GeV and constitutes all the
Dark Matter.Comment: 22page
Atmospheric Neutrino Oscillations, theta(13) and Neutrino Mass Hierarchy
We derive predictions for the Nadir angle (theta(n)) dependence of the ratio
N(mu)/N(e) of the rates of the mu-like and e-like multi-GeV events measured in
water-Cerenkov detectors in the case of 3-neutrino oscillations of the
atmospheric nu(e) (antinu(e)) and nu(mu) (antinu(mu)), driven by one neutrino
mass squared difference, |Delta m2(31)| ~ (2.5 - 3.0) x 10^(-3) eV^2 >> Delta
m2(21). This ratio is particularly sensitive to the Earth matter effects in the
atmospheric neutrino oscillations, and thus to the values of sin^2(theta(13))
and sin^2(theta(23)), theta(13) and theta(23) being the neutrino mixing angle
limited by the CHOOZ and Palo Verde experiments and that responsible for the
dominant atmospheric nu(mu) -> nu(tau) (antinu(mu) -> antinu(tau))
oscillations. It is also sensitive to the type of neutrino mass spectrum which
can be with normal (Delta m2(31) > 0) or with inverted (Delta m2(31) < 0)
hierarchy. We show that for sin^2(theta(13)) > 0.01, sin^2(theta(23)) > 0.5 and
at cos(theta(n)) > 0.4, the Earth matter effects modify substantially the
theta(n)-dependence of the ratio N(mu)/N(e) and in a way which cannot be
reproduced with sin^2(theta(13)) = 0 and a different value of sin^2(theta(23)).
For normal hierarchy the effects can be as large as ~ 25% for cos(theta(n)) ~
(0.5 - 0.8), can reach ~ 35% in the Earth core bin cos(theta(n)) ~ (0.84 -
1.0), and might be observable. They are typically by ~ 10% smaller in the
inverted hierarchy case. An observation of the Earth matter effects in the
Nadir angle distribution of the ratio N(mu)/N(e) would clearly indicate that
sin^2(theta(13)) > 0.01 and sin^2(theta(23)) > 0.50.Comment: 22 p
On the Neutrino Mass Spectrum and Neutrinoless Double-Beta Decay
Assuming 3-nu mixing, neutrino oscillation explanation of the solar and
atmospheric neutrino data and of the first KamLAND results, massive Majorana
neutrinos and neutrinoless double-beta decay generated only by the (V-A)
charged current weak interaction via the exchange of the three Majorana
neutrinos, we analyze in detail the possibility of determining the type of the
neutrino mass spectrum by measuring of the effective Majorana mass || in
neutrinoless double-beta decay. The three possible types of neutrino mass
spectrum are considered: i) normal hierarchical (NH), m1 << m2 << m3, ii)
inverted hierarchical (IH), m1 << m2 \simeq m3, and iii) quasi-degenerate (QD),
m1 \simeq m2 \simeq m3 \geq 0.20 eV. The uncertainty in the measured value of
|| due to the imprecise knowledge of the relevant nuclear matrix elements is
taken into account in the analysis. We derive the ranges of values of tan^2
theta_\odot, theta_\odot being the mixing angle which controls the solar
neutrino oscillations, and of the nuclear matrix element uncertainty factor,
for which the measurement of || would allow one to discriminate between the
NH and IH, NH and QD and IH and QD spectra.Comment: 18 pages, 2 figures; the text includes 3 tables; results and
conclusions unchanged, the KamLAND data taken into account, correspondingly
references changed, text shortened; version submitted for publicatio
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