2,665 research outputs found
The Dyer-Roeder distance-redshift relation in inhomogeneous universes
Using Monte-Carlo methods, we determine the best-fit value of the homogeneity
parameter alpha in the Dyer-Roeder distance-redshift relation for a variety of
redshifts, inhomogeneity models and cosmological parameter values. The relation
between alpha and the fraction of compact objects, f_p, is found to be
approximately linear. This relation can be parametrized with reasonable
accuracy for all cases treated in this paper by alpha = a*f_p, where a = 0.6.Comment: 5 pages, 10 figures, submitted to Phys.Rev.
Search for Supersymmetric Dark Matter with Superfluid He3 (MACHe3)
MACHe3 (MAtrix of Cells of superfluid He3) is a project of a new detector for
direct Dark Matter search, using superfluid He3 as a sensitive medium. This
paper presents a phenomenological study done with the DarkSUSY code, in order
to investigate the discovery potential of this project of detector, as well as
its complementarity with existing and planned devices.Comment: 15 pages, 5 figures, submitted to Phys. Letters B, minor changes in
the tex
Two photon annihilation of Kaluza-Klein dark matter
We investigate the fermionic one-loop cross section for the two photon
annihilation of Kaluza-Klein (KK) dark matter particles in a model of universal
extra dimensions (UED). This process gives a nearly mono-energetic gamma-ray
line with energy equal to the KK dark matter particle mass. We find that the
cross section is large enough that if a continuum signature is detected, the
energy distribution of gamma-rays should end at the particle mass with a peak
that is visible for an energy resolution of the detector at the percent level.
This would give an unmistakable signature of a dark matter origin of the
gamma-rays, and a unique determination of the dark matter particle mass, which
in the case studied should be around 800 GeV. Unlike the situation for
supersymmetric models where the two-gamma peak may or may not be visible
depending on parameters, this feature seems to be quite robust in UED models,
and should be similar in other models where annihilation into fermions is not
helicity suppressed. The observability of the signal still depends on largely
unknown astrophysical parameters related to the structure of the dark matter
halo. If the dark matter near the galactic center is adiabatically contracted
by the central star cluster, or if the dark matter halo has substructure
surviving tidal effects, prospects for detection look promising.Comment: 17 pages, 3 figures; slightly revised versio
Managers' and employees' experiences of how managers' wellbeing impacts their leadership behaviours in Swedish small businesses
BACKGROUND: There is a growing interest in managers' wellbeing due to the observed associations between their wellbeing and leadership behaviours, and between leadership behaviours and employees' wellbeing. However, it is still unclear how managers' wellbeing influences their practiced leadership across different workplace contexts, which specific behaviours are affected, and how this varies across time. OBJECTIVE: The purpose of this study was therefore to explore managers' and employees' experiences and perceptions regarding the consequences of managers' wellbeing for their leadership behaviours in small businesses. METHODS: Semi-structured interviews were conducted with 39 participants (20 managers and 19 employees) working at 12 Swedish small firms, and analysed using content analysis. RESULTS: The findings showthat managers were more constructive when they felt well, and more passively destructive when unwell. Variations in managers' wellbeing influenced their mood, energy level, and performance, as well as the company's working climate. However, these destructive leadership variations did not have a substantial impact, because several protective factors were present. CONCLUSION: This study shows that the wellbeing of managers in small businesses has perceptible consequences for their leadership behaviours. The study also shows that sustained leadership behaviours may coexist with temporary variations of these behaviours on a constructive-destructive continuum depending on the leader's wellbeing. Overall, the findings contribute to a more nuanced and dynamic understanding of how the interaction between managers' wellbeing and their behaviours unfolds in the particular context of small companies
The Photovoltaic Crisis and the Demand-side Generation in Spain
The RES-E promotion policy in Spain gave priority to the photovoltaic (henceforth, PV) ground-mounted installations. For years, the coupling of customer-side generation coupled with excess energy exports was never specifically considered. However, some months ago this option was suggested as a way to recover the Spain��s PV sector from the current moratorium on the RES-E policy. A decree draft on on-site generation was issued, its central point being the consideration of electricity exports as delayed consumption rights. But several barriers hinder its entry into force. Unfortunately, Spain could be losing an important opportunity for encouraging PV investments while retail grid parity is being reached. This working paper analyzes the different types of PV demand-side generation from the point of view of consumer-generators and evaluates the economic and technical features of the regulation proposed in Spain and to date still pending
Constraining dark energy
In this paper we propose a mechanism that protects theories violating a
holographic bound suggested in arXiv:1203.5476 from developing accelerated
expansion. The mechanism builts on work on transplanckian physics, and a
non-trivial choice of vacuum states. If correct, it lends further support for
detectable signatures in the CMBR signalling new physics.Comment: 8 pages. arXiv admin note: text overlap with arXiv:astro-ph/0606474.
Minor misprints correcte
A Tentative Gamma-Ray Line from Dark Matter Annihilation at the Fermi Large Area Telescope
The observation of a gamma-ray line in the cosmic-ray fluxes would be a
smoking-gun signature for dark matter annihilation or decay in the Universe. We
present an improved search for such signatures in the data of the Fermi Large
Area Telescope (LAT), concentrating on energies between 20 and 300 GeV. Besides
updating to 43 months of data, we use a new data-driven technique to select
optimized target regions depending on the profile of the Galactic dark matter
halo. In regions close to the Galactic center, we find a 4.6 sigma indication
for a gamma-ray line at 130 GeV. When taking into account the look-elsewhere
effect the significance of the observed excess is 3.2 sigma. If interpreted in
terms of dark matter particles annihilating into a photon pair, the
observations imply a dark matter mass of 129.8\pm2.4^{+7}_{-13} GeV and a
partial annihilation cross-section of = 1.27\pm0.32^{+0.18}_{-0.28}
x 10^-27 cm^3 s^-1 when using the Einasto dark matter profile. The evidence for
the signal is based on about 50 photons; it will take a few years of additional
data to clarify its existence.Comment: 23 pages, 9 figures, 3 tables; extended discussion; matches published
versio
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