6,666 research outputs found
The meaning of S-D dominance
The dominance of S and D pairs in the description of deformed nuclei is one
of the facts that provided sustain to the Interacting Boson Approximation. In
Ref.(J. Dukelsky and S. Pittel, Phys. Rev. Lett. 86, 4791, 2001.), using an
exactly solvable model with a repulsive pairing interaction between bosons it
has been shown that the ground state is described almost completely in terms of
S and D bosons. In the present paper we study the excited states obtained
within this exactly solvable hamiltonian and show that in order to obtain a
rotational spectra all the other degrees of freedom are needed.Comment: Are S and D pairs enough to describe deformed nuclei
Accurate calculations of the WIMP halo around the Sun and prospects for its gamma-ray detection
Galactic weakly interacting massive particles (WIMPs) may scatter off solar
nuclei to orbits gravitationally bound to the Sun. Once bound, the WIMPs
continue to lose energy by repeated scatters in the Sun, eventually leading to
complete entrapment in the solar interior. While the density of the bound
population is highest at the center of the Sun, the only observable signature
of WIMP annihilations inside the Sun is neutrinos. It has been previously
suggested that although the density of WIMPs just outside the Sun is lower than
deep inside, gamma rays from WIMP annihilation just outside the surface of the
Sun, in the so called WIMP halo around the Sun, may be more easily detected. We
here revisit this problem using detailed Monte Carlo simulations and detailed
composition and structure information about the Sun to estimate the size of the
gamma-ray flux. Compared to earlier simpler estimates, we find that the
gamma-ray flux from WIMP annihilations in the solar WIMP halo would be
negligible; no current or planned detectors would be able to detect this flux.Comment: 18 pages, 7 figures, latex, updated to match published version
Variation of the Diameter of the Sun as Measured by the Solar Disk Sextant (SDS)
The balloon-borne Solar Disk Sextant (SDS) experiment has measured the
angular size of the Sun on seven occasions spanning the years 1992 to 2011. The
solar half-diameter -- observed in a 100-nm wide passband centred at 615 nm --
is found to vary over that period by up to 200 mas, while the typical estimated
uncertainty of each measure is 20 mas. The diameter variation is not in phase
with the solar activity cycle; thus, the measured diameter variation cannot be
explained as an observational artefact of surface activity. Other possible
instrument-related explanations for the observed variation are considered but
found unlikely, leading us to conclude that the variation is real. The SDS is
described here in detail, as is the complete analysis procedure necessary to
calibrate the instrument and allow comparison of diameter measures across
decades.Comment: 41 pages; appendix and 2 figures added plus some changes in text
based on referee's comments; to appear in MNRA
Debranding in Fantasy Realms: Perceived Marketing Opportunities within the Virtual World
This paper discusses the application of the concept of debranding within immersive virtual environments. In particular the issue of the media richness and vividness of experience is considered in these experience realms that may not be conducive to traditional branding invasive strategies. Brand equity is generally seen to be the desired outcome of branding strategies and the authors suggest that unless the virtual domains are considered as sacred spaces then brand equity may be compromised. The application of the above concepts is applied to the differing social spaces that operate within the different experience realms. The ideas of resonance, presence and interactivity are considered here. They lead to the development of a constructed positioning by the participants. Through the process of debranding, marketers may be able to enter these sacred spaces without negative impact to the brand. Perception of these virtual spaces was found to be partially congruent with this approach to branding. It thus presents a number of challenges for the owners of such virtual spaces and also virtual worlds in increasing the commercial utilization of investment in these environments
Event generator to construct cross sections for the multiphonon excitation of a set of collective vibrational modes
The construction of differential cross sections as a function of excitation
energy for systems with a collection of low- and high-lying intrinsic
vibrational modes has been attempted in the past. A prescription is proposed
that simplifies the implementation of such calculation schemes with a
remarkable reduction in computational time.Comment: 6 pages, 3 figures, to be published in Phys. Rev.
Gamma rays from ultracompact primordial dark matter minihalos
Ultracompact minihalos have recently been proposed as a new class of dark
matter structure. These minihalos would be produced by phase transitions in the
early Universe or features in the inflaton potential, and constitute
non-baryonic massive compact halo objects (MACHOs) today. We examine the
prospect of detecting ultracompact minihalos in gamma-rays if dark matter
consists of self-annihilating particles. We compute present-day fluxes from
minihalos produced in the electron-positron annihilation epoch, and the QCD and
electroweak phase transitions in the early Universe. Even at a distance of 100
pc, minihalos produced during the electron-positron annihilation epoch should
be eminently detectable today, either by the Fermi satellite, current Air
Cherenkov telescopes, or even in archival EGRET data. Within ~1 pc, minihalos
formed in the QCD phase transition would have similar predicted fluxes to the
dwarf spheroidal galaxies targeted by current indirect dark matter searches, so
might also be detectable by present or upcoming experiments.Comment: 5 pages, 3 figures. Minor update to match published version of
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