|
|
Aguiar, P., Rafecas, M., Ortuño, J. E., Kontaxakis, G., Santos, A., Pavia, J., et al. (2010). Geometrical and Monte Carlo projectors in 3D PET reconstruction. Med. Phys., 37(11), 5691–5702.
Abstract: Purpose: In the present work, the authors compare geometrical and Monte Carlo projectors in detail. The geometrical projectors considered were the conventional geometrical Siddon ray-tracer (S-RT) and the orthogonal distance-based ray-tracer (OD-RT), based on computing the orthogonal distance from the center of image voxel to the line-of-response. A comparison of these geometrical projectors was performed using different point spread function (PSF) models. The Monte Carlo-based method under consideration involves an extensive model of the system response matrix based on Monte Carlo simulations and is computed off-line and stored on disk. Methods: Comparisons were performed using simulated and experimental data of the commercial small animal PET scanner rPET. Results: The results demonstrate that the orthogonal distance-based ray-tracer and Siddon ray-tracer using PSF image-space convolutions yield better images in terms of contrast and spatial resolution than those obtained after using the conventional method and the multiray-based S-RT. Furthermore, the Monte Carlo-based method yields slight improvements in terms of contrast and spatial resolution with respect to these geometrical projectors. Conclusions: The orthogonal distance-based ray-tracer and Siddon ray-tracer using PSF image-space convolutions represent satisfactory alternatives to factorizing the system matrix or to the conventional on-the-fly ray-tracing methods for list-mode reconstruction, where an extensive modeling based on Monte Carlo simulations is unfeasible.
|
|
|
|
Fileviez Perez, P., Iminniyaz, H., Rodrigo, G., & Spinner, S. (2010). Gauge mediated supersymmetry breaking via seesaw mechanisms. Phys. Rev. D, 81(9), 095013–12pp.
Abstract: We present a simple scenario for gauge mediated supersymmetry breaking (GMSB) where the messengers are also the fields that generate neutrino masses. We show that the simplest such scenario corresponds to the case where neutrino masses are generated through the type I and type III seesaw mechanisms. The entire supersymmetric spectrum and Higgs masses are calculable from only four input parameters. Since the electroweak symmetry is broken through a doubly radiative mechanism, meaning a nearly zero B term at the messenger scale which runs down to acceptable values, one obtains quite a constrained spectrum for the supersymmetric particles whose properties we describe. We refer to this mechanism as "nu GMSB.''
|
|
|
|
Choi, K. Y., Lopez-Fogliani, D. E., Muñoz, C., & Ruiz de Austri, R. (2010). Gamma-ray detection from gravitino dark matter decay in the μnu SSM. J. Cosmol. Astropart. Phys., 03(3), 028–14pp.
Abstract: The μnu SSM provides a solution to the mu-problem of the MSSM and explains the origin of neutrino masses by simply using right-handed neutrino superfields. Given that R-parity is broken in this model, the gravitino is a natural candidate for dark matter since its lifetime becomes much longer than the age of the Universe. We consider the implications of gravitino dark matter in the μnu SSM, analyzing in particular the prospects for detecting gamma rays from decaying gravitinos. If the gravitino explains the whole dark matter component, a gravitino mass larger than 20 GeV is disfavored by the isotropic diffuse photon background measurements. On the other hand, a gravitino with a mass range between 0.1 – 20 GeV gives rise to a signal that might be observed by the FERMI satellite. In this way important regions of the parameter space of the μnu SSM can be checked.
|
|
|
|
Martinelli, M., Lopez Honorez, L., Melchiorri, A., & Mena, O. (2010). Future CMB cosmological constraints in a dark coupled universe. Phys. Rev. D, 81(10), 103534–7pp.
Abstract: Cosmic microwave background satellite missions as the ongoing Planck experiment are expected to provide the strongest constraints on a wide set of cosmological parameters. Those constraints, however, could be weakened when the assumption of a cosmological constant as the dark energy component is removed. Here we show that it will indeed be the case when there exists a coupling among the dark energy and the dark matter fluids. In particular, the expected errors on key parameters as the cold dark matter density and the angular diameter distance at decoupling are significantly larger when a dark coupling is introduced. We show that it will be the case also for future satellite missions as EPIC, unless CMB lensing extraction is performed.
|
|
|
|
Yamagata-Sekihara, J., Cabrera, D., Vicente Vacas, M. J., & Hirenzaki, S. (2010). Formation of phi Mesic Nuclei. Prog. Theor. Phys., 124(1), 147–162.
Abstract: We consider the structure and formation of the phi mesic nuclei to investigate the experimental feasibility of the observation of signals of the phi mesic nucleus formation. phi mesic nuclei are considered to be very important objects to study the in-medium modification of the phi-meson spectral function at finite density. We consider ((p) over bar, phi), (gamma, p) and (pi(-), n) reactions to produce a phi-meson inside the nucleus and evaluate the effects of its medium modifications to the reaction cross sections. We also estimate the consequences of the uncertainties of the in-medium (K) over bar self-energy to the phi-nucleus interaction. We find that it may be possible to see peak structures in the reaction spectra for the strong attractive potential cases. On the other hand, for strong absorptive interaction cases with relatively weak attraction, it is very difficult to observe clear peaks and we may need to know the spectrum shape in a wide energy region to deduce the properties of phi.
|
|
