2,820 research outputs found
Cosmological implications of an evolutionary quantum gravity
The cosmological implications of an evolutionary quantum gravity are analyzed
in the context of a generic inhomogeneous model. The Schr\"{o}dinger problem is
formulated and solved in the presence of a scalar field, an ultrarelativistic
matter and a perfect gas regarded as the dust-clock. Considering the actual
phenomenology, it is shown how the evolutionary approach overlaps the
Wheeler-DeWitt one.Comment: 4 pages; to appear in the proceedings of the II Stueckelberg
Workshop, Int.J.Mod.Phys.A, references adde
Quantum Dynamics of the Taub Universe in a Generalized Uncertainty Principle framework
The implications of a Generalized Uncertainty Principle on the Taub
cosmological model are investigated. The model is studied in the ADM reduction
of the dynamics and therefore a time variable is ruled out. Such a variable is
quantized in a canonical way and the only physical degree of freedom of the
system (related to the Universe anisotropy) is quantized by means of a modified
Heisenberg algebra. The analysis is performed at both classical and quantum
level. In particular, at quantum level, the motion of wave packets is
investigated. The two main results obtained are as follows. i) The classical
singularity is probabilistically suppressed. The Universe exhibits a stationary
behavior and the probability amplitude is peaked in a determinate region. ii)
The GUP wave packets provide the right behavior in the establishment of a
quasi-isotropic configuration for the Universe.Comment: 10 pages, 4 figures; v2: section added, to appear on PR
Modification of Heisenberg uncertainty relations in non-commutative Snyder space-time geometry
We show that the Euclidean Snyder non-commutative space implies infinitely
many different physical predictions. The distinct frameworks are specified by
generalized uncertainty relations underlying deformed Heisenberg algebras.
Considering the one-dimensional case in the minisuperspace arena, the bouncing
Universe dynamics of loop quantum cosmology can be recovered.Comment: 5 pages; title changed, to appear in PR
High performance astrophysics computing
The application of high end computing to astrophysical problems, mainly in
the galactic environment, is under development since many years at the Dep. of
Physics of Sapienza Univ. of Roma. The main scientific topic is the physics of
self gravitating systems, whose specific subtopics are: i) celestial mechanics
and interplanetary probe transfers in the solar system; ii) dynamics of
globular clusters and of globular cluster systems in their parent galaxies;
iii) nuclear clusters formation and evolution; iv) massive black hole formation
and evolution; v) young star cluster early evolution. In this poster we
describe the software and hardware computational resources available in our
group and how we are developing both software and hardware to reach the
scientific aims above itemized.Comment: 2 pages paper presented at the Conference "Advances in Computational
Astrophysics: methods, tools and outcomes", to be published in the ASP
Conference Series, 2012, vol. 453, R. Capuzzo-Dolcetta, M. Limongi and A.
Tornambe' ed
Probing the formation history of the nuclear star cluster at the Galactic Centre with millisecond pulsars
The origin of the Nuclear Star Cluster in the centre of our Galaxy is still
unknown. One possibility is that it formed after the disruption of stellar
clusters that spiralled into the Galactic Centre due to dynamical friction. We
trace the formation of the Nuclear Star Cluster around the central black hole,
using state-of-the-art N-body simulations, and follow the dynamics of the
neutron stars born in the clusters. We then estimate the number of Millisecond
Pulsars (MSPs) that are released in the Nuclear Star Cluster, during its
formation. The assembly and tidal dismemberment of globular clusters lead to a
population of MSPs distributed over a radius of about 20 pc, with a peak near 3
pc. No clustering is found on the sub-parsec scale. We simulate the
detectability of this population with future radio telescopes like the MeerKAT
radio telescope and SKA1, and find that about of order ten MSPs can be observed
over this large volume, with a paucity of MSPs within the central parsec. This
helps discriminating this scenario from the in-situ formation model for the
Nuclear Star Cluster that would predict an over abundance of MSPs closer to the
black hole. We then discuss the potential contribution of our MSP population to
the gamma-ray excess at the Galactic Centre.Comment: 11 pages, 8 figures, accepted for publication in MNRA
Deciding the Criteria Is Not Enough: Moral Issues to Consider for a Fair Allocation of Scarce ICU Resources
During the first wave of the COVID-19 pandemic in Italy, practitioners had to make tragic decisions regarding the allocation of scarce resources in the ICU. The Italian debate has paid a lot of attention to identifying the specific regulatory criteria for the allocation of resources in the ICU; in this paper, however, we argue that deciding such criteria is not enough for the implementation of fair and transparent allocative decisions. In this respect, we discuss three ethical issues: (a) in the Italian context, the treating physician, rather than a separate committee, was generally the one responsible for the allocation decision; (b) although many allocative guidelines have supported moral equivalence between withholding and withdrawing treatments, some health professionals have continued to consider it a morally problematic aspect; and (c) the health workers who have had to make the aforementioned decisions or even only worked in ICU during the pandemic often experienced moral distress. We conclude by arguing that, even if these problems are not directly related to the above-mentioned issues of distributive justice, they can nevertheless directly affect the quality and ethics of the implementation of allocative criteria, regardless of those chosen
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