10,209 research outputs found
Quantum motion with trajectories: beyond the Gaussian beam approximation
A quantum model based on a Euler-Lagrange variational approach is proposed.
In analogy with the classical transport, our approach maintain the description
of the particle motion in terms of trajectories in a configuration space. Our
method is designed to describe correction to the motion of nearly localized
particles due to quantum phenomena. We focus on the simulation of the motion of
light nuclei in ab initio calculations. Similarly to the Gaussian beam method,
our approach is based on a ansatz for the particle wave function. We discuss
the completeness of our ansatz and the connection of our results with the Bohm
trajectories approach
Stochastic model for quantum spin dynamics in magnetic nanostructures
We develop a numerical model that reproduces the thermal equilibrium and the
spin transfer mechanisms in magnetic nanomaterials. We analyze the coherent
two-particle spin exchange interaction and the electron-electron collisions.
Our study is based on a quantum atomistic approach and the particle dynamics is
performed by using a Monte Carlo technique. The coherent quantum evolution of
the atoms is interrupted by instantaneous collisions with itinerant electrons.
The collision processes are associated to the quantum collapse of the local
atomic wave function. We show that particle-particle interactions beyond the
molecular field approximation can be included in this framework. Our model is
able to reproduce the thermal equilibrium and strongly out-of-equilibrium
phenomena such as the ultrafast dynamics of the magnetization in nanomatrials
Wigner model for quantum transport in graphene
The single graphene layer is a novel material consisting of a flat monolayer
of carbon atoms packed in a two-dimensional honeycomb-lattice, in which the
electron dynamics is governed by the Dirac equation. A pseudo-spin phase-space
approach based on the Wigner-Weyl formalism is used to describe the transport
of electrons in graphene including quantum effects. Our full-quantum mechanical
representation of the particles reveals itself to be particularly close to the
classical description of the particle motion. We analyze the Klein tunneling
and the correction to the total current in graphene induced by this phenomenon.
The equations of motion are analytically investigated and some numerical tests
are presented. The temporal evolution of the electron-hole pairs in the
presence of an external electric field and a rigid potential step is
investigated. The connection of our formalism with the Barry-phase approach is
also discussed
Are observations of the galaxy cluster Abell 1689 consistent with a neutrino dark matter scenario?
Recent weak and strong lensing data of the galaxy cluster A1689 are modelled
by dark fermions that are quantum degenerate within some core. The gas density,
deduced from X-ray observations up to 1 Mpc and obeying a cored power law, is
taken as input, while the galaxy mass density is modelled. An additional dark
matter tail may arise from cold or warm dark matter, axions or non-degenerate
neutrinos. The fit yields that the fermions are degenerate within a 430 kpc
radius. The fermion mass is a few eV and the best case involves 3 active plus 3
sterile neutrinos of equal mass, for which we deduce eV. The eV
mass range will be tested in the KATRIN experiment.Comment: 5 pages latex, 5 figures. Accepted for MNRAS Letter
Prediction for the neutrino mass in the KATRIN experiment from lensing by the galaxy cluster A1689
The KATRIN experiment in Karlsruhe Germany will monitor the decay of tritium,
which produces an electron-antineutrino. While the present upper bound for its
mass is 2 eV/, KATRIN will search down to 0.2 eV. If the dark matter
of the galaxy cluster Abell 1689 is modeled as degenerate isothermal fermions,
the strong and weak lensing data may be explained by degenerate neutrinos with
mass of 1.5 eV. Strong lensing data beyond 275 kpc put tension on the
standard cold dark matter interpretation. In the most natural scenario, the
electron antineutrino will have a mass of 1.5 eV/, a value that will be
tested in KATRIN.Comment: 13 pages, 5 figure
From the Equations of Motion to the Canonical Commutation Relations
The problem of whether or not the equations of motion of a quantum system
determine the commutation relations was posed by E.P.Wigner in 1950. A similar
problem (known as "The Inverse Problem in the Calculus of Variations") was
posed in a classical setting as back as in 1887 by H.Helmoltz and has received
great attention also in recent times. The aim of this paper is to discuss how
these two apparently unrelated problems can actually be discussed in a somewhat
unified framework. After reviewing briefly the Inverse Problem and the
existence of alternative structures for classical systems, we discuss the
geometric structures that are intrinsically present in Quantum Mechanics,
starting from finite-level systems and then moving to a more general setting by
using the Weyl-Wigner approach, showing how this approach can accomodate in an
almost natural way the existence of alternative structures in Quantum Mechanics
as well.Comment: 199 pages; to be published in "La Rivista del Nuovo Cimento"
(www.sif.it/SIF/en/portal/journals
X-ray and Sunyaev-Zel'dovich scaling relations in galaxy clusters
[Abridged] We present an analysis of the scaling relations between X-ray
properties and Sunyaev-Zel'dovich (SZ) parameters for a sample of 24 X-ray
luminous galaxy clusters observed with Chandra and with measured SZ effect.
These objects are in the redshift range 0.14--0.82 and have X-ray bolometric
luminosity L>10^45 erg/s. We perform a spatially resolved spectral analysis and
recover the density, temperature and pressure profiles of the ICM, just relying
on the spherical symmetry of the cluster and the hydrostatic equilibrium
hypothesis. We observe that the correlations among X-ray quantities only are in
agreement with previous results obtained for samples of high-z X-ray luminous
galaxy clusters. On the relations involving SZ quantities, we obtain that they
correlate with the gas temperature with a logarithmic slope significantly
larger than the predicted value from the self-similar model. The measured
scatter indicates, however, that the central Compton parameter y_0 is a proxy
of the gas temperature at the same level of other X-ray quantities like
luminosity. Our results on the X-ray and SZ scaling relations show a tension
between the quantities more related to the global energy of the system (e.g.
gas temperature, gravitating mass) and the indicators of the structure of the
ICM (e.g. gas density profile, central Compton parameter y_0), showing the most
significant deviations from the values of the slope predicted from the
self-similar model in the L-T, L-M_{tot}, M_{gas}-T, y_0-T relations. When the
slope is fixed to the self-similar value, these relations consistently show a
negative evolution suggesting a scenario in which the ICM at higher redshift
has lower both X-ray luminosity and pressure in the central regions than the
expectations from self-similar model.Comment: MNRAS in press - Minor revision to match published versio
- …