8,509 research outputs found
Correlations and realistic interactions in doubly closed shell nuclei
We review the latest variational calculations of the ground state properties
of doubly closed shell nuclei, from C to Pb, with semirealistic
and realistic two- and three-nucleon interactions. The studies are carried on
within the framework of the correlated basis function theory and integral
equations technique, with state dependent correlations having central and
tensor components. We report results for the ground state energy, one- and
two-body densities and static structure functions. For O and Ca
we use modern interactions and find that the accuracy of the method is
comparable to that attained in nuclear matter with similar hamiltonians, giving
nuclei underbound by 2 MeV/A. The computed Coulomb sums are in complete
agreement with the latest analysis of the experimental data.Comment: 11 Latex pages, 2 ps figures. Talk delivered at the 10th
International Conference on Recent Progress In Many-Body Theories, Seattle
1999. To appear in "Advances in Quantum Many-Body Theory", vol.3, World
Scientifi
Estimating the tolerance of species to the effects of global environmental change
Global environmental change is affecting species distribution and their
interactions with other species. In particular, the main drivers of
environmental change strongly affect the strength of interspecific interactions
with considerable consequences to biodiversity. However, extrapolating the
effects observed on pair-wise interactions to entire ecological networks is
challenging. Here we propose a framework to estimate the tolerance to changes
in the strength of mutualistic interaction that species in mutualistic networks
can sustain before becoming extinct. We identify the scenarios where generalist
species can be the least tolerant. We show that the least tolerant species
across different scenarios do not appear to have uniquely common
characteristics. Species tolerance is extremely sensitive to the direction of
change in the strength of mutualistic interaction, as well as to the observed
mutualistic trade-offs between the number of partners and the strength of the
interactions.Comment: Nature Communications 4, Article number: 2350, (2013
Extremal Hairy Black Holes
We consider a gravitating system consisting of a scalar field minimally
coupled to gravity with a self-interacting potential and an U(1)
electromagnetic field. Solving the coupled Einstein-Maxwell-scalar system we
find exact hairy charged black hole solutions with the scalar field regular
everywhere. We go to the zero temperature limit and we study the effect of the
scalar field on the near horizon geometry of an extremal black hole. We find
that except a critical value of the charge of the black hole there is also a
critical value of the charge of the scalar field beyond of which the extremal
black hole is destabilized. We study the thermodynamics of these solutions and
we find that if the space is flat then at low temperature the
Reissner-Nordstr\"om black hole is thermodynamically preferred, while if the
space is AdS the hairy charged black hole is thermodynamically preferred at low
temperature.Comment: 17 pages. Match with the journal version accepted by JHEP. arXiv
admin note: substantial text overlap with arXiv:1309.216
Hawking radiation and propagation of massive charged scalar field on a three-dimensional G\"{o}del black hole
In this paper we consider the three-dimensional G\"{o}del black hole as a
background and we study the vector particle tunneling from this background in
order to obtain the Hawking temperature. Then, we study the propagation of a
massive charged scalar field and we find the quasinormal modes analytically,
which turns out be unstable as a consequence of the existence of closed
time-like curves. Also, we consider the flux at the horizon and at infinity,
and we compute the reflection and transmission coefficients as well as the
absorption cross section. Mainly, we show that massive charged scalar waves can
be superradiantly amplified by the three-dimensional G\"{o}del black hole and
that the coefficients have an oscillatory behavior. Moreover, the absorption
cross section is null at the high frequency limit and for certain values of the
frequency.Comment: 18 pages, 12 figures. Accepted for publication in General Relativity
and Gravitatio
How structurally stable are global socioeconomic systems?
The stability analysis of socioeconomic systems has been centered on
answering whether small perturbations when a system is in a given quantitative
state will push the system permanently to a different quantitative state.
However, typically the quantitative state of socioeconomic systems is subject
to constant change. Therefore, a key stability question that has been
under-investigated is how strong the conditions of a system itself can change
before the system moves to a qualitatively different behavior, i.e., how
structurally stable the systems is. Here, we introduce a framework to
investigate the structural stability of socioeconomic systems formed by the
network of interactions among agents competing for resources. We measure the
structural stability of the system as the range of conditions in the
distribution and availability of resources compatible with the qualitative
behavior in which all the constituent agents can be self-sustained across time.
To illustrate our framework, we study an empirical representation of the global
socioeconomic system formed by countries sharing and competing for
multinational companies used as proxy for resources. We demonstrate that the
structural stability of the system is inversely associated with the level of
competition and the level of heterogeneity in the distribution of resources.
Importantly, we show that the qualitative behavior of the observed global
socioeconomic system is highly sensitive to changes in the distribution of
resources. We believe this work provides a methodological basis to develop
sustainable strategies for socioeconomic systems subject to constantly changing
conditions
Strong flavour changing effective operator contributions to single top quark production
We study the effects of dimension six effective operators on the production
of single top quarks at the LHC. The operator set considered includes terms
with effective gluon interactions and four-fermion terms. Analytic expressions
for the several partonic cross sections of single top production will be
presented, as well as the results of their integration on the parton density
functions.Comment: 20 pages, 7 fig
Motion and collision of particles near DST Black holes
We consider Deser-Sarioglu-Tekin (DST) black holes as background and we study
such the motion of massive particles as the collision of two spinning particles
in the vicinity of its horizon. New kinds of orbits are allowed for small
deviations of General Relativity, but the behavior of the collision is similar
to the one observed for General Relativity. Some observables like bending of
light and the perihelion precession are analyzed.Comment: 21 pages and 10 figures. New versio
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