685 research outputs found
Does magnetic pressure affect the ICM dynamics?
A possible discrepancy found in the determination of mass from gravitational
lensing data, and from X-rays observations, has been largely discussed in the
latest years (for instance, Miralda-Escude & Babul (1995)). Another important
discrepancy related to these data is that the dark matter is more centrally
condensed than the X-ray-emitting gas, and also with respect to the galaxy
distribution (Eyles et al. 1991). Could these discrepancies be consequence of
the standard description of the ICM, in which it is assumed hydrostatic
equilibrium maintained by thermal pressure? We follow the evolution of the ICM,
considering a term of magnetic pressure, aiming at answering the question
whether or not these discrepancies can be explained via non-thermal terms of
pressure. Our results suggest that the magnetic pressure could only affect the
dynamics of the ICM on scales as small as < 1kpc. Our models are constrained by
the observations of large and small scale fields and we are successful at
reproducing available data, for both Faraday rotation limits and inverse
Compton limits for the magnetic fields. In our calculations the radius (from
the cluster center) in which magnetic pressure reaches equipartition is smaller
than radii derived in previous works, as a consequence of the more realistic
treatment of the magnetic field geometry and the consideration of a sink term
in the cooling flow.Comment: 8 pages with 7 figures included. MNRAS accepted. Minor changes in the
section of discussions and conclusions. Also available at
http://www.iac.es/publicaciones/preprints.htm
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Responding to Vaccine Safety Signals during Pandemic Influenza: A Modeling Study
Background: Managing emerging vaccine safety signals during an influenza pandemic is challenging. Federal regulators must balance vaccine risks against benefits while maintaining public confidence in the public health system. Methods: We developed a multi-criteria decision analysis model to explore regulatory decision-making in the context of emerging vaccine safety signals during a pandemic. We simulated vaccine safety surveillance system capabilities and used an age-structured compartmental model to develop potential pandemic scenarios. We used an expert-derived multi-attribute utility function to evaluate potential regulatory responses by combining four outcome measures into a single measure of interest: 1) expected vaccination benefit from averted influenza; 2) expected vaccination risk from vaccine-associated febrile seizures; 3) expected vaccination risk from vaccine-associated Guillain-Barre Syndrome; and 4) expected change in vaccine-seeking behavior in future influenza seasons. Results: Over multiple scenarios, risk communication, with or without suspension of vaccination of high-risk persons, were the consistently preferred regulatory responses over no action or general suspension when safety signals were detected during a pandemic influenza. On average, the expert panel valued near-term vaccine-related outcomes relative to long-term projected outcomes by 3∶1. However, when decision-makers had minimal ability to influence near-term outcomes, the response was selected primarily by projected impacts on future vaccine-seeking behavior. Conclusions: The selected regulatory response depends on how quickly a vaccine safety signal is identified relative to the peak of the pandemic and the initiation of vaccination. Our analysis suggested two areas for future investment: efforts to improve the size and timeliness of the surveillance system and behavioral research to understand changes in vaccine-seeking behavior
Cosmological implications of the KATRIN experiment
The upcoming Karlsruhe Tritium Neutrino (KATRIN) experiment will put
unprecedented constraints on the absolute mass of the electron neutrino,
\mnue. In this paper we investigate how this information on \mnue will
affect our constraints on cosmological parameters. We consider two scenarios;
one where \mnue=0 (i.e., no detection by KATRIN), and one where
\mnue=0.3eV. We find that the constraints on \mnue from KATRIN will affect
estimates of some important cosmological parameters significantly. For example,
the significance of and the inferred value of depend
on the results from the KATRIN experiment.Comment: 13 page
Fluid phonons and inflaton quanta at the protoinflationary transition
Quantum and thermal fluctuations of an irrotational fluid are studied across
the transition regime connecting a protoinflationary phase of decelerated
expansion to an accelerated epoch driven by a single inflaton field. The
protoinflationary inhomogeneities are suppressed when the transition to the
slow roll phase occurs sharply over space-like hypersurfaces of constant energy
density. If the transition is delayed, the interaction of the quasi-normal
modes related, asymptotically, to fluid phonons and inflaton quanta leads to an
enhancement of curvature perturbations. It is shown that the dynamics of the
fluctuations across the protoinflationary boundaries is determined by the
monotonicity properties of the pump fields controlling the energy transfer
between the background geometry and the quasi-normal modes of the fluctuations.
After corroborating the analytical arguments with explicit numerical examples,
general lessons are drawn on the classification of the protoinflationary
transition.Comment: 30 pages, 3 figure
The Physics of Cluster Mergers
Clusters of galaxies generally form by the gravitational merger of smaller
clusters and groups. Major cluster mergers are the most energetic events in the
Universe since the Big Bang. Some of the basic physical properties of mergers
will be discussed, with an emphasis on simple analytic arguments rather than
numerical simulations. Semi-analytic estimates of merger rates are reviewed,
and a simple treatment of the kinematics of binary mergers is given. Mergers
drive shocks into the intracluster medium, and these shocks heat the gas and
should also accelerate nonthermal relativistic particles. X-ray observations of
shocks can be used to determine the geometry and kinematics of the merger. Many
clusters contain cooling flow cores; the hydrodynamical interactions of these
cores with the hotter, less dense gas during mergers are discussed. As a result
of particle acceleration in shocks, clusters of galaxies should contain very
large populations of relativistic electrons and ions. Electrons with Lorentz
factors gamma~300 (energies E = gamma m_e c^2 ~ 150 MeV) are expected to be
particularly common. Observations and models for the radio, extreme
ultraviolet, hard X-ray, and gamma-ray emission from nonthermal particles
accelerated in these mergers are described.Comment: 38 pages with 9 embedded Postscript figures. To appear in Merging
Processes in Clusters of Galaxies, edited by L. Feretti, I. M. Gioia, and G.
Giovannini (Dordrecht: Kluwer), in press (2001
Some doubts on the validity of the foreground Galactic contribution subtraction from microwave anisotropies
The Galactic foreground contamination in CMBR anisotropies, especially from
the dust component, is not easily separable from the cosmological or
extragalactic component. In this paper, some doubts will be raised concerning
the validity of the methods used to date to remove Galactic dust emission in
order to show that none of them achieves its goal.
First, I review the recent bibliography on the topic and discuss critically
the methods of foreground subtraction: the cross-correlation with templates,
analysis assuming the spectral shape of the Galactic components, the "maximum
entropy method", "internal linear combination", and "wavelet-based high
resolution fitting of internal templates". Second, I analyse the galactic
latitude dependence from WMAP data. The frequency dependence is discussed with
the data in the available literature. The result is that all methods of
subtracting the Galactic contamination are inaccurate. The galactic latitude
dependence analysis or the frequency dependence of the anisotropies in the
range 50-250 GHz put a constraint on the maximum Galactic contribution in the
power spectrum to be less than a ~10% (68% C. L.) for a ~1 degree scale, and
possibly higher for larger scales.
The origin of most of the signal in the CMBR anisotropies is not Galactic. In
any case, the subtraction of the Galaxy is not accurate enough to allow a
"precision Cosmology"; other sources of contamination (extragalactic, solar
system) are also present.Comment: 24 pages, 1 figure, accepted to be published in J. Astrophys. Ast
Time Uncertainty in Quantum Gravitational Systems
It is generally argued that the combined effect of Heisenberg principle and
general relativity leads to a minimum time uncertainty. Most of the analyses
supporting this conclusion are based on a perturbative approach to
quantization. We consider a simple family of gravitational models, including
the Einstein-Rosen waves, in which the (non-linearized) inclusion of gravity
changes the normalization of time translations by a monotonic energy-dependent
factor. In these circumstances, it is shown that a maximum time resolution
emerges non-perturbatively only if the total energy is bounded. Perturbatively,
however, there always exists a minimum uncertainty in the physical time.Comment: (4 pages, no figures) Accepted for publication in Physical Review
Fermion-scalar interactions with domain wall fermions
Domain wall fermions are defined on a lattice with an extra direction the
size of which controls the chiral properties of the theory. When gauge fields
are coupled to domain wall fermions the extra direction is treated as an
internal flavor space. Here it is found that this is not the case for scalar
fields. Instead, the interaction takes place only along the link that connects
the boundaries of the extra direction. This reveals a richness in the way
different spin particles are coupled to domain wall fermions. As an
application, 4-Fermi models are studied using large N techniques and the
results are supported by numerical simulations with N=2. It is found that the
chiral properties of domain wall fermions in these models are good across a
large range of couplings and that a phase with parity-flavor broken symmetry
can develop for negative bare masses if the number of sites along the extra
direction is finite.Comment: LaTeX, 17 pages, 8 eps figures; comment regarding the width of Aoki
phase added in sec. 3; references adde
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