1,238 research outputs found
Haloes of k-Essence
We study gravitationally bound static and spherically symmetric
configurations of k-essence fields. In particular, we investigate whether these
configurations can reproduce the properties of dark matter haloes. The classes
of Lagrangians we consider lead to non-isotropic fluids with barotropic and
polytropic equations of state. The latter include microscopic realizations of
the often-considered Chaplygin gases, which we find can cluster into dark
matter halo-like objects with flat rotation curves, while exhibiting a dark
energy-like negative pressure on cosmological scales. We complement our studies
with a series of formal general results about the stability and initial value
formulation of non-canonical scalar field theories, and we also discuss a new
class of de Sitter solutions with spacelike field gradients.Comment: 34pages, single column double spacing, 7 figures, 3 Tables, RevTex4.
Additional references and minor clarifications. To be submitted to JCA
General conditions for scale-invariant perturbations in an expanding universe
We investigate the general properties of expanding cosmological models which
generate scale-invariant curvature perturbations in the presence of a variable
speed of sound. We show that in an expanding universe, generation of a
super-Hubble, nearly scale-invariant spectrum of perturbations over a range of
wavelengths consistent with observation requires at least one of three
conditions: (1) accelerating expansion, (2) a speed of sound faster than the
speed of light, or (3) super-Planckian energy density.Comment: 4 pages, RevTe
Can We See Lorentz-Violating Vector Fields in the CMB?
We investigate the perturbation theory of a fixed-norm, timelike
Lorentz-violating vector field. After consistently quantizing the vector field
to put constraints on its parameters, we compute the primordial spectra of
perturbations generated by inflation in the presence of this vector field. We
find that its perturbations are sourced by the perturbations of the inflaton;
without the inflaton perturbation the vector field perturbations decay away
leaving no primordial spectra of perturbations. Since the inflaton perturbation
does not have a spin-1 component, the vector field generically does not
generate any spin-1 ``vector-type'' perturbations. Nevertheless, it will modify
the amplitude of both the spin-0 ``scalar-type'' and spin-2 ``tensor-type''
perturbation spectra, leading to violations of the inflationary consistency
relationship.Comment: 36 pages, 1 fig, RevTex4, Submitted to PR
Near Scale Invariance with Modified Dispersion Relations
We describe a novel mechanism to seed a nearly scale invariant spectrum of
adiabatic perturbations during a non-inflationary stage. It relies on a
modified dispersion relation that contains higher powers of the spatial
momentum of matter perturbations. We implement this idea in the context of a
massless scalar field in an otherwise perfectly homogeneous universe. The
couplings of the field to background scalars and tensors give rise to the
required modification of its dispersion relation, and the couplings of the
scalar to matter result in an adiabatic primordial spectrum. This work is meant
to explicitly illustrate that it is possible to seed nearly scale invariant
primordial spectra without inflation, within a conventional expansion history.Comment: 7 pages and no figures. Uses RevTeX
Psychiatric nurses experiences regarding physical restraint
Introduction: Physical restraint is a commonly used intervention in mental health institutions. Restraint
is used to preserve safety and security, at the same time, it causes physical physiological negative
effects on patients, as well as nurses. Nurses are the main professionals in charge of restraint, and they
suffer its impact directly.
Objective: The purpose of this review is to analyse psychiatric nurses’ experiences when applying
physical restraint.
Methodology: This systematic review of the literature performed its search in three databases (PubMed,
PsychInfo and CINHAL). With terms like “Psychiatry”, “Nurse”, “Experiences” and “Restraint” it elected
171 articles from 2012-2022, the number was reduced to 11 final articles.
Results: Four main categories related to nurses’ experiences were found. Firstly, individual, and
professional characteristics. Secondly, the level of knowledge regarding restraint nurses possess.
Thirdly, nurses’ attitudes, emotions, ideas, and ethical debates towards restraint. Finally, nurses’
practices.
Conclusion: Psychiatric nurses experiences regarding restraint should continue to be studied. There
exists a relation between knowledge, attitudes and practices that needs to be investigated in order to
improve the quality of care.Introducción: La contención mecánica es una práctica habitual en las unidades de psiquiatría. A pesar
de utilizarse para mantener la seguridad. Puede acarrear consecuencias físicas y psicológicas
negativas en pacientes cómo en enfermeras. Estas últimas sufren su impacto directamente.
Objetivo: Este estudio de la literatura busca analizar las experiencias de las enfermeras, en unidades
psiquiátricas, a la hora de llevar a cabo una contención mecánica.
Metodología: Se ha realizado una búsqueda bibliográfica en tres bases de datos (PubMed, PsychInfo
y CINHAL). Mediante términos similares a “Psiquiatría”, “Enfermera”, “Experiencias” y “Contención” se
seleccionaron 171 artículos publicados entre los años 2012 y 2022. El número de artículos se redujo a
11.
Resultados: Los resultados de esta investigación se dividen en cuatro categorías. Comenzando por las
características individuales y profesionales de las enfermeras. Siguiendo por el nivel de conocimiento
aplicado a las contenciones mecánicas que poseen las enfermeras. A continuación, las actitudes,
emociones y dilemas éticos alrededor de dicha práctica. Finalmente, cómo se refleja todo lo
anteriormente mencionado en las prácticas de enfermería.Conclusión: Las experiencias de las enfermeras psiquiátricas deben seguir siendo estudiadas. Se ha
hallado una relación entre conocimientos, actitudes y prácticas que debe seguir siendo investigada para
mejorar la calidad de los cuidados
Creating Statistically Anisotropic and Inhomogeneous Perturbations
In almost all structure formation models, primordial perturbations are
created within a homogeneous and isotropic universe, like the one we observe.
Because their ensemble averages inherit the symmetries of the spacetime in
which they are seeded, cosmological perturbations then happen to be
statistically isotropic and homogeneous. Certain anomalies in the cosmic
microwave background on the other hand suggest that perturbations do not
satisfy these statistical properties, thereby challenging perhaps our
understanding of structure formation. In this article we relax this tension. We
show that if the universe contains an appropriate triad of scalar fields with
spatially constant but non-zero gradients, it is possible to generate
statistically anisotropic and inhomogeneous primordial perturbations, even
though the energy momentum tensor of the triad itself is invariant under
translations and rotations.Comment: 20 pages, 1 figure. Uses RevTeX
Where does Cosmological Perturbation Theory Break Down?
We apply the effective field theory approach to the coupled metric-inflaton
system, in order to investigate the impact of higher dimension operators on the
spectrum of scalar and tensor perturbations in the short-wavelength regime. In
both cases, effective corrections at tree-level become important when the
Hubble parameter is of the order of the Planck mass, or when the physical wave
number of a cosmological perturbation mode approaches the square of the Planck
mass divided by the Hubble constant. Thus, the cut-off length below which
conventional cosmological perturbation theory does not apply is likely to be
much smaller than the Planck length. This has implications for the
observability of "trans-Planckian" effects in the spectrum of primordial
perturbations.Comment: 25 pages, uses FeynM
Trans-Planckian wimpzillas
Two previously proposed conjectures--gravitational trans-Planckian particle
creation in the expanding universe, and the existence of ultra-heavy stable
particles with masses up to the Planck scale (wimpzillas)--are combined in a
proposal for trans-Planckian particle creation of wimpzillas. This new scenario
leads to a huge enhancement in their production compared to mechanisms put
forward earlier. As a result, it requires the trans-Planckian particle creation
parameter to be rather small to avoid overproduction of such particles, much
less than that is required for observable effects in the primordial
perturbation spectrum. This ensures also that wimpzillas are mainly created at
the end of primordial inflation. Conditions under which trans-Planckian
wimpzillas can constitute the present dark matter are determined.Comment: Replaced with the version to be published in JCAP. Division into
sections introduced, discussion expanded, references added, conclusions
unchange
Preheating in Derivatively-Coupled Inflation Models
We study preheating in theories where the inflaton couples derivatively to
scalar and gauge fields. Such couplings may dominate in natural models of
inflation, in which the flatness of the inflaton potential is related to an
approximate shift symmetry of the inflaton. We compare our results with
previously studied models with non-derivative couplings. For sufficiently heavy
scalar matter, parametric resonance is ineffective in reheating the universe,
because the couplings of the inflaton to matter are very weak. If scalar matter
fields are light, derivative couplings lead to a mild long-wavelength
instability that drives matter fields to non-zero expectation values. In this
case however, long-wavelength fluctuations of the light scalar are produced
during inflation, leading to a host of cosmological problems. In contrast,
axion-like couplings of the inflaton to a gauge field do not lead to production
of long-wavelength fluctuations during inflation. However, again because of the
weakness of the couplings to the inflaton, parametric resonance is not
effective in producing gauge field quanta.Comment: 10 pages, 9 figure
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