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

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

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

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