4,450 research outputs found
Gravitational wave constraints on dark sector models
We explore the constraints on dark sector models imposed by the recent
observation of coincident gravitational waves and gamma rays from a binary
neutron star merger, GW170817. Rather than focusing on specific models as has
been considered by other authors, we explore this in the context of the
equation of state approach of which the specific models are special cases.
After confirming the strong constraints found by others for Horndeski,
Einstein-Aether and massive gravity models, we discuss how it is possible to
construct models which might evade the constraints from GW170817 but still
leading to cosmologically interesting modifications to gravity. Possible
examples are ``miracle cancellations" such as in models, nonlocal models
and higher-order derivatives. The latter two rely on the dimensionless ratio of
the wave number of the observed gravitational waves to the Hubble expansion
rate being very large () which is used to suppress modifications
to the speed of gravitational waves.Comment: 10 page
Cosmological perturbation theory in Generalized Einstein-Aether models
We investigate the evolution of cosmological perturbations in models of dark
energy described by a time-like unit normalized vector field specified by a
general function , so-called Generalized
Einstein-Aether models. First we study the background dynamics of such models
via a designer approach in an attempt to model this theory as dark energy. We
find that only one specific form of this designer approach matches CDM
at background order and we also obtain a differential equation which
must satisfy for general CDM cosmologies. We also
present the equations of state for perturbations in Generalized Einstein-Aether
models, which completely parametrize these models at the level of linear
perturbations. A generic feature of modified gravity models is that they
introduce new degrees of freedom. By fully eliminating these we are able to
express the gauge invariant entropy perturbation and the scalar, vector, and
tensor anisotropic stresses in terms of the perturbed fluid variables and
metric perturbations only. These can then be used to study the evolution of
perturbations in the scalar, vector, and tensor sectors and we use these to
evolve the Newtonian gravitational potentials.Comment: 26 pages, 4 figures, 3 tables, submitted to PR
Internal energy dissipation in Enceladus's ocean from tides and libration and the role of inertial waves
Enceladus is characterised by a south polar hot spot associated with a large
outflow of heat, the source of which remains unclear. We compute the viscous
dissipation resulting from tidal and libration forcing in the moon's subsurface
ocean using the linearised Navier-Stokes equation in a 3-dimensional spherical
model. We conclude that libration is the dominant cause of dissipation at the
linear order, providing up to about 0.001 GW of heat to the ocean, which
remains insufficient to explain the (about) 10 GW observed by Cassini. We also
illustrate how resonances with inertial modes can significantly augment the
dissipation. Our work is an extension to Rovira-Navarro et al. [2019] to
include the effects of libration. The model developed here is readily
applicable to the study of other moons and planets
Recommended from our members
Primer on adult patient satisfaction in perioperative settings.
The topic of patient satisfaction has gained increasing importance over the past decade. Due to the impact of patient satisfaction on health care quality, understanding factors that predict satisfaction is vital. The purpose of this review is to examine the literature and identify factors related to patient perioperative satisfaction as well as predictive variables that, if modified, can enhance satisfaction scores of patients undergoing surgery. Our review reports that patient satisfaction scores are affected by modifiable factors such as clinician-patient communication, information provision to patients, and operational function of a hospital. Non-modifiable factors affecting patient satisfaction scores include patient demographics such as gender, age, and education. In order to enhance patient perioperative satisfaction, we suggest that anesthesiologists and surgeons focus their efforts on enhancing their communication skills and providing information that is appropriately tailored to the understanding of their patients
Patterns on liquid surfaces: cnoidal waves, compactons and scaling
Localized patterns and nonlinear oscillation formation on the bounded free
surface of an ideal incompressible liquid are analytically investigated .
Cnoidal modes, solitons and compactons, as traveling non-axially symmetric
shapes are discused. A finite-difference differential generalized Korteweg-de
Vries equation is shown to describe the three-dimensional motion of the fluid
surface and the limit of long and shallow channels one reobtains the well known
KdV equation. A tentative expansion formula for the representation of the
general solution of a nonlinear equation, for given initial condition is
introduced on a graphical-algebraic basis. The model is useful in multilayer
fluid dynamics, cluster formation, and nuclear physics since, up to an overall
scale, these systems display liquid free surface behavior.Comment: 14 pages RevTex, 5 figures in p
Recommended from our members
Draft Genome Sequences of Two Vibrio parahaemolyticus Strains Associated with Gastroenteritis after Raw Seafood Ingestion in Colorado.
Vibrio parahaemolyticus is a Gram-negative pathogen associated with gastrointestinal and wound infections after exposure to raw seafood or contaminated waters. We report here the whole-genome sequences of two stool isolates (CDC-AM50933 and CDC-AM43539) from patients in Colorado presenting with gastroenteritis after ingesting raw seafood
- …