Unified model of baryonic matter and dark components

We investigate an interacting two-fluid cosmological model and introduce a scalar field representation by means of a linear combination of the individual energy densities. Applying the integrability condition to the scalar field equation we show that this "exotic quintessence" is driven by an exponential potential and the two-fluid mixture can be considered as a model of three components. These components are associated with baryonic matter, dark matter and dark energy respectively. We use the Simon, Verde & Jimenez (2005) determination of the redshift dependence of the Hubble parameter to constrain the current density parameters of this model. With the best fit density parameters we obtain the transition redshift between non accelerated and accelerated regimes z_{acc}=0.66 and the time elapsed since the initial singularity t_0= 19.8 Gyr. We study the perturbation evolution of this model and find that the energy density perturbation decreases with the cosmological time.Comment: 8 pages, 6 figures A new section adde

Linear and non-linear perturbations in dark energy models

I review the linear and second-order perturbation theory in dark energy models with explicit interaction to matter in view of applications to N-body simulations and non-linear phenomena. Several new or generalized results are obtained: the general equations for the linear perturbation growth; an analytical expression for the bias induced by a species-dependent interaction; the Yukawa correction to the gravitational potential due to dark energy interaction; the second-order perturbation equations in coupled dark energy and their Newtonian limit. I also show that a density-dependent effective dark energy mass arises if the dark energy coupling is varying.Comment: 12 pages, submitted to Phys. Rev; v2: added a ref. and corrected a typ

Observational constraints on an interacting dark energy model

We use observations of cosmic microwave background anisotropies, supernova luminosities and the baryon acoustic oscillation signal in the galaxy distribution to constrain the cosmological parameters in a simple interacting dark energy model with a time-varying equation of state. Using a Monte Carlo Markov Chain technique we determine the posterior likelihoods. Constraints from the individual data sets are weak, but the combination of the three data sets confines the interaction constant $\Gamma$ to be less than 23% of the expansion rate of the Universe $H_0$; at 95% CL $-0.23 < \Gamma/H_0 < +0.15$. The CMB acoustic peaks can be well fitted even if the interaction rate is much larger, but this requires a larger or smaller (depending on the sign of interaction) matter density today than in the non-interacting model. Due to this degeneracy between the matter density and the interaction rate, the only observable effect on the CMB is a larger or smaller integrated Sachs-Wolfe (ISW) effect. While SN or BAO data alone do not set any direct constraints on the interaction, they exclude the models with very large matter density, and hence indirectly constrain the interaction rate when jointly analysed with the CMB data. To enable the analysis described in this paper, we present in a companion paper [arXiv:0907.4981] a new systematic analysis of the early radiation era solution to find the adiabatic initial conditions for the Boltzmann integration.Comment: 16 pages, 10 figures. V2: Improved typography (2-column format); References and a motivation of CPL parametrization added; Accepted by MNRA

Perturbation evolution with a non-minimally coupled scalar field

We recently proposed a simple dilaton-derived quintessence model in which the scalar field was non-minimally coupled to cold dark matter, but not to `visible' matter. Such couplings can be attributed to the dilaton in the low energy limit of string theory, beyond tree level. In this paper we discuss the implications of such a model on structure formation, looking at its impact on matter perturbations and CMB anisotropies. We find that the model only deviates from $\Lambda$CDM and minimally coupled theories at late times, and is well fitted to current observational data. The signature left by the coupling, when it breaks degeneracy at late times, presents a valuable opportunity to constrain non-minimal couplings given the wealth of new observational data promised in the near future.Comment: Version appearing in Physical Review D. 10 pages, 9 figs. Comparison with SN1a and projected MAP results, and appendix adde

Observational constraints on the braneworld model with brane-bulk energy exchange

We investigate the viability of the braneworld model with energy exchange between the brane and bulk, by using the most recent observational data related to the background evolution. We show that this energy exchange behaves like a source of dark energy and can alter the profile of the cosmic expansion. The new Supernova Type Ia (SNIa) Gold sample, Supernova Legacy Survey (SNLS) data, the position of the acoustic peak at the last scattering surface from the Wilkinson Microwave Anisotropy Probe (WMAP) observations and the baryon acoustic oscillation peak found in the Sloan Digital Sky Survey (SDSS) are used to constrain the free parameters of this model. To infer its consistency with the age of the Universe, we compare the age of old cosmological objects with what computed using the best fit values for the model parameters. At 68% level of confidence, the combination of Gold sample SNIa, Cosmic Microwave Background (CMB) shift parameter and SDSS databases provide $\Omega_m=0.29_{-0.02}^{+0.03}$, $\Omega_{A}=-0.71_{-0.03}^{+0.03}$ and $\mu=-0.40_{-0.26}^{+0.28}$, hence a spatially flat Universe with $\Omega_K=0.00_{-0.04}^{+0.04}$. The same combination with SNLS supernova observation give $\Omega_m=0.27_{-0.02}^{+0.02}$, $\Omega_{A}=-0.74_{-0.02}^{+0.04}$ and $\mu=0.00_{-0.30}^{+0.30}$ consequently provides a spatially flat Universe $\Omega_K=-0.01_{-0.03}^{+0.04}$. These results obviously seem to be compatible with the most recent WMAP results indicating a flat Universe.Comment: 17 pages and 18 figures, V2: Added comments, references, explained some topics related to the matter power spectrum as a robust constraint, accepted for publication in Mon. Not. R. Astron. So

Cluster number counts dependence on dark energy inhomogeneities and coupling to dark matter

Cluster number counts can be used to test dark energy models. We investigate dark energy candidates which are coupled to dark matter. We analyze the cluster number counts dependence on the amount of dark matter coupled to dark energy. Further more, we study how dark energy inhomogeneities affect cluster abundances. It is shown that increasing the coupling reduces significantly the cluster number counts, and that dark energy inhomogeneities increases cluster abundances. Wiggles in cluster number counts are shown to be a specific signature of coupled dark energy models. Future observations will possibly detect such oscillations and discriminate among the different dark energy models.Comment: 9 pages, 8 figures. Further extensions on section on discriminating models with future surveys. Accepted for publication in Mon. Not. Roy. Astro. So

Cosmology and Astrophysical Constraints of Gauss-Bonnet Dark Energy

Cosmological consequences of a string-motivated dark energy scenario featuring a scalar field coupled to the Gauss-Bonnet invariant are investigated. We study the evolution of the universe in such a model, identifying its key properties. The evolution of the homogeneous background and cosmological perturbations, both at large and small scales, are calculated. The impact of the coupling on galaxy distributions and the cosmic microwave background is examined. We find the coupling provides a mechanism to viably onset the late acceleration, to alleviate the coincidence problem, and furthermore to effectively cross the phantom divide at the present while avoiding a Big Rip in the future. We show the model could explain the present cosmological observations, and discuss how various astrophysical and cosmological data, from the Solar system, supernovae Ia, cosmic microwave background radiation and large scale structure constrain it.Comment: 6 pages, 3 figures. References added. Accepted for publication in Phys. Lett.

Number counts in homogeneous and inhomogeneous dark energy models

In the simple case of a constant equation of state, redshift distribution of collapsed structures may constrain dark energy models. Different dark energy models having the same energy density today but different equations of state give quite different number counts. Moreover, we show that introducing the possibility that dark energy collapses with dark matter (``inhomogeneous'' dark energy) significantly complicates the picture. We illustrate our results by comparing four dark energy models to the standard $\Lambda$-model. We investigate a model with a constant equation of state equal to -0.8, a phantom energy model and two scalar potentials (built out of a combination of two exponential terms). Although their equations of state at present are almost indistinguishable from a $\Lambda$-model, both scalar potentials undergo quite different evolutions at higher redshifts and give different number counts. We show that phantom dark energy induces opposite departures from the $\Lambda$-model as compared with the other models considered here. Finally, we find that inhomogeneous dark energy enhances departures from the $\Lambda$-model with maximum deviations of about 15% for both number counts and integrated number counts. Larger departures from the $\Lambda$-model are obtained for massive structures which are rare objects making it difficult to statistically distinguish between models.Comment: 10 pages, 11 figures. Version accepted for publication in A&

Carotid artery dissections from TCAR as reported by the Food and Drug Administration

BACKGROUND: Transcarotid artery revascularization (TCAR) is hybrid procedure that allows carotid stenting using direct surgical access of the carotid artery to restore blood flow through the carotid artery. It has shown the lowest perioperative stroke rate when compared with any prospective trial of transfemoral carotid artery stenting. However, intraoperative injuries related to the procedure and its management are not well characterized. We anticipate that this analysis will add qualitative insight in further characterizing adverse outcomes of this novel technology. METHODS: The FDA maintains a database called the MAUDE (Manufacturer and User Facility Device Experience) for surveillance of all medical devices approved for use. This database was queried for all cases associated with Silk Road Medical’s ENROUTE Transcarotid Neuroprotection System from September 2016 to October 2020.. Case narratives related to patient injuries were individually analyzed to determine type (carotid artery dissection) and time of injury (intraoperative, recovery, post-discharge follow- up). Carotid artery dissection (CD) reporting was further analyzed for associated procedural event at the time of injury, number of access attempts to CD repair, and type of CD repair. RESUTS: Of the 115 unique incidents in the database, there were 58 CDs. Most were identified intraoperatively (n=55), while 3 were incidentally identified postoperatively. Overall, sheath placement was the most common procedural event attributed to CD (n=34). There was adequate narrative information about CD repair in 54 patients where 52 of them were performed intraoperatively. There were total of 28 endovascular repair and 24 open surgical repairs of CDs from TCAR procedure. There was no significant difference in rate of endovascular and open surgical repair of CDs that did not need additional access attempts. However, rate of open surgical repair was significantly higher in CDs with persistent failure to engage the true lumen in 2 or more additional access attempts. Total of 4 strokes were associated with CD. Two occurred during recovery from TCAR admission where one was not intervened per physician’s discretion despite evidence of dissection during the procedure. The other was associated with a fall from a hypotensive event 7 hours after an endovascular CD repair. One incident of stroke occurred intraoperatively during a conversion to CEA as a result of CD. One incident of stroke occurred 4 days after TCAR procedure in which a CD was identified during the stroke evaluation Conclusion: Carotid artery dissection is the most common injury related to TCAR as reported on MAUDE database. Most common procedural event associated CD was sheath placement. Rate of open surgical repair was significantly higher than endovascular repair in dissections with persistent failure to engage true lumen despite additional access attempts. This should add to qualitative insight among vascular surgery community regarding intraoperative management of carotid artery dissections from a TCAR procedure.https://scholarscompass.vcu.edu/gradposters/1144/thumbnail.jp

Cosmic microwave background: polarization and temperature anisotropies from symmetric structures

I consider the case of anisotropies in the Cosmic Microwave Background (CMB) from one single ordered perturbation source, or seed, existing well before decoupling between matter and radiation. Such structures could have been left by high energy symmetries breaking in the early universe. I focus on the cases of spherical and cylindrical symmetry of the seed. I give general analytic expressions for the polarization and temperature linear perturbations, factoring out of the Fourier integral the dependence on the photon propagation direction and on the geometric coordinates describing the seed. I show how the CMB perturbations manifestly reflect the symmetries of their seeds. CMB anisotropies are obtained with a line of sight integration. This treatment highlights the undulatory properties of the CMB. I show with numerical examples how the polarization and temperature perturbations propagate beyond the size of their seeds, reaching the CMB sound horizon at the time considered. Just like the waves from a pebble thrown in a pond, CMB anisotropy from a seed intersecting the last scattering surface appears as a series of temperature and polarization waves surrounding the seed, extending on the scale of the CMB sound horizon at decoupling, roughly $1^{o}$ in the sky. Each wave is characterized by its own value of the CMB perturbation, with the same mean amplitude of the signal coming from the seed interior. These waves could allow to distinguish relics from high energy processes of the early universe from point-like astrophysical sources, because of their angular extension and amplitude. Also, the marked analogy between polarization and temperature signals offers cross correlation possibilities for the future Planck Surveyor observations.Comment: 21 pages, seven postscript figures, final version accepted for publication in Phys.Rev.