Bose-Einstein Condensate Dark Matter Halos confronted with galactic rotation curves

We present a comparative confrontation of both the Bose-Einstein Condensate (BEC) and the Navarro-Frenk-White (NFW) dark halo models with galactic rotation curves. We employ 6 High Surface Brightness (HSB), 6 Low Surface Brightness (LSB), and 7 dwarf galaxies with rotation curves falling into two classes. In the first class rotational velocities increase with radius over the observed range.The BEC and NFW models give comparable fits for HSB and LSB galaxies of this type, while for dwarf galaxies the fit is significantly better with the BEC model. In the second class the rotational velocity of HSB and LSB galaxies exhibits long flat plateaus, resulting in better fit with the NFW model for HSB galaxies and comparable fits for LSB galaxies. We conclude that due to its central density cusp avoidance the BEC model fits better dwarf galaxy dark matter distribution. Nevertheless it suffers from sharp cutoff in larger galaxies, where the NFW model performs better. The investigated galaxy sample obeys the Tully-Fisher relation, including the particular characteristics exhibited by dwarf galaxies. In both models the fitting enforces a relation between dark matter parameters: the characteristic density and the corresponding characteristic distance scale with an inverse power.Comment: published versio

Do supernovae favor tachyonic Big Brake instead de Sitter?

We investigate whether a tachyonic scalar field, encompassing both dark energy and dark matter-like features will drive our universe towards a Big Brake singularity or a de Sitter expansion. In doing this it is crucial to establish the parameter domain of the model, which is compatible with type Ia supernovae data. We find the 1-sigma contours and evolve the tachyonic sytem into the future. We conclude, that both future evolutions are allowed by observations, Big Brake becoming increasingly likely with the increase of the positive model parameter k.Comment: 8 pages, 6 figures, to be published in the Proceedings of the Invisible Universe International Conference, Paris, 2009, Ed. J. M. Alimi; v2: reference

Slowly rotating Bose-Einstein Condensate confronted with the rotation curves of 12 dwarf galaxies

We assemble a database of 12 dwarf galaxies, for which optical (R-band) and near-infrared ($3.6\mu m$) surface brightness density together with spectroscopic rotation curve data are available, in order to test the slowly rotating Bose-Einstein Condensate (srBEC) dark matter model. We aim to establish the angular velocity range compatible with observations, bounded from above by the requirement of finite size halos, to check the modelfits with the dataset, and the universality of the BEC halo parameter $\mathcal{R}$. We construct the spatial luminosity density of the stellar component of the dwarf galaxies based on their $3.6\mu m$ and R-band surface brightness profiles, assuming an axisymmetric baryonic mass distribution. We build up the gaseous component by employing a truncated disk model. We fit a baryonic plus dark matter combined model, parametrized by the M/L ratios of the baryonic components and parameters of the srBEC (the central density $\rho_c$, size of the static BEC halo $\mathcal{R}$, angular velocity $\omega$) to the rotation curves. The $3.6\mu m$ surface brightness of 6 galaxies indicates the presence of a bulge and a disk component. The shape of the $3.6\mu m$ and R-band spatial mass density profiles being similar is consistent with the stellar mass of the galaxies emerging wavelength-independent. The srBEC model fits the rotation curve of 11 galaxies out of 12 within $1\sigma$ significance level, with the average of $\mathcal{R}$ as 7.51 kpc and standard deviation of 2.96 kpc. This represents an improvement over the static BEC modelfit. For the well-fitting 11 galaxies the angular velocities allowing for a finite size srBEC halo are $<2.2\times 10^{-16}$ 1/s. For a scattering length of the BEC particle of $a\approx 10^6$ fm, the mass of the BEC particle is slightly better constrained than in the static case as $m\in[1.26\times10^{-17}\div3.08\times10^{-17}]$ eV/c$^2$.Comment: 9 pages, 4 tables, 5 figures, submitted to A&

Secular momentum transport by gravitational waves from spinning compact binaries

We present a closed system of coupled first order differential equations governing the secular linear momentum loss of a compact binary due to emitted gravitational waves, with the leading order relativistic and spin-orbit perturbations included. In order to close the system, the secular evolution equations of the linear momentum derived from the dissipative dynamics are supplemented with the secular evolutions of the coupled angular variables, as derived from the conservative dynamics © 2010 IOP Publishing Ltd