Quadratic deformation of Minkowski space

We present a deformation of the Minkowski space as embedded into the conformal space (in the formalism of twistors) based in the quantum versions of the corresponding kinematic groups. We compute explicitly the star product, whose Poisson bracket is quadratic. We show that the star product although defined on the polynomials can be extended differentiably. Finally we compute the Eucliden and Minkowskian real forms of the deformation.Comment: Presented at XVII European Workshop on String Theory 2011. Padova (Italy) September 05-09; Fortschr. Phys. 1-7 (2012

Dark matter from dark energy-baryonic matter couplings

We present a scenario in which a scalar field dark energy is coupled to the trace of the energy momentum tensor of the baryonic matter fields. In the slow-roll regime, this interaction could give rise to the cosmological features of dark matter. We work out the cosmological background solutions and fit the parameters of the model using the Union 2 supernovae data set. Then, we develop the cosmological perturbations up to linear order, and we find that the perturbed variables have an acceptable behavior, in particular the density contrast of baryonic matter grows similar to that in the $\Lambda$CDM model for a suitable choice of the strength parameter of the coupling.Comment: 10 pages, 8 figures, in this version small typos are corrected and it matches the published version in Phys. Rev. D15, January 201

Empirical distributions of galactic λ\lambda spin parameters from the SDSS

Using simple dimensional arguments for both spiral and elliptical galaxies, we present formulas to derive an estimate of the halo spin parameter $\lambda$ for any real galaxy, in terms of common observational parameters. This allows a rough estimate of $\lambda$, which we apply to a large volume limited sample of galaxies taken from the SDSS data base. The large numbers involved (11,597) allow the derivation of reliable $\lambda$ distributions, as signal adds up significantly in spite of the errors in the inferences for particular galaxies. We find that if the observed distribution of $\lambda$ is modeled with a log-normal function, as often done for this distribution in dark matter halos that appear in cosmological simulations, we obtain parameters $\lambda_{0}=0.04 \pm 0.005$ and $\sigma_{\lambda}=0.51 \pm 0.05$, interestingly consistent with values derived from simulations. For spirals, we find a good correlation between empirical values of $\lambda$ and visually assigned Hubble types, highlighting the potential of this physical parameter as an objective classification tool.Comment: 8 pages, 6 figures, expanded final version, MNRAS (in press

Ratio between inbreeding and coancestry rates as a measure of population subdivision. Preliminary results

Ponencia publicada en ITEA, vol. 104Uno de los factores que provocan incrementos de consanguinidad superiores a los que se esperarían en función del tamaño de la población es la subdivisión de las poblaciones. La medida de la subdivisión de poblaciones no resulta sencilla. Se presenta una medida de subdivisión de poblaciones que se obtiene a partir de la información de pedigree. Se basa en la comparación directa de los incrementos de coascendencia en relación a los incrementos de endogamia por generación discreta equivalente, establecidos ambos a partir de la media de valores individuales de esos parámetros. La utilidad del parámetro desde el punto de vista descriptivo se ilustra con la ayuda de una población simulada y de dos poblaciones reales con diferentes escenarios de subdivisión.Subdivision is one of the factors leading to increase in inbreeding higher than those expected regarding population size. Measuring population subdivision is not straightforward given that it is established rather diffuse. A measure of population subdivision from pedigrees is presented. It is based on the direct comparison of the increases in coancestry and the increases in inbreeding computed over equivalent discrete generation. Coancestry and inbreeding rates were established from the average of individual values of those parameters. The usefulness of the new parameter from a descriptive point of view is illustrated using a simulated population and two real populations with an opposed scenario regarding subdivision