Period-Luminosity-Colour distribution and classification of Galactic oxygen-rich LPVs

The absolute K magnitudes and kinematic parameters of about 350 oxygen-rich Long-Period Variable stars are calibrated, by means of an up-to-date maximum-likelihood method, using Hipparcos parallaxes and proper motions together with radial velocities and, as additional data, periods and V-K colour indices. Four groups, differing by their kinematics and mean magnitudes, are found. For each of them, we also obtain the distributions of magnitude, period and de-reddened colour of the base population, as well as de-biased period-luminosity-colour relations and their two-dimensional projections. The SRa semiregulars do not seem to constitute a separate class of LPVs. The SRb appear to belong to two populations of different ages. In a PL diagram, they constitute two evolutionary sequences towards the Mira stage. The Miras of the disk appear to pulsate on a lower-order mode. The slopes of their de-biased PL and PC relations are found to be very different from the ones of the Oxygen Miras of the LMC. This suggests that a significant number of so-called Miras of the LMC are misclassified. This also suggests that the Miras of the LMC do not constitute a homogeneous group, but include a significant proportion of metal-deficient stars, suggesting a relatively smooth star formation history. As a consequence, one may not trivially transpose the LMC period-luminosity relation from one galaxy to the other.Comment: 13 pages, 23 figures. Accepted for publication in A&A

Envelope tomography of long-period variable stars: I. The Schwarzschild mechanism and the Balmer emission lines

This paper is the first one in a series devoted to the study of the dynamics of the atmospheres of long-period variable stars. Results from a two-month-long monitoring of the Mira variables RT Cyg and X Oph around maximum light with the ELODIE spectrograph at the Haute-Provence Observatory are presented. The monitoring covers phases 0.80 to 1.16 for RT Cyg and phases 0.83 to 1.04 for X Oph. The cross-correlation profile of the spectrum of RT Cyg with a K0 III mask confirms that the absorption lines of RT Cyg in the optical domain appear double around maximum light. No line doubling was found in the optical spectrum of X Oph around maximum light, indicating that this feature is not common to all long-period variables. This paper also presents the application to RT Cyg of a new tomographic technique deriving the velocity field across the atmosphere by cross-correlating the optical spectrum with numerical masks constructed from synthetic spectra and probing layers of increasing depths. This technique reveals that both the temporal evolution of the line doubling, and its variation with depth in the atmosphere of RT Cyg, are consistent with the ``Schwarzschild scenario''. This scenario relates the temporal evolution of the red and blue peaks of the double absorption lines to the progression of a shock wave in the atmosphere. The temporal evolution of the Balmer Halpha, H beta, Hgamma and Hdelta emission lines around maximum light is also presented for RT Cyg and X Oph. The velocity variations of Halpha and of the absorption lines are discussed in the framework of two competing models for the formation of Balmer emission lines in long-period variable stars.Comment: 11 pages, 8 figures, Latex, accepted for publication in Astronomy and Astrophysics main journal. Also available at http://www-astro.ulb.ac.be/Html/ps.htm

Revisiting Minimal Lepton Flavour Violation in the Light of Leptonic CP Violation

The Minimal Lepton Flavour Violation (MLFV) framework is discussed after the recent indication for CP violation in the leptonic sector. Among the three distinct versions of MLFV, the one with degenerate right-handed neutrinos will be disfavoured, if this indication is confirmed. The predictions for leptonic radiative rare decays and muon conversion in nuclei are analysed, identifying strategies to disentangle the different MLFV scenarios. The claim that the present anomalies in the semi-leptonic $B$-meson decays can be explained within the MLFV context is critically re-examined concluding that such an explanation is not compatible with the present bounds from purely leptonic processes.Comment: 36 pages, 4 figures. V2: References added; version accepted for publication on JHE

Structure and three-body decay of 9^9Be resonances

The complex-rotated hyperspherical adiabatic method is used to study the decay of low-lying $^9$Be resonances into one neutron and two $\alpha$-particles. We investigate the six resonances above the break-up threshold and below 6 MeV: $1/2^\pm$, $3/2^\pm$ and $5/2^\pm$. The short-distance properties of each resonance are studied, and the different angular momentum and parity configurations of the $^8$Be and $^5$He two-body substructures are determined. We compute the branching ratio for sequential decay via the $^8$Be ground state which qualitatively is consistent with measurements. We extract the momentum distributions after decay directly into the three-body continuum from the large-distance asymptotic structures. The kinematically complete results are presented as Dalitz plots as well as projections on given neutron and $\alpha$-energy. The distributions are discussed and in most cases found to agree with available experimental data.Comment: 12 pages, 10 figures. To appear in Physical Review

Momentum distributions from three-body decaying 9Be and 9B resonances

The complex-rotated hyperspherical adiabatic method is used to study the decay of low-lying $^9$Be and $^9$B resonances into $\alpha$, $\alpha$ and $n$ or $p$. We consider six low-lying resonances of $^9$Be ($1/2^\pm$, $3/2^\pm$ and $5/2^\pm$) and one resonance of $^9$B ($5/2^-$) to compare with. The properties of the resonances at large distances are decisive for the momentum distributions of the three decaying fragments. Systematic detailed energy correlations of Dalitz plots are presented.Comment: 4 pages, 2 figures. Proceedings of the SOTANCP2 conference held in Brussels in May 201

A Way to Dynamically Overcome the Cosmological Constant Problem

The Cosmological Constant problem can be solved once we require that the full standard Einstein Hilbert lagrangian, gravity plus matter, is multiplied by a total derivative. We analyze such a picture writing the total derivative as the covariant gradient of a new vector field (b_mu). The dynamics of this b_mu field can play a key role in the explanation of the present cosmological acceleration of the Universe.Comment: 5 page

Torsion cycles as non-local magnetic sources in non-orientable spaces

Non-orientable spaces can appear to carry net magnetic charge, even in the absence of magnetic sources. It is shown that this effect can be understood as a physical manifestation of the existence of torsion cycles of codimension one in the homology of space.Comment: 17 pages, 4 figure