The formation of young B/PS bulges in edge-on barred galaxies

We report about the fact that the stellar population that is born in the gas inflowing towards the central regions can be vertically unstable leading to a B/PS feature remarkably bluer that the surrounding bulge. Using new chemodynamical simulations we show that this young population does not remain as flat as the gaseous nuclear disc and buckles out of the plane to form a new boxy bulge. We show that such a young B/PS bulge can be detected in colour maps.Comment: 2 pages, 5 figures, to appear in IAU Symposium 245, Formation and Evolution of Galaxy Bulges, M. Bureau, E. Athanassoula, and B. Barbuy (eds.), Oxford, 16-20 July 200

Asteroseismology with the WIRE satellite

I give a summary of results from the WIRE satellite, which has been used to observe bright stars from 1999-2000 and 2003-2006. The WIRE targets are monitored for up to five weeks with a duty cycle of 30-40%. The aim has been to characterize the flux variation of stars across the Hertzsprung-Russell diagram. I present an overview of the results for solar-like stars, delta Scuti stars, giant stars, and eclipsing binaries.Comment: Accepted for publication in CoAst. Proceedings of the Vienna Workshop on the Future of Asteroseismology (September 2006). 8 pages, 2 figure

The Inert Doublet Model : a new archetype of WIMP dark matter?

The Inert Doublet Model (IDM) is a two doublet extension of the Higgs-Brout-Englert sector of the Standard Model with a Z_2 symmetry in order to prevent FCNC. If the Z_2 symmetry is not spontaneously broken, the lightest neutral extra scalar is a dark matter candidate. We briefly review the phenomenology of the model, emphasizing its relevance for the issue of Electroweak Symmetry Breaking (EWSB) and the prospects for detection of dark matter.Comment: Contribution the 10th International Conference on Topics in Astroparticle and Underground Physics (TAUP 2007), Sendai, Japan, 11-15 Sep 200

Relating leptogenesis and dark matter

A scenario that relates the abundance of dark matter to the baryon asymmetry of the Universe is presented. In this scenario, based on a left-right extension of the Standard Model, dark matter is made of light, ~ 1 GeV, right-handed Majorana neutrinos.Comment: 4 pages, 1 figure, to appear in the proceedings of 40th Rencontres de Moriond, Electroweak Interactions and Unified Theories, March 11 - 18, 200

On the growth behaviour of Hironaka quotients

We consider a finite analytic morphism \phi = (f,g) : (X,p)\to (\C^2,0) where $(X,p)$ is a complex analytic normal surface germ and $f$ and $g$ are complex analytic function germs. Let $\pi : (Y,E_{Y})\to (X,p)$ be a good resolution of $\phi$ with exceptional divisor $E_{Y}=\pi ^{-1}(p)$. We denote $G(Y)$ the dual graph of the resolution $\pi$. We study the behaviour of the Hironaka quotients of $(f,g)$ associated to the vertices of $G(Y)$. We show that there exists maximal oriented arcs in $G(Y)$ along which the Hironaka quotients of $(f,g)$ strictly increase and they are constant on the connected components of the closure of the complement of the union of the maximal oriented arcs

Evidence of resonant mode coupling and the relationship between low and high frequencies in a rapidly rotating A star

In the theory of resonant mode coupling, the parent and child modes are directly related in frequency and phase. The oscillations present in the fast rotating Delta Scuti star KIC 8054146 allow us to test the most general and generic aspects of such a theory. The only direct way to separate the parent and coupled (child) modes is to examine the correlations in amplitude variability between the different frequencies. For the dominant family of related frequencies, only a single mode and a triplet are the origins of nine dominant frequency peaks ranging from 2.93 to 66.30 cycles per day (as well as dozens of small-amplitude combination modes and a predicted and detected third high-frequency triplet). The mode-coupling model correctly predicts the large amplitude variations of the coupled modes as a product of the amplitudes of the parent modes, while the phase changes are also correctly modeled. This differs from the behavior of 'normal' combination frequencies in that the amplitudes are three orders of magnitude larger and may exceed even the amplitudes of the parent modes. We show that two dominant low frequencies at 5.86 and 2.93 cycles per day in the gravity-mode region are not harmonics of each other, and their properties follow those of the almost equidistant high-frequency triplet. We note that the previously puzzling situation of finding two strong peaks in the low-frequency region related by nearly a factor of two in frequency has been seen in other Delta Scuti stars as well.Comment: To be published in the Astrophysical Journa

Effective field theory approach to N=4 supersymmetric Yang-Mills at finite temperature

We study the perturbation expansion of the free energy of N=4 supersymmetric SU(N) Yang-Mills at finite temperature in powers of 't Hooft's coupling g^2 N in the large N limit. Infrared divergences are controlled by constructing a hierarchy of two 3 dimensional effective field theories. This procedure is applied to the calculation of the free energy to order (g^2 N)^(3/2), but it can be extended to higher order corrections.Comment: LaTeX, 10 pages, 1 figure, uses eps

Constraints on Light WIMP candidates from the Isotropic Diffuse Gamma-Ray Emission

Motivated by the measurements reported by direct detection experiments, most notably DAMA, CDMS-II, CoGeNT and Xenon10/100, we study further the constraints that might be set on some light dark matter candidates, M_DM ~ few GeV, using the Fermi-LAT data on the isotropic gamma-ray diffuse emission. In particular, we consider a Dirac fermion singlet interacting through a new Z' gauge boson, and a scalar singlet S interacting through the Higgs portal. Both candidates are WIMP (Weakly Interacting Massive Particles), i.e. they have an annihilation cross-section in the pbarn range. Also they may both have a spin-independent elastic cross section on nucleons in the range required by direct detection experiments. Although being generic WIMP candidates, because they have different interactions with Standard Model particles, their phenomenology regarding the isotropic diffuse gamma-ray emission is quite distinct. In the case of the scalar singlet, the one-to-one correspondence between its annihilation cross-section and its spin-independent elastic scattering cross-section permits to express the constraints from the Fermi-LAT data in the direct detection exclusion plot, sigma_n^0--M_DM. Depending on the astrophysics, we argue that it is possible to exclude the singlet scalar dark matter candidate at 95 % CL. The constraints on the Dirac singlet interacting through a Z' are comparatively weaker.Comment: 18 pages, 13 figures, replaced to match with the published versio