35,345 research outputs found
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 is a complex analytic normal surface germ and and are
complex analytic function germs. Let be a good
resolution of with exceptional divisor . We denote
the dual graph of the resolution . We study the behaviour of the
Hironaka quotients of associated to the vertices of . We show
that there exists maximal oriented arcs in along which the Hironaka
quotients of 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
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