3,586 research outputs found
Majorana Dark Matter in Minimal Higgs Portal Models after LUX
We consider the Singlet Majorana fermion dark matter model, in which the
standard model particles interact with the dark sector through the mixing of a
singlet scalar and the Higgs boson. In this model both the dark matter and the
singlet scalar carry lepton number, the latter being a bilepton. We suppose the
existence of a symmetry, remnant of some high energy local symmetry
breaking, that stabilizes the Majorana fermion. We analyzed the parameter space
of this model and found that the lepton number symmetry breaking scale, drove
by the singlet scalar, is constrained to be within hundreds to thousands of
GeV, so as to conform with the observed dark matter relic density. Finally, we
address the direct detection and invisible Higgs decay complementarity,
confronting our model with recent LUX and LHC constraints, as well as XENON1T
prospects.Comment: 20 pages, 12 figure
NTT infrared imaging of star cluster candidates towards the central parts of the Galaxy
We address the issue whether the central parts of the Galaxy harbour young
clusters other than Arches, Quintuplet and the Nuclear Young Cluster. A large
sample of centrally projected cluster candidates has been recently identified
from the 2MASS J, H and Ks Atlas. We provide a catalogue of higher angular
resolution and deeper images for 57 2MASS cluster candidates, obtained with the
near-IR camera SOFI at the ESO NTT telescope. We classify 10 objects as star
clusters, some of them deeply embedded in gas and/or dust clouds. Three other
objects are probably star clusters, although the presence of dust in the field
does not exclude the possibility of their being field stars seen through
low-absorption regions. Eleven objects are concentrations of stars in areas of
little or no gas, and are classified as dissolving cluster candidates. Finally,
31 objects turned out to be the blend of a few bright stars, not resolved as
such in the low resolution 2MASS images. By combining the above results with
other known objects we provide an updated sample of 42 embedded clusters and
candidates projected within 7 degrees. As a first step we study Object 11 of
Dutra & Bica (2000) projected at approximately 1 degree from the nucleus. We
present H and Ks photometry and study the colour-magnitude diagram and
luminosity function. Object 11 appears to be a less massive cluster than Arches
or Quintuplet, and it is located at a distance from the Sun d=8 kpc, with a
visual absorption Av=15.Comment: accepted to A&A, 9 pages, 10 figure
MeV Dark Matter Complementarity and the Dark Photon Portal
We discuss the phenomenology of an MeV-scale Dirac fermion coupled to the
Standard Model through a dark photon with kinetic mixing with the
electromagnetic field. We compute the dark matter relic density and explore the
interplay of direct detection and accelerator searches for dark photons. We
show that precise measurements of the temperature and polarization power
spectra of the Cosmic Microwave Background Radiation lead to stringent
constraints, leaving a small window for the thermal production of this MeV dark
matter candidate. The forthcoming MeV gamma-ray telescope e-ASTROGAM will offer
important and complementary opportunities to discover dark matter particles
with masses below 10 MeV. Lastly, we discuss how a late-time inflation episode
and freeze-in production could conspire to yield the correct relic density
while being consistent with existing and future constraints.Comment: 27 pages, 7 figures. It matched published versio
Remarks on supersymmetry of quantum systems with position-dependent effective masses
We apply the supersymmetry approach to one-dimensional quantum systems with
spatially-dependent mass, by including their ordering ambiguities dependence.
In this way we extend the results recently reported in the literature.
Furthermore, we point out a connection between these systems and others with
constant masses. This is done through convenient transformations in the
coordinates and wavefunctions.Comment: 8 pages, 1 figur
Effective Action for QED with Fermion Self-Interaction in D=2 and D=3 Dimensions
In this work we discuss the effect of the quartic fermion self-interaction of
Thirring type in QED in D=2 and D=3 dimensions. This is done through the
computation of the effective action up to quadratic terms in the photon field.
We analyze the corresponding nonlocal photon propagators nonperturbatively in %
\frac{k}{m}, where k is the photon momentum and m the fermion mass. The poles
of the propagators were determined numerically by using the Mathematica
software. In D=2 there is always a massless pole whereas for strong enough
Thirring coupling a massive pole may appear . For D=3 there are three regions
in parameters space. We may have one or two massive poles or even no pole at
all. The inter-quark static potential is computed analytically in D=2. We
notice that the Thirring interaction contributes with a screening term to the
confining linear potential of massive QED_{2}. In D=3 the static potential must
be calculated numerically. The screening nature of the massive QED
prevails at any distance, indicating that this is a universal feature of % D=3
electromagnetic interaction. Our results become exact for an infinite number of
fermion flavors.Comment: Latex, 13 pages, 3 figure
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