278 research outputs found
Fermi Bubbles: an Elephant in the Gamma-ray Sky
The Fermi bubbles are one of the most remarkable features in the gamma-ray
sky revealed by the Fermi Large Area Telescope (LAT). The nature of the
gamma-ray emission and the origin of the bubbles are still open questions. In
this note, we will review some basic features of leptonic and hadronic modes of
gamma-ray production. At the moment, gamma rays are our best method to study
the bubbles, but in order to resolve the origin of the bubbles multi-wavelength
and multi-messenger observations will be crucial.Comment: Published in proceedings for RICAP16 conferenc
Del Pezzo singularities and SUSY breaking
An analytic construction of compact Calabi-Yau manifolds with del Pezzo
singularities is found. We present complete intersection CY manifolds for all
del Pezzo singularities and study the complex deformations of these
singularities. An example of the quintic CY manifold with del Pezzo 6
singularity and some number of conifold singularities is studied in details.
The possibilities for the 'geometric' and ISS mechanisms of dynamical SUSY
breaking are discussed. As an example, we construct the ISS vacuum for the del
Pezzo 6 singularity.Comment: 40 pages, 5 figures, v2: references adde
Galactic center gamma-ray excess and the Fermi bubbles
Galactic center (GC) is expected to be the brightest source of possible dark
matter (DM) annihilation signal. Excess gamma-ray emission has been detected by
several groups. Both DM and more conventional astrophysical explanations of the
excess have been proposed. In this report, we discuss possible effects of
modeling the Fermi bubbles at low latitudes on the GC excess. We consider a
template of the Fermi bubbles at low latitudes derived by assuming that the
spectrum between 1 GeV and 10 GeV at low latitudes is the same as at high
latitudes. We argue that the presence of the Fermi bubbles near the GC may have
a significant influence on the spectrum of the GC excess, especially at
energies above 10 GeV.Comment: Proceedings of LaThuile 2017 conferenc
Hard and bright gamma-ray emission at the base of the Fermi bubbles
The Fermi bubbles (FBs) are large gamma-ray emitting lobes extending up to
in latitude above and below the Galactic center (GC). Although the FBs
were discovered 8 years ago, their origin and the nature of the gamma-ray
emission are still unresolved. Understanding the properties of the FBs near the
Galactic plane may provide a clue to their origin. Previous analyses of the
gamma-ray emission at the base of the FBs, what remains after subtraction of
Galactic foregrounds, have shown an increased intensity compared to the FBs at
high latitudes, a hard power-law spectrum without evidence of a cutoff up to
approximately 1 TeV, and a displacement of the emission to negative longitudes
relative to the GC. We analyze 9 years of Fermi Large Area Telescope data in
order to study in more detail the gamma-ray emission at the base of the FBs,
especially at energies above 10 GeV. We confirm that the gamma-ray emission at
the base of the FBs is well described by a simple power law up to 1 TeV
energies. The 95% confidence lower limit on the cutoff energy is about 500 GeV.
It has larger intensity than the FBs emission at high latitudes and is shifted
to the west (negative longitudes) from the GC. If the emission at the base of
the FBs is indeed connected to the high-latitude FBs, then the shift of the
emission to negative longitudes disfavors models where the FBs are created by
the supermassive black hole at the GC. We find that the gamma-ray spectrum can
be explained either by gamma rays produced in hadronic interactions or by
leptonic inverse Compton scattering. In the hadronic scenario, the emission at
the base of the FBs can be explained either by several hundred supernova
remnants (SNRs) near the Galactic center or by about 10 SNRs at a distance of ~
1 kpc. In the leptonic scenario, the necessary number of SNRs is a factor of a
few larger than in the hadronic scenario. (abridged)Comment: 24 pages, 18 figures, published in A&
Hopf algebra of ribbon graphs and renormalization
Connes and Kreimer have discovered a Hopf algebra structure behind
renormalization of Feynman integrals. We generalize the Hopf algebra to the
case of ribbon graphs, i.e. to the case of theories with matrix fields. The
Hopf algebra is naturally defined in terms of surfaces corresponding to ribbon
graphs. As an example, we discuss renormalization of theory and the
1/N expansion.Comment: 34 pages, 9 figures, Latex; improved styl
Spectral components analysis of diffuse emission processes
We develop a novel method to separate the components of a diffuse emission
process based on an association with the energy spectra. Most of the existing
methods use some information about the spatial distribution of components,
e.g., closeness to an external template, independence of components etc., in
order to separate them. In this paper we propose a method where one puts
conditions on the spectra only. The advantages of our method are: 1) it is
internal: the maps of the components are constructed as combinations of data in
different energy bins, 2) the components may be correlated among each other, 3)
the method is semi-blind: in many cases, it is sufficient to assume a
functional form of the spectra and determine the parameters from a maximization
of a likelihood function. As an example, we derive the CMB map and the
foreground maps for seven yeas of WMAP data. In an Appendix, we present a
generalization of the method, where one can also add a number of external
templates.Comment: 21 pages, 7 figure
On the Geometry of Metastable Supersymmetry Breaking
We give a concise geometric recipe for constructing D-brane gauge theories
that exhibit metastable SUSY breaking. We present two simple examples in terms
of branes at deformed CY singularities.Comment: 31 pages, 9 figures, v2: references adde
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