236 research outputs found
Non-binding of Flavor-Singlet Hadrons to Nuclei
Strongly attractive color forces in the flavor singlet channel may lead to a
stable H dibaryon. Here we show that an H or other compact, flavor singlet
hadron is unlikely to bind to nuclei, so that bounds on exotic isotopes do not
exclude their stability. Remarkably, a stable H appears to evade other
experimental constraints as well, when account is taken of its expected compact
spatial wavefunction.Comment: 10 pages, 2 figure
Bremsstrahlung gamma rays from light Dark Matter
We discuss the often-neglected role of bremsstrahlung processes on the
interstellar gas in computing indirect signatures of Dark Matter (DM)
annihilation in the Galaxy, particularly for light DM candidates in the
phenomenologically interesting O(10) GeV mass range. Especially from directions
close to the Galactic Plane, the expected gamma-ray spectrum is altered via two
effects: directly, by the photons emitted in the bremsstrahlung process on the
interstellar gas by energetic electrons which are among the DM annihilation
byproducts; indirectly, by the modification of the same electron spectrum, due
to the additional energy loss process in the diffusion-loss equation (e.g. the
resulting inverse Compton emission is altered). We quantify the importance of
the bremsstrahlung emission in the GeV energy range, showing that it is the
dominant component of the gamma-ray spectrum for some cases. We also find that,
in regions in which bremsstrahlung dominates energy losses, the related
gamma-ray emission is only moderately sensitive to possible large variations in
the gas density. Still, we stress that, for computing precise spectra in the
(sub-)GeV range, it is important to obtain a reliable description of the inner
Galaxy gas distribution as well as to compute self-consistently the gamma
emission and the solution to the diffusion-loss equation. For example, these
are crucial issues to quantify and interpret meaningfully gamma-ray map
`residuals' in terms of (light) DM annihilations.Comment: 17 pages, 5 figures, 1 table; references added, changed to match the
published versio
A Window in the Dark Matter Exclusion Limits
We consider the cross section limits for light dark matter candidates
( to 10 GeV). We calculate the interaction of dark matter in the crust
above underground dark matter detectors and find that in the intermediate cross
section range, the energy loss of dark matter is sufficient to fall below the
energy threshold of current underground experiments. This implies the existence
of a window in the dark matter exclusion limits in the micro-barn range.Comment: 10 pages, 8 figure
Galactic Center gamma-ray "excess" from an active past of the Galactic Centre?
Several groups have recently claimed evidence for an unaccounted gamma-ray
excess over {the} diffuse backgrounds at few GeV in {the} Fermi-LAT data in a
region around the Galactic Center, consistent with a dark matter annihilation
origin. We demonstrate that the main spectral and angular features of this
excess can be reproduced if they are mostly due to inverse Compton emission
from high-energy electrons injected in a burst event of ~10^52 - 10^53erg
roughly O(10^6) years ago. We consider this example as a proof of principle
that time-dependent phenomena need to be understood and accounted for -
together with detailed diffuse foregrounds and unaccounted "steady state"
astrophysical sources - before any robust inference can be made about dark
matter signals at the Galactic Center. In addition, we point out that the
timescale suggested by our study, which controls both the energy cutoff and the
angular extension of the signal, intriguingly matches (together with the energy
budget) what is indirectly inferred by other evidences suggesting a very active
Galactic Center in the past, for instance related to intense star formation and
accretion phenomena.Comment: 6 pages, 4 figures. Minor scale correction plus a typo in a figure
label. Conclusions unchange
Consequences of DM/antiDM Oscillations for Asymmetric WIMP Dark Matter
Assuming the existence of a primordial asymmetry in the dark sector, a
scenario usually dubbed Asymmetric Dark Matter (aDM), we study the effect of
oscillations between dark matter and its antiparticle on the re-equilibration
of the initial asymmetry before freeze-out, which enable efficient
annihilations to recouple. We calculate the evolution of the DM relic abundance
and show how oscillations re-open the parameter space of aDM models, in
particular in the direction of allowing large (WIMP-scale) DM masses. A typical
wimp with a mass at the EW scale (\sim 100 GeV - 1 TeV) presenting a primordial
asymmetry of the same order as the baryon asymmetry naturally gets the correct
relic abundance if the DM-number-violating Delta(DM) = 2 mass term is in the
\sim meV range. The re-establishment of annihilations implies that constraints
from the accumulation of aDM in astrophysical bodies are evaded. On the other
hand, the ordinary bounds from BBN, CMB and indirect detection signals on
annihilating DM have to be considered.Comment: 27 pages, 6+1 figures; v2: version submitted to JCAP for publication,
one new figure and one new table added, summary plots slightly revised, a few
clarifications added, main point emphasized, results unchange
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