899 research outputs found
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
Sterile neutrinos, lepton asymmetries, primordial elements: how much of each?
We investigate quantitatively the extent to which having a primordial
leptonic asymmetry (n_nu \neq n_nubar) relaxes the bounds on light sterile
neutrinos imposed by BBN and LSS. We adopt a few assumptions that allow us to
solve the neutrino evolution equations over a broad range of mixing parameters
and asymmetries. For the general cases of sterile mixing with the electron or
muon neutrino, we identify the regions that can be reopened. For the particular
case of a LSND-like sterile neutrino, soon to be rejected or confirmed by
MiniBooNE, we find that an asymmetry of the order of 10^-4 is needed to lift
the conflicts with cosmology.Comment: 18 pages, 2 figures. v2: References and minor comments added. Matches
version published on PR
AMS-02 antiprotons, at last! Secondary astrophysical component and immediate implications for Dark Matter
Using the updated proton and helium fluxes just released by the AMS-02
experiment we reevaluate the secondary astrophysical antiproton to proton ratio
and its uncertainties, and compare it with the ratio preliminarly reported by
AMS-02. We find no unambiguous evidence for a significant excess with respect
to expectations. Yet, some preference for a flatter energy dependence of the
diffusion coefficient starts to emerge. Also, we provide a first assessment of
the room left for exotic components such as Galactic Dark Matter annihilation
or decay, deriving new stringent constraints.Comment: 12 pages, 5 figures; Comments and clarifications added (including an
appendix), matches version published on JCA
Pseudo-Familon Dark Matter
Motivated by a model of pseudo-Majoron dark matter, we show how the breaking
of a global symmetry that acts nontrivially in lepton generation space can lead
to a viable pseudo-familon dark matter candidate. Unlike the pseudo-Majoron,
the pseudo-familon in our model decays primarily to charged leptons and can
account for the excess observed in the cosmic ray electron and positron
spectra.Comment: 12 pages LaTeX, 1 figur
Correlation experiments in nonlinear quantum mechanics
We show how one can compute multiple-time multi-particle correlation
functions in nonlinear quantum mechanics in a way which guarantees locality of
the formalism.Comment: Section on causally related corelation experiments is added (Russian
roulette with a cheating player as an analogue of nonlinear EPR problem); to
be published in Phys. Lett. A 301 (2002) 139-15
MetodologĂa de la enseñanza de la filosofĂa desde el punto de vista antropolĂłgico
Fil: Cirelli, Alberto D..
Universidad Nacional de CĂłrdob
Can multistate dark matter annihilation explain the high-energy cosmic ray lepton anomalies?
Multistate dark matter (DM) models with small mass splittings and couplings
to light hidden sector bosons have been proposed as an explanation for the
PAMELA/Fermi/H.E.S.S. high-energy lepton excesses. We investigate this proposal
over a wide range of DM density profiles, in the framework of concrete models
with doublet or triplet dark matter and a hidden SU(2) gauge sector that mixes
with standard model hypercharge. The gauge coupling is bounded from below by
the DM relic density, and the Sommerfeld enhancement factor is explicitly
computable for given values of the DM and gauge boson masses M, mu and the
(largest) dark matter mass splitting delta M_{12}. Sommerfeld enhancement is
stronger at the galactic center than near the Sun because of the radial
dependence of the DM velocity profile, which strengthens the inverse Compton
(IC) gamma ray constraints relative to usual assumptions. We find that the
PAMELA/Fermi/H.E.S.S. lepton excesses are marginally compatible with the model
predictions, and with CMB and Fermi gamma ray constraints, for M ~ 800 GeV, mu
~ 200 MeV, and a dark matter profile with noncuspy Einasto parameters alpha >
0.20, r_s ~ 30 kpc. We also find that the annihilating DM must provide only a
subdominant (< 0.4) component of the total DM mass density, since otherwise the
boost factor due to Sommerfeld enhancement is too large.Comment: 20 pages, 12 figures; v2: Corrected branching ratio for ground state
DM annihilations into leptons, leading to boost factors that are larger than
allowed. Added explicit results for doublet DM model. Some conclusions
changed; main conclusion of tension between inverse Compton constraints and
N-body simulations of halo profiles is unchange
Diffuse gamma ray constraints on annihilating or decaying Dark Matter after Fermi
We consider the diffuse gamma ray data from FERMI first year observations and
compare them to the gamma ray fluxes predicted by Dark Matter annihilation or
decay (both from prompt emission and from Inverse Compton Scattering), for
different observation regions of the sky and a range of Dark Matter masses,
annihilation/decay channels and Dark Matter galactic profiles. We find that the
data exclude large regions of the Dark Matter parameter space not constrained
otherwise and discuss possible directions for future improvements. Also, we
further constrain Dark Matter interpretations of the e+e- PAMELA/FERMI spectral
anomalies, both for the annihilating and the decaying Dark Matter case: under
very conservative assumptions, only models producing dominantly mu+mu- and
assuming a cored Dark Matter galactic profile can fit the lepton data with
masses around 2 TeV.Comment: 16 pages, 4 figures. v2: Matches version published on Nuclear Physics
B; discussion on the uncertainties related to magnetic field models added in
an appendix, some typos corrected and some references added, conclusions
unchange
Thermal decoupling and the smallest subhalo mass in dark matter models with Sommerfeld-enhanced annihilation rates
We consider dark matter consisting of weakly interacting massive particles
(WIMPs) and revisit in detail its thermal evolution in the early universe, with
a particular focus on models where the annihilation rate is enhanced by the
Sommerfeld effect. After chemical decoupling, or freeze-out, dark matter no
longer annihilates but is still kept in local thermal equilibrium due to
scattering events with the much more abundant standard model particles. During
kinetic decoupling, even these processes stop to be effective, which eventually
sets the scale for a small-scale cutoff in the matter density fluctuations.
Afterwards, the WIMP temperature decreases more quickly than the heat bath
temperature, which causes dark matter to reenter an era of annihilation if the
cross-section is enhanced by the Sommerfeld effect. Here, we give a detailed
and self-consistent description of these effects. As an application, we
consider the phenomenology of simple leptophilic models that have been
discussed in the literature and find that the relic abundance can be affected
by as much two orders of magnitude or more. We also compute the mass of the
smallest dark matter subhalos in these models and find it to be in the range of
about 10^{-10} to 10 solar masses; even much larger cutoff values are possible
if the WIMPs couple to force carriers lighter than about 100 MeV. We point out
that a precise determination of the cutoff mass allows to infer new limits on
the model parameters, in particular from gamma-ray observations of galaxy
clusters, that are highly complementary to existing constraints from g-2 or
beam dump experiments.Comment: minor changes to match published versio
Avoiding BBN Constraints on Mirror Models for Sterile Neutrinos
We point out that in models that explain the LSND result for neutrino
oscillation using the mirror neutrinos, the big bang nucleosynthesis constraint
can be avoided by using the late time phase transition that only helps to mix
the active and the sterile neutrinos. We discuss the astrophysical as well as
cosmological implications of this proposal.Comment: 5 pages, latex; more discussion added; results unchange
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