956 research outputs found
Lepton flavor violation in lopsided models and a neutrino mass model
A widely adopted theoretical scheme to account for the neutrino oscillation
phenomena is the see-saw mechanism together with the ``lopsided'' mass
matrices, which is generally realized in the framework of supersymmetric grand
unification. We will show that this scheme leads to large lepton flavor
violation at low energy if supersymmetry is broken at the GUT or Plank scale.
Especially, the branching ratio of already exceeds the present
experimental limit. We then propose a phenomenological model, which can account
for the LMA solution to the solar neutrino problem and at the same time predict
branching ratio of below the present limit.Comment: 15 pages, 4 figure
Perspective of Galactic dark matter subhalo detection on Fermi from the EGRET observation
The perspective of the detectability of Galactic dark matter subhaloes on the
Fermi satellite is investigated in this work. Under the assumptions that dark
matter annihilation accounts for the "GeV excess" of the Galactic diffuse
-rays discovered by EGRET and the -ray flux is dominated by the
contribution from subhaloes of dark matter, we calculate the expected number of
dark matter subhaloes that Fermi may detect. We show that Fermi may detect a
few tens to several hundred subhaloes in 1-year all sky survey. Since EGRET
observation is taken as a normalization, this prediction is independent of the
particle physics property of dark matter. The uncertainties of the prediction
are discussed in detail. We find that the major uncertainty comes from the mass
function of subhaloes, i.e., whether the subhaloes are "point like" (high-mass
rich) or "diffuse like" (low-mass rich). Other uncertainties like the
background estimation and the observational errors will contribute a factor of
.Comment: 16 pages, 4 figures and 1 table, accepted for publication in Chinese
Physics
Cosmic e^\pm, \bar p, \gamma and neutrino rays in leptocentric dark matter models
Dark matter annihilation is one of the leading explanations for the recently
observed excesses in cosmic rays by PAMELA, ATIC, FERMI-LAT and HESS.
Any dark matter annihilation model proposed to explain these data must also
explain the fact that PAMELA data show excesses only in spectrum but
not in anti-proton. It is interesting to ask whether the annihilation mode into
anti-proton is completely disallowed or only suppressed at low energies. Most
models proposed have negligible anti-protons in all energy ranges. We show that
the leptocentric dark matter model can explain the
excesses with suppressed anti-proton mode at low energies, but at higher
energies there are sizable anti-proton excesses. Near future data from PAMELA
and AMS can provide crucial test for this type of models. Cosmic ray
data can further rule out some of the models. We also show that this model has
interesting cosmic neutrino signatures.Comment: Latex 20 pages and five figures. References adde
Diffuse -rays and flux from dark matter annihilation -- a model for consistent results with EGRET and cosmic ray data
In this work we develop a new propagation model for the Galactic cosmic rays
based on the GALPROP code, including contributions from dark matter
annihilation. The model predicts compatible Galactic diffuse ray
spectra with EGRET data in all sky regions. It also gives consistent results of
the diffuse ray longitude and latitude distributions. Further the
results for B/C, Be/Be, proton, electron and antiproton spectra are
also consistent with cosmic ray measurements. In the model we have taken a
universal proton spectrum throughout the Galaxy without introducing large
fluctuation for the proton energy loss is negligible. The dark matter
annihilation signals are `boosted' after taking the contribution from subhalos
into account. Another interesting feature of the model is that it gives better
description of the diffuse rays when taking the source distribution
compatible with supernova remnants data, which is different from previous
studies.Comment: 29 pages, 13 figures; the published versio
Slow diffusion around pulsar -ray halos and its impact on cosmic rays propagation
The diffusion coefficients around the pulsar -ray halos are highly
suppressed compared with the value in the interstellar medium. It is suggested
in the literature that the -ray halos can be explained by a
ballistic-diffusive (BD) propagation without slow diffusion. However our
calculation shows that the BD propagation can not account for the -ray
halo profile well. Furthermore the transfer efficiency of the pulsar spin down
energy to the high energy electrons and positrons is even larger than 1 in the
BD scenario. Therefore slow diffusion is necessary to account for the pulsar
-ray halos. Taking the slow diffusion into account the contribution of
positron flux originated from nearby pulsars to the AMS-02 data is reexamined.
We may also expect a slow diffusion disk of the Milky Way as many such slow
diffusion regions exist. The positron contribution to the AMS-02 data from dark
matter annihilation in the new propagation model is also reexamined. We find
that the dark matter scenario satisfies all the -ray limits in the new
propagation model.Comment: 10 pages, 8 figures. Proceedings of the 38th International Cosmic Ray
Conference (ICRC2023) in Nagoya, Japa
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