539 research outputs found
Decaying axinolike dark matter: Discriminative solution to small-scale issues
The latest Lyman- forest data severely constrain the conventional
warm dark matter solution to small-scale issues in the cold dark matter
paradigm. It has been also reported that unconstrained astrophysical processes
may address the issues. In response to this situation, we revisit the decaying
dark matter solution to the issues, discussing possible signatures to
discriminate decaying dark matter from astrophysical processes as a solution to
small-scale issues. We consider an axinolike particle (ALPino) decaying into an
axionlike particle (ALP) and gravitino with the lifetime around the age of the
Universe. The ALPino mass is sub-PeV and slightly ()
larger than the gravitino mass, and thus the dark matter abundance does not
alter virtually after the ALPino decays. On the other hand, the gravitino
produced from the ALPino decay obtains a kick velocity of , which is sufficiently larger than a circular velocity of dwarf galaxies to
impact their dark matter distributions. The Lyman- forest constraints
are relieved since only a small fraction (%) of dark matter experiences
the decay at that time. Decaying dark matter is thus promoted to a viable
solution to small-scale issues. The ALPino relic abundance is determined
predominantly by the decay of the lightest ordinary supersymmetric particle.
The monochromatic ALP emission from the ALPino decay is converted to photon under the Galactic magnetic field. The morphology of the
gamma-ray flux shows a distinctive feature of the model when compared to
decaying dark matter that directly decays into photons. Once detected, such
distinctive signals discriminate the decaying dark matter solution to
small-scale issues from unconstrained astrophysical processes.Comment: 6 pages, 3 figures; discussions improved, version accepted in PR
Probing the origin of 750 GeV diphoton excess with the precision measurements at the ILC
The recently reported diphoton excess at the LHC may imply the existence of a
new resonance with a mass of about 750 GeV which couples to photons via loops
of new charged particles. In this letter, we study the possibility to test such
models at the ILC, paying attention to the new charged particles responsible
for the diphoton decay of the resonance. We show that they affect the
scattering processes (with denoting Standard Model
fermions) at the ILC, which makes it possible to indirectly probe the new
charged particles even if they are out of the kinematical reach. We also show
that the discriminations of the diphoton models may be possible based on a
study of the angular distributions of .Comment: 14 pages, 5 figure
Mixed axion-wino dark matter
A variety of supersymmetric models give rise to a split mass spectrum
characterized by very heavy scalars but sub-TeV gauginos, usually with a
wino-like LSP. Such models predict a thermally-produced underabundance of
wino-like WIMP dark matter so that non-thermal DM production mechanisms are
necessary. We examine the case where theories with a wino-like LSP are
augmented by a Peccei-Quinn sector including an axion-axino-saxion
supermultiplet in either the SUSY KSVZ or SUSY DFSZ models and with/without
saxion decays to axions/axinos. We show allowed ranges of PQ breaking scale f_a
for various cases which are generated by solving the necessary coupled
Boltzmann equations. We also present results for a model with
radiatively-driven naturalness but with a wino-like LSP.Comment: 25 pages including 14 .png figure
Colder Freeze-in Axinos Decaying into Photons
We point out that 7 keV axino dark matter (DM) in the R-parity violating
(RPV) supersymmetric (SUSY) Dine-Fischler-Srednicki-Zhitnitsky model can
simultaneously reproduce the 3.5keV X-ray excess, and evade stringent
constraints from the Ly-alpha forest data. Peccei-Quinn symmetry breaking
naturally generates both axino interactions with minimal SUSY standard model
particles and RPV interactions. The RPV interaction introduces an
axino-neutrino mixing and provides axino DM as a variant of sterile neutrino
DM, whose decay into a monochromatic photon can be detected by X-ray
observations. Axinos, on the other hand, are produced by freeze-in processes of
thermal particles in addition to the Dodelson-Widrow mechanism of sterile
neutrinos. The resultant phase space distribution tends to be colder than the
Fermi-Dirac distribution. The inherent entropy production from late-time saxion
decay makes axinos even colder. The linear matter power spectrum satisfies even
the latest and strongest constraints from the Ly-alpha forest data.Comment: 5 pages, 4 figure
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