2,822 research outputs found
Explanation of the 511 keV line: Cascade annihilating dark matter with the Be anomaly
A possible dark matter (DM) explanation about the long-standing issue of the
Galactic 511 keV line is explored in this paper. For DM cascade annihilations
of concern, a DM pair annihilates into unstable
, and decays into with new
interactions suggested by the Be anomaly. Considering the constraints from
the effective neutrino number and the 511 keV gamma-ray
emission, a range of DM is obtained, MeV. The typical DM annihilation cross section today is about 3.3
cm s, which can give an explanation about the 511 keV
line. The MeV scale DM may be searched by the DM-electron scattering, and the
upper limit set by the CMB s-wave annihilation is derived in DM direct
detections.Comment: 7 pages, 3 figures, in twocolum
Dark photon portal dark matter with the 21-cm anomaly
A strong absorption profile was reported by the EDGES Collaboration, which
indicates the hydrogen gas being colder than expected. It could be signatures
of non-gravitational interactions between normal matter and dark matter (DM),
and a potential explanation is that a small fraction of millicharged DM
scatters with normal matter, with the DM mass in tens of MeV. To obtain the
small fraction of millicharged DM and meanwhile being tolerant with by the
constraints, the dark photon portal scalar and vector millicharged DM are
explored in this paper. We consider that the mass of dark photon is slightly
above twice of the millicharged DM mass, and thus the millicharged DM
predominantly annihilates in p-wave during the freeze-out period, with the
annihilation being enhanced near the resonance. The dark photon mainly decays
into millicharged DM, and couplings of dark photon with SM particles could be
allowed by the lepton collision experiments. The corresponding parameter spaces
are derived. Future lepton collision experiments can be employed to search for
millicharged DM via the production of the invisible dark photon.Comment: 6 pages, 2 figures, discussions added, the accepted version, EPJ
The new interaction suggested by the anomalous Be transition sets a rigorous constraint on the mass range of dark matter
The WIMPs are considered one of the favorable dark matter (DM) candidates,
but as the upper bounds on the interactions between DM and standard model (SM)
particles obtained by the upgraded facilities of DM direct detections get lower
and lower. Researchers turn their attentions to search for less massive DM
candidates, i.e. light dark matter of MeV scale. The recently measured
anomalous transition in Be suggests that there exists a vectorial boson
which may mediate the interaction between DM and SM particles. Based on this
scenario, we combine the relevant cosmological data to constrain the mass range
of DM, and have found that there exists a model parameter space where the
requirements are satisfied, a range of 16.7
MeV for scalar DM, and 16.7 MeV for vectorial
DM is demanded. Then a possibility of directly detecting such light DM
particles via the DM-electron scattering is briefly studied in this framework.Comment: 13 Pages, 7 figures, references added, version accepted by journa
Could the 21-cm absorption be explained by the dark matter suggested by Be transitions?
The stronger than expected 21-cm absorption was observed by EDGES recently,
and another anomaly of Be transitions would be signatures of new
interactions. These two issues may be related to each other, e.g., pseudoscalar
mediated fermionic millicharged dark matter (DM), and the 21-cm absorption
could be induced by photon mediated scattering between MeV millicharged DM and
hydrogen. This will be explored in this paper. For fermionic millicharged DM
with masses in a range of , the
p-wave annihilation would be dominant during DM
freeze-out. The s-wave annihilation is tolerant by constraints from CMB and the 21-cm absorption. The
millicharged DM can evade constraints from direct detection experiments. The
process of with the invisible decay could be employed to search for the millicharged DM, and future high
intensity sources, such as NA62, will do the job.Comment: 6 pages, 2 figures, the accepted version, EPJ
Tamed loops: a way to obtain finite loop results without UV divergences
For loops with UV divergences, finite physical results obtained via mean the physical transition amplitudes of loops are not well-defined.
In this paper, a presumption that the physical contributions of loops are
finite with UV regions being insignificant is proposed, and a new method of
UV-free scheme is introduced to derive finite physical results. In this scheme,
finite loop results can be obtained without UV divergences, and the hierarchy
problem of Higgs mass can be solved without fine-tuning.Comment: 7 pages, 6 figure
Development of Roof Insulation Material from Low Density Polyethylene (LDPE), Kapok Fibre and Maerogel
The roof thermal performance exerts a strong influence in controlling the building’s interior temperature. In Malaysia, people are suffering of the hot weather throughout the year especially during daytime. This research aims to develop the most effective roof insulation materials. In order to achieve that, three types of composite roof insulation samples are created through compression molding. Besides, tensile test and thermal conductivity test are conducted. Also, simulation of the thermal performance of the composites are done by using Autodesk Ecotect. All of the composites are found to be effective as they capable to maintain the indoor temperature at lesser than 34°C which is the limit of acceptable thermal comfort temperature limit (Makaremi, Salleh, Jaafar, & GhaffarianHoseini, 2012; Wijewardane & Jayasinghe, 2008)
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