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Can a Higgs portal Dark Matter be compatible with the anti-proton cosmic-ray?
Okada, H.,Toma, T. North-Holland Pub. Co 2012 Physics letters: B Vol.713 No.3
Recent direct detection experiments of Dark Matter (DM), CoGeNT and DAMA implicate a light DM of a few GeV. Such a light DM would generate a large amount of anti-proton since suppression for anti-proton flux from DM annihilation is ineffective. We discuss whether a light dark matter with mass of 5-15 GeV, which is especially in favor of the recent experiments reported by CoGeNT, is compatible with the anti-proton no excess in the cosmic-ray. In view of the direct detection of DM and no anti-proton excess in the cosmic-ray both, we show that a Dirac DM is favored than a scalar one since there is no s-wave of the annihilation cross section for the Dirac DM. A large elastic cross section for direct detection can be obtained through the additional light Higgs exchange. We show an allowed region that simultaneously satisfies the DM relic density, the elastic cross section favored by CoGeNT and also the constraint of H<SUB>L</SUB>ZZ coupling of the light Higgs boson by LEP.
Effect of degenerate particles on internal bremsstrahlung of Majorana dark matter
Okada, H.,Toma, T. North-Holland Pub. Co 2015 Physics letters. Section B Vol.750 No.-
Gamma-rays induced by annihilation or decay of dark matter can be its smoking gun signature. In particular, gamma-rays generated by internal bremsstrahlung of Majorana and real scalar dark matter is promising since it can be a leading emission of sharp gamma-rays. However in the case of Majorana dark matter, its cross section for internal bremsstrahlung cannot be large enough to be observed by future gamma-ray experiments if the observed relic density is assumed to be thermally produced. In this paper, we introduce some degenerate particles with Majorana dark matter, and show they lead enhancement of the cross section. As a result, increase of about one order of magnitude for the cross section is possible without conflict with the observed relic density, and it would be tested by the future gamma-ray experiments such as GAMMA-400 and Cherenkov Telescope Array (CTA). In addition, the constraints of perturbativity, positron observation by the AMS experiment and direct search for dark matter are discussed.
3.55 keV X-ray line signal from excited dark matter in radiative neutrino model
Okada, H.,Toma, T. Elsevier 2014 Physics letters: B Vol.737 No.-
We study an exciting dark matter scenario in a radiative neutrino model to explain the X-ray line signal at 3.55 keV recently reported by XMN-Newton X-ray observatory using data of various galaxy clusters and Andromeda galaxy. We show that the required large cross section for the up-scattering process to explain the X-ray line can be obtained via the resonance of the pseudo-scalar. Moreover, this model can be compatible with the thermal production of dark matter and the constraint from the direct detection experiment.
Classically conformal radiative neutrino model with gauged B-L symmetry
Okada, H.,Orikasa, Y. North-Holland Pub. Co 2016 Physics letters. Section B Vol.760 No.-
We propose a classically conformal model in a minimal radiative seesaw, in which we employ a gauged B-L symmetry in the standard model that is essential in order to work the Coleman-Weinberg mechanism well that induces the B-L symmetry breaking. As a result, nonzero Majorana mass term and electroweak symmetry breaking simultaneously occur. In this framework, we show a benchmark point to satisfy several theoretical and experimental constraints. Here theoretical constraints represent inert conditions and Coleman-Weinberg condition. Experimental bounds come from lepton flavor violations (especially μ→eγ), the current bound on the Z<SUP>'</SUP> mass at the CERN Large Hadron Collider, and neutrino oscillations.
Neutron and proton energy spectra from the non-mesonic weak decays of HeΛ5 and CΛ12
Okada, S.,Ajimura, S.,Aoki, K.,Banu, A.,Bhang, H.C.,Fukuda, T.,Hashimoto, O.,Hwang, J.I.,Kameoka, S.,Kang, B.H.,Kim, E.H.,Kim, J.H.,Kim, M.J.,Maruta, T.,Miura, Y.,Miyake, Y.,Nagae, T.,Nakamura, M.,Nak Elsevier 2004 Physics letters: B Vol.597 No.3
<P><B>Abstract</B></P><P>We have simultaneously measured the energy spectra of neutrons and protons emitted in the non-mesonic weak decays of HeΛ5 and CΛ12 hypernuclei produced via the (<SUP>π+</SUP>,<SUP>K+</SUP>) reaction with much higher statistics than those of previous experiments. The neutron-to-proton yield ratios for both hypernuclei at a high energy threshold (60 MeV) were approximately equal to two, which suggests that the ratio of the neutron- and proton-induced decay channels, <SUB>Γn</SUB>(Λn→nn)/<SUB>Γp</SUB>(Λp→np), is about 0.5. In the neutron energy spectra, we found that the yield of the low-energy component is unexpectedly large, even for HeΛ5.</P>
The Weak Decay Widths of Λ Hypernuclei
H. Bhang,S. Ajimura,K. Aoki,A. Banu,T. Fukuda,O. Hashimoto,J. I. Hwang,S. Kameoka,B. H. Kang,E. Kim,김정호,T. Maruta,Y. Miura,Y. Miyake,T. Nagae,M. Nakamura,S. N. Nakamura,H. Noumi,S. Okada,Y. Okayasu,H. 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
We have measured both the mesonic and nonmesonic weak decay widths of ^(12)_ΛC. For the mesonic decay, we have improved the accuracy of Γ_π^0 so that it reduced the error of Γ_(nm) from ≥10% to ≤5%. For the nonmesonic decay, we have solved the long standing Γ_n/Γ_p puzzle by measuring the ratio 0.51 ± 0.14 in the exclusive measurement. At the same time we have measured the width of the 3-body nonmesonic decay Γ_(2N) = 0.27 ± 0.13 for the first time. Combining the accurate Γ_n/Γ_p ratio and the first measured value Γ_(2N), we have finally obtained the Γ_n and Γ_p themselves taking account of the 3-body process. We have measured all the weak decay widths of _(12)_ΛC so that it provides the first complete set of widths for the investigation of ΔS = 1 baryon-baryon weak interaction.
Renormalizable model for neutrino mass, dark matter, muon g-2 and 750 GeV diphoton excess
Okada, H.,Yagyu, K. North-Holland Pub. Co 2016 Physics letters. Section B Vol.756 No.-
We discuss a possibility to explain the 750 GeV diphoton excess observed at the LHC in a three-loop neutrino mass model which has a similar structure to the model by Krauss, Nasri and Trodden. Tiny neutrino masses are naturally generated by the loop effect of new particles with their couplings and masses to be of order 0.1-1 and TeV, respectively. The lightest right-handed neutrino, which runs in the three-loop diagram, can be a dark matter candidate. In addition, the deviation in the measured value of the muon anomalous magnetic moment from its prediction in the standard model can be compensated by one-loop diagrams with exotic multi-charged leptons and scalar bosons. For the diphoton event, an additional isospin singlet real scalar field plays the role to explain the excess by taking its mass of 750 GeV, where it is produced from the gluon fusion production via the mixing with the standard model like Higgs boson. We find that the cross section of the diphoton process can be obtained to be a few fb level by taking the masses of new charged particles to be about 375 GeV and related coupling constants to be order 1.