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Dark photon relic dark matter production through the dark axion portal
Kaneta, Kunio,Lee, Hye-Sung,Yun, Seokhoon American Physical Society 2017 Physical Review D Vol.95 No.11
<P>We present a new mechanism to produce the dark photon (gamma') in the early Universe with the help of the axion (a) using a recently proposed dark axion portal. The dark photon, a light gauge boson in the dark sector, can be relic dark matter if its lifetime is long enough. The main process we consider is a variant of the Primakoff process fa -> f gamma' mediated by a photon, which is possible with the axion-photon-dark photon coupling. The axion is thermalized in the early Universe because of the strong interaction and it can contribute to the nonthermal dark photon production through the dark axion portal coupling. It provides a two-component dark matter sector, and the relic density deficit issue of the axion dark matter can be addressed by the compensation with the dark photon. The dark photon dark matter can also address the reported 3.5 keV x-ray excess via the gamma'->gamma a decay.</P>
Diphoton channel at the LHC experiments to find a hint for a new heavy gauge boson
Kaneta, Kunio,Kang, Subeom,Lee, Hye-Sung World Scientific 2016 International Journal of Modern Physics A Vol.31 No.27
<P> Recently there has been a huge interest in the diphoton excess around 750 GeV reported by both ATLAS and CMS collaborations, although the newest analysis with more statistics does not seem to support the excess. Nevertheless, the diphoton channel at the LHC experiments are a powerful tool to probe a new physics. One of the most natural explanations of a diphoton excess, if it occurs, could be a new scalar boson with exotic colored particles. In this setup, it would be legitimate to ask what is the role of this new scalar in nature. A heavy neutral gauge boson [Formula: see text] is one of the traditional targets of the discovery at the collider experiments with numerous motivations. While the Landau-Yang theorem dictates the diphoton excess cannot be this spin-1 gauge boson, there is a strong correlation of a new heavy gauge boson and a new scalar boson which provides a mass to the gauge boson being at the same mass scale. In this paper, we point out a simple fact that a new scalar with a property similar to the recently highlighted 750 GeV would suggest an existence of a TeV scale [Formula: see text] gauge boson that might be within the reach of the LHC Run 2 experiments. We take a scenario of the well-motivated and popular gauged [Formula: see text] symmetry and require the gauge coupling unification to predict the mass and other properties of the [Formula: see text] and illustrate the discovery of the [Formula: see text] would occur during the LHC experiments. </P>
Portal Connecting Dark Photons and Axions
Kaneta, Kunio,Lee, Hye-Sung,Yun, Seokhoon American Physical Society 2017 Physical Review Letters Vol.118 No.10
<P>The dark photon and the axion (or axionlike particle) are popular light particles of the hidden sector. Each of them has been actively searched for through the couplings called the vector portal and the axion portal. We introduce a new portal connecting the dark photon and the axion (axion-photon-dark photon, axion-dark photon-dark photon), which emerges in the presence of the two particles. This dark axion portal is genuinely new couplings, not just from a product of the vector portal and the axion portal, because of the internal structure of these couplings. We present a simple model that realizes the dark axion portal and discuss why it warrants a rich phenomenology.</P>
Jinno, Ryusuke,Kaneta, Kunio,Oda, Kin-ya American Physical Society 2018 Physical review. D Vol.97 No.2
<P>We propose a realization of cosmic inflation with the Higgs field when the Higgs potential has degenerate vacua by employing the recently proposed idea of hill-climbing inflation. The resultant inflationary predictions exhibit a sizable deviation from those of the ordinary Higgs inflation.</P>
Hillclimbing inflation in metric and Palatini formulations
Jinno, Ryusuke,Kaneta, Kunio,Oda, Kin-ya,Park, Seong Chan North-Holland Pub. Co 2019 Physics letters. Section B Vol.791 No.-
<P><B>Abstract</B></P> <P>A new setup of cosmic inflation with a periodic inflaton potential and conformal factor is discussed in the metric and Palatini formulations of gravity. As a concrete example, we focus on a natural-inflation-like inflaton potential, and show that the inflationary predictions fall into the allowed region of cosmic microwave background observations in both formulations.</P>
Sterile neutrino dark matter from right-handed neutrino oscillations
Kadota, Kenji,Kaneta, Kunio American Physical Society 2018 Physical Review D Vol.97 No.11
<P>We study a scenario where sterile neutrino (either warm or cold) dark matter (DM) is produced through (nonresonant) oscillations among right-handed neutrinos (RHNs) and can constitute the whole DM in the Universe, in contrast to the conventional sterile neutrino production through its mixing with the left-handed neutrinos. The lightest RHN can be sterile neutrino DM whose mixing with left-handed neutrinos is sufficiently small while heavier RHNs can have non-negligible mixings with left-handed neutrinos to explain the neutrino masses by the seesaw mechanism. We also demonstrate that, in our scenario, the production of sterile RHN DM from the decay of a heavier RHN is subdominant compared with the RHN oscillation production due to the x-ray and small-scale structure constraints.</P>
Kanemura, Shinya,Kaneta, Kunio,Machida, Naoki,Odori, Shinya,Shindou, Tetsuo American Physical Society 2016 Physical Review D Vol.94 No.1
<P>In the composite Higgs models, originally proposed by Georgi and Kaplan, the Higgs boson is a pseudo Nambu-Goldstone boson (pNGB) of spontaneous breaking of a global symmetry. In the minimal version of such models, global SO(5) symmetry is spontaneously broken to SO(4), and the pNGBs form an isospin doublet field, which corresponds to the Higgs doublet in the Standard Model (SM). Predicted coupling constants of the Higgs boson can in general deviate from the SM predictions, depending on the compositeness parameter. The deviation pattern is determined also by the detail of the matter sector. We comprehensively study how the model can be tested via measuring single and double production processes of the Higgs boson at the LHC and future electron-positron colliders. The possibility to distinguish the matter sector among the minimal composite Higgs models is also discussed. In addition, we point out differences in the cross section of double Higgs boson production from the prediction in other new physics models.</P>
Jinno, Ryusuke,Kaneta, Kunio American Physical Society 2017 Physical Review D Vol.96 No.4
<P>We propose a new class of inflationary models in which inflation takes place while the inflaton is climbing up a potential hill due to a coupling to gravity. We study their attractor behavior, and investigate its relation with known attractors. We also discuss a possible realization of this type of models with natural inflation, and show that the inflationary predictions come well within the region consistent with the observation of the cosmic microwave background.</P>