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Chun E.J.,Korea Institute for Advanced Study
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

We show that supersymmetric axion models breaking the PQ symmetry by the interplay of non-renormalizable supersymmetric terms and soft supersymmetry breaking terms provide a natural framework not only for generating the axion scale from soft supersymmetry breaking scale m3/2 but also for enhancing it during inflation by factor of order HI/m3/2 where H I ≃ 1014GeV according to the recent BICEP2 result. In this scheme, the PQ symmetry can stay broken throughout the whole history of the Universe if the reheat temperature is below 1010GeV, or m3/2 when the PQ fields couple strongly to thermal (Standard Model) particles. It is also shown that parametric resonance during preheating is not effective enough to induce non-thermal PQ symmetry restoration. As a consequence, axion models with the QCD anomaly N D W > 1 can be made free from the domain wall problem while the axion isocurvature perturbation is suppressed sufficiently for the axion scale during inflation larger than about MP(Ωah2/0.12)1/2(Fa/1012GeV)0.6GeV. © 2014 Elsevier B.V. Source


Park J.-C.,Korea Institute for Advanced Study | Park S.C.,Sungkyunkwan University
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2013

In light of the recent observation of the Fermi-LAT 130 GeV gamma-ray line, we suggest a model of scalar dark matter in a hidden sector, which can decay into two (hidden) photons. The process is radiatively induced by a GUT scale fermion in the loop, which is charged under a hidden sector U(1), and the kinetic mixing (~εFμνF'μν) enables us to fit the required decay width for the Fermi-LAT peak. The model does not allow any dangerous decay channels into light standard model particles. © 2012 Elsevier B.V. Source


Kang Z.,Korea Institute for Advanced Study
European Physical Journal C | Year: 2015

In this article we propose a class of extremely light feebly interacting massive particle, FImPs. They are combination of feebly interacting massive particle with scale invariance, by which DM stability, mass origin and relic density are inherently related. In the scale invariant version of the Standard Model (SM) with three right-handed neutrinos (νSISM), the lightest N1 realizes the FImP scenario. In this example scalar singlets, which are intrinsic to the νSISM, generate mass and relic density for this FImP simultaneously. Moreover, they are badly needed for electroweak symmetry spontaneously breaking. Interestingly, a 7.1 keV N1 with correct relic density, which can explain the recent 3.55 keV X-ray line, lies in the bulk parameter space of our model. © 2015, The Author(s). Source


Tang Y.,Korea Institute for Advanced Study
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

It is generally expected that adding light sterile species would increase the effective number of neutrinos, Neff. In this paper we discuss a scenario that Neff can actually decrease due to the neutrino oscillation effect if sterile neutrinos have self-interactions. We specifically focus on the eV mass range, as suggested by the neutrino anomalies. With large self-interactions, sterile neutrinos are not fully thermalized in the early Universe because of the suppressed effective mixing angle or matter effect. As the Universe cools down, flavor equilibrium between active and sterile species can be reached after big bang nucleosynthesis (BBN) epoch, but leading to a decrease of Neff. In such a scenario, we also show that the conflict with cosmological mass bounds on the additional sterile neutrinos can be relaxed further when more light species are introduced. To be consistent with the latest Planck results, at least 3 sterile species are needed. © 2015 The Author. Source


Kang Z.,Korea Institute for Advanced Study
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

Combining feebly interacting massive particle (FIMP) dark matter (DM) with scale invariance (SI) leads to extremely light FIMP (thus the FI. mP) with FI. mP miracle, i.e., the mass and relic generations of FI. mP DM share the same dynamics. In this paper we show that due to the lightness of FI. mP, it, especially for a scalar FI. mP, can easily accommodate large DM self-interaction. For a fermionic FI. mP, such as the sterile neutrino, self-interaction additionally requires a mediator which is another FI. mP, a scalar boson with mass either much lighter or heavier than the FI. mP DM. DM self-interaction opens a new window to observe FI. mP (miracle), which does not leave traces in the conventional DM searches. As an example, FI. mP can account for the offsets between the centroid of DM halo and stars of galaxies recently observed in the galaxy cluster Abel 3827. © 2015 The Author. Source

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