Korea Institute for Advanced Study

Seoul, South Korea

Korea Institute for Advanced Study

Seoul, South Korea

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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.


Ko P.,Korea Institute for Advanced Study | Tang Y.,Korea Institute for Advanced Study
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

We propose an ultraviolet complete theory for cold dark matter (CDM) and sterile neutrinos that can accommodate both cosmological data and neutrino oscillation experiments within 1σ level. We assume a new U(1)X dark gauge symmetry which is broken at ~O(MeV) scale resulting light dark photon. Such a light mediator for DM's self-scattering and scattering-offsterile neutrinos can resolve three controversies for cold DM on small cosmological scales: cusp vs. core, too-big-to-fail and missing satellites. We can also accommodate ~O(1)eV scale sterile neutrinos as the hot dark matter (HDM) and can fit some neutrino anomalies from neutrino oscillation experiments within 1σ. Finally, the right amount of HDM can make a sizable contribution to dark radiation, and also helps to reconcile the tension between the data on the tensor-to-scalar ratio reported by Planck and BICEP2 Collaborations. © 2014 The Authors.


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.


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

CMS and ATLAS have searched for a doubly-charged boson H±± which may arise from type II seesaw in the 7 TeV run at the LHC by considering pair or associated production of doubly-charged bosons under the assumption of degenerate triplet scalars. In this work, we consider non-degenerate triplet components with the mass gap ΔM ~ 1-40 GeV which leads to enhanced pair-production cross-sections of H±± added by the gauge decays of the heavier neutral and singly-charged bosons. We reevaluate the constraints in the ΔM-MH++ plane depending on the triplet vacuum expectation value vΔ in the type II seesaw model which are much more stringent than the current search limits. We further study the possibility of observing same-sign tetra-lepton signals in the allowed parameter space which can be probed in the future runs of the LHC © 2013 The Authors. Published by Elsevier B.V.


Chun E.J.,Korea Institute for Advanced Study
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

The Kim-Nilles mechanism relates the μ term with the axion scale f a, leading to the axino-Higgsino-Higgs Yukawa coupling of order μ/f a. This can bring a dangerous thermal production of axinos. If the axino is stable, its mass has to be as small as O(0.1keV), or the reheat temperature should be lower than O(10GeV) taking the lower axion scale 10 10GeV in order not to overclose the Universe. If the axino decays to a neutralino, the overproduced neutralinos can reannihilate appropriately to saturate the observed dark matter density if the annihilation rate is of order 10 -8 GeV -2 for the axion scale larger than about 1011GeV. Thus, a light Higgsino-like lightest supersymmetric particle with a sizable bino mixture becomes a good dark matter candidate whose nucleonic cross section is larger than about 10 -45cm 2. © 2011 American Physical Society.


Lee K.,Korea Institute for Advanced Study
Nuclear Physics B | Year: 2015

We investigate α'-corrections of heterotic double field theory up to quadratic order in the language of supersymmetric O(D, D+dim G) gauged double field theory. After introducing double-vielbein formalism with a parametrization which reproduces heterotic supergravity, we show that supersymmetry for heterotic double field theory up to leading order α'-correction is obtained from supersymmetric gauged double field theory. We discuss the necessary modifications of the symmetries defined in supersymmetric gauged double field theory. Further, we construct supersymmetric completion at quadratic order in α'. © 2015 The Author.


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.


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.


Chun E.J.,Korea Institute for Advanced Study
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

The Dirac nature of the gauginos (and also the Higgsinos) can be realized in R-symmetric supersymmetry models. In this class of models, the Dirac bino (or wino) with a small mixture of the Dirac Higgsinos is a good dark matter candidate. When the seesaw mechanism with Higgs triplet superfields is implemented to account for the neutrino masses and mixing, the leptogenesis driven by the heavy triplet decay is shown to produce not only the matter-antimatter asymmetry, but also the asymmetric relic density of the Dirac gaugino dark matter. The dark matter mass turns out to be controlled by the Yukawa couplings of the heavy Higgs triplets, and it can be naturally at the weak scale for a mild hierarchy of the Yukawa couplings. © 2011 American Physical Society.


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).

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