arXiv subjects

Kwang Sik Jeong

Publications and source records attributed to Kwang Sik Jeong.

At least 55 records · Page 3Linked to original sources

arXiv2013

Higgs mixing and diphoton rate enhancement in NMSSM models

We study the implications of the LHC Higgs signals on the Higgs mixing in the next-to-minimal supersymmetric standard model (NMSSM). The Higgs couplings can depart from their values in the standard model (SM) due to mixing effects. However the Higgs signal rate in the WW and ZZ channels can remain close to the SM values, as observed at the LHC, even if the SM-like Higgs boson with a mass near 125 GeV has a large singlet component. This allows to get a sizable enhancement in the Higgs to diphoton rate through the charged-higgsino loop contribution, as well as a sizable reduction of the Higgs to bb and tautau rates through the mixing effects, with little deviation in the WW and ZZ signal rates from the SM prediction. We find that an enhancement of diphoton signals by a factor of 1.5 or more, and also a reduction of bb and tautau signals by a factor of 0.5, can be obtained in the region of parameter space consistent with the constraints on the higgsino mass parameter and the singlet coupling to the Higgs doublets, which determine the Higgs mixing.

hep-ph↗

arXiv2013

A Parallel World in the Dark

The baryon-dark matter coincidence is a long-standing issue. Interestingly, the recent observations suggest the presence of dark radiation, which, if confirmed, would pose another coincidence problem of why the density of dark radiation is comparable to that of photons. These striking coincidences may be traced back to the dark sector with particle contents and interactions that are quite similar, if not identical, to the standard model: a dark parallel world. It naturally solves the coincidence problems of dark matter and dark radiation, and predicts a sterile neutrino(s) with mass of ${\cal O}(0.1 - 1)$\,eV, as well as self-interacting dark matter made of the counterpart of ordinary baryons. We find a robust prediction for the relation between the abundance of dark radiation and the sterile neutrino, which can serve as the smoking-gun evidence of the dark parallel world.

hep-ph↗

arXiv2012

Hybrid inflation in high-scale supersymmetry

In hybrid inflation, the inflaton generically has a tadpole due to gravitational effects in supergravity, which significantly changes the inflaton dynamics in high-scale supersymmetry. We point out that the tadpole can be cancelled if there is a supersymmetry breaking singlet with gravitational couplings, and in particular, the cancellation is automatic in no-scale supergravity. We consider the LARGE volume scenario as a concrete example and discuss the compatibility between the hybrid inflation and the moduli stabilization. We also point out that the dark radiation generated by the overall volume modulus decay naturally relaxes a tension between the observed spectral index and the prediction of the hybrid inflation.

hep-ph↗

arXiv2012

A Gravitino-rich Universe

The gravitino may well play an important role in cosmology, not only because its interactions are Planck-suppressed and therefore long-lived, but also because it is copiously produced via various processes such as particle scatterings in thermal plasma, and (pseudo) modulus and inflaton decays. We study a possibility that the early Universe was gravitino-rich from various aspects. In particular, a viable cosmology is possible, if high-scale supersymmetry is realized in nature as suggested by the recent discovery of the standard-model like Higgs boson of mass about 125-126 GeV. We find that the Universe can be even gravitino-dominated, in which case there will be an entropy dilution by the gravitino decay. If the gravitino abundance is proportional to the reheating temperature, both the maximal baryon asymmetry in leptogenesis and the dark matter from the gravitino decay become independent of the reheating temperature. The dark matter candidate is the Wino-like neutralino, whose mass is suppressed compared to the anomaly-mediation relation.

hep-ph↗

arXiv2012

Light Higgsino in Heavy Gravitino Scenario with Successful Electroweak Symmetry Breaking

We consider, in the context of the minimal supersymmetric standard model, the case where the gravitino weighs 10^6 GeV or more, which is preferred by various cosmological difficulties associated with unstable gravitinos. Despite the large Higgs mixing parameter B together with the little hierarchy to other soft supersymmetry breaking masses, a light higgsino with an electroweak scale mass leads to successful electroweak symmetry breaking, at the price of fine-tuning the higgsino mixing mu parameter. Furthermore the light higgsinos produced at the decays of gravitinos can constitute the dark matter of the universe. The heavy squark mass spectrum of O(10^4) GeV can increase the Higgs boson mass to about 125 GeV or higher.

hep-ph↗

arXiv2012

Singlet-doublet Higgs mixing and its implications on the Higgs mass in the PQ-NMSSM

We examine the implications of singlet-doublet Higgs mixing on the properties of a Standard Model (SM)-like Higgs boson within the Peccei-Quinn invariant extension of the NMSSM (PQ-NMSSM). The SM singlet added to the Higgs sector connects the PQ and visible sectors through a PQ-invariant non-renormalizable Kähler potential term, making the model free from the tadpole and domain-wall problems. For the case that the lightest Higgs boson is dominated by the singlet scalar, the Higgs mixing increases the mass of a SM-like Higgs boson while reducing its signal rate at collider experiments compared to the SM case. The Higgs mixing is important also in the region of parameter space where the NMSSM contribution to the Higgs mass is small, but its size is limited by the experimental constraints on the singlet-like Higgs boson and on the lightest neutralino constituted mainly by the singlino whose Majorana mass term is forbidden by the PQ symmetry. Nonetheless the Higgs mixing can increase the SM-like Higgs boson mass by a few GeV or more even when the Higgs signal rate is close to the SM prediction, and thus may be crucial for achieving a 125 GeV Higgs mass, as hinted by the recent ATLAS and CMS data. Such an effect can reduce the role of stop mixing.

hep-ph↗

arXiv2012

Light Higgsino from Axion Dark Radiation

The recent observations imply that there is an extra relativistic degree of freedom coined dark radiation. We argue that the QCD axion is a plausible candidate for the dark radiation, not only because of its extremely small mass, but also because in the supersymmetric extension of the Peccei-Quinn mechanism the saxion tends to dominate the Universe and decays into axions with a sizable branching fraction. We show that the Higgsino mixing parameter mu is bounded from above when the axions produced at the saxion decays constitute the dark radiation: mu \lesssim 300 GeV for a saxion lighter than 2m_W, and mu less than the saxion mass otherwise. Interestingly, the Higgsino can be light enough to be within the reach of LHC and/or ILC even when the other superparticles are heavy with mass about 1 TeV or higher. We also estimate the abundance of axino produced by the decays of Higgsino and saxion.

hep-ph↗

arXiv2012

Anarchy and Leptogenesis

We study if leptogenesis works successfully together with the neutrino mass anarchy hypothesis. We find that the predicted neutrino mass spectrum is sensitive to the reheating temperature or the inflaton mass, while the distributions of the neutrino mixing angles and CP violation phases remain intact as determined by the invariant Haar measure of U(3). In the case of thermal leptogenesis, the light neutrino mass distribution agrees well with the observations if the reheating temperature is O(10^{9-11}) GeV. The mass spectrum of the right-handed neutrinos and the neutrino Yukawa matrix exhibit a certain pattern, as a result of the competition between random matrices with elements of order unity and the wash-out effect. Non-thermal leptogenesis is consistent with observation only if the inflaton mass is larger than or comparable to the typical right-handed neutrino mass scale. Cosmological implications are discussed in connection with the 125GeV Higgs boson mass.

hep-ph↗

arXiv2012

Peccei-Quinn invariant extension of the NMSSM

We study a Peccei-Quinn invariant extension of the next-to-minimal supersymmetric Standard Model (NMSSM), which turns out to be free from the tadpole and domain wall problems. Having a non-renormalizable coupling to the axion superfield, the SM singlet added to the Higgs sector can naturally generate an effective Higgs mu term around the weak scale. In the model, the lightest neutralino is dominated by the singlino, which gets a mass only through mixing with the neutral Higgsinos. We explore the phenomenological consequences resulting from the existence of such a relatively light neutralino. The coupling of the SM singlet to the Higgs doublets is constrained by the experimental bound on the invisible Z-boson decay width. Under this constraint, we examine the properties of the SM-like Higgs boson paying attention to its mass and decays. We also demonstrate a UV completion of the model in SU(5) grand unified theory with a missing-partner mechanism.

hep-ph↗

arXiv2011

Gauge mediation to effective SUSY through U(1)s with a dynamical SUSY breaking, and string compactification

We investigate the possibility of U(1)' mediation, leading to an effective SUSY where the first two family sfermions are above 100 TeV but the third family sfermions and the Higgs doublets are in the TeV region(or the light stop case). The U(1)' gaugino, Zprimino, needs not to be at a TeV scale, but needs to be somewhat lighter than the messenger scale. We consider two cases, one the mediation is only through U(1)' and the other through U(1)' and the electroweak hypercharge U(1)_Y. In the SUSY field theory framework, we calculate the superpartner mass spectra for these two cases. We also point out that the particle species needed for these mechanisms are already obtained from a Z(12-I) orbifold compactification.

hep-ph↗

arXiv2011

Axion model in gauge-mediated supersymmetry breaking and a solution to the mu/Bmu problem

We present a simple supersymmetric axion model that can naturally explain the origin of the Higgs mu and Bmu terms in gauge mediation while solving the strong CP problem. To stabilize the Peccei-Quinn scale, we consider mixing between the messenger fields that communicate the supersymmetry and Peccei-Quinn symmetry breaking to the visible sector. Such mixing leads to the radiative stabilization of the Peccei-Quinn scale. In the model, a Higgs coupling to the axion superfield generates the B parameter at the soft mass scale while a small mu term is induced after the Peccei-Quinn symmetry breaking. We also explore the phenomenological and cosmological aspects of the model, which crucially depend on the saxion and axino interactions with the ordinary particles induced by the Higgs coupling to the axion superfield.

hep-ph↗

arXiv2011

Mixed Mediation of Supersymmetry Breaking with Anomalous U(1) Gauge Symmetry

Models with anomalous U(1) gauge symmetry contain various superfields which can have nonzero supersymmetry breaking auxiliary components providing the origin of soft terms in the visible sector, e.g. the U(1) vector superfield, the modulus or dilaton superfield implementing the Green-Schwarz anomaly cancellation mechanism, U(1)-charged but standard model singlet matter superfield required to cancel the Fayet-Iliopoulos term, and finally the supergravity multiplet. We examine the relative strength between these supersymmetry breaking components in a simple class of models, and find that various different mixed mediations of supersymmetry breaking, involving the modulus, gauge, anomaly and D-term mediations, can be realized depending upon the characteristics of D-flat directions and how those D-flat directions are stabilized with a vanishing cosmological constant. We identify two parameters which represent such properties and thus characterize how the various mediations are mixed. We also discuss the moduli stabilization and soft terms in a variant of KKLT scenario, in which the visible sector Kähler modulus is stabilized by the D-term potential of anomalous U(1) gauge symmetry.

hep-ph↗

arXiv2009

Thermal inflation and baryogenesis in heavy gravitino scenario

We present a thermal inflation model that incorporates the Affleck-Dine leptogenesis in heavy gravitino/moduli scenario, which solves the moduli-induced gravitino problem while producing a correct amount of baryon asymmetry and relic dark matter density. The model involves two singlet flat directions stabilized by radiative corrections associated with supersymmetry breaking, one direction that generates the Higgs μand B parameters, and the other direction that generates the scale of spontaneous lepton number violation. The dark matter is provided by the lightest flatino which might be identified as the axino if the model is assumed to have a U(1)_{PQ} symmetry to solve the strong CP problem. We derive the conditions for the model to satisfy various cosmological constraints coming from the Big-Bang nucleosynthesis and the dark matter abundance.

hep-ph↗

arXiv2009

Sparticle masses in deflected mirage mediation

We discuss the sparticle mass patterns that can be realized in deflected mirage mediation scenario of supersymmetry breaking, in which the moduli, anomaly, and gauge mediations all contribute to the MSSM soft parameters. Analytic expression of low energy soft parameters and also the sfermion mass sum rules are derived, which can be used to interpret the experimentally measured sparticle masses within the framework of the most general mixed moduli-gauge-anomaly mediation. Phenomenological aspects of some specific examples are also discussed.

hep-ph↗

arXiv2008

Moduli stabilization with F-term uplifting in heterotic string theory

We discuss the role of F-term uplifting in stabilizing moduli within the framework of heterotic string theory. It turns out that the uplifting sector plays an important role in fixing the volume modulus at one of the self-dual points of a modular invariant potential. For the volume modulus stabilized at a self-dual point, the F-term uplifting leads to the dilation stabilization which can naturally yield the mirage mediation pattern of soft supersymmetry breaking terms. Generalizing to the case with anomalous U(1) gauge symmetry, we also find that the U(1) sector generically gives a contribution to sfermion masses comparable to the dilaton mediated one while maintaining the mirage mediation pattern.

hep-th↗

arXiv2008

Flavor and CP conserving moduli mediated SUSY breaking in flux compactification

In certain class of flux compactification, moduli mediated supersymmetry (SUSY) breaking preserves flavor and CP at leading order in the perturbative expansion controlled by the vacuum expectation value of the messenger modulus. Nevertheless there still might be dangerous flavor or CP violation induced by higher order Kähler potential. We examine the constraints on such SUSY breaking scheme imposed by low energy flavor and/or CP violating observables. It is found that all phenomenological constraints can be satisfied even for generic form of higher order Kähler potential and sparticle spectra in the sub-TeV range, under plausible assumptions on the size of higher order correction and flavor mixing angles. This implies for instance that mirage mediation scheme of SUSY breaking, which involves such modulus mediation together with an anomaly mediation of comparable size, and also the modulus-dominated mediation realized in flux compactification can be free from the SUSY flavor and CP problems, while giving gaugino and sfermion masses in the sub-TeV range.

hep-ph↗

arXiv2007

Sequestered uplifting and the pattern of soft supersymmetry breaking terms

We examine the pattern of soft supersymmetry breaking terms in moduli stabilization, where an uplifting potential is provided by spontaneously broken supersymmetry in a generic sequestered sector. From stationary conditions, we derive the relation between moduli F-term vacuum expectation values which does not depend on the details of sequestered uplifting. This moduli F-term relation is crucial for identifying the dominant source of soft terms of visible fields.

hep-th↗

arXiv2007

TeV Scale Mirage Mediation and Natural Little SUSY Hierarchy

TeV scale mirage mediation has been proposed as a supersymmetry breaking scheme reducing the fine tuning for electroweak symmetry breaking in the minimal supersymmetric extension of the standard model. We discuss a moduli stabilization set-up for TeV scale mirage mediation which allows an extra-dimensional interpretation for the origin of supersymmetry breaking and naturally gives an weak-scale size of the Higgs B-parameter. The set-up utilizes the holomorphic gauge kinetic functions depending on both the heavy dilaton and the light volume modulus whose axion partners are assumed to be periodic fields. We also examine the low energy phenomenology of TeV scale mirage mediation, particularly the constraints from electroweak symmetry breaking and FCNC processes.

hep-ph↗