arXiv subjects

Gi-Chol Cho

Publications and source records attributed to Gi-Chol Cho.

At least 37 records · Page 2Linked to original sources

arXiv2013

Production and decay of a heavy radion in Randall-Sundrum model at the LHC

We study production and decay of a radion predicted in the Randall-Sundrum model at the LHC. The radion is a scalar particle and its production and decay channels are quite similar to those of the Higgs boson. We find constraints on the model parameter space taking account of the results of the Higgs boson search at the LHC. We also study a possibility discriminating the radion from the scalar particles in the other model such as the supersymmetric standard model at the LHC experiments.

hep-ph↗

arXiv2013

Sensitivity of the LHC to Kaluza-Klein gluon in two b-jets decay channel

We study a possibility of observation of the first Kaluza-Klein (KK) excitation of gluon in a warped extra dimension model at the LHC. In our analysis, we adopt the KK gluon mass and the b-quark coupling to the KK gluon as model parameters and study the sensitivity of the ATLAS experiment to observe the KK gluon through the two $b$-jets channel.

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arXiv2013

LHC sensitivity to Kalzua-Klein gluon in two b-jets decay channel

We examine a possibility to discover a Kaluza-Klein (KK) excitation of gluon in a warped extra dimension model at the Large Hadron Collider focusing on a decay channel of the KK gluon into a $b$-quark pair. It is known that, in a certain extension of the warped extra dimension model, the third generation quarks could strongly couple to the KK gluon owing to appropriate bulk fermion mass parameters. Taking account of kinematical cuts to reduce background events, we show the model parameter space which leads to a significance larger than 5$σ$ with the integrated luminosity of 10 (100) ${\rm fb}^{-1}$.

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arXiv2011

The MSSM confronts the precision electroweak data and the muon g-2

We update the electroweak study of the predictions of the Minimal Supersymmetric Standard Model (MSSM) including the recent results on the muon anomalous magnetic moment, the weak boson masses, and the final precision data on the Z boson parameters from LEP and SLC. We find that the region of the parameter space where the slepton masses are a few hundred GeV is favored from the muon g-2 for \tanβ\ltsim 10, whereas for \tanβ\simeq 50 heavier slepton mass up to \sim 1000 GeV can account for the reported 3.2 σdifference between its experimental value and the Standard Model (SM) prediction. As for the electroweak measurements, the SM gives a good description, and the sfermions lighter than 200 GeV tend to make the fit worse. We find, however, that sleptons as light as 100 to 200 GeV are favored also from the electroweak data, if we leave out the jet asymmetry data that do not agree with the leptonic asymmetry data. We extend the survey of the preferred MSSM parameters by including the constraints from the b \to s γtransition, and find favorable scenarios in the minimal supergravity, gauge-, and mirage-mediation models of supersymmetry breaking.

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arXiv2011

Constraints on R-parity violating interactions in supersymmetric standard model from leptonic decays of D_s and B^+ mesons

We study leptonic decays D_s\to τνand B^+ \to τνin R-parity violating (RPV) supersymmetric standard model. The interference between the s-channel slepton exchange and the t-channel squark exchange diagrams could be destructive in a certain model parameter region so that sizable RPV couplings are allowed. Contributions from the RPV interactions to the final states with the lepton flavor violation (LFV), τν_μ(τν_e), are also examined taking account of constraints on the RPV couplings from the other LFV processes.

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arXiv2010

Leptonic decays of D_s and B^+ mesons in supersymmetric standard model with R-parity violating interactions

We investigate leptonic decays $D_s \to τν_τ$ and $B^+ \to τν_τ$ in R-parity violating (RPV) supersymmetric standard model. Taking account of interference between the s-channel slepton exchange and the $t$-channel squark exchange diagrams, we find that the supersymmetric contributions are cancelled between two diagrams so that the RPV couplings could be sizable under the experimental bounds. Constraints on the relative sign between the RPV couplings in $s$- and $t$-channel diagrams are also discussed.

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arXiv2010

Kaluza-Klein gluon and b-jet forward-backward asymmetry

The forward-backward asymmetry of $b$-quark jets on the $Z$-pole measured at LEP/SLD experiments shows us -2.8-$σ$ deviation from the Standard Model (SM) prediction. We examine a possibility of Kaluza-Klein (KK) gluon to explain the $\afbb$ data in a scenario based on the warped extra dimension model by Randall and Sundrum. In this scenario, the KK gluon strongly couples to $b$-quark by an appropriate choice of the bulk quark mass terms. We find that the $\afbb$ data could be explained if the KK gluon mass is few hundred GeV. Constraints on our scenario from the hadron collider experiments are discussed.

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arXiv2007

Decay of Charged Higgs boson in a scenario of SUSY breaking inspired neutrino mass

In some class of supersymmetric models, small neutrino mass is given as a consequence of the supersymmetry (SUSY) breaking. Phenomenologically interesting features of this scenario are as follows: (i) the right-handed sneutrino mass could be as low as TeV scale due to the Giudice-Masiero mechanism, and (ii) a scalar trilinear interaction of Higgs-slepton-(right-handed) sneutrino could be sizable without suppression by the small neutrino Yukawa coupling. We study some phenomenological aspects of this scenario focusing on the scalar trilinear interaction. We show that the 1-loop correction by sneutrino exchange to the lightest Higgs boson mass destructively interferes with top-stop contributions in the minimal SUSY Standard Model. We find that a decay of charged Higgs boson into sneutrino and charged slepton is sizably enhanced and hence it gives rise to a distinctive signal at future collider experiments in some parameter space.

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arXiv2005

Neutron electric dipole moment and flavor changing interactions in supersymmetric theories

Supersymmetric contributions to the neutron electric dipole moment (EDM) are studied taking account of the flavor changing interactions. We found that the gluino contribution is sensitive to the flavor changing interaction. Enhancement of neutron EDM via flavor mixing effects is possible when the squark mass difference between the different generations is sizable. As an example, the results of the SUSY SU(5) GUT with right-handed neutrinos are briefly discussed.

hep-ph↗

arXiv2004

Search for extra gauge bosons in Little Higgs models at a linear collider

A generic feature of little Higgs models is presence of extra neutral gauge bosons. In the littlest Higgs model, the neutral extra gauge boson A_H is lightest among the extra particles and could be as light as a few hundred GeV, which may be produced directly at an e^+ e^- linear collider. We study production and decay of A_H at the linear collider and compare them with those of Z' bosons in supersymmetric E_6 models.

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arXiv2004

Search for a light extra gauge boson in Littlest Higgs model at a linear collider

Littlest Higgs model predicts some extra particles beyond the Standard Model. Among them, an extra neutral gauge boson A_H is lightest and its mass could be a few hundred GeV. We study production and decay of A_H at future e^+ e^- inear collider and compare them with those of Z' bosons in supersymmetric (SUSY) E_6 models. We find that, if the extra gauge boson mass is smaller than \sqrt{s} of the linear collider, the forward-backward asymmetries of b- and c-quarks at the A_H pole differ significantly from those given by the Z' bosons, and are useful to test the littlest Higgs model and SUSY E_6 models.

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arXiv2004

'TeV Gamma-ray Crisis' and an Anisotropic Space Model

To solve the `TeV gamma crisis', we examine a model whose one spatial direction is discretized at a high energy scale. Assuming the standard extra-galactic IR photon distribution, we evaluate the mean free-path of a energetic photon which acquires an effective mass in the model. For a wide range of the value of the lattice energy scale between a few TeV and around $10^{10}$ GeV, the mean free-path of a TeV energy photon can be enlarged enough to solve the `crisis'. Taking into account the effects of the universe expansion, we find bounds of the lattice constant.

astro-ph↗

arXiv2004

Cosmological gravitino problem confronts electroweak physics

A generic feature of gauge-mediated supersymmetry breaking models is that the gravitino is the lightest supersymmetric particle (LSP). In order not to overclose the universe, the gravitino LSP should be light enough (~ 1 keV), or appropriately heavy (~ 1 GeV). We study further constraints on the mass of the gravitino imposed by electroweak experiments, i.e., muon g-2 measurements, electroweak precision measurements, and direct searches for supersymmetric particles at LEP2. We find that the heavy gravitino is strongly disfavored from the lower mass bound on the next-to-LSP. The sufficiently light gravitino, on the other hand, has rather sizable allowed regions in the model parameter space.

hep-ph↗

arXiv2003

TeV Colored Higgsinos in Alternative Grand Unified Theories

Recently, a type of GUT models with an extra dimension in AdS space can successfully solve the doublet-triplet problem, maintain proton stability, and allow the colored Higgs bosons and colored Higgsinos in the TeV mass region. We study the hadronic production and detection of these TeV colored Higgsinos and Higgs bosons. If the colored Higgsino is lighter than the colored Higgs boson, the colored Higgs boson will decay into a colored Higgsino and a gluino or a gravitino, and vice versa. The signatures would be stable massive charged particles with jets or missing energies.

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arXiv2003

Hadronic production of light color-triplet Higgs bosons: an alternative signature for GUT

The conventional signature for grand unified theories (GUT) is the proton decay. Recently, some models in extra dimensions or with specific discrete symmetries, which aim at solving the doublet-triplet problem, allow the color-triplet in the TeV mass region by suppressing the Yukawa couplings of the triplets to matter fermions. We study the hadronic production and detection of these TeV colored Higgs bosons as an alternative signature for GUT, which would behave like massive stable charged particles in particle detectors producing a striking signature of a charged track in the central tracking system and being ionized in the outer muon chamber. We found that the LHC is sensitive to a colored Higgs boson up to about 1.5 TeV. If the color-triplets are stable in cosmological time scale, they may constitute an interesting fraction of the dark matter.

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arXiv2002

CERN LEP2 constraint on 4D QED having dynamically generated spatial dimension

We study 4D QED in which one spatial dimension is dynamically generated from 3D action, following the mechanism proposed by Arkani-Hamed, Cohen and Georgi. In this model, the generated fourth dimension is discretized by an interval parameter $a$. We examine the phenomenological constraint on the parameter $a$ coming from the collider experiments on the QED process $e^+ e^- \to γγ$. It is found that the LEP2 experiments give the constraint of $1/a \simgt 461\gev$. Expected bound on the same parameter $a$ at the future $e^+ e^-$ linear collider is briefly discussed.

hep-ph↗

arXiv2002

On the possibility of a very light A^0 at low \tanβ

The searches at LEP II for the processes e^+e^-\to h^0Z and e^+e^-\to h^0A^0 in the Minimal Supersymmetric Standard Model (MSSM) fail to exclude regions of the m_h,m_A plane where \tanβ<1, thus allowing a very light A^0 (m_A< 20 GeV). Such a parameter choice would predict a light H^\pm with m_{H^\pm}< m_W. Although the potentially large branching ratio for H^\pm \to A^0 W^* would ensure that H^\pm also escaped detection in direct searches at LEP II and the Tevatron Run I, we show that this elusive parameter space is overwhelmingly disfavoured by electroweak precision measurements.

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arXiv2002

Light bottom squark and gluino confront electroweak precision measurements

We address the compatibility of a light sbottom (mass $2\sim 5.5 \gev$) and a light gluino (mass $12\sim 16 \gev$) with electroweak precision measurements. Such light particles have been suggested to explain the observed excess in the $b$ quark production cross section at the Tevatron. The electroweak observables may be affected by the sbottom and gluino through the SUSY-QCD corrections to the $Zbb$ vertex. We examine, in addition to the SUSY-QCD corrections, the electroweak corrections to the gauge boson propagators from the stop which are allowed to be light from the SU(2)$_L$ symmetry. We find that this scenario is strongly disfavored from electroweak precision measurements unless the heavier sbottom mass eigenstate is lighter than $180\gev$ and the left-right mixing in the stop sector is sufficiently large. This implies that one of the stops should be lighter than about $98\gev$.

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