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Yeong Gyun Kim

Publications and source records attributed to Yeong Gyun Kim.

At least 37 records · Page 2Linked to original sources
arXiv2008

Singlet fermionic dark matter as a natural higgs portal model

We propose a renormalizable model of a fermionic dark matter by introducing a gauge singlet Dirac fermion and a real singlet scalar. The bridges between the singlet sector and the standard model sector are only the singlet scalar interaction terms with the standard model Higgs field. The singlet fermion couples to the standard model particles through the mixing between the standard model Higgs and singlet scalar and is naturally a weakly interacting massive particle (WIMP). The measured relic abundance can be explained by the singlet fermionic dark matter as the WIMP within this model. Collider implication of the singlet fermionic dark matter is also discussed. Predicted is the elastic scattering cross section of the singlet fermion into target nuclei for a direct detection of the dark matter. Search of the direct detection of the dark matter provides severe constraints on the parameters of our model.

hep-ph↗
arXiv2008

Comment on `A collider signature of the supersymmetric golden region'

We show that $Z$ polarization measurement is useful for distinguishing the signal decay chain of the `golden region' in the minimal supersymmetric standard model(MSSM) parameter space, which involves the stop decay of $\tilde t_2 \to \tilde t_1 + Z$, from other decay chains involving the neutralino decay of $\tildeχ_2^0 \to \tildeχ_1^0 + Z$ in different MSSM scenarios.

hep-ph↗
arXiv2008

Singlet fermionic dark matter

We propose a renormalizable model of a fermionic dark matter by introducing a gauge singlet Dirac fermion and a real singlet scalar. The bridges between the singlet sector and the standard model sector are only the singlet scalar interaction terms with the standard model Higgs field. The singlet fermion couples to the standard model particles through the mixing between the standard model Higgs and singlet scalar and is naturally a weakly interacting massive particle (WIMP). The measured relic abundance can be explained by the singlet fermionic dark matter as the WIMP within this model. Collider implication of the singlet fermionic dark matter is also discussed. Predicted is the elastic scattering cross section of the singlet fermion into target nuclei for a direct detection of the dark matter. Search of the direct detection of the dark matter provides severe constraints on the parameters of our model.

hep-ph↗
arXiv2008

Measuring the top quark mass with m_T2 at the LHC

We investigate the possibility to measure the top quark mass using the collider variable $m_{T2}$ at the LHC experiment. Monte Carlo studies of $m_{T2}$ are performed with the events corresponding to the dilepton decays of $t\bar{t}$ produced at the LHC with 10 $fb^{-1}$ integrated luminosity. Our analysis suggests that the top quark mass can be determined by the $m_{T2}$ variable alone with a good precision at the level of 1 GeV.

hep-ph↗
arXiv2007

Measuring superparticle masses at hadron collider using the transverse mass kink

We present a detailed study of the collider observable $m_{T2}$ applied for pair-produced superparticles decaying to visible particles and a pair of invisible lightest supersymmetric particles (LSPs). Analytic expressions of the maximum of $m_{T2}$ over all events ($m_{T2}^{\rm max}$) are derived. It is noticed that if the decay product of each superparticle involves more than one visible particles, $m_{T2}^{\rm max}$ being a function of the {\it trial} LSP mass ${m}_χ$ has a kink structure at ${m}_χ=$ true LSP mass, which can be used to determine the mother superparticle mass and the LSP mass simultaneously. To see how well $m_{T2}^{\rm max}$ can be constructed from collider data, a Monte-Carlo analysis of the gluino $m_{T2}$ is performed for some superparticle spectra.

hep-ph↗
arXiv2007

Gluino Stransverse Mass

We introduce a new observable, 'gluino stransverse mass', which is an application of the Cambridge $m_{T2}$ variable to the process where gluinos are pair produced in proton-proton collision and each gluino subsequently decays into two quarks and one LSP, $i.e. \tilde{g}\tilde{g} \to qq\tildeχ_1^0\ qq\tildeχ_1^0$. We show that the gluino stransverse mass can be utilized to measure the gluino and the lightest neutralino masses separately, and also the (1st and 2nd generation) squark masses if lighter than the gluino mass, thereby providing a good first look at the pattern of sparticle masses experimentally.

hep-ph↗
arXiv2007

TeV scale partial mirage unification and neutralino dark matter

We study the TeV scale partial mirage unification scenario, where the gluino and wino masses are degenerate around a TeV scale, but the bino mass is not degenerate. This scenario has phenomenologically interesting aspects. First, because of the degeneracy between the gluino and wino masses, this scenario does not have the little hierarchy problem, that is, the higgisino mass is around 150 GeV. The lightest superparticle is a mixture of the bino and higgsino, and can lead to a right amount of thermal relic density as a dark matter candidate.

hep-ph↗
arXiv2006

The minimal model of fermionic dark matter

We explore the minimal extension of the Standard Model with fermionic cold dark matter. The interactions between the dark matter and the Standard Model matters are described by the non-renormalizable dimension-5 term. We show that the measured relic abundance of the cold dark matter can be explained in our model and predict the direct detection cross section. The direct search of the dark matter provides severe constraints on the mass and coupling of the minimal fermionic dark matter with respect to the Higgs boson mass.

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arXiv2005

$B_s \to μ^+ μ^-$ and the upward-going muon flux from the WIMP annihilation in the sun or the earth

We consider the upward-going muon flux due to the WIMP annihilations in the cores of the sun and the earth, including the upper bound on the branching ratio for $B_s \to μ^+ μ^-$ decay. We find that the constraint from $B_s \to μ^+ μ^-$ is very strong in most parameter space, and exclude the supergravity parameter space regions where the expected upward-going muon fluxes are within the expected reach of AMANDA II.

hep-ph↗
arXiv2005

Neutralino dark matter scattering and $B_s \to μ^+ μ^-$ in SUSY models

It is pointed out that there is a strong correlation between the neutralino dark matter scattering cross section $σ_{\tildeχ p}$ and the branching ratio for $B_s \to μ^+ μ^-$ within minimal supergravity (mSUGRA) and its extensions. This correlation arises mainly from $\tanβ$ and heavy neutral Higgs mass dependence, and shows a nice interplay between vastly different two observables within supersymmetric models. Current upper limit on $B(B_s \to μ^+ μ^-) < 5.8 \times 10^{-7}$ excludes substantial parameter space where $σ_{\tildeχ p}$ is within the CDMS sensitivity region.

hep-ph↗
arXiv2004

Soft Wilson lines in soft-collinear effective theory

The effects of the soft gluon emission in hard scattering processes at the phase boundary are resummed in the soft-collinear effective theory (SCET). In SCET, the soft gluon emission is decoupled from the energetic collinear part, and is obtained by the vacuum expectation value of the soft Wilson-line operator. The form of the soft Wilson lines is universal in deep inelastic scattering, in the Drell-Yan process, in the jet production from e+e- collisions, and in the gamma* gamma* -> pi0 process, but its analytic structure is slightly different in each process. The anomalous dimensions of the soft Wilson-line operators for these processes are computed along the light-like path at leading order in SCET and to first order in alpha_s, and the renormalization group behavior of the soft Wilson lines is discussed.

hep-ph↗
arXiv2004

Time dependent CP asymmetry in $B^0 \to ρ^0 γ$ decay to probe the origin of CP violation

Since the CP violation in the $B$ system has been investigated up to now only through processes related to the $B$--$\bar{B}$ mixing, urgently required is new way of study for the CP violation and establishing its origin in the $B$ system independent of the mixing process. In this work, we explore the exclusive $ B^0 \to ρ^0 γ$ decay to obtain the time-dependent CP asymmetry in $b \to d$ decay process in the standard model and the supersymmetric model. We find that the complex RL and RR mass insertion to the squark sector in the MSSM can lead to a large CP asymmetry in $b \to d γ$ decay through the gluino-squark diagrams, which is not predicted in the Standard Model induced by the $B$--$\bar{B}$ mixing.

hep-ph↗
arXiv2004

Implication of the weak phase $β$ measured in $B \to ργ$ decay

We explore the exclusive $ B^0 \to ρ^0 γ$ decay to obtain the time-dependent CP asymmetry in $b \to d γ$ decay process. We find that the complex RL and RR mass insertion to the squark sector in the MSSM can lead to a large deviation of CP asymmetry from that predicted in the Standard Model.

hep-ph↗
arXiv2002

Upper and Lower Limits on Neutralino WIMP Mass and Spin--Independent Scattering Cross Section, and Impact of New (g-2)_{mu} Measurement

We derive the allowed ranges of the spin--independent interaction cross section $\sigsip$ for the elastic scattering of neutralinos on proton for wide ranges of parameters of the general Minimal Supersymmetric Standard Model. We investigate the effects of the lower limits on Higgs and superpartner masses from colliders, as well as the impact of constraints from $\bsgamma$ and the new measurement of $\gmtwo$ on the upper and lower limits on $\sigsip$. We further explore the impact of the neutralino relic density, including coannihilation, and of theoretical assumptions about the largest allowed values of the supersymmetric parameters. For $μ>0$, requiring the latter to lie below $1\tev$ leads to $\sigsip\gsim 10^{-11}\pb$ at $\mchi\sim100\gev$ and $\sigsip\gsim 10^{-8}\pb$ at $\mchi\sim1\tev$. When the supersymmetric parameters are allowed above $1\tev$, for $440\gev \lsim \mchi\lsim 1020 \gev$ we derive a {\em parameter--independent lower limit} of $\sigsip \gsim 2\times 10^{-12}\pb$. (No similar lower limits can be set for $μ<0$ nor for $1020\gev\lsim\mchi\lsim2.6\tev$.) Requiring $\abundchi<0.3$ implies a {\em parameter--independent upper limit} $\mchi\lsim2.6\tev$. The new $\epem$--based measurement of $(g-2)_μ$ restricts $\mchi\lsim 350\gev$ at $1 σ$ CL and $\mchi\lsim515\gev$ at $2 σ$ CL, and implies $μ>0$. The largest allowed values of $\sigsip$ have already become accessible to recent experimental searches.

hep-ph↗
arXiv2001

Implications of Muon anomalous magnetic moment for Direct detection of Neutralino Dark Matter

We investigate the implications of the recent measurement of muon anomalous magnetic moment for the direct detection of neutralino dark matter in the three different SUSY models: mSUGRA, a model with non-universal Higgs mass, and an SO(10) GUT model. We consider two extreme scenario for $Δa_μ$ bound, i.e. $27 \times 10^{-10} < Δa_μ< 59 \times 10^{-10}$ (1$σ$ bound) and $0 < Δa_μ< 11 \times 10^{-10}$ ($2σ$ below). In mSUGRA model, the counting ratio may be above the sensitivity of the future experiments when parameters are within $1σ$ bound of $Δa_μ$. However, the $Ω_χ$ tends to be high compared to the currently favored value $Ω=0.3$. For models with the non-universal scalar masses, the possibility to have the consistent $Ω_χ$ and the high counting ratio is open up in the region of parameter space where Higgsino mass $μ$ is smaller than mSUGRA prediction. In particular, in the SO(10) model, the LSP dark matter detection rate may be enhanced by almost one order of magnitude compared to mSUGRA and the model with non-universal Higgs mass, for cosmologically acceptable $Ω_χ h^2$. The highest detection rate of LSP dark matter occurs in the region where the LSP constitutes a subdominant part of local halo DM. Implication of SUSY mass parameter measurement under the cosmological constraint is also discussed.

hep-ph↗
arXiv2001

Possible Supersymmetric Effects on Angular Distributions in $B \to K^* (\to K π) \ell^+ \ell^- $ Decays

We investigate the angular distributions of the rare B decay, $B \to K^* (\to K π) \ell^+ \ell^-$, in general supersymmetric extensions of the standard model. We consider the new physics contributions from the operators $O_{7,8,9,10}$ in small invariant mass region of lepton pair. We show that the azimuthal angle distribution of the decay can tell us the new physics effects clearly from the behavior of the distribution, even if new physics does not change the decay rate substantially from the standard model prediction.

hep-ph↗
arXiv2001

Direct Detection of Neutralino Dark Matter and the Anomalous Dipole Moment of the Muon

We compare predictions for the spin-independent contribution to the neutralino-proton scattering cross section $\sig$ and for the anomalous magnetic dipole moment of the muon, $a_μ= (g_μ-2)/2$, in models with gravity-mediated supersymmetry breaking. We nearly always find a positive correlation between these two measurables, i.e. scenarios with larger $a_μ$ also tend to have larger $\sig$, but the detailed prediction differs greatly between models. In particular, we find that for the popular mSUGRA scenario with universal soft breaking masses at the scale of Grand Unification, measurements of $a_μ$ currently seem more promising. On the other hand, if scalar soft breaking masses at the GUT scale receive sizable contributions from SO(10) D-terms, one often finds scenarios with large $\sig$ but $a_μ$ below the currently foreseen sensitivity. A string-inspired model with non-universal scalar spectrum at the GUT scale falls between these two cases.

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