arXiv subjects

C. S. Kim

Publications and source records attributed to C. S. Kim.

At least 55 records · Page 3Linked to original sources

arXiv2017

Decay of $B^\pm \to τ^\pm +$ "missing momentum" and direct measurement of the mixing parameter $U_{τN}$

We derive the decay widths for the leptonic decays of heavy charged pseudoscalars to massive sterile neutrinos, $M^{\pm} \to \ell^{\pm} + N$, within the frameworks involving the Standard Model and two-Higgs doublets (type II). We then apply the result to $B^\pm \to τ^\pm +$ "missing momentum" of the Belle/BaBar experimental results, in order to measure directly the relevant parameter space, including the mixing parameter $U_{τN}$.

hep-ph↗

arXiv2016

Prompt atmospheric neutrino flux from the various QCD models

We evaluate the prompt atmospheric neutrino flux using the different QCD models for heavy quark production including the $b$ quark contribution. We include the nuclear correction and find it reduces the fluxes by $10 \% - 50\%$ according to the models. Our heavy quark results are compared with experimental data from RHIC, LHC and LHCb.

hep-ph↗

arXiv2016

Prompt atmospheric neutrino flux

We evaluate the prompt atmospheric neutrino flux including nuclear correction and $B$ hadron contribution in the different frameworks: NLO perturbative QCD and dipole models. The nuclear effect is larger in the prompt neutrino flux than in the total charm production cross section, and it reduces the fluxes by $10\% - 30\%$ depending on the model. We also investigate the uncertainty using the QCD scales allowed by the charm cross section data from RHIC and LHC experiments.

hep-ph↗

arXiv2016

Prompt atmospheric neutrino fluxes: perturbative QCD models and nuclear effects

We evaluate the prompt atmospheric neutrino flux at high energies using three different frameworks for calculating the heavy quark production cross section in QCD: NLO perturbative QCD, $k_T$ factorization including low-$x$ resummation, and the dipole model including parton saturation. We use QCD parameters, the value for the charm quark mass and the range for the factorization and renormalization scales that provide the best description of the total charm cross section measured at fixed target experiments, at RHIC and at LHC. Using these parameters we calculate differential cross sections for charm and bottom production and compare with the latest data on forward charm meson production from LHCb at $7$ TeV and at $13$ TeV, finding good agreement with the data. In addition, we investigate the role of nuclear shadowing by including nuclear parton distribution functions (PDF) for the target air nucleus using two different nuclear PDF schemes. Depending on the scheme used, we find the reduction of the flux due to nuclear effects varies from $10\%$ to $50 \%$ at the highest energies. Finally, we compare our results with the IceCube limit on the prompt neutrino flux, which is already providing valuable information about some of the QCD models.

hep-ph↗

arXiv2016

A Model for Pseudo-Dirac Neutrinos: Leptogenesis and Ultra-High Energy Neutrinos

We propose a model where sterile neutrinos are introduced to make light neutrinos to be pseudo-Dirac particles. It is shown how tiny mass splitting necessary for realizing pseudo-Dirac neutrinos can be achieved. Within the model, we show how leptogenesis can be successfully generated. Motivated by the recent observation of very high energy neutrino events at IceCube, we study a possibility to observe the effects of the pseudo-Dirac property of neutrinos by performing astronomical-scale baseline experiments to uncover the oscillation effects of very tiny mass splitting. Using the result of global fit to neutrino data for the input of neutrino mixing angles and CP phase at $1σ$ C.L. and fixing neutrino energy and mass splittings, we study how the oscillation effects induced by pseudo-Dirac neutrinos may affect the track-to-shower ratio obtained from IceCube data. We also discuss future prospect to observe the effects of the pseudo-Dirac property of neutrinos at high energy neutrino experiments.

hep-ph↗

arXiv2016

Distinguishing Dirac/Majorana Sterile Neutrinos at the LHC

We study the purely leptonic decays of $W^\pm \to e^\pm e^\pm μ^\mp ν$ and $μ^\pm μ^\pm e^\mp ν$ produced at the LHC, induced by sterile neutrinos with mass $m_N$ below $M_W$ in the intermediate state. Since the final state neutrino escapes detection, one cannot tell whether this process violates lepton number, what would indicate a Majorana character for the intermediate sterile neutrino. Our study shows that when the sterile neutrino mixings with electrons and muons are different enough, one can still discriminate between the Dirac and Majorana character of this intermediate neutrino by simply counting and comparing the above decay rates. After performing collider simulations and statistical analysis, we find that at the $14~\text{TeV}$ LHC with an integrated luminosity of $3000~\text{fb}^{-1}$, for two benchmark scenarios $m_N$ = 20 GeV and 50 GeV, at least a $3σ$ level of exclusion on the Dirac case can be achieved for disparities as mild as e.g. $|U_{Ne}|^2 < 0.7~ |U_{Nμ}|^2$ or $|U_{Nμ}|^2 < 0.7~ |U_{N e}|^2$, provided that $|U_{Ne}|^2$, $|U_{Nμ}|^2$ are both above $\sim 2\times 10^{-6}$.

hep-ph↗

arXiv2016

Constraints on the $U(1)_L$ gauge boson in a wide mass range

There is a growing interest for the search of new light gauge bosons. The small mass of a new boson can turn various kinds of low-energy experiments to a new discovery machine, depending on their couplings to the standard model particles. It is important to understand the properties of each type of gauge boson and their current constraints for a given mass. While the dark photon (which couples to the electric charges) and the $U(1)_{B-L}$ gauge boson have been well studied in an extensive mass range, the $U(1)_L$ gauge boson has not been fully investigated yet. We consider the gauge boson of the $U(1)_L$ in a wide mass range $m_{Z'} \approx 0 - 10^{12} ~\ev$ and investigate the constraints on its coupling from various experiments, discussing the similarities and differences from the dark photon and the $U(1)_{B-L}$ gauge boson.

hep-ph↗

arXiv2016

Constraints on $Z^\prime$ Boson within Minimal Flavor Violation

We explore a $Z^\prime$ boson coupled only with the Standard Model (SM) fermions ($Z^\prime f\bar{f}$) in the framework of Minimal Flavor Violation. We study its effects on the processes with lepton flavor violation $\ell_j\to \ell_i\ell_k\bar{\ell}_l$, $\ell_j\to\ell_iγ$, $μ^{-}N\to e^- N$, quark flavor changing neutral currents $b\to s \ell^+\ell^-$, neutral $B$ and $K$ meson mixing, and $e^+e^-\to f\bar{f}$ at the LEP experiment to constrain the parameter space of $Z^\prime$ mass and couplings. We find that among those relevant processes, $μ\to eγ$, $μ\to 3e$, $μ$-$e$ conversion and $e^+e^-\to f\bar{f}$ can put more stringent bounds on $Z^\prime f\bar{f}$ couplings normalized by $Z^\prime$ mass. Its implications on various processes are obtained, such as $B$ and $K$ mixing and $B/K\to M \ell_1 \bar\ell_2$ decays. In addition, we also make analysis on $Z^\prime$ signatures at the LHC with $\sqrt{s}=8$ and 13 TeV.

hep-ph↗

arXiv2016

Light Dark Matter and Dark Radiation

Light dark-matter ($M\leq20$ MeV) particles freeze out after neutrino decoupling. If the dark-matter particle couples to a neutrino or an electromagnetic plasma, the late time entropy production from dark-matter annihilation can change the neutrino-to-photon temperature ratio, and equally the effective number of neutrinos $N_{eff}$. We study the non-equilibrium effects of dark-matter annihilation on the $N_{eff}$ and the effects by using a thermal equilibrium approximation. Both results are constrained with Planck observations. We demonstrate that the lower bounds of the dark-matter mass and the possibilities of the existence of additional radiation particles are more strongly constrained for dark-matter annihilation process in non-equilibrium.

astro-ph.HE↗

arXiv2016

Exploring top quark FCNC within 2HDM type III in association with flavor physics

The top quark flavor changing neutral current (FCNC) process is an excellent probe to search for new physics in top sector since the Standard Model expectation is extremely suppressed. We explore Higgs-mediated top quark FCNC, focusing on $H$-$t$-$c$ Yukawa coupling $λ_{ct}$ within the general two Higgs doublet model. After electroweak symmetry breaking the top quark FCNC couplings are included in the charged Higgs Yukawa sector so that they contribute to various processes in flavor physics. To probe $λ_{ct}$, we study anomalous single top production and the same sign top pair production at the LHC in association with flavor physics from the tree-level processes $B\to D^{(*)}τν$, $B\to τν$ as well as from the loop-level processes $B_d \to X_s γ$, $B_{d,s}-{\overline B}_{d,s}$ mixing. We perform combined analysis of all the constraints regarding the fine-tuning argument to fit the data and discuss future prospect. The recently updated measurements on $B\to D^{(*)}τν$ still prefer large $λ_{ct}$, but we show that the current bound on the same sign top pair production at the LHC gives the most significant upper bound on $λ_{ct}$ to be less than $10\sim30$ depending on neutral heavy Higgs masses. We also find that for the given upper bound on $λ_{ct}$, $B\to D^{(*)}τν$ put significant lower bound on $H$-$τ$-$τ$ Yukawa coupling, and the bound is proportional to the charged Higgs mass.

hep-ph↗

arXiv2015

Oscillation of heavy sterile neutrino in decay of $B \to μe π$

In a scenario with two almost mass degenerate heavy sterile Majorana neutrinos with a mass $\sim 1$ GeV, we present the semileptonic decay widths of heavy charged pseudoscalars such as $B$ mesons, either lepton-number-violating ($B^{\pm} \to μ^{\pm} e^{\pm} π^{\mp}$), or lepton-number-conserving ($B^{\pm} \to μ^{\pm} e^{\mp} π^{\pm}$), mediated by such on-shell neutrinos. It had been explained in the literature that such decays may be eventually detected, and that they can present even detectable CP violation effects. In this work we point out that, in addition, such decays may present detectable effects of heavy neutrino oscillation, allowing us to extract the oscillation length and thus the heavy neutrino mass difference $ΔM_N$, as well as a CP-violating Majorana phase.

hep-ph↗

arXiv2015

Investigation of Dark Matter in Minimal 3-3-1 Models

It is shown that the 3-3-1 model with the minimal lepton content can work as two-Higgs-triplet 3-3-1 model while leaving the other scalars as inert particles responsible for dark matter. We study two cases of dark matter corresponding to the doublet and singlet scalar candidates. We figure out the parameter spaces in the WMAP allowed region of the relic density. The indirect and direct searches for dark matter in both cases are investigated by using micrOMEGAs.

hep-ph↗

arXiv2015

Probing the Majorana neutrinos and their CP violation in decays of charged scalar mesons $π, K, D, D_s, B, B_c$

Some of the outstanding questions of particle physics today concern the neutrino sector, in particular whether there are more neutrinos than those already known and whether they are Dirac or Majorana particles.There are different ways to explore these issues. In this article we describe neutrino-mediated decays of charged pseudoscalar mesons such as $π^{\pm}$, $K^{\pm}$ and $B^{\pm}$, in scenarios where extra neutrinos are heavy and can be on their mass shell. We discuss semileptonic and leptonic decays of such kinds. We investigate possible ways of using these decays in order to distinguish between the Dirac and Majorana character of neutrinos. Further, we argue that there are significant possibilities of detecting CP violation in such decays when there are at least two almost degenerate Majorana neutrinos involved. This latter type of scenario fits well into the known neutrino minimal standard model ($ν$MSM) which could simultaneously explain the Dark Matter and Baryon Asymmetry of the Universe.

hep-ph↗

arXiv2015

Axial-Vector Emitting Weak Nonleptonic Deacys of $Ω_c^0$ Baryon

The axial-vector emitting weak hadronic decays of $Ω_c^0$ baryon are investigated. After employing the factorization and the pole model framework to predict their branching ratios, we derive the symmetry breaking effects on axial-vector-meson-baryon couplings and effects of flavor dependence on baryon-baryon weak transition amplitudes and, consequently, on their branching ratios. We found that the W-exchange process contributions dominate $p$-wave meson emitting decays of $Ω_c^0$ baryon.

hep-ph↗

arXiv2015

Model-Independent Analysis of CP Violation in Charmed Meson Decays

We present a model-independent analysis of CP violation, inspired by recent experimental observations, in charmed meson decays. The topological diagram approach is used to study direct CP asymmetries for singly Cabibbo-suppressed two-body hadronic decays of charmed mesons. We extract the magnitudes and relative phases of the corresponding topological amplitudes from available experimental information. In order to get more precise and reliable estimates of direct CP asymmetries, we take into account contributions from all possible strong penguin amplitudes, including the internal $b$-quark penguin contributions. We also study flavor SU(3) symmetry breaking effects in these decay modes and consequently, predict direct CP asymmetries of unmeasured modes.

hep-ph↗

arXiv2015

Renormalization Group Evolution of Neutrino Parameters in Presence of Seesaw Threshold Effects and Majorana Phases

We examine the renormalization group evolution (RGE) for different mixing scenarios in the presence of seesaw threshold effects from high energy scale (GUT) to the low electroweak (EW) scale in the Standard Model (SM) and Minimal Supersymmetric Standard Model (MSSM). We consider four mixing scenarios namely Tri-Bimaximal Mixing, Bimaximal Mixing, Hexagonal Mixing and Golden Ratio Mixing which come from different flavor symmetries at the GUT scale. We find that the Majorana phases play an important role in the RGE running of these mixing patterns along with the seesaw threshold corrections. We present a comparative study of the RGE of all these mixing scenarios both with and without Majorana CP phases when seesaw threshold corrections are taken into consideration. We find that in the absence of these Majorana phases both the RGE running and seesaw effects may lead to $θ_{13}<$ 5$^\circ$ at low energies both in the SM and MSSM. However, if the Majorana phases are incorporated to the mixing matrix the running can be enhanced both in the SM and MSSM. Even by incorporating non zero Majorana CP phases in the SM, we do not get $θ_{13}$ in its present 3$σ$ range. The current values of the two mass squared differences and mixing angles including $θ_{13}$ can be produced in the MSSM case with tan$β$ = 10 and non zero Majorana CP phases at low energy. We also calculate the order of effective Majorana mass and Jarlskog Invariant for each scenario under consideration.

hep-ph↗

arXiv2015

Inflation and leptogenesis in the 3-3-1-1 model

We consider the SU(3)_C \otimes SU(3)_L \otimes U(1)_X \otimes U(1)_N (3-3-1-1) model at the GUT scale with implication for inflation and leptogenesis. The mass spectra of the neutral Higgs bosons and neutral gauge bosons are reconsidered when the scale of the 3-3-1-1 breaking is much larger than that of the ordinary SU(3)_C \otimes SU(3)_L \otimes U(1)_X (3-3-1) breaking. We investigate how the 3-3-1-1 model generates an inflation by identifying the scalar field that spontaneously breaks the U(1)_N symmetry to inflaton as well as including radiative corrections for the inflaton potential. We figure out the parameter spaces appeared in the inflaton potential that satisfy the conditions for an inflation model and obtain the inflaton mass an order of 10^{13} GeV. The inflaton can dominantly decay into a pair of light Higgs bosons or a pair of heavy Majorana neutrinos which lead, respectively, to a reheating temperature of 10^9 GeV order appropriate to a thermal leptogenesis scenario or to a reduced reheating temperature corresponding to a non-thermal leptogenesis scenario. We calculate the lepton asymmetry which yields baryon asymmetry successfully for both the thermal and non-thermal cases.

hep-ph↗

arXiv2014

CP Violation with Majorana neutrinos in K Meson Decays

We study the possibility of having CP asymmetries in the decay Kaon(+/-) -> pion(-/+) lepton(+/-) lepton(+/-) (lepton = muon or electron). This decay violates Lepton Number by two units and occurs only if there are Majorana particles that mediate the transition. Even though the absolute rate is highly suppressed by current bounds, we search for Majorana neutrino scenarios where the CP asymmetry arising from the lepton sector could be sizeable. This is indeed the case if there are two or more Majorana neutrinos with similar masses in the range around 10^2 MeV. In particular, the asymmetry is potentially near unity if two neutrinos are nearly degenerate, in the sense that the mass difference is similar to the decay rate. The full decay, however, may be difficult to detect not only because of the suppression caused by the heavy-to-light lepton mixing, but also because of the long lifetime of the heavy neutrino, which would induce large space separation between the two vertices where the charge leptons are produced. This particular problem should be less serious in heavier meson decays, as they involve heavier neutrinos with shorter lifetimes.

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