arXiv subjects

C. S. Kim

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

At least 73 records · Page 4Linked to original sources

arXiv2014

Prediction of leptonic CP phase from perturbatively modified tribimaximal (or bimaximal) mixing

We consider the perturbatively modified tribimaximal (or bimaximal) mixing to estimate the (Dirac-type) CP phase in neutrino mixing matrix. The expressions for the CP phase are derived from the equivalence between the standard parametrization of the neutrino mixing matrix for the Majorana neutrino and modified tribimaximal or bimaximal mixing matrices with appropriate CP phases. Carrying out numerical analysis based on the current experimental results for neutrino mixing angles, we can predict the values of the CP phase for several possible cases.

hep-ph↗

arXiv2014

Color dipole cross section and inelastic structure function

Instead of starting from a theoretically motivated form of the color dipole cross section in the dipole picture of deep inelastic scattering, we start with a parametrization of the deep inelastic structure function for electromagnetic scattering with protons, and then extract the color dipole cross section. Using the parametrizations of $F_2(ξ=x \ {\rm or}\ W^2,Q^2)$ by Donnachie-Landshoff and Block et al., we find the dipole cross section from an approximate form of the presumed dipole cross section convoluted with the perturbative photon wave function for virtual photon splitting into a color dipole with massless quarks. The color dipole cross section determined this way reproduces the original structure function within about 10\% for $0.1$ GeV$^2\leq Q^2\leq 10$ GeV$^2$. We discuss the large and small form of the dipole cross section and compare with other parameterizations.

hep-ph↗

arXiv2014

Radiative and Seesaw Threshold Corrections to the $S_3$ Symmetric Neutrino Mass Matrix

We systematically analyze the radiative corrections to the $S_3$ symmetric neutrino mass matrix at high energy scale, say the GUT scale, in the charged lepton basis. There are significant corrections to the neutrino parameters both in the Standard Model (SM) and Minimal Supersymmetric Standard Model (MSSM) with large tan$β$, when the renormalization group evolution (RGE) and seesaw threshold effects are taken into consideration. We find that in the SM all three mixing angles and atmospheric mass squared difference are simultaneously obtained in their current 3$σ$ ranges at the electroweak scale. However, the solar mass squared difference is found to be larger than its allowed 3$σ$ range at the low scale in this case. There are significant contributions to neutrino masses and mixing angles in the MSSM with large tan$β$ from the RGEs even in the absence of seesaw threshold corrections. However, we find that the mass squared differences and the mixing angles are obtained in their current 3$σ$ ranges at low energy when the seesaw threshold effects are also taken into account in the MSSM with large tan$β$.

hep-ph↗

arXiv2014

Top Yukawa coupling measurement with indefinite CP Higgs in $e^+e^-\to t\bar{t}Φ$

We consider the issue of the top quark Yukawa coupling measurement in a model in dependent and general case with the inclusion of CP-violation in the coupling. Arguably the best process to study this coupling is the associa ted production of Higgs boson along with a $t\bar t$ pair in a machine like the International Linear Collider (ILC). While detailed analyses of the sensitivity of the measurement assuming a Standard Model (SM) - like coupling are available in the context of ILC, conclude that th e coupling could be pinned down at about 10\% level with modest luminosity, our investigations show that the scenario could be different in case of a more general coupling. The modified Lorentz structure resulting in a changed functional dependence of the cross section on the couplin g, along with the difference in the cross section itself leads to considerable deviation in the sensitivity. Our studies with an ILC of center of mass energies of 500 GeV, 800 GeV and 1000 GeV show that moderate CP-mixing in the Higgs sector could change the sensitivity to about 20\ %, while it could be worsened to 75\% in cases which could accommodate more dramatic changes in the coupling. While detailed considerations of the decay distributions point to a need for a relook at the analysis strategy followed for the case of SM such as for a model independent analysis of the top quark Yukawa coupling measurement. This study strongly suggests that, a joint analysis of the CP properties and the Yukawa coupling measurement would be the way forward at the ILC and that caution must be excercised in the measurem ent of the Yukawa couplings and the conclusions drawn from it.

hep-ph↗

arXiv2014

CP violation in lepton number violating semihadronic decays of $K, D, D_s, B, B_c$

We study the CP violation in lepton number violating meson decays $M^{\pm} \to \ell_1^{\pm} \ell_2^{\pm} M^{' \mp}$, where $M$ and $M^{'}$ are pseudoscalar mesons, $M=K, D, D_s, B, B_c$ and $M^{'}=π, K, D, D_s$, and the charged leptons are $\ell_1, \ell_2 = e, μ$. It turns out that the CP-violating difference $S_{-}(M) \equiv [Γ(M^- \to \ell_1^- \ell_2^- M^{' +})-Γ(M^+ \to \ell_1^+ \ell_2^+ M^{' -})]$ can become appreciable when two intermediate on-shell Majorana neutrinos $N_j$ ($j=1,2$) participate in these decays. Our calculations show that the asymmetry becomes largest when the masses of $N_1$ and $N_2$ are almost degenerate, i.e., when the mass difference $ΔM_N$ becomes comparable with the (small) decay widths $Γ_N$ of these neutrinos: $ΔM_N \not\gg Γ_N$. We show that in such a case, the CP ratio ${\cal A}_{CP}(M) \equiv [Γ(M^- \to \ell_1^- \ell_2^- M^{' +})-Γ(M^+ \to \ell_1^+ \ell_2^+ M^{' -})]/[Γ(M^- \to \ell_1^- \ell_2^- M^{' +})+Γ(M^+ \to \ell_1^+ \ell_2^+ M^{' -})]$ becomes a quantity $\sim 1$. The observation of CP violation in these decays would be consistent with the existence of the well-motivated $ν$MSM model with two almost degenerate heavy neutrinos in the mass range between $M_N \sim 0.1$-$10^1$ GeV.

hep-ph↗

arXiv2014

Triplet Dark Matter from leptogenesis

A triplet dark matter candidate from thermal leptogenesis is considered with building a model. The model is based on the standard two Higgs doublet model and seesaw mechanism with Higgs triplets. The parameters (couplings and masses) are adjusted for the observed small neutrino mass and the leptogenesis. Dark matter particles can annihilate and decay in this model. The time evolution of the dark matter number is governed by (co)annihilations in the expanding universe, and its mass is constrained by the observed relic density. The dark matter can decay into final states with three leptons (two charged leptons and one neutrino). We investigate whether the decay in the galaxy can account for cosmic ray anomalies in the positron and electron spectrum. A noticeable point is that if the dark matter decays into each lepton with different branching ratios, cosmic ray anomalies in AMS-02 measurements of the positron fraction and the Fermi LAT measurements of the electrons-plus-positrons flux could be simultaneously accounted for from its decay products. The leptogenesis within this model is studied in an appendix.

hep-ph↗

arXiv2014

Remarks on the lifetime of sterile neutrinos and the effect on detection of rare meson decays M+ -> M'- lepton+ lepton+

We review the detection of the Delta L=2 semileptonic meson decays of the form M(+) -> M'(-) lepton(+) lepton(-) that we studied in a previous work, mediated by a Majorana neutrino with a mass in the range between the masses of the initial and final mesons. For such range of masses, the Majorana neutrino will go on its mass shell and the two charged leptons will appear at displaced vertices or, if the lifetime is long enough, most secondary vertices will fall outside the detector. We study the consequences of this effect on the experimental searches and limits that can be extracted.

hep-ph↗

arXiv2014

CP violations in $π^{\pm}$ Meson Decay

We study the pion decays with intermediate on-shell neutrinos $N$ into two electrons and a muon, $π^{\pm} \to e^{\pm} N \to e^{\pm} e^{\pm} μ^{\mp} ν$. We investigate the branching ratios ${\rm Br}_{\pm} = [Γ(π^- \to e^- e^- μ^+ ν) \pm Γ(π^+ \to e^+e^+μ^-ν)]/Γ(π^- \to {\rm all})$ and the CP asymmetry ratio ${\cal A}_{\rm CP} = {\rm Br}_{-}/{\rm Br}_{+}$ for such decays, in the scenario with two different on-shell neutrinos. If $N$ is Dirac, only the lepton number conserving (LC) decays contribute (LC: $ν= ν_e$ or ${\bar ν}_e$); if $N$ is Majorana, both LC and lepton number violating (LV) decays contribute (LV: $ν={\bar ν}_μ$ or $ν=ν_μ$). The results show that the CP asymmetry ${\cal A}_{\rm CP}$ is in general very small, but increases and becomes $\sim 1$ when the masses of the two intermediate neutrinos get closer to each other, i.e., when their mass difference becomes comparable with their decay width, $ΔM_N \not\gg Γ_N$. The observation of CP violation in pion decays would be consistent with the existence of the well-motivated $ν$MSM model with two almost degenerate heavy neutrinos.

hep-ph↗

arXiv2013

Magnetic Moments of Bottom Baryons: Effective mass and Screened Charge

We calculate the magnetic moments of low lying heavy flavor bottom baryons using effective quark mass and shielded quark charge scheme. We obtain the magnetic moments of both $J^P = 1/2^+$ and $J^P = 3/2^+$ baryon states. We compare our predictions with other theoretical approaches.

hep-ph↗

arXiv2013

Charge Asymmetry of Weak Boson Production at the LHC and the Charm Content of the Proton

We investigate the production of the weak bosons $W^+$, $W^-$ and $Z$ at the LHC as a function of their rapidity, reconstructed {\it experimentally} from their leptonic decay. We show that the measurements provide a powerful tool for constraining the parton distribution functions, as was already the case for the lower energy $p\bar{p}$ collider data. We study the charge asymmetry determining the $u$ and $d$ distribution functions using the reconstructed $W^+$, $W^-$ rapidities. We also show how the ratio of the $W$ and $Z$ boson rapidity distributions directly probes the charm quark distribution function of the proton.

hep-ph↗

arXiv2013

Implication of a vanishing element in 3+1 Scenario

In this paper we study the phenomenological implications of the one zero textures of low energy neutrino mass matrices in presence of a sterile neutrino. We consider the 3+1 scheme and use the results from global fit for short baseline neutrino oscillation data which provides the bounds on the three additional mixing angles. We find that the mass matrix elements $m_{αβ}$ ($α, β= e, μ, τ$) involving only the active states can assume vanishing values in the allowed parameter space for all the mass spectrum. Among the mass matrix elements connecting the active and sterile states, $m_{es}$ and $m_{μs}$ can become small only for the quasi-degenerate neutrinos. The element $m_{τs}$ on the other hand can vanish even for lower values of masses since the 3-4 mixing angle only has an upper bound from current data. The mass matrix element ($m_{ss}$) involving only the sterile state stays $\sim$ $\mathcal{O}$(1) eV in the whole parameter region. We study the possible correlations between the sterile mixing angles and the Majorana phases to give a zero element in the mass matrix.

hep-ph↗

arXiv2013

First Estimates of Nonleptonic $B_c \to AT$ Weak Decays

We obtain the first estimates of branching ratios for the weak decays of $B_c$ meson decaying to two orbitally excited mesons namely, axial-vector meson ($A$) and tensor meson ($T$), in the final state. We calculate $B_c \to T$ transition form factors using the Isgur-Scora-Grinstein-Wise II framework and consequently predict branching ratios of $ B_c \to AT $ decays in Cabibbo-Kobayashi-Maskawa favored and suppressed modes.

hep-ph↗

arXiv2013

Vector like leptons with extended Higgs sector

We examined the influence of additional scalar doublet on the parameter space of the Standard Model supplemented with a generation of new vector like leptons. In particular we identified the viable regions of parameter space by inspecting various constraints especially electroweak precision (S, T and U) parameters. We demonstrated that the additional scalar assists in alleviating the tension of electroweak precision constraints and thus permitting larger Yukawa mixing and mass splittings among vector like species. We also compared and contrasted the regions of parameter space pertaining to the latest LHC Higgs to diphoton channel results in this scenario with vector like leptons in single Higgs doublet and pure two Higgs doublet model case.

hep-ph↗

arXiv2013

$B\to DK^*_{0,2}$ Decays: PQCD analysis to determine CP violation phase angle $γ$

$B^\pm \to (D^0, \bar D^0, D_{CP})K^{*\pm}_{0,2}$ decays are helpful in determining the CP violation angle $γ$, and we analyze these decay processes within the perturbative QCD approach based on $k_T$ factorization. We found that the branching ratio of $B^-\to D^0 K^{*-}_0$ can reach the order of $10^{-4}$, due to the enhancement of nonfactorizable contributions in color-suppressed $D^0$-emission, while the branching ratio of $B^-\to \bar D^0 K^{*-}_0$ is of the order $10^{-5}$. The ratio of decay amplitudes is about 3 times larger than the one in the channel $B^\pm\to D K^\pm$. Large branching ratios provide a good opportunity to observe $ B^\pm \to D K^{*\pm}_2$ on the ongoing and forthcoming experimental facilities and consequently these channels may be of valuable avail in reducing the errors in the CP violation phase angle $γ$. We also explore the possible time-dependent CP asymmetries of $B_s$ decay into a scalar meson to determine the phase angle $γ$.

hep-ph↗

arXiv2013

Spontaneous CP Violation in $A_4$ Flavor Symmetry and Leptogenesis

We propose a simple renormalizable model for the spontaneous CP violation based on $SU(2)_{L}\times U(1)_{Y}\times A_{4}$ symmetry in a radiative seesaw mechanism, which can be guaranteed by an extra $Z_{2}$ symmetry. In our model CP is spontaneously broken at high energies, after breaking of flavor symmetry, by a complex vacuum expectation value of $A_{4}$-triplet and gauge singlet scalar field. We show that the spontaneously generated CP phase could become a natural source of leptogenesis, %CP violation for neutrino oscillation and leptogenesis, respectively. Then, and also investigate CP violation at low energies in the lepton sector and show how the CP phases in PMNS could be arisen through spontaneous symmetry breaking mechanism. As a numerical study, interestingly, we show that the normal mass hierarchy favors relatively large values of $θ_{13}$, large deviations from maximality of $θ_{23}<π/4$ and Dirac-CP phase $0^{\circ}\leqδ_{CP}\leq50^{\circ}$ and $300^{\circ}\leqδ_{CP}\leq360^{\circ}$. For the inverted hierarchy case, the experimentally measured values of $θ_{13}$ favors $θ_{23}>π/4$ and discrete values of $δ_{CP}$ around $100^{\circ},135^{\circ},255^{\circ}$ and $300^{\circ}$. Finally, with a successful leptogenesis our numerical results give more predictive values on the Dirac CP phase: for the normal mass hierarchy $1^{\circ}\lesssimδ_{CP}\lesssim10^{\circ}$ and for inverted one $δ_{CP}\sim100^{\circ},135^{\circ},300^{\circ}$.

hep-ph↗

arXiv2013

Charmless $B_{u,d,s}\to VT$ decays in perturbative QCD approach

Motivated by the experimental data, we study charmless $B_{u,d,s}\to VT$ ($V$ and $T$ denote light vector and tensor mesons respectively) decays in the perturbative QCD approach. The predictions of branching ratios, polarization fractions and direct CP violations are given in detail. Specifically, within this approach we have calculated the polarization fractions and the branching ratios of $B\to ϕ(K_2^{*-}, \bar K_2^{*0})$ which agree well with the observed experimental data, however the branching ratios of $B\to ω(K_2^{*-}, \bar K_2^{*0})$ are hard to be explained, where the polarization fractions are well accommodated. The tree dominated channels with a vector meson emitted have longitudinal polarization fraction of 90%, while the penguin dominating ones have subtle polarization fractions. Fortunately, most branching ratios of $B_{u,d}$ decays are of the order $10^{-6}$, which would be straight forward for experimental observations. For the $B_s$ decays the branching ratios can reach the order of $10^{-6}$ in tree dominated decays, while in penguin dominated decays those are of order of $10^{-7}$ which require more experimental data to be observed.

hep-ph↗

arXiv2013

Branching ratios of $B_c$ Meson Decaying to Vector and Axial-Vector Mesons

We investigate the weak decays of $B_c$ mesons in Cabibbo-Kobayashi-Maskawa favored and suppressed modes. We present a detailed analysis of the $B_c$ meson decaying to vector meson (V) and axial-vector meson (A) in the final state. We also give the form factors involving $B_c \to A$ transition in the Isgur-Scora-Grinstein-Wise II framework and consequently, predict the branching ratios of $B_c \to V A$ and $AA$ decays.

hep-ph↗

arXiv2013

Dipole-interacting Fermionic Dark Matter in positron, antiproton, and gamma-ray channels

Cosmic ray signals from dipole-interacting dark matter annihilation are considered in the positron, antiproton and photon channels. The predicted signals in the positron channel could nicely account for the excess of positron fraction from Fermi LAT, PAMELA, HEAT and AMS-01 experiments for the dark matter mass larger than 100 GeV with a boost (enhancement) factor of 30-80. No excess of antiproton over proton ratio at the experiments also gives a severe restriction for this scenario. With the boost factors, the predicted signals from Galactic halo and signals as mono-energetic gamma-ray lines (monochromatic photons) for the region close to the Galactic center are investigated. The gamma-ray excess of recent tentative analyses based on Fermi LAT data and the potential probe of the monochromatic lines at a planned experiment, AMS-02, are also considered.

astro-ph.HE↗