arXiv subjects

Yong-Yeon Keum

Publications and source records attributed to Yong-Yeon Keum.

At least 19 recordsLinked to original sources

arXiv2013

TeV cosmic-ray proton and helium spectra in the myriad model

Recent measurements of cosmic ray proton and helium spectra show a hardening above a few hundreds of GeV. This excess is hard to understand in the framework of the conventional models of Galactic cosmic ray production and propagation. We propose here to explain this anomaly by the presence of local sources (myriad model). Cosmic ray propagation is described as a diffusion process taking place inside a two-zone magnetic halo. We calculate the proton and helium fluxes at the Earth between 50 GeV and 100 TeV. Improving over a similar analysis, we consistently derive these fluxes by taking into account both local and remote sources for which a unique injection rate is assumed. We find cosmic ray propagation parameters compatible with B/C measurements and for which the proton and helium spectra remarkably agree with the PAMELA and CREAM measurements over four decades in energy.

astro-ph.HE↗

arXiv2009

Propagation of Neutrinos through Magnetized Gamma-Ray Burst Fireball

The neutrino self-energy is calculated in a weakly magnetized plasma consists of electrons, protons, neutrons and their anti-particles and using this we have calculated the neutrino effective potential up to order $M^{-4}_W$. In the absence of magnetic field it reduces to the known result. We have also calculated explicitly the effective potentials for different backgrounds which may be helpful in different environments. By considering the mixing of three active neutrinos in the medium with the magnetic field we have derived the survival and conversion probabilities of neutrinos from one flavor to another and also the resonance condition is derived. As an application of the above, we considered the dense and relativistic plasma of the Gamma-Ray Bursts fireball through which neutrinos of 5-30 MeV can propagate and depending on the fireball parameters they may oscillate resonantly or non-resonantly from one flavor to another. These MeV neutrinos are produced due to stellar collapse or merger events which trigger the Gamma-Ray Burst. The fireball itself also produces MeV neutrinos due to electron positron annihilation, inverse beta decay and nucleonic bremsstrahlung. Using the three neutrino mixing and considering the best fit values of the neutrino parameters, we found that electron neutrinos are hard to oscillate to another flavors. On the other hand, the muon neutrinos and the tau neutrinos oscillate with equal probability to one another, which depends on the neutrino energy, temperature and size of the fireball. Comparison of oscillation probabilities with and without magnetic field shows that, they depend on the neutrino energy and also on the size of the fireball. By using the resonance condition, we have also estimated the resonance length of the propagating neutrinos as well as the baryon content of the fireball.

hep-ph↗

arXiv2009

$SU(4)_L \times U(1)_X$ models with little Higgs

We discuss the aspects of the fermions and gauge bosons in $SU(4)_L \times U(1)_X$ models with little Higgs. We introduce a set of fermions which ensures the cancellation of gauge anomaly, and explicitly show the cancellation of one-loop quadratic divergence to the Higgs mass from all fermion multiplets and all gauge bosons. We present the interactions of the standard model fermions with the physical gauge bosons. We also discuss some phenomenological implications of the model based on recent experimental results.

hep-ph↗

arXiv2009

Neutrino Oscillation in Magnetized Gamma-Ray Burst Fireball

Neutrinos of energy about 5-20 MeV are produced due to the stellar collapse or merger events that trigger the Gamma-Ray Burst. Also low energy MeV neutrinos are produced within the fireball due to electron positron annihilation and nucleonic bremsstrahlung. Many of these neutrinos will propagate through the dense and relativistic magnetized plasma of the fireball. We have studied the possibility of resonant oscillation of $ν_e\leftrightarrow ν_{μ,τ}$ by taking into account the neutrino oscillation parameters from SNO, SuperKamiokande and Liquid Scintillator Detector. Using the resonance condition we have calculated the resonance length for these neutrinos and also the fireball observables like lepton asymmetry and the baryon load are estimated based on the assumed fireball radius of 100 Km.

hep-ph↗

arXiv2008

Neutrino Masses from Cosmological Probes in Interacting Neutrino Dark-Energy Models

We investigate whether interaction between massive neutrinos and quintessence scalar field is the origin of the late time accelerated expansion of the universe. We present explicit formulas of the cosmological linear perturbation theory in the neutrinos probes of dark-energy model, and calculate cosmic microwave background anisotropies and matter power spectra. In these models, the evolution of the mass of neutrinos is determined by the quintessence scalar field, which is responsible for a varying effective equation of states: $ω_{eff}(z)$ goes down -1. We consider several types of scalar field potential and put constraints on the coupling parameter between neutrinos and dark energy. By combining data from cosmic microwave background (CMB) experiments including the WMAP 3-year results, large scale structure with 2dFGRS data sets, we constrain the hypothesis of massive neutrinos in the mass-varying neutrino scenario. Assuming the flatness of the universe, the constraint we can derive from the current observation is $\sum m_ν < 0.45$ eV at 1$σ$ (0.87 eV at 2$σ$) confidence level for the sum over three species of neutrinos. The dynamics of scalar field and the impact of scalar field perturbations on cosmic microwave background anisotropies are discussed. We also discuss on the instability issue of the our model and confirm that neutrinos are stable against the density fluctuation.

hep-ph↗

arXiv2008

Cosmological Signatures of the Interaction between Dark-Energy and Massive Neutrinos

We investigate whether interaction between massive neutrinos and quintessence scalar field is the origin of the late time accelerated expansion of the universe. We present cosmological perturbation theory in neutrinos probe interacting dark-energy models, and calculate cosmic microwave background anisotropies and matter power spectrum. In these models, the evolution of the mass of neutrinos is determined by the quintessence scalar field, which is responsible for the cosmic acceleration today. We consider several types of scalar field potentials and put constraints on the coupling parameter between neutrinos and dark energy. Assuming the flatness of the universe, the constraint we can derive from the current observation is $\sum m_ν < 0.87 eV$ at the 95 % confidence level for the sum over three species of neutrinos. We also discuss on the stability issue of the our model and on the impact of the scattering term in Boltzmann equation from the mass-varying neutrinos.

astro-ph↗

arXiv2008

Neutrino Mass Bounds from Neutrinoless Double Beta Decays and Large Scale Structures

We investigate the way how the total mass sum of neutrinos can be constrained from the neutrinoless double beta decay and cosmological probes with cosmic microwave background (WMAP 3-year results), large scale structures including 2dFGRS and SDSS data sets. First we discuss, in brief, on the current status of neutrino mass bounds from neutrino beta decays and cosmic constrain within the flat $ΛCMD$ model. In addition, we explore the interacting neutrino dark-energy model, where the evolution of neutrino masses is determined by quintessence scalar filed, which is responsable for cosmic acceleration today. Assuming the flatness of the universe, the constraint we can derive from the current observation is $\sum m_ν < 0.87$eV at the 95 % confidence level, which is consistent with $\sum m_ν < 0.68$eV in the flat $ΛCDM$ model. Finally we discuss the future prospect of the neutrino mass bound with weak-lensing effects.

hep-ph↗

arXiv2008

Primordial Neutrinos, Cosmological Perturbations in Interacting Dark-Energy Model: CMB and LSS

We present cosmological perturbation theory in neutrinos probe interacting dark-energy models, and calculate cosmic microwave background anisotropies and matter power spectrum. In these models, the evolution of the mass of neutrinos is determined by the quintessence scalar field, which is responsible for the cosmic acceleration today. We consider several types of scalar field potentials and put constraints on the coupling parameter between neutrinos and dark energy. Assuming the flatness of the universe, the constraint we can derive from the current observation is $\sum m_ν < 0.87 eV$ at the 95 % confidence level for the sum over three species of neutrinos. We also discuss on the stability issue of the our model and on the impact of the scattering term in Boltzmann equation from the mass-varying neutrinos.

astro-ph↗

arXiv2007

Probing for Dynamics of Dark-Energy in Mass Varying Neutrinos: Cosmic Microwave Background Radiation and Large Scale Structure

We present cosmological perturbation theory in neutrino probe interacting dark-energy models, and calculate cosmic microwave background anisotropies and matter power spectrum. In these models, the evolution of the mass of neutrinos is determined by the quintessence scalar field, which is responsible for the cosmic acceleration today. We consider several types of scalar field potentials and put constraints on the coupling parameter between neutrinos and dark energy. Assuming the flatness of the universe, the constraint we can derive from the current observation is $\sum m_ν < 0.87 eV$ at the 95 % confidence level for the sum over three species of neutrinos.

hep-ph↗

arXiv2006

A_4 flavour symmetry breaking scheme for understanding quark and neutrino mixing angles

We propose a spontaneous A_4 flavour symmetry breaking scheme to understand the observed pattern of quark and neutrino mixing. The fermion mass eigenvalues are arbitrary, but the mixing angles are constrained in such a way that the overall patterns are explained while also leaving sufficient freedom to fit the detailed features of the observed values, including CP violating phases. The scheme realises the proposal of Low and Volkas to generate zero quark mixing and tribimaximal neutrino mixing at tree-level, with deviations from both arising from small corrections after spontaneous A_4 breaking. In the neutrino sector, the breaking is A_4 --> Z_2, while in the quark and charged-lepton sectors it is A_4 --> Z_3 = C_3. The full theory has A_4 completely broken, but the two different unbroken subgroups in the two sectors force the dominant mixing patterns to be as stated above. Radiative effects within each sector are shown to deviate neutrino mixing from tribimaximal, while maintaining zero quark mixing. Interactions between the two sectors -- "cross-talk" -- induce nonzero quark mixing, and additional deviation from tribimaximal neutrino mixing. We discuss the vacuum alignment challenge the scenario faces, and suggest three generic ways to approach the problem. We follow up one of those ways by sketching how an explicit model realising the symmetry breaking structure may be constructed.

hep-ph↗

arXiv2005

Perturbative SO(10) Grand Unification

We consider a phenomenologically viable SO(10) grand unification model of the unification scale $M_G$ around $10^{16} $ GeV which reproduces the MSSM at low energy and allows perturbative calculations up to the Planck scale $M_P$ or the string scale $M_{st}$. Both requirements strongly restrict a choice of Higgs representations in a model. We propose a simple SO(10) model with a set of Higgs representations $\{2 \times {\bf 10} + {\bf \bar{16}} + {\bf 16} + {\bf 45} \}$ and show its phenomenological viability. This model can indeed reproduce the low-energy experimental data relating the charged fermion masses and mixings. Neutrino oscillation data can be consistently incorporated in the model, leading to the right-handed neutrino mass scale $M_R \simeq M_G^2/M_P$. Furthermore, there exists a parameter region which results the proton life time consistent with the experimental results.

hep-ph↗

arXiv2005

Nonfactorizable contributions to $B \to D^{(*)} M$ decays

While the factorization assumption works well for many two-body nonleptonic $B$ meson decay modes, the recent measurement of $\bar B\to D^{(*)0}M^0$ with $M=π$, $ρ$ and $ω$ shows large deviation from this assumption. We analyze the $B\to D^{(*)}M$ decays in the perturbative QCD approach based on $k_T$ factorization theorem, in which both factorizable and nonfactorizable contributions can be calculated in the same framework. Our predictions for the Bauer-Stech-Wirbel parameters, $|a_2/a_1|= 0.43\pm 0.04$ and $Arg(a_2/a_1)\sim -42^\circ$ and $|a_2/a_1|= 0.47\pm 0.05$ and $Arg(a_2/a_1)\sim -41^\circ$, are consistent with the observed $B\to Dπ$ and $B\to D^*π$ branching ratios, respectively. It is found that the large magnitude $|a_2|$ and the large relative phase between $a_2$ and $a_1$ come from color-suppressed nonfactorizable amplitudes. Our predictions for the ${\bar B}^0\to D^{(*)0}ρ^0$, $D^{(*)0}ω$ branching ratios can be confronted with future experimental data.

hep-ph↗

arXiv2004

Phenomenological Application of $k_T$ factorization

We discuss applications of the perturbative QCD approach in the exclusive non-leptonic two body B-meson decays. We briefly review its ingredients and some important theoretical issues on the factorization approaches. PQCD results are compatible with present experimantal data for the charmless B-meson decays. We predict the possibility of large direct CP asymmetry in $B^0 \to π^{+}π^{-}$ $(23\pm7 %)$ and $B^0\to K^{+}π^{-}$ $(-17\pm5%)$. We also investigate the Branching ratios, CP asymmetry and isopsin symmetry breaking in radiative $B \to (K^*/ρ) γ$ decays.

hep-ph↗

arXiv2002

Determination of weak phases $ϕ_2$ and $ϕ_3$ from $B\to ππ,Kπ$ in the pQCD method

We look at two methods to determine the weak phases $ϕ_2$ and $ϕ_3$ from $B \to ππ$ and $Kπ$ decays within the perturbative QCD approach. We obtain quite interesting bounds on $ϕ_2$ and $ϕ_3$ from experimental measurements in asymmetric B-factory: $55^o \leq ϕ_2 \leq 100^o$ and $51^o \leq ϕ_3 \leq 129^o$. Specially we predict the possibility of large direct CP violation effect in $B^0 \to π^{+}π^{-}$ decay with $A_{cp}^{dir}(B\to π^{+} π^{-})=(23\pm7)$ %.

hep-ph↗

arXiv2002

Determination of weak phases $ϕ_2$ and $ϕ_3$ from $B\to ππ,Kπ$ in the pQCD method

We look at two methods to determine the weak phases $ϕ_2$ and $ϕ_3$ from $B \to ππ$ and $Kπ$ decays within the perturbative QCD approach. We obtain quite interesting bounds on $ϕ_2$ and $ϕ_3$ from recent experimental measurements in asymmetric B-factory: $55^o \leq ϕ_2 \leq 100^o$ and $51^o \leq ϕ_3 \leq 129^o$. Specially we predict the possibility of large direct CP violation effect in $B^0 \to π^{+}π^{-}$ decay with $A_{cp}^{dir}(B\to π^{+} π^{-})=(23\pm7)$ %.

hep-ph↗

arXiv2002

Perturbative QCD analysis of $B \to ϕK^* $ decays

We study the first observed charmless $B\to VV$ modes, the $B\toϕK^*$ decays, in perturbative QCD formalism. The obtained branching ratios $B(B\toϕK^*)\sim 15 \times 10^{-6}$ are larger than $\sim 9\times 10^{-6}$ from QCD factorization. The comparison of the predicted magnitudes and phases of the different helicity amplitudes, and branching ratios with experimental data can test the power counting rules, the evaluation of annihilation contributions, and the mechanism of dynamical penguin enhancement in perturbative QCD, respectively.

hep-ph↗

arXiv2002

B -> J/psi K^* Decays in QCD Factorization

The hadronic decay B -> J K^* is analyzed within the framework of QCD factorization. The spin amplitudes A_0, A_\parallel and A_\perp in the transversity basis and their relative phases are studied using various different form-factor models for B-K^* transition. The effective parameters a_2^h for helicity h=0,+,- states receive different nonfactorizable contributions and hence they are helicity dependent, contrary to naive factorization where a_2^h are universal and polarization independent. QCD factorization breaks down even at the twist-2 level for transverse hard spectator interactions. Although a nontrivial strong phase for the A_\parallel amplitude can be achieved by adjusting the phase of an infrared divergent contribution, the present QCD factorization calculation cannot say anything definite about the phase phi_\parallel. Unlike B -> J/psi K decays, the longitudinal parameter a_2^0 for B -> J/psi K^* does not receive twist-3 corrections and is not large enough to account for the observed branching ratio and the fraction of longitudinal polarization. Possible enhancement mechanisms for a_2^0 are discussed.

hep-ph↗

arXiv2001

Perturbative QCD analysis of $B \to ϕK$ decays and Power counting

We investigate exclusive nonleptonic $B$ meson decays $B\toϕK$ in perturbative QCD formalism. It is shown that the end-point (logarithmic and linear) singularities in decay amplitudes do not exist, after $k_T$ and threshold resummations are included. Power counting for emission and annihilation topologies of diagrams, including both factorizable and nonfactorizable ones, is discussed with Sudakov effects taken into account. Our predictions for the branching ratios $B(B\toϕK)\sim 10 \times 10^{-6}$ are larger than those ($\sim 4 \times 10^{-6}$) from the factorization approach because of dynamical enhancement of penguin contributions. Whether this enhancement is essential for penguin-dominated modes can be justified by experimental data.

hep-ph↗