Searcharxiv⌕ Search

arXiv subjects

J. D. Kim

Publications and source records attributed to J. D. Kim.

At least 19 recordsLinked to original sources
arXiv2006

Pinning in nonmagnetic borocarbides

The field dependences of the Labush parameter in nonmagnetic borocarbides are measured by a method that does not require achieving a critical state. The expected values of the critical current are estimated. The values obtained are two order of magnitude greater than the results of "direct" measurements performed on the basis of transport (magnetic) experiments. A giant peak effect, which the collective pinning model describes quantitavely well, is observed in the field dependences of the Labush parameter in Y-based borocarbides.

cond-mat.supr-con↗
arXiv2006

Magnus force and acoustic Stewart-Tolman effect in type II superconductors

At zero magnetic field we have observed an electromagnetic radiation from superconductors subjected by a transverse elastic wave. This radiation has an inertial origin, and is a manifestation of the acoustic Stewart-Tolman effect. The effect is used for implementing a method of measurement of an effective Magnus force in type II superconductors. The method does not require the flux flow regime and allows to investigate this force for almost the whole range of the existence of the mixed state. We have studied behavior of the gyroscopic force in nonmagnetic borocarbides and Nb. It is found that in borocarbides the sign of the gyroscopic force in the mixed state is the same as in the normal state, and its value (counted for one vortex of unit length) has only a weak dependence on the magnetic field. In Nb the change of sign of the gyroscopic force under the transition from the normal to the mixed state is observed.

cond-mat.supr-con↗
arXiv2005

Comparative analysis of specific heat of YNi2B2C using nodal and two-gap models

The magnetic field dependence of low temperature specific heat in YNi2B2C was measured and analyzed using various pairing order parameters. At zero magnetic field, the two-gap model which has been successfully applied to MgB2 and the point-node model, appear to describe the superconducting gap function of YNi2B2C better than other models based on the isotropic s-wave, the d-wave line nodes, or the s+g wave. The two energy gaps, delta_L=2.67 meV and delta_S=1.19 meV are obtained. The observed nonlinear field dependence of electronic specific heat coefficient, gamma(H)~H0.47, is quantitatively close to gamma(H)~H0.5 expected for nodal superconductivity or can be qualitatively explained using two-gap scenario. Furthermore, the positive curvature in Hc2(T) near Tc is qualitatively similar to that in the other two-gap superconductor MgB2.

cond-mat.supr-con↗
arXiv2005

Muonium-antimuonium conversion in models with heavy neutrinos

We study muonium-antimuonium conversion and mu+ e- to mu- e+ scattering within two different lepton-flavor-violating models with heavy neutrinos: model I is a typical seesaw that violates lepton number as well as flavor; model II has a neutrino mass texture where lepton number is conserved. We look for the largest possible amplitudes of these processes that are consistent with current bounds. We find that model I has very limited chance of providing an observable signal, except if a finely tuned condition in parameter space occurs. Model II, on the other hand, requires no fine tuning and could cause larger effects. However, the maximum amplitude provided by this model is still two orders of magnitude below the sensitivity of current experiments: one predicts an effective coupling G_MM up to 10^{-4}G_F for heavy neutrino masses near 10 TeV. We have also clarified some discrepancies in previous literature on this subject.

hep-ph↗
arXiv2002

A Flexible Parametrization of CKM matrix via Singular-Value-Decomposition Method

We investigate a flexible method in which we can test the unitarity of the quark flavor mixing matrix step-by-step. Singular-Value-Decomposition (SVD) techniques are used in analyzing the mixing matrix over a broader parameter region than the unitarity region. Unitary constraints make us extract CP violating properties without any specific parametrization when the magnitudes of at least three mixing matrix elements in three generation quark mixing are given. This method can also be applied to the analysis of lepton flavor mixing, in which only a few moduli are presently measured.

hep-ph↗
arXiv2002

Top quark Kaluza-Klein mode mixing in the Randall-Sundrum bulk Standard Model and Constraint from Δρ

Randall-Sundrum scenario with all the standard model (SM) fermions and gauge bosons in the bulk is phenomenologically studied. Even though the simple assumption of universal bulk fermion mass m_ψleads to the same Kaluza-Klein (KK) mass spectrum for all the SM fermions and thus suppresses new contributions to Flavor-Changing-Neutral-Current and the ρparameter, large Yukawa coupling of the top quark generates its KK mode mixing and breaks the degeneracy: unacceptably large contribution to Δρoccurs. With a different bulk fermion mass to SU(2) singlet bottom quark, we demonstrate that there exists some parameter space to satisfy the Δρconstraint.

hep-ph↗
arXiv2002

Top quark Kaluza-Klein mode mixing in the Randall-Sundrum bulk Standard Model and B -> X_s gamma

We study top quark Kaluza-Klein (KK) mode mixing in the Randall-Sundrum scenario with all the SM fermions and gauge bosons in the bulk. Even though the simple assumption of universal bulk fermion mass m_psi leads to the same KK mass spectrum for all the SM fermions and thus suppresses new contributions to the flavor changing neutral current and the rho parameter, large Yukawa coupling of the top quark generates the mixing among its KK modes and breaks the degeneracy: Unacceptably large contribution to rho occurs. In order to satisfy the rho constraint, we relax the model by assigning a different bulk fermion mass to SU(2) singlet bottom quark, and demonstrate that there exists some limited parameter space where the $Δρ$ constraint is satisfied. It is also shown that the current measurement of Br(B -> X_s + gamma) can be accommodated in this modified model, and one sigma level precision constrains the effective weak scale k_{EW} such as k_{EW} ~ 3 TeV for m_psi/k=-0.4, where k_{EW} is the warp-suppressed AdS_5 curvature.

hep-ph↗
arXiv2002

On Lepton Flavor Violation in Tau Decays

We study lepton flavor violation (LFV) in tau decays induced by heavy Majorana neutrinos within two models: (I) the Standard Model with additional right-handed heavy Majorana neutrinos, i.e., a typical seesaw-type model; (II) the Standard Model with left-handed and right-handed neutral singlets, which are inspired by certain scenarios of SO(10)models and heterotic superstring models with E_6 symmetry. We calculate various LFV branching ratios and a T-odd asymmetry. The seesaw Model I predicts very small branching ratios for LFV processes in most of the parameter space, although in a very restricted parameter region it can reach maximal branching ratios Br(tau to mu gamma) approx 10^-9 and Br(tau to 3mu) approx 10^-10. In contrast, Model II may show branching ratios Br(tau to e gamma) approx 10^-8 and Br(tau to 3e) < 10^-9, over a sizable region of the parameter space, large enough to be tested by experiments in the near future.

hep-ph↗
arXiv2001

Muon Anomalous Magnetic Moment (g-2)_mu and the Randall-Sundrum Model

We study the effects of the Kaluza-Klein gravitons in the Randall-Sundrum model on the recent BNL measurements of the muon (g-2) deviation from the standard model prediction. By examining the J-partial wave unitarity bounds of the elastic process gamma+gamma->gamma+gamma, the cut-off on the number of massive KK gravitons, n_c, has been introduced. We found that the recently measured (Delta a_mu) can be accommodated in the RS model, within the natural parameter space allowed by the perturbative unitarity. For example, dozens (hundreds) of the n_c for Lambda_pi=1-2 TeV (3 TeV) can explain the reported Delta a_mu.

hep-ph↗
arXiv2000

Neutrino Masses and Leptonic CP Violation

Neutrino oscillations as solutions of the solar neutrino problems and the atmospheric neutrino deficits may restrict neutrino mass squared differences and mixing angles in three-neutrino mixing scheme. Currently we have several solutions depending on the interpretations of the solar neutrino problems. Combining the neutrino oscillation solutions and a mass matrix ansatz, we investigated the neutrino mass bounds and found possible leptonic CP-violating rephasing-invariant quantity $J^{l}_{\tiny CP} \leq 0.012$ for large mixing angle MSW and just-so vacuum oscillations solutions, and $J^{l}_{\tiny CP} \leq 0.0013$ for small mixing angle MSW solution.

hep-ph↗
arXiv1999

Hierarchical Quark Mixing and Bimaximal Lepton Mixing on the Same Footing

We show that not only the hierarchical quark CKM mixing matrix but also the "bimaximal" lepton flavor mixing matrix can be derived from the same mass matrix ansatz based on the broken permutation symmetry, by assuming the hierarchy of neutrino masses to be $m_1\simeq m_2 <<m_3$. We also reproduce the recently measured angle of unitary triangle, $\sin 2β$, as well as all the observed experimental values of $V_{\tiny CKM}$ of the quark CKM matrix. And we predict Jarlskog rephasing invariant quantity, $J_{\tiny CP} \simeq 0.18 \times 10^{-4}$, and the upper bound of the same quantity in the lepton sector, $J^l_{\tiny CP} \leq 0.012$, which may be indeed large enough to generate the lepton number violation of the universe.

hep-ph↗
arXiv1997

Pulsar Velocity with Three-Neutrino Oscillations in Non-adiabatic Processes

We have studied the position dependence of neutrino energy on the Kusenko-Segrè mechanism as an explanation of the proper motion of pulsars. The mechanism is also examined in three-generation mixing of neutrinos and in a non-adiabatic case. The position dependence of neutrino energy requires the higher value of magnetic field such as $B\sim 3\times 10^{15}$ Gauss in order to explain the observed proper motion of pulsars. It is shown that possible non-adiabatic processes decrease the neutrino momentum asymmetry, whereas an excess of electron neutrino flux over other flavor neutrino fluxes increases the neutrino momentum asymmetry. It is also shown that a general treatment with all three neutrinos does not modify the result of the two generation treatment if the standard neutrino mass hierarchy is assumed.

hep-ph↗
arXiv1996

Medium Effects on the CP phases and Dynamical Mixing Angles in the Neutrino Mixing Matrix

The concepts of effective and dynamical neutrino mixing matrices are introduced in order to describe the behavior of neutrinos in matter. The former relates weak eigenstates to mass eigenstates, whereas the latter relates weak eigenstates to energy eigenstates in matter. It is shown that the dynamical mixing angles enable us to express the neutrino survival probability in the Sun without any resort to the Landau-Zener transition probability for the non-adiabatic process. Also discussed are effective CP violating phases that appear in the effective and dynamical mixing matrices in matter. Both two and three generation cases are discussed using the solar neutrinos as an example.

hep-ph↗
arXiv1996

Square Root Singularity in Boundary Reflection Matrix

Two-particle scattering amplitudes for integrable relativistic quantum field theory in 1+1 dimensions can normally have at most singularities of poles and zeros along the imaginary axis in the complex rapidity plane. It has been supposed that single particle amplitudes of the exact boundary reflection matrix exhibit the same structure. In this paper, single particle amplitudes of the exact boundary reflection matrix corresponding to the Neumann boundary condition for affine Toda field theory associated with twisted affine algebras $a_{2n}^{(2)}$ are conjectured, based on one-loop result, as having a new kind of square root singularity.

hep-th↗
arXiv1996

Root Systems and Boundary Bootstrap

The principle of boundary bootstrap plays a significant role in the algebraic study of the purely elastic boundary reflection matrix $K_a(θ)$ for integrable quantum field theory defined on a space-time with a boundary. However, general structure of that principle in the form as was originally introduced by Fring and Köberle has remained unclear. In terms of a new matrix $J_a(θ)=\sqrt{K_a(θ)/K_{\bar{a}}(iπ+θ)}$, the boundary bootstrap takes a simple form. Incidentally, a hypothesised expression of the boundary reflection matrix for simply-laced $ADE$ affine Toda field theory defined on a half line with the Neumann boundary condition is obtained in terms of geometrical quantities of root systems à la Dorey.

hep-th↗
arXiv1995

Boundary Reflection Matrix for $D_4^{(1)}$ Affine Toda Field Theory

We present one loop boundary reflection matrix for $d_4^{(1)}$ Toda field theory defined on a half line with the Neumann boundary condition. This result demonstrates a nontrivial cancellation of non-meromorphic terms which are present when the model has a particle spectrum with more than one mass. Using this result, we determine uniquely the exact boundary reflection matrix which turns out to be \lq non-minimal' if we assume the strong-weak coupling \lq duality'.

hep-th↗
arXiv1995

Boundary Reflection Matrix in Perturbative Quantum Field Theory

We study boundary reflection matrix for the quantum field theory defined on a half line using Feynman's perturbation theory. The boundary reflection matrix can be extracted directly from the two-point correlation function. This enables us to determine the boundary reflection matrix for affine Toda field theory with the Neumann boundary condition modulo `a mysterious factor half'.

hep-th↗