Joohan Lee

First limit on WIMP cross section with low background CsI(Tℓ) crystal detector

Abstract The Korea Invisible Mass Search (KIMS) Collaboration has been carrying out WIMP search experiment with CsI ( T l ) crystal detectors at the YangYang Underground Laboratory. A successful reduction of the internal background of the crystal was done and a good pulse shape discrimination was achieved. We report the first result on WIMP search obtained with 237 kgu2009days data using one full-size CsI ( T l ) crystal of 6.6 kg mass.

Dirac operators on coset spaces

The Dirac operator for a manifold Q, and its chirality operator when Q is even dimensional, have a central role in noncommutative geometry. We systematically develop the theory of this operator when Q=G/H, where G and H are compact connected Lie groups and G is simple. An elementary discussion of the differential geometric and bundle theoretic aspects of G/H, including its projective modules and complex, Kahler and Riemannian structures, is presented for this purpose. An attractive feature of our approach is that it transparently shows obstructions to spin- and spinc-structures. When a manifold is spinc and not spin, U(1) gauge fields have to be introduced in a particular way to define spinors, as shown by Avis, Isham, Cahen, and Gutt. Likewise, for manifolds like SU(3)/SO(3), which are not even spinc, we show that SU(2) and higher rank gauge fields have to be introduced to define spinors. This result has potential consequences for string theories if such manifolds occur as D-branes. The spectra and eigen...

Bogomol'nyi equations of Chern-Simons Higgs theory from a generalized abelian Higgs model

Abstract We consider a generalization of the abelian Higgs model by introducing a dielectric function and study its Bogomolnyi limit. The Bogomolnyi equations of Chern-Simons Higgs theory are obtained as a particular case. We study soliton solutions in the theory and find a criterion under which the theory allows both topological and nontopological solitons. It is also shown that these Bogomolnyi equations can be obtained through dimensional reduction of four dimensional SU (2) self-dual Yang-Mills equations in a curved space, where the metric itself depends on the gauge potential.

Search for low-mass dark matter with CsI(Tl) crystal detectors

We present a search for low-mass ( ≤ 20 GeV / c 2 ) weakly interacting massive particles (WIMPs), strong candidates of dark matter particles, using the low-background CsI(Tl) detector array of the Korea Invisible Mass Search experiment. With a total data exposure of 24,524.3xa0kg days, we search for WIMP interaction signals produced by nuclei recoiling from WIMP-nuclear elastic scattering with visible energies between 2 and 4xa0keVee (electron-equivalent energy). The observed energy distribution of candidate events is consistent with null signals, and upper limits of the WIMP-proton spin-independent interaction are set with a 90% confidence level. The observed limit covers most of the low-mass region of parameter space favored by the DAMA annual modulation signal assuming the standard halo model.

Conformal Invariance in Einstein-Cartan-Weyl space

We consider conformally invariant form of the actions in Einstein, Weyl, Einstein–Cartan and Einstein–Cartan–Weyl space in general dimensions (> 2) and investigate the relations among them. In Weyl space, the observational consistency condition for the vector field determining non-metricity of the connection can be obtained from the equation of motion. In Einstein–Cartan space a similar role is played by the vector part of the torsion tensor. We consider the case where the trace part of the torsion is the Kalb–Ramond type of field. In this case, we express conformally invariant action in terms of two scalar fields of conformal weight -1, which can be cast into some interesting form. We discuss some applications of the result.

Dynamics of BPS states in the Dirac-Born-Infeld theory

The Dirac-Born-Infeld action with transverse scalar fields is considered to study the dynamics of various BPS states. We first describe the characteristic properties of the so-called 1/2 and 1/4 BPS states on the D3 brane, which can be interpreted as F/D-strings ending on a D3-brane in Type IIB string theory picture. We then study the response of the BPS states to low energy excitations of massless fields on the brane, the scalar fields representing the shape fluctuation of the brane and U(1) gauge fields describing the open string excitations on the D-brane. This leads to an identification of interactions between BPS states including the static potentials and the kinetic interactions.

de Sitter nonlinear sigma model and accelerating universe

We consider a cosmology with a noncompact nonlinear sigma model. The target space is of de Sitter type and four scalar fields are introduced. The potential is absent but cosmological constant term {lambda} is added. One of the scalar fields is time dependent and the remaining three fields have no time dependence but only spatial dependence. We show that a very simple ansatz for the scalar fields results in the accelerating universe with an exponential expansion at late times. It is pointed out that the presence of the energy density and pressure coming from the spatial variation of the three scalar fields plays an essential role in our analysis which includes {lambda}=0 as a special case and it discriminate from the standard {lambda}-dominated acceleration. We perform a stability analysis of the solutions and find that some solutions are classically stable and attractor. We also present a nonperturbative solution which asymptotically approaches an exponential acceleration and discuss possible cosmological implications in relation to dark energy. It turns out that the equation of state approaches asymptotically {omega}=-1 both from above and below, but the crossing does not occur. It predicts present value of {omega}{approx}-1{+-}0.07, which is within the region allowed by themorexa0» observational data. This solution also exhibits a power law expansion at early times, and the energy density of the scalar fields mimics that of the stiff matter.«xa0less

Supersymmetric monopole quantum mechanics on a sphere

We study

N = 4 supersymmetric quantum mechanics with magnetic monopole

N=2

Higher dimensional cosmological model with a phantom field

supersymmetric quantum mechanics of a charged particle on sphere in the background of Dirac magnetic monopole. We adopt