Piljin Yi

Bio: Piljin Yi is an academic researcher from Korea Institute for Advanced Study. The author has contributed to research in topics: Supersymmetry & Magnetic monopole. The author has an hindex of 36, co-authored 124 publications receiving 4616 citations. Previous affiliations of Piljin Yi include Stanford University & Cornell University.

Monopoles and instantons on partially compactified D -branes

Abstract: Motivated by the recent D-brane constructions of world-volume monopoles and instantons, we study the supersymmetric SU(N) Yang-Mills theory on S{sup 1}{times}R{sup 3+1}, spontaneously broken by a Wilson loop In addition to the usual N{minus}1 fundamental monopoles, the Nth Bogomol{close_quote}nyi-Prasad-Sommerfield monopole appears from the Kaluza-Klein sector When all N monopoles are present, net magnetic charge vanishes and the solution can be reinterpreted as a Wilson-loop instanton of unit Pontryagin number The instanton-multimonopole moduli space is explicitly constructed, and seen to be identical to a Coulomb phase moduli space of a U(1){sup N} gauge theory in 2+1 dimensions related to Kronheimer{close_quote}s gauge theory of SU(N)-type This extends the results by Intriligator and Seiberg to the finite couplings that, in the infrared limit of Kronheimer{close_quote}s theory, the Coulomb phase parametrizes a centered SU(N) instanton We also elaborate on the case of restored SU(N) symmetry {copyright} {ital 1997} {ital The American Physical Society}

Chiral Dynamics of Baryons from String Theory

Abstract: We study baryons in a holographic model of QCD by Sakai and Sugimoto, realized as small instantons with fundamental string hairs. We introduce an effective field theory of the baryons in the five-dimensional setting, and show that the instanton interpretation implies a particular magnetic coupling. Dimensional reduction to four dimensions reproduces the usual chiral effective action, and, in particular, we estimate the axial coupling ${g}_{A}$ between baryons and pions and the magnetic dipole moments, both of which are proportional to ${N}_{c}$. We extrapolate to finite ${N}_{c}$ and discuss subleading corrections.

Witten index and wall crossing

Abstract: We compute the Witten index of one-dimensional gauged linear sigma models with at least $$ \mathcal{N} $$ = 2 supersymmetry. In the phase where the gauge group is broken to a finite group, the index is expressed as a certain residue integral. It is subject to a change as the Fayet-Iliopoulos parameter is varied through the phase boundaries. The wall crossing formula is expressed as an integral at infinity of the Coulomb branch. The result is applied to many examples, including quiver quantum mechanics that is relevant for BPS states in d = 4 $$ \mathcal{N} $$ =2 theories.

Quantum electrodynamics

Abstract: THE subject of quantum electrodynamics is extremely difficult, even for the case of a single electron. The usual method of solving the corresponding wave equation leads to divergent integrals. To avoid these, Prof. P. A. M. Dirac* uses the method of redundant variables. This does not abolish the difficulty, but presents it in a new form, which may be dealt with in two ways. The first of these needs only comparatively simple mathematics and is directly connected with an elegant general scheme, but unfortunately its wave functions apply only to a hypothetical world and so its physical interpretation is indirect. The second way has the advantage of a direct physical interpretation, but the mathematics is so complicated that it has not yet been solved even for what appears to be the simplest possible case. Both methods seem worth further study, failing the discovery of a third which would combine the advantages of both.

Rolling Tachyon

Abstract: We discuss construction of classical time dependent solutions in open string (field) theory, describing the motion of the tachyon on unstable D-branes Despite the fact that the string field theory action contains infinite number of time derivatives, and hence it is not a priori clear how to set up the initial value problem, the theory contains a family of time dependent solutions characterized by the initial position and velocity of the tachyon field We write down the world-sheet action of the boundary conformal field theories associated with these solutions and study the corresponding boundary states For D-branes in bosonic string theory, the energy momentum tensor of the system evolves asymptotically towards a finite limit if we push the tachyon in the direction in which the potential has a local minimum, but hits a singularity if we push it in the direction where the potential is unbounded from below

Tachyon Matter

Abstract: It is shown that classical decay of unstable D-branes in bosonic and superstring theories produces pressureless gas with non-zero energy density. The energy density is stored in the open string fields, even though around the minimum of the tachyon potential there are no open string degrees of freedom. We also give a description of this phenomenon in an effective field theory.