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String Theory, Field Theory, and Quantum Gravity
Prof. Piljin Yi works on string theories, field theories, and gravity. He is widely recognized for an existence proof of D0brane bound states via an index computation, which remains arguably the most direct evidence for the hypothetical Mtheory, believed to encompass all known superstring theories as conjectured by E. Witten. He has recently returned to an indepth investigation of index theorems in physics context, refining this D0brane study and producing a sweeping generalization of the celebrated AtiyahSinger theorem to the gauged systems. He is also an expert on supersymmetric solitons, and authored a series of landmark papers.
Emergence of closed strings as coherent objects in unstable open string theories is another of his important legacy, with potential applications to stringy cosmology and, more importantly, with farreaching implications for the elusive string field theory. A holographic study of nucleons, an unusual excursion, with some impact, to real world physics has been presented in plenary sessions of influential nuclear physics meetings. He has been invited for plenary talks at the prestigious Strings Conferences in 2003 and in 2013, respectively, and currently serves in the International Advisory Committee thereof.


Publication at kias
NUMBER  P18079 
AUTHOR  Yi, Piljin 
TITLE  Index Theorems for Gauge Theories 
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JOURNAL  JOURNAL OF THE KOREAN PHYSICAL SOCIETY, 2018 
ABSTRACT  We review the topological invariants that count supersymmetric states for gauge theories, with an emphasis on string theory applications. In particular, the enumerative index and the twisted partition functions are carefully distinguished by how continuum sectors are handled. The recent localization routine has led to a systematic computation of the latter, and we offer a mechanism for extracting the truly enumerative indices when the continuum sector originates in the Coulomb branch. This leads to a satisfactory conclusion of a twentyyear saga of D0brane bound state problems. We close with broad comments on how the wallcrossing manifests in the index theorems, and define the Quiver/GLSM invariants, which are entirely immune under the wallcrossing. 

Publication at kias
NUMBER  P18005 
AUTHOR  Yi, Piljin,Lee, Sungjay,Hwang, Chiung 
TITLE  Holonomy saddles and supersymmetry 
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JOURNAL  PHYSICAL REVIEW D, 2018 
ABSTRACT  In gauge theories on a spacetime equipped with a circle, the holonomy variables, living in the Cartan torus, play special roles. With their periodic nature properly taken into account, we find that a supersymmetric gauge theory in d dimensions tends to reduce in the small radius limit to a disjoint sum of multiple (d 1) dimensional theories at distinct holonomies, called Hsaddles. The phenomenon occurs regardless of the spacetime dimensions, and here we explore such Hsaddles for d = 4 N = 1 theories on T2 fibered over Sigma(g), in the limits of elongated T2. This naturally generates novel relationships between 4d and 3d partition functions, including ones between 4d and 3d Witten indices, and also leads us to reexamine recent studies of the Cardy exponents and the Casimir energies and of their purported connections to the 4d anomalies. 

Publication at kias
NUMBER  P17009 
AUTHOR  Yi, Piljin 
TITLE  Dparticles on orientifolds and rational invariants 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2017 
ABSTRACT  We revisit the DO bound state problems, of the M/IIA duality, with the Orientifolds. The cases of 04 and 08 have been studied recently, from the perspective of fivedimensional theories, while the case of O0 has been much neglected. The computation we perform for D0O0 states boils down to the Witten indices for N = 16 O(m) and Sp(n) quantum mechanics, where we adapt and extend previous analysis by the authors. The twisted partition function Omega, obtained via localization, proves to be rational, and we establish a precise relation between Omega and the integral Witten index I, by identifying continuum contributions sector by sector. The resulting Witten index shows surprisingly large numbers of threshold bound states but in a manner consistent with Mtheory. We close with an exploration on how the ubiquitous rational invariants of the wallcrossing physics would generalize to theories with Orientifolds. 

Publication at kias
NUMBER  P17029 
AUTHOR  Yi, Piljin,Hwang, Chiung 
TITLE  Twisted partition functions and Hsaddles 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2017 
ABSTRACT  While studying supersymmetric Ggauge theories, one often observes that a zeroradius limit of the twisted partition function Omega(G) is computed by the partition function Z(G) in one less dimensions. We show how this type of identification fails generically due to integrations over Wilson lines. Tracing the problem, physically, to saddles with reduced effective theories, we relate Omega(G) to a sum of distinct Z(H)s and classify the latter, dubbed Hsaddles. This explains why, in the context of pure YangMills quantum mechanics, earlier estimates of the matrix integrals Z(G) had failed to capture the recently constructed bulk index Ibulk(G). The purported agreement between 4d and 5d instanton partition functions, despite such subtleties also present in the ADHM data, is explained. 

Publication at kias
NUMBER  P17001 
AUTHOR  Yi, Piljin,Hwang, Chiung 
TITLE  Fundamental vortices, wallcrossing, and particlevortex duality 
ARCHIVE  1703.00213 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2017 
ABSTRACT  We explore 1d vortex dynamics of 3d supersymmetric YangMills theories, as inferred from factorization of exact partition functions. Under Seiberglike dualities, the 3d partition function must remain invariant, yet it is not a priori clear what should happen to the vortex dynamics. We observe that the 1d quivers for the vortices remain the same, and the net effect of the 3d duality map manifests as 1d WallCrossing phenomenon; although the vortex number can shift along such duality maps, the ranks of the 1d quiver theory are unaffected, leading to a notion of fundamental vortices as basic building blocks for topological sectors. For Aharonytype duality, in particular, where one must supply extra chiral fields to couple with monopole operators on the dual side, 1d wallcrossings of an in finite number of vortex quiver theories are neatly and collectively encoded by 3d determinant of such extra chiral fields. As such, 1d wallcrossing of the vortex theory encodes the particlevortex duality embedded in the 3d Seiberglike duality. For N = 4, the Dbrane picture is used to motivate this 3d/1d connection, while, for N = 2, this 3d/1d connection is used to finetune otherwise ambiguous vortex dynamics. We also prove some identities of 3d supersymmetric partition functions for the Aharony duality using this vortex wallcrossing interpretation. 

Publication at kias
NUMBER  P16012 
AUTHOR  Yi, Piljin 
TITLE  Witten Index for Noncompact Dynamics 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2016 
ABSTRACT  

Publication at kias
NUMBER  P14039 
AUTHOR  Yi, Piljin 
TITLE  Witten index and wall crossing 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2015 
ABSTRACT  We compute the Witten index of onedimensional gauged linear sigma models with at least 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 FayetIliopoulos 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 N = 2 theories. 

Publication at kias
NUMBER  P15014 
AUTHOR  Yi, Piljin 
TITLE  Mutation, Witten index, and quiver invariant 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2015 
ABSTRACT  We explore Seiberglike dualities, or mutations, for quiver quantum mechanics in the context of wallcrossing. In contrast to higher dimensions, the 1d Seibergduality must be performed with much care. With fixed FayetIliopoulos constants, at most two nodes can be mutated, one left and the other right, mapping a chamber of a quiver into a chamber of a mutated quiver. We delineate this complex pattern for triangle quivers and show how the Witten indices are preserved under such finely chosen mutations. On the other hand, the quiver invariants, or wallcrossingsafe part of supersymmetric spectra, mutate more straightforwardly, whereby a quiver is mapped to a quiver. The mutation rule that preserves the quiver invariant is different from the usual one, however, which we explore and confirm numerically. 

Publication at kias
NUMBER  P13059 
AUTHOR  Yi, Piljin 
TITLE  Exact partition functions on RP2 and orientifolds 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2014 
ABSTRACT  We consider gauged linear sigma models (GLSM) on RP2, obtained from a parity projection of S2. The theories admit squashing deformation, much like GLSM on S2, which allows us to interpret the partition function as the overlap amplitude between the vacuum state and crosscap states. From these, we extract the central charge of Orientifold planes, and observe that the Gamma class makes a prominent appearance as in the recent Dbrane counterpart. We also repeat the computation for the mirror LandauGinzburg theory, which naturally brings out the thetadependence as a relative sign between two holonomy sectors on RP2. We also show how our results are consistent with known topological properties of Dbrane and Orientifold plane worldvolumes, and discuss what part of the wrapped Dbrane/Orientifold central charge should be attributed to the quantum volumes. 

Publication at kias
NUMBER  P13056 
AUTHOR  Yi, Piljin,Lee, SeungJoo,Wang, ZhaoLong 
TITLE  Abelianization of BPS quivers and the refined Higgs index 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2014 
ABSTRACT  We count Higgs phase BPS states of general nonAbelian quiver, possibly with loops, by mapping the problem to its Abelian, or toric, counterpart and imposingWeyl invariance later. Precise Higgs index computation is particularly important for quivers with superpotentials; the Coulomb phase index is recently shown to miss important BPS states, dubbed intrinsic Higgs states or quiver invariants. We demonstrate how the refined Higgs index is naturally decomposed to a sum over partitions of the charge. We conjecture, and show in simple cases, that this decomposition expresses the Higgs index as a sum over a set of partitioninduced Abelian quivers of the same total charge but generically of smaller rank. Unlike the previous approach inspired by a similar decomposition of the Coulomb index, our formulae compute the quiver invariants directly, and thus offer a selfcomplete routine for counting BPS states. 

Publication at kias
NUMBER  P17063 
AUTHOR  Yi, Piljin 
TITLE  Two Approaches to Holographic Baryons/Nuclei 
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JOURNAL  FEWBODY SYSTEMS, 2013 
ABSTRACT  We overview baryons in a string theoretical holographic QCD. In the large N (c) limit, the baryon can be viewed in two different ways. The first is a holographic lift of Skyrmion, except that not only pions but also an infinite number of spin 1 mesons are used to construct the solitonic baryon. This approach has been pursued to give an infinitely predictive model of mesonbaryon dynamics. After a brief review, we comment on the alternative picture where the baryon is viewed as wrapped Dbranes, which leads to a quantum mechanical description involving matrices. The two approaches give surprisingly similar answers for some quantities, such as hadronic size of baryons and repulsive cores, even though they represent two very different approximations. 

Publication at kias
NUMBER  P12054 
AUTHOR  Yi, Piljin 
TITLE  CONSTRUCTIVE WALLCROSSING AND SEIBERG WITTEN 
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JOURNAL  INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 2013 
ABSTRACT  We outline a comprehensive and firstprinciple solution to the wallcrossing problem in D = 4 N = 2 SeibergWitten theories. We start with a brief review of the multicentered nature of the typical BPS states and of how this allows them to disappear abruptly as parameters or vacuum moduli are continuously changed. This means that the wallcrossing problem is really a bound state formation/dissociation problem. A low energy dynamics for arbitrary collections of dyons is derived, with the proximity to the socalled marginal stability wall playing the role of the small expansion parameter. We discover that the low energy dynamics of such BPS dyons cannot be reduced to one on the classical moduli space, M, yet the index can be phrased in terms of M. The socalled rational invariant, first seen in KontsevichSoibelman formalism of wallcrossing, is shown to incorporate Bose/Fermi statistics automatically. Furthermore, an equivariant version of the index is shown to compute the protected spin character of the underlying D = 4 N = 2 theory, where SO(3) J isometry of M is identified as a diagonal subgroup of rotation SU(2) L and Rsymmetry SU(2) (R). 

Publication at kias
NUMBER  P12037 
AUTHOR  Yi, Piljin,Lee, SeungJoo,Wang, ZhaoLong 
TITLE  BPS states, refined indices, and quiver invariants 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2012 
ABSTRACT  For D = 4 BPS state construction, counting, and wallcrossing thereof, quiver quantum mechanics offers two alternative approaches, the Coulomb phase and the Higgs phase, which sometimes produce inequivalent counting. The authors have proposed, in arXiv:1205.6511, two conjectures on the precise relationship between the two, with some supporting evidences. Higgs phase ground states are naturally divided into the Intrinsic Higgs sector, which is insensitive to wallcrossings and thus an invariant of quiver, plus a pulledback ambient cohomology, conjectured to be an onetoone image of Coulomb phase ground states. In this note, we show that these conjectures hold for all cyclic quivers with Abelian nodes, and further explore angular momentum and Rcharge content of individual states. Along the way, we clarify how the protected spin character of BPS states should be computed in the Higgs phase, and further determine the entire Hodge structure of the Higgs phase cohomology. This shows that, while the Coulomb phase states are classified by angular momentum, the Intrinsic Higgs states are classified by Rsymmetry. 

Publication at kias
NUMBER  P12030 
AUTHOR  Yi, Piljin,Lee, SeungJoo,Wang, ZhaoLong 
TITLE  Quiver invariants from intrinsic Higgs states 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2012 
ABSTRACT  In study of fourdimensional BPS states, quiver quantum mechanics plays a central role. The Coulomb phases capture the multicentered nature of such states, and are well understood in the context of wallcrossing. The Higgs phases are given typically by Fterminduced complete intersections in the ambient Dterminduced varieties, and the ground states can be far more numerous than the Coulomb phase counterparts. We observe that the Higgs phase BPS states are naturally and geometrically grouped into two parts, with one part given by the pulledback cohomology from the Dterminduced ambient space. We propose that these pulledback states are in onetoone correspondence with the Coulomb phase states. This also leads us to conjecture that the index associated with the rest, intrinsic to the Higgs phase, is a fundamental invariant of quivers, independent of branches. For simple circular quivers, these intrinsic Higgs states belong to the middle cohomology and thus are all angular momentum singlets, supporting the singlecenter black hole interpretation. 

Publication at kias
NUMBER  P11082 
AUTHOR  Yi, Piljin 
TITLE  Dbrane anomaly inflow revisited 
ARCHIVE  1201.0762 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2012 
ABSTRACT  Axial and gravitational anomaly of field theories, when embedded in string theory, must be accompanied by canceling inflow. We give a selfcontained overview for various worldvolume theories, and clarify the role of smeared magnetic sources in Ibrane/Dbrane cases. The proper anomaly descent of the source, as demanded by regularity of RR field strengths Hs, turns out to be an essential ingredient. We show how this allows correct inflow to be generated for all such theories, including selfdual cases, and also that the mechanism is now insensitive to the choice between the two related but inequivalent forms of Dbrane ChernSimons couplings. In particular, SO(6)(R) axial anomaly of d = 4 maximal SYM is canceled by the inflow onto D3branes via the standard minimal coupling to C4. We also propose how, for the anomaly cancelation, the four types of Orientifold planes should be coupled to the spacetime curvatures, of which conflicting claims existed previously. 

Publication at kias
NUMBER  P11067 
AUTHOR  Yi, Piljin 
TITLE  Fournucleon contact interactions from holographic QCD 
ARCHIVE  1111.3118 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2012 
ABSTRACT  We calculate the low energy constants of fournucleon interactions in an effective chiral Lagrangian in holographic QCD. We start with a D4D8 model to obtain mesonnucleon interactions and then integrate out massive mesons to obtain the fournucleon interactions in 4D. We end up with two low energy constants at the leading order and seven of them at the next leading order, which is consistent with the effective chiral Lagrangian. The values of the low energy constants are evaluated with the first five KaluzaKlein resonances. 

Publication at kias
NUMBER  P11033 
AUTHOR  Yi, Piljin,Wang, Zhaolong 
TITLE  Ab initio wallcrossing 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2011 
ABSTRACT  We derive supersymmetric quantum mechanics of n BPS objects with 3n position degrees of freedom and 4n fermionic partners with SO(4) Rsymmetry. The potential terms, essential and sufficient for the index problem for nonthreshold BPS states, are universal, and 2(n  1) dimensional classical moduli spaces Mn emerge from zero locus of the potential energy. We emphasize that there is no natural reduction of the quantum mechanics to Mn, contrary to the conventional wisdom. Nevertheless, via an indexpreserving deformation that breaks supersymmetry partially, we derive a Dirac index on Mn as the fundamental state counting quantity. This rigorously fills a missing link in the Coulomb phase wallcrossing formula in literature. We then impose Bose/Fermi statistics of identical centers, and derive the general wallcrossing formula, applicable to both BPS black holes and BPS dyons. Also explained dynamically is how the rational invariant similar to Omega(beta)/p(2), appearing repeatedly in wallcrossing formulae, can be understood as the universal multiplicative factor due to p identical, coincident, yet unbound, BPS particles of charge beta. Along the way, we also clarify relationships between field theory state countings and quantum mechanical indices. 

Publication at kias
NUMBER  P11003 
AUTHOR  Yi, Piljin 
TITLE  Framed BPS states, moduli dynamics, and wallcrossing 
ARCHIVE  1102.1729 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2011 
ABSTRACT  We formulate supersymmetric low energy dynamics for BPS dyons in stronglycoupled N = 2 SeibergWitten theories, and derive wallcrossing formulae thereof. For BPS states made up of a heavy core state and n probe (halo) dyons around it, we derive a reliable supersymmetric moduli dynamics with 3n bosonic coordinates and 4n fermionic superpartners. Attractive interactions are captured via a set of supersymmetric potential terms, whose detail depends only on the charges and the special Kahler data of the underlying N = 2 theories. The small parameters that control the approximation are not electric couplings but the mass ratio between the core and the probe, as well as the distance to the marginal stability wall where the central charges of the probe and of the core align. Quantizing the dynamics, we construct BPS bound states and derive the primitive and the semiprimitive wallcrossing formulae from the first principle. We speculate on applications to line operators and Darboux coordinates, and also about extension to supergravity setting. 

Publication at kias
NUMBER  P11009 
AUTHOR  Yi, Piljin 
TITLE  Nucleonnucleon potential in holographic QCD 
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JOURNAL  NUCLEAR PHYSICS A, 2010 
ABSTRACT  We derive the nucleonnucleon potential in the D4D8 model of holographic QCD. The nucleonnucleon potential emerges from oneboson exchange picture with massless pseudoscalars and an infinite tower of spin one mesons. We observe in particular that the tensor coupling of the rho meson with nucleon comes out naturally larger than the vector coupling, whereas for omega mesons and axial mesons, such tensor couplings are completely absent. The potential is universally repulsive similar to 1/r(2) at short distance, and has the usual longdistance attractive behavior similar to 1/r(3) along a isospin singlet and spin triplet channel. Both the large N(c) form and the finite Nc form are given. In the former, a shallow classical minimum of depth similar to 0.1M(KK)N(c)/lambda forms at about rM(KK) similar or equal to 5.5. We discuss shallow bound states of nucleons with the holographic potential. 

Publication at kias
NUMBER  P10007 
AUTHOR  Yi, Piljin 
TITLE  A matrix model for baryons and nuclear forces 
ARCHIVE  arXiv:1003.4988 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2010 
ABSTRACT  We propose a new matrix model describing multibaryon systems. We derive the action from open string theory on the wrapped baryon vertex Dbranes embedded in the D4D8 model of large Nc holographic QCD. The positions of k baryons are unified into k x k matrices, with spin/isospin of the baryons encoded in a set of kvectors. Holographic baryons are known to be very small in the large t Hooft coupling limit, and our model offers a better systematic approach to dynamics of such baryons at short distances. We compute energetics and spectra (k = 1), and also shortdistance nuclear force (k = 2). In particular, we obtain a new size of the holographic baryon and find a precise form of the repulsive core of nucleons. This matrix model complements the instanton soliton picture of holographic baryons, whose small size turned out to be well below the natural length scale of the approximation involved there. Our results show that, nevertheless, the basic properties of holographic baryons obtained there are robust under stringy corrections within a few percents. 

Publication at kias
NUMBER  P09052 
AUTHOR  Yi, Piljin,Lee, Sungjay 
TITLE  A study of WallCrossing: flavored kinks in D=2 QED 
ARCHIVE  arXiv:0902.4515 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2010 
ABSTRACT  We study spectrum of D = 2 N = (2, 2) QED with N + 1 massive charged chiral multiplets, with care given to precise supermultiplet countings. In the infrared the theory flows to CPN model with twisted masses, where we construct generic flavored kink solitons for the large mass regime, and study their quantum degeneracies. These kinks are qualitatively different and far more numerous than those of small mass regime, with features reminiscent of multipronged (p, q) string web, complete with the wallcrossing behavior. It has been also conjectured that spectrum of this theory is equivalent to the hypermultiplet spectrum of a certain D = 4 SeibergWitten theory. We find that the correspondence actually extends beyond hypermultiplets in D = 4, and that many of the relevant indices match. However, a D = 2 BPS state is typically mapped to several different kind of dyons whose individual supermultiplets are rather complicated; the match of index comes about only after summing over indices of these different dyons. We note general wallcrossing behavior of flavored BPS kink states, and compare it to those of D = 4 dyons. 

Publication at kias
NUMBER  P09008 
AUTHOR  Yi, Piljin 
TITLE  Holographic deuteron and nucleonnucleon potential 
ARCHIVE  0902.4048 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2009 
ABSTRACT  We compute the potential between a pair of nucleons in the D4D8 holographic QCD. In the large t Hooft coupling limit, lambda >> 1, the hadronic size of the baryon is small similar to 1/root lambda MKK, and their interaction with mesons are well approximated by a set of dimension four and five operators. The nucleonnucleon potential emerges from oneboson exchange picture involving massless pseudoscalars and an infinite tower of spin one mesons. We find in particular that rho meson exchanges are dominated by a dimension five derivative coupling of tensor type, whereas for rho mesons and axial mesons, such tensor couplings are completely absent. The potential is universally repulsive similar to 1/r(2) at short distance, and has the usual longdistance attractive behavior similar to 1/r(3) along a isosinglet and spin triplet channel. Both the large Nc form and the finite Nc form are given. In the former, a shallow classical minimum of depth similar to 0.1M(KK) Nc/lambda forms at around rM(KK) similar or equal to 5.5. 

Publication at kias
NUMBER  P08054 
AUTHOR  Yi, Pijin 
TITLE  A Holographic QCD and Baryons from String Theory 
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JOURNAL  PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT, 2009 
ABSTRACT  A holographic QCD deals with the gauge invariant observables of QCD in the large Nc and large t Hooft coupling limit, according to the general idea of gauge/gravity duality. A very appealing example is based on a D4D8 brane complex in string theory. In this note, we review how this model is capable of reproducing physics of pious, vector mesons and baryons, in a unifying picture based on a holographic flavor gauge field. In particular, the baryon show Lip as quantized instanton soliton of the flavor gauge field, which gives us a natural and extremely simple framework for determining all baryonmeson interactions. We give some of the simplest predictions of the model which are remarkably good when compared to experimental data. We close with comments. 

Publication at kias
NUMBER  P08062 
AUTHOR  Yi, Piljin,Lee, Sungjay,Lee, KiMyeong 
TITLE  A nonperturbative test of M2brane theory 
ARCHIVE  0809.1771 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2008 
ABSTRACT  We discuss nonperturbative effects in the ABJM model due to monopole instantons. We begin by constructing the instanton solutions in the U(2) x U(2) model, explicitly, and computing the Euclidean action. The Wickrotated Lagrangian is complex and its BPS monopole instantons are found to be a delicate version of the usual t HooftPolyakov monopole solutions. They are generically 1/3 BPS but become 1/2 BPS at special locus in the moduli space of two M2branes, yet each instanton carries eight fermionic zero modes, regardless of the vacuum choice. The low energy effective action induced by monopole instantons are quartic order in derivatives. The resulting vertices are nonperturbative in 1/k, as expected, but are rational functions of the vacuum moduli. We also analyze the system of two M2branes in the supergravity framework and compute the higher order interactions via 11dimensional supergraviton exchange. The comparison of the two shows that the instanton vertices are precisely reproduced by this M2brane picture, supporting the proposal that the ABJM model describes multiple M2branes. 

Publication at kias
NUMBER  P08030 
AUTHOR  Yi, Piljin 
TITLE  A holographic QCD and excited baryons from string theory 
ARCHIVE  0804.2926 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2008 
ABSTRACT  We study baryons of arbitrary isospin in a stringy holographic QCD model. In this D4D8 holographic setting, the flavor symmetry is promoted to a gauge symmetry in the bulk, and produces, as KK modes of the gauge field, pions and spin one mesons of low energy QCD. Baryons of arbitrary isospins are represented as instanton solitons with isospin and spin quantum numbers locked, in a manner similar to the Skyrmion model. The soliton picture leads to a natural effective field theory of arbitrary baryons interacting with mesons. Couplings of baryons to axial mesons, including pions, are dominated in the large Nc limit by a direct coupling to the flavor field strength in five dimensions. We delineate the relevant couplings and determine their strengths. This work generalizes part of refs. [8, 10] to all excited baryons. Due to technical difficulties in introducing relativistic higher spin fields, we perform all computations in the nonrelativistic regime, which suffices for the leading Nc predictions. 

Publication at kias
NUMBER  P07071 
AUTHOR  Yi, Piljin,Yee, HoUng 
TITLE  Nucleon form factors and hidden symmetry in holographic QCD 
ARCHIVE  arXiv:0710.4615 
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JOURNAL  PHYSICAL REVIEW D, 2008 
ABSTRACT  The vector dominance of the electromagnetic form factors both for mesons and baryons arises naturally in holographic QCD, where both the number of colors and the t Hooft coupling are taken to be very large, offering a bonafide derivation of the notion of vector dominance. The crucial ingredient for this is the infinite tower of vector mesons in the approximations made which share features that are characteristic of the quenched approximation in lattice QCD. We approximate the infinite sum by contributions from the lowest four vector mesons of the tower which turn out to saturate the charge and magnetic moment sum rules within a few percent and compute them totally free of unknown parameters for momentum transfers Q(2)less than or similar to 1 GeV2. We identify certain observables that can be reliably computed within the approximations and others that are not, and discuss how the improvement of the latter can enable one to bring holographic QCD closer to QCD proper. 

Publication at kias
NUMBER  P07017 
AUTHOR  Yi, Piljin,Yee, HoUng 
TITLE  Dynamics of baryons from string theory and vector dominance 
ARCHIVE  arXiv:0705.2632 
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JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2007 
ABSTRACT  We consider a holographic model of QCD from string theory, a la Sakai and Sugimoto, and study baryons. In this model, mesons are collectively realized as a fivedimensional U(NF) = U(1) x SU(NF) YangMills field and baryons are classically identified as SU(NF) solitons with a unit Pontryagin number and Nc electric charges. The soliton is shown to be very small in the large t Hooft coupling limit, allowing us to introduce an effective field B. Its coupling to the mesons are dictated by the soliton structure, and consists of a direct magnetic coupling to the SU(NF) field strength as well as a minimal coupling to the U(NF)gauge field. Upon the dimensional reduction, this effective action reproduces all interaction terms between nucleons and an infinite tower of mesons in a manner consistent with the large Nc expansion. We further find that all electromagnetic interactions, as inferred from the same effective action via a holographic prescription, are mediated by an infinite tower of vector mesons, rendering the baryon electromagnetic form factors completely vectordominated as well. We estimate nucleonmeson couplings and also the anomalous magnetic moments, which compare well with nature. 

Publication at kias
NUMBER  P07004 
AUTHOR  Yi, Piljin,Yee, HoUng 
TITLE  Chiral dynamics of baryons from string theory 
ARCHIVE  hepth/0701276 
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JOURNAL  PHYSICAL REVIEW D, 2007 
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 fivedimensional 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 Nc. We extrapolate to finite Nc and discuss subleading corrections. 

Publication at kias
NUMBER  P06041 
AUTHOR  Yi, Piljin,Weinberg, Erick J. 
TITLE  Magnetic monopole dynamics, supersymmetry, and duality 
ARCHIVE  hepth/0609055 
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JOURNAL  PHYSICS REPORTSREVIEW SECTION OF PHYSICS LETTERS, 2007 
ABSTRACT  We review the properties of BPS, or supersymmetric, magnetic monopoles, with an emphasis on their lowenergy dynamics and their classical and quantum bound states. After an overview of magnetic monopoles, we discuss the BPS limit and its relation to supersymmetry. We then discuss the properties and construction of multimonopole solutions with a single nontrivial Higgs field. The lowenergy dynamics of these monopoles is most easily understood in terms of the moduli space and its metric. We describe in detail several known examples of these. This is then extended to cases where the unbroken gauge symmetry include a nonAbelian factor. We next turn to the generic supersymmetric YangMills (SYM) case, in which several adjoint Higgs fields are present. Working first at the classical level, we describe the effects of these additional scalar fields on the monopole dynamics, and then include the contribution of the fermionic zero modes to the lowenergy dynamics. The resulting lowenergy effective theory is itself supersymmetric. We discuss the quantization of this theory and its quantum BPS states, which are typically composed of several loosely bound compact dyonic cores. We close with a discussion of the Dbrane realization of N = 4 SYM monopoles and dyons and explain the ADHMN construction of monopoles from the Dbrane point of view. (c) 2006 Elsevier B.V. All rights reserved. 

Publication at kias
NUMBER  P06029 
AUTHOR  Yi, Piljin,Kim, Seok 
TITLE  A heterotic flux background and calibrated fivebranes 
ARCHIVE  hepth/0607091 
FILE  
JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2006 
ABSTRACT  We consider, in flux compactification of heterotic string theory, spacetimefilling fivebranes. Stabilizing the fivebrane involves minimizing the combined energy density of the tension and a Coulomb potential associated with an internal 2dimensional wrapping. After reviewing the generalized calibration under such circumstances, we consider a particular internal manifold based on a T2 bundle over a conformally rescaled K3. Here, we find two distinct types of wrapping. In one class, the fivebrane wraps the fibre T2 which belongs to a cyclic homotopy group. The winding number is not extensive, yet it maps to D3brane number under a Uduality map to type IIB side. We justify this by comparing properties of the two sides in detail. Fivebranes may also wrap a topological 2cycle of K3, by saturating a standard calibration requirement with respect to a closed Kahler 2form J(K3) of K3. We close with detailed discussion on Ftheory dual of these objects and related issues. 

Publication at kias
NUMBER  P06018 
AUTHOR  Yi, Piljin,Kimura, Tetsuji 
TITLE  Comments on heterotic flux compactifications 
ARCHIVE  hepth/0605247 
FILE  
JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2006 
ABSTRACT  In heterotic flux compactification with supersymmetry, three different connections with torsion appear naturally, all in the form omega + aH. Supersymmetry condition carries a = 1, the Dirac operator has a = 1/3, and higher order term in the effective action involves a = 1. With a view toward the gauge sector, we explore the geometry with such torsions. After reviewing the supersymmetry constraints and finding a relation between the scalar curvature and the flux, we derive the squared form of the zero mode equations for gauge fermions. With dH = 0, the operator has a positive potential term, and the mass of the unbroken gauge sector appears formally positive definite. However, this apparent contradiction is avoided by a nogo theorem that the compactification with H not equal 0 and dH = 0 is necessarily singular, and the formal positivity is invalid. With dH not equal 0, smooth compactification becomes possible. We show that, at least near smooth supersymmetric solution, the size of H2 should be comparable to that of dH and the consistent truncation of the action has to keep alphaR2 term. A warp factor equation of motion is rewritten with alphaR2 contribution included precisely, and some limits are considered. 

Publication at kias
NUMBER  P05057 
AUTHOR  Yi, Piljin 
TITLE  Brane inflation, decay of Dbranes, and reheating of the universe 
ARCHIVE  
FILE  
JOURNAL  PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT, 2006 
ABSTRACT  In string theory realization of inflationary universe, one often encounters an unstable system of Dbranes as a source of cosmological constant. The exit from such a brane inflation is triggered by decay of the unstable Dbrane system and produces predominantly heavy closed string modes. This sets the initial condition for reheating, which becomes then the question of how these heavy strings decay down to lighter modes. For a realistic universe, the process has to be such that we find a universe whose expansion is mainly driven by Standard model particle content at least until the time of Nucleosynthesis. In this talk, we outline how the reheating of a realistic universe might be possible in the context of KKLMMT type scenarios, pointing out serious dangers of overproducing graviton sector particles and also of heavy relics. 

Publication at kias
NUMBER  P05037 
AUTHOR  Yi, PJ 
TITLE  Reheating the Universe after string theory inflation 
ARCHIVE  hepth/0507257 
FILE  
JOURNAL  PHYSICAL REVIEW D, 2005 
ABSTRACT  In string theory realizations of inflation, the endpoint of inflation is often braneantibrane annihilation. We consider the processes of reheating of the standard model universe after brane inflation. We identify the channels of inflaton energy decay, cascading from tachyon annihilation through massive closed string loops, KK modes, and brane displacement moduli to the lighter standard model particles. Cosmological data constrains scenarios by putting stringent limits on the fraction of reheating energy deposited in gravitons and nonstandard sector massive relics. We estimate the energy deposited into various light degrees of freedom in the open and closed string sectors, the timing of reheating, and the reheating temperature. Production of gravitons is significantly suppressed in warped inflation. However, we predict a residual gravitational radiation background at the level Omega(GW)similar to 10(8) of the present cosmological energy density. We also extend our analysis to multiple throat scenarios. A viable reheating would be possible in a single throat or in a certain subclass of multiple throat scenarios of the KKLMMT type inflation model, but overproduction of massive KaluzaKlein (KK) modes poses a serious problem. The problem is quite severe if some inner manifold comes with approximate isometries (angular KK modes) or if there exists a throat of modest length other than the standard model throat, possibly associated with some hidden sector (lowlying KK modes). 

Publication at kias
NUMBER  P04036 
AUTHOR  Yi, PJ 
TITLE  Winding strings and decay of Dbranes with flux 
ARCHIVE  hepth/0409050 
FILE  
JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2005 
ABSTRACT  We study the boundary state associated with the decay of an unstable Dbrane with uniform electric field, 1 > e > 0 in the string units. Compactifying the Dbrane along the direction of the electric field, we find that the decay process is dominated by production of closed strings with some winding numbers; closed strings produced are such that the winding mode carries precisely the fraction e of the individual string energy. This supports the conjecture that the final state at tree level is composed of winding strings with heavy oscillations turned on. As a corollary, we argue that the closed strings disperse into spacetime at a much slower rate than the case without electric field. 

Publication at kias
NUMBER  P04014 
AUTHOR  Yi, PJ,Yee, HU,Lee, KM 
TITLE  The N=1*theories on R1+2 x S1 with twisted boundary conditions 
ARCHIVE  hepth/0403076 
FILE  
JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2004 
ABSTRACT  We explore the N = 1* theories compactifted on a circle with twisted boundary conditions. The gauge algebra of these theories are the socalled twisted affine Lie algebra. We propose the exact superpotentials by guessing the sum of all monopoleinstanton contributions and also by requiring SL(2,Z) modular properties. The latter is inherited from the N = 4 theory, which will be justified in the M theory setting. Interestingly all twisted theories possess full SL(2, Z) invariance, even though none of them are simplylaced. We further notice that these superpotentials are associated with certain integrable models widely known as elliptic CalogeroMoser models. Finally, we argue that the glueball superpotential must be independent of the compactification radius, and thus of the twisting, and confirm this by expanding it in terms of glueball superfield in weak coupling expansion. 

Publication at kias
NUMBER  P04008 
AUTHOR  Yi, PJ,Yee, HU 
TITLE  Open/closed duality, unstable Dbranes and coarsegrained closed strings 
ARCHIVE  Hepth/0402027 
FILE  
JOURNAL  NUCLEAR PHYSICS B, 2004 
ABSTRACT  At the final stage of unstable Dbrane decay in the effective field theory approach, all energy and momentum of the initial state are taken up by two types of fluids, known as string fluid and tachyon matter. In this note, we compare motion of this fluid system to that of macroscopic collection of stretched closed strings and find a precise match at classical level. The string fluid reflects low frequency undulation of the stretched strings while the tachyon matter encodes the average effect of high frequency oscillations turned on those strings. In particular, the combined fluid system has been known to have a reduced speed of light, depending on the composition, and we show that this property is exactly reproduced in classical motion on the closed string side. Finally we illustrate how the tachyon matter may be viewed as an effective degrees of freedom carrying high frequency energymomentum of NambuGoto strings by coarsegraining the dynamics of the latter. (C) 2004 Elsevier B.V. All rights reserved. 

Publication at kias
NUMBER  P04005 
AUTHOR  Yi, PJ,Suyama, T 
TITLE  A holographic view on matrix model of black hole 
ARCHIVE  hepth/0401078 
FILE  
JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2004 
ABSTRACT  We investigate a deformed matrix model proposed by Kazakov et.al. in relation to Wittens twodimensional black hole. The existing conjectures assert the equivalence of the two by mapping each to a deformed c = 1 theory called the sineLiouville theory. We point out that the matrix theory in question may be naturally interpreted as a gauged quantum mechanics deformed by insertion of an exponentiated Wilson loop operator, which gives us more direct and holographic map between the two sides. The matrix model in the usual scaling limit must correspond to the bosonic SL(2, R)/U(1) theory in genus expansion but exact in alpha. We successfully test this by computing the Wilson loop expectation value and comparing it against the bulk computation. For the latter, we employ the alphaexact geometry proposed by Dijkgraaf, Verlinde, and Verlinde, which was further advocated by Tseytlin. We close with comments on open problems. 

Publication at kias
NUMBER  P03033 
AUTHOR  Yi, PJ 
TITLE  String fluid, tachyon matter, and domain walls 
ARCHIVE  hepth/0305229 
FILE  
JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2003 
ABSTRACT  We study classical dynamics of an open string tachyon T of unstable Dpbrane coupled to the gauge field A(mu). In the vacuum with vanishing potential, V = 0, two fluidlike degrees of freedom, string fluid and tachyon matter, survive the tachyon condensation. We offer general analysis of the associated hamiltonian dynamics in arbitrary background. The canonical field equations are organized into two sets, fluid equations of motion augmented by an integrability condition. We show that a large class of motionless and degenerate family of classical solutions exist and represent arbitrary transverse distribution of tachyon matter and flux lines. We further test their stability by perturbing the fluid equation up to the second order. Second half of this note considers possibility of V not equal 0 in the dynamics. We incorporate V in the hamiltonian equation of motion and consider interaction between domain walls and string fluid. During initial phase of tachyon condensation, topological defect at T = 0 is shown to attract nearby and parallel flux lines. The final state is fundamental strings absorbed and spread in some singular D (p1) brane soliton. When string fluid is transverse to the domain wall, the latter is known to turn into a smooth solution. We point out that a minimal solution of this sort exists and saturates a BPS energy bound of fundamental string ending on a D(p1) brane. 

Publication at kias
NUMBER  P03045 
AUTHOR  Yi, P 
TITLE  Tachyon tube and supertube 
ARCHIVE  hepth/0307184 
FILE  
JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2003 
ABSTRACT  We search for tubular solutions in unstable D3brane. With critical electric field E = 1, solutions representing supertubes, which are supersymmetric bound states of fundamental strings, D0branes, and a cylindrical D2brane, are found and shown to exhibit BPSlike property. We also point out that boosting such a tachyon tube solution generates string flux winding around the tube, resulting in helical electric fluxes on the D2brane. We also discuss issues related to fundamental string, absence of magnetic monopole, and finally more tachyon tubes with noncritical electric field. 

Publication at kias
NUMBER  P02081 
AUTHOR  Yi, P 
TITLE  Instantons of M(atrix) theory in PPwave background 
ARCHIVE  hepth/0301120 
FILE  
JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2003 
ABSTRACT  M(atrix) theory in PPwave background possesses a discrete set of classical vacua, all of which preserves 16 supersymmetry and interpretable as collection of giant gravitons. We find euclidean instanton solutions that interpolate between them, and analyze their properties. Supersymmetry prevents direct mixing between different vacua but still allows effect of instanton to show up in higher order effective interactions, such as analog of v(4) interaction of flat space M(atrix) theory. An explicit construction of zero modes is performed, and Goldstone zero modes, bosonic and fermionic, are identified. We further generalize this to massive M(atrix) theory that includes fundamental hypermultiplets, corresponding to insertion of longitudinal fivebranes in the background. After a brief comparison to their counterparts in AdS x S, we close with a summary. 

Publication at kias
NUMBER  P02045 
AUTHOR  Yi, PJ,Lee, KM 
TITLE  Deformed matrix theories with N=8 and fivebranes in the PP wave background 
ARCHIVE  hepth/0207264 
FILE  
JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2002 
ABSTRACT  M(atrix) theory is known to be massdeformed in the ppwave background and still retains all 16 dynamical supersymmetries. We consider generalization of such deformations on super YangMills quantum mechanics (SYQM) with less supersymmetry. In particular this includes N = 8 U(N) SYQM with a single adjoint and any number of fundamental hypermultiplets, which is a ppwave deformation of DLCQ matrix theory of fivebranes. With k greater than or equal to 1 fivebranes, we show that a rich vacuum structure exists, with many continuous family of solutions that preserve all dynamical supersymmetries. The vacuum moduli space contains Copies Of Cpk1 of various sizes. 

Publication at kias
NUMBER  P02051 
AUTHOR  Yi, PJ 
TITLE  Tachyon condensates, carrollian contraction of Lorentz group, and fundamental strings 
ARCHIVE  hepth/0209034 
FILE  
JOURNAL  JOURNAL OF HIGH ENERGY PHYSICS, 2002 
ABSTRACT  We study the rolling tachyon condensate in the presence of a gauge field. The generic vacuum admits both a rolling tachyon, (T) over dot, and a uniform electric field, (E) over right arrow, which together affect the effective metric governing the fluctuations of open string modes. If one suppresses the gauge field altogether, the lightcone collapses completely. This is the carrollian limit, with vanishing speed of light and no possible propagation of signals. In the presence of a gauge field, however, the lightcone is squeezed to the shape of a fan, allowing propagation of signals along the direction of +/(E) over right arrow at speed (E) over right arrow less than or equal to 1. This shows that there are perturbative degrees of freedom propagating along electric flux lines. Such causal behavior appears to be a very general feature of tachyon effective lagrangian with runway potentials. We speculate on how this may be connected to appearance of fundamental strings. 

Publication at kias
NUMBER  P01052 
AUTHOR  Yi, P,Michishita, Y 
TITLE  Dbrane probe and closed string tachyons 
ARCHIVE  hepth/0111199 
FILE  
JOURNAL  PHYSICAL REVIEW D, 2002 
ABSTRACT  We consider a Dbrane probe in the unstable string background associated with flux branes. The twist in the spacetime metric reponsible for supersymmetry breaking is shown to manifest itself in the mixing of open Wilson lines with the phases of some adjoint matter fields, resulting in a nonlocal and nonsupersymmetric form of YangMills theory as the probe dynamics. This provides a setup where one can study the fate of a large class of unstable closed string theories that includes as a limit type 0 theories and various orbifolds of type II and type 0 theories. We discuss the limit of C/Z(n) orbifold in some detail and speculate on the couplings with closed string tachyons. 

Publication at kias
NUMBER  P01040 
AUTHOR  Yi, PJ,Lee, K 
TITLE  Discrete light cone quantization of fivebranes, large N screening, and L2 harmonic forms on Calabi manifolds 
ARCHIVE  hepth/0109217 
FILE  
JOURNAL  PHYSICAL REVIEW D, 2002 
ABSTRACT  We find one explicit L2 harmonic form for every Calabi manifold. Calabi manifolds are known to arise in the low energy dynamics of solitons in YangMills theories, and the L2 harmonic form corresponds to the supersymmetric ground state. As the normalizable ground state of a single U(N) instanton, it is related to the bound state of a single D0 to multiple coincident D4s in the noncommutative setting, or equivalently a unit KaluzaKlein mode in the discrete light cone quantization of fivebrane worldvolume theory. As the ground state of nonAbelian massless monopoles realized around a monopoleantimonopole pair, it shows how the long range force between the pair is screened in a manner reminiscent of the large N behavior of the quarkantiquark potential found in AdS/CFT correspondence. 

Publication at kias
NUMBER  P00022 
AUTHOR  Yi, PJ 
TITLE  Counting YangMills dyons with index theorems 
ARCHIVE  hepth/0005275 
FILE  
JOURNAL  PHYSICAL REVIEW D, 2000 
ABSTRACT  We count the supersymmetric bound states of many distinct BPS monopoles in N=4 YangMills theories and in pure N=2 YangMills theories. The novelty here is that we work in generic Coulombic vacua where more than one adjoint Higgs fields are turned on. The number of purely magnetic bound states is again found to be consistent with the electromagnetic duality of the N=4 SU(n) theory, as expected. We also count dyons of generic electric charges, which correspond to 1/4 BPS dyons in N=4 theories and 1/2 BPS dyons in N = 2 theories. Surprisingly, the degeneracy of dyons is typically much larger than would be accounted for by a single supermultiplet of appropriate angular momentum, implying many supermultiplets of the same charge and the same mass. 

Publication at kias
NUMBER  P00002 
AUTHOR  Yi, PJ 
TITLE  Confinement on the brane 
ARCHIVE  hepth/0002223 
FILE  
JOURNAL  NUCLEAR PHYSICS B, 2000 
ABSTRACT  A nonperturbative confinement mechanism has been proposed to explain the fate of the unbroken gauge group on the worldvolume of annihilating DbraneantiDbrane pairs. In this paper, we examine this phenomenon closely from several different perspectives. Existence of the confinement mechanism is most easily seen by noticing that the fundamental string emerges as the confined electric flux string at the end of the annihilation process. After reviewing the confinement proposal in general, this is shown explicitly in the D2antiD2 case in the Mtheory limit, Finally, we address the crucial issue of whether and how confinement occurs in the weakly coupled limit of string theory. (C) 2000 Elsevier Science B.V. All rights reserved. 

Publication at kias
NUMBER  P99106 
AUTHOR  Yi, PJ,Lee, K 
TITLE  Complete supersymmetric quantum mechanics of magnetic monopoles in N=4 super YangMills theory 
ARCHIVE  hepth/9912083 
FILE  
JOURNAL  PHYSICAL REVIEW D, 2000 
ABSTRACT  We find the most general low energy dynamics of 1/2 BPS monopoles in the N = 4 supersymmetric YangMills (SYM) theories when all six adjoint Higgs expectation values an turned on. When only one Higgs value is turned on, the Lagrangian is purely kinetic. When all the remaining five are turned on a little bit, however, this moduli space dynamics is augmented by five independent potential terms, each in the form of half the squared norm of a Killing vector field on the moduli space. A generic stationary configuration of the monopoles can be interpreted as stable nonBPS dyons, previously found as nonplanar string webs connecting D3branes. The supersymmetric extension is also found explicitly, and gives the complete quantum mechanics of monopoles in N = 4 SYM theory. 

Publication at kias
NUMBER  P99103 
AUTHOR  Yi, PJ 
TITLE  Monopole dynamics and BPS dyons in N=2 superYangMills theories 
ARCHIVE  hepth/9912082 
FILE  
JOURNAL  PHYSICAL REVIEW D, 2000 
ABSTRACT  We determine the lowenergy dynamics of monopoles in pure N = 2 YangMills theories for points in the vacuum moduli space where the two Higgs fields are not aligned. The dynamics is governed by a supersymmetric quantum mechanics with potential terms and four real supercharges. The corresponding superalgebra contains a central charge but nevertheless supersymmetric states preserve all four supercharges. The central charge depends on the sign of the electric charges and consequently so does the BPS spectrum. We focus on the SU(3) case where certain BPS states are realized as zero modes of a Dirac operator on TaubNUT space twisted by the triholomorphic Killing vector field. We show that the BPS spectrum includes hypermultiplets that are consistent with the strong and weakcoupling behavior of SeibergWitten theory. 

Publication at kias
NUMBER  P99104 
AUTHOR  Yi, PJ,Lee, K 
TITLE  Quantum spectrum of instanton solitons in fivedimensional noncommutative U(N) theories 
ARCHIVE  hepth/9911186 
FILE  
JOURNAL  PHYSICAL REVIEW D, 2000 
ABSTRACT  We explore quantum states of instanton solitons in fivedimensional noncommutative YangMills theories. We start with maximally supersymmetric U(N) theory compactified on a circle S1, and derive the lowenergy dynamics of instanton solitons, or calorons, which is no longer singular. Quantizing the lowenergy dynamics, we find N physically distinct ground states with a unit Pontryagin number and no electric charge. These states have a natural Dstring interpretation. The conclusion remains unchanged as we decompactify S1, as long as we stay in the Coulomb phase by turning on adjoint Higgs expectation values. 

Publication at kias
NUMBER  P99006 
AUTHOR  Yi, PJ 
TITLE  Membranes from fivebranes and fundamental strings from Dpbranes 
ARCHIVE  hepth/9901159 
FILE  
JOURNAL  NUCLEAR PHYSICS B, 1999 
ABSTRACT  We argue that the M2brane is realized as a topological soliton on a coincident pair of M5 and antiM5branes, as the two fivebranes annihilate each other. The topology and quantum numbers of this worldvolume soliton are discussed in some detail, and its formation is explained qualitatively. It follows from a compactification that a D4antiD4 pair annihilate and produce type II fundamental strings. The phenomenon is best described as the confinement of a worldvolume U(1) gauge held on D4antiD4, where the confined electric flux string is identified as the fundamental string. This generalizes to other DpantiDp systems, and solves a puzzle recently pointed out by Witten. (C) 1999 Elsevier Science B.V. All rights reserved. 
 Professor of Physics, Korea Institute for Advanced Study, Seoul, Sept. 1998 
 Board of Trustee, Gwangju Institute of Science and Technology (GIST), Oct. 2019 
 Board of Trustee, The Happiness Foundation, Mar. 2019
 Research Council, Institute for Basic Science, Jan. 2015
 Vice President, Korea Institute for Advanced Study, Nov. 2016  Dec. 2019
 Chair, School of Physics, Korea Institute for Advanced Study, Jan. 2014  Aug. 2016
 Visiting Professor, Stanford University, Stanford, Winter & Fall Quarters, 2008
 Member, Institute for Advanced Study, Princeton, Fall Semester, 2004
 Visiting Professor, University of Chicago, Chicago, February 2001
 Research Associate, Newman Lab, Cornell University, Ithaca, Sept.1997  May 1999
 Postdoctoral Research Scientist, Columbia University, New York, Sept.1994  Aug. 1997
 Ph.D. California Institute of Technology, Pasadena, June 1994
 Invited Review Speaker, Strings Conference, Seoul, 2013
 Leading Scientist, The Korea Academy of Science and Technology, 2013
 Top 100 Nationwide Research Output, KISTEP, Korea, 2008
 MEST Research & Development Top 50 Projects, Korea, 2007
 Outstanding Scientist, The Korea Academy of Science and Technology. 2007
 Invited Speaker, Strings Conference, Kyoto, 2003
 Outstanding Young Reseacher Award, APS March Meeting, 1998
 Fellow, Korea Foundation for Advanced Study, 19871994
 Prime Minister Award for Academic Excellence, Commencement, Seoul National University, February 1987
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