Searcharxiv⌕ Search

arXiv subjects

Xing-Chang Song

Publications and source records attributed to Xing-Chang Song.

At least 19 recordsLinked to original sources
arXiv2005

Flat Currents of the Green-Schwarz Superstrings in AdS_5 x S^1 and AdS_3 x S^3 backgrounds

We construct a one-parameter family of flat currents in AdS_5 x S^1 and AdS_3 x S^3 Green-Schwarz superstrings, which would naturally lead to a hierarchy of classical conserved nonlocal charges. In the former case we rewrite the AdS_5 x S^1 string using a new Z_4-graded base of the superalgebra su(2,2|2). In both cases the existence of the Z_4 grading in the superalgebras plays a key role in the construction. As a result, we find that the flat currents, when formally written in terms of the G_0-gauge invariant lowercase 1-forms, take the same form as the one in AdS_5 x S^5 case.

hep-th↗
arXiv2004

The Narrow $Θ_5$ Pentaquark As The First Non-planar Hadron With the Diamond Structure And Negative Parity

Using the picture of the flux tube model, we propose that the $Θ_5$ pentaquark as the first candidate of the three-dimensional non-planar hadron with the extremely stable diamond structure. The up and down quarks lie at the corners of the diamond while the anti-strange quark sits in the center. Various un-excited color flux tubes between the five quarks bind them into a stable and narrow color-singlet. Such a configuration allows the lowest state having the negative parity naturally. The decay of the $Θ_5$ pentaquark into the nucleon and kaon requires the breakup of the non-planar diamond configuration into two conventional planar hadrons, which involves some kind of structural phase transition as in the condensed matter physics. Hence the width of the $Θ^+$ pentaquark should be narrow despite that it lies above the kaon nucleon threshold. We suggest that future lattice QCD calculation adopt non-planar interpolating currents to explore the underlying structure of the $Θ_5$ pentaquark.

hep-ph↗
arXiv2001

Spontaneous Symmetry Broken Condition in (De)Constructing Dimensions from Noncommutative Geometry

In this short report, a brief introduction to Arkani-Hamed, Cohen, Georgi model (ACG-model, (de)constructing dimensions model), whose main characters are that extra-dimensional space-time are generated dynamically from a four-dimensional gauge theory and that extra dimensions are lattices, will be given first. Then after a concise review of NCG on cyclic groups, actions for gauge fields along extra dimensions will be constructed by virtue of NCG and classical (vacuum) solutions will be solved, with low energy phenomenology being classified accordingly. As a conclusion, the behavior of spontaneous symmetry broken within ACG-model can be determined by noncommutative Yang-Mills theory.

hep-ph↗
arXiv2001

Geometric Origin of Staggered Fermion: Direct Product K-Cycle

Staggered formalism of lattice fermion can be cast into a form of direct product K-cycle in noncommutative geometry. The correspondence between this staggered K-cycle and a canonically defined K-cycle for finitely generated abelian group where lattice appears as a special case is proved.

hep-lat↗
arXiv2001

Structure and Representation Theory for Double Group of Four-Dimensional Cubic Group

Hypercubic groups in any dimension are defined and their conjugate classifications and representation theories are derived. Double group and spinor representation are introduced. A detailed calculation is carried out on the structures of four-dimensional cubic group $O_4$ and its double group, as well as all inequivalent single-valued representations and spinor representations of $O_4$. All representations are derived adopting Clifford theory of decomposition of induced representations. Based on these results, single-valued and spinor representations of the orientation-preserved subgroup of $O_4$ are calculated.

hep-lat↗
arXiv2001

Noncommutative Geometry of Lattice and Staggered Fermions

Differential structure of a d-dimensional lattice, which is essentially a noncommutative exterior algebra, is defined using reductions in first order and second order of universal differential calculus in the context of noncommutative geometry (NCG) developed by Dimakis et al. This differential structure can be realized adopting a Dirac-Connes operator proposed by us recently within Connes' NCG. With matrix representations being specified, our Dirac-Connes operator corresponds to staggered Dirac operator, in the case that dimension of the lattice equals to 1, 2 and 4.

hep-th↗
arXiv2001

Vacuum Solutions of Classical Gravity on Cyclic Groups from Noncommutative Geometry

Based on the observation that the moduli of a link variable on a cyclic group modify Connes' distance on this group, we construct several action functionals for this link variable within the framework of noncommutative geometry. After solving the equations of motion, we find that one type of action gives nontrivial vacuum solution for gravity on this cyclic group in a broad range of coupling constants and that such solutions can be expressed with Chebyshev's polynomials.

gr-qc↗
arXiv2001

Connes' Distance of One-Dimensional Lattices: General Cases

Connes' distance formula is applied to endow linear metric to three 1D lattices of different topology, with a generalization of lattice Dirac operator written down by Dimakis et al to contain a non-unitary link-variable. Geometric interpretation of this link-variable is lattice spacing and parallel transport.

math-ph↗
arXiv2001

A New Solution to Ginsparg-Wilson Relation from Generalized Staggered Fermion

A generalized anti-hermitian staggered Dirac operator is formulated. Its relation with noncommutative geometry is briefly reviewed. Once this anti-hermitian operator is modified to be ``$γ^5$-hermitian'', it will provide a new solution to Ginsparg-Wilson relation, basing on an abstract algebraic analysis of Neuberger's overlap construction and a redefinition of chirality.

hep-lat↗
arXiv2001

Wilson Action of Lattice Gauge Fields with An Additional Term from Noncommutative Geometry

Differential structure of lattices can be defined if the lattices are treated as models of noncommutative geometry. The detailed construction consists of specifying a generalized Dirac operator and a wedge product. Gauge potential and field strength tensor can be defined based on this differential structure. When an inner product is specified for differential forms, classical action can be deduced for lattice gauge fields. Besides the familiar Wilson action being recovered, an additional term, related to the non-unitarity of link variables and loops spanning no area, emerges.

hep-th↗
arXiv2001

Dirac-Connes Operator on Discrete Abelian Groups and Lattices

A kind of Dirac-Connes operator defined in the framework of Connes' NCG is introduced on discrete abelian groups; it satisfies a Junk-free condition, and bridges the NCG composed by Dimakis, Müller-Hoissen and Sitarz and the NCG of Connes. Then we apply this operator to d-dimensional lattices.

hep-th↗
arXiv2001

Pythagoras' Theorem on a 2D-Lattice from a "Natural" Dirac Operator and Connes' Distance Formula

One of the key ingredients of A. Connes' noncommutative geometry is a generalized Dirac operator which induces a metric(Connes' distance) on the state space. We generalize such a Dirac operator devised by A. Dimakis et al, whose Connes' distance recovers the linear distance on a 1D lattice, into 2D lattice. This Dirac operator being "naturally" defined has the so-called "local eigenvalue property" and induces Euclidean distance on this 2D lattice. This kind of Dirac operator can be generalized into any higher dimensional lattices.

hep-th↗
arXiv2000

Structure and representation theory of double group of four-dimensional cubic group

We generalize the concept of cubic group into any dimension and derive their conjugate classifications and representation theorys. Double group and spinor representation are defined. A detailed calculation is carried out on the structures of four-dimensional cubic group $O_4$ and its double group, as well as all inequivalent single-valued representations and spinor representations of $O_4$ . All representations are derived adopting Clifford theory of decomposition of induced representations.

hep-lat↗