Rigid superstrings

A recently proposed bosonic string action containing a term proportional to the world sheet is supersymmetrized in the light-cone gauge. We compute the one-loop contribution to the β function of the new coupling constant and find that the asymptotic freedom present in the bosonic case is not destroyed by the addition of the fermionic degrees of freedom.     

Geometric properties of QCD string from Willmore functional

The extremum of the Willmore-like functional for m-dimensional Riemannian manifold immersed in d-dimensional Riemannian manifold under normal variations is studied and various cases of interest are examined. This study is used to relate the parameters of QCD string action, including the Polyakov–Kleinert extrinsic curvature action, with the geometric properties of the world sheet. The world sheet has been shown to have negative stiffness on the basis of the geometric considerations.     

Classical dynamics of the rigid string from the Willmore functional

A new approach for investigating the classical dynamics of the relativistic string model with rigidity is proposed. It is based on the embedding of the string world surface into a space of constant curvature. It is shown that the rigid string in flat space-time is described by the Euler-Lagrange equation for the Willmore functional in a space-time of constant curvature K = −γ/(2α), where γ and α are constants in front of the Nambu-Goto term and the curvature term in the rigid string action, respectively. For simplicity the Euclidean version of the rigid string in three-dimensional space-time is considered. The Willmore functional (the action for the “Willmore string”) is obtained by dropping the Nambu-Goto term in the Polyakov-Kleinert action for the rigid string. Such a “reduction” of the rigid string model would be useful, for example, by applying some results about the Nambu-Goto string dynamics in the de Sitter universe to the rigid string model in the Minkowski space-time. It also allows us to use numerous mathematical results about Willmore surfaces in the context of the physical problem.     

Beltrami parametrization for superstrings

We introduce a parametrization of the metric and supersymmetry structure of the superstring world sheet which permits the derivation of the superstring action for general backgrounds. Factorization is explicit at each step of the construction.     

A two-dimensional superfield formulation of the heterotic string

The density superfield and Einstein action for two-dimensional (2,0) supergravity are derived. The irreducible superfields of the heterotic string are discussed, and they are coupled to (2,0) supergravity. The locally (2,0) supersymmetric action for the heterotic string is presented in both superfields and component fields. For flat world sheet geometry, the globally (2,0) supersymmetric non-linear sigma model, and the associated Virasoro constraints, are derived. This formalism is applicable to (p,0) supersymmetry for any positive integer p.     

Bosonic strings and complex structures

We write the action of the bosonic string in terms of two-dimensional complex structures rather than of two-dimensional metrics. We describe in some detail the behaviour under reparametrization of the world sheet, and in particular we give an expression for the two-dimensional diffeomorphism anomaly. We describe a possible gauge-fixing procedure for the BRST quantization.     

应用于水下能分辨粒径10 μm～500 μm尾流气泡的成像系统

 针对尾流气泡成像存在的难点,采用片光源切片扫描与高速摄影相结合的技术手段,研制了一套水下激光成像系统。该系统采用激光片光照明,避免了尾流区气泡图像层叠;设计了3组倍率可切换镜头,实现了对大动态范围（10 μm～500 μm）粒径小气泡的成像;将镜头分成前后组,以平行光中继,通过片光与前镜组的同步移动,可实现尾流区一定体积内气泡图像的采样,同时还能保证扫描过程中始终成像清晰。此系统通过在海域进行试验,放置深度为5 m,气泡由目标船产生,产生气泡粒径范围10 μm～2 000 μm,结果表明,系统成像效果良好,满足项目技术要求。     

Nonperturbative corrections to 4D string theory effective actions from SL(2,Z) duality and supersymmetry

We find the D(-1)- and D1-brane instanton contributions to the hypermultiplet moduli space of type IIB string compactifications on Calabi-Yau threefolds. These combine with known perturbative and world sheet instanton corrections into a single modular invariant function that determines the hypermultiplet low-energy effective action.     

Suppression of radiation in a momentum-nonconserving nonlinear interaction

We have considered the quadratic nonlinear radiation from a thin dipole sheet in front of a mirror. Radiation at the second-harmonic (SH) frequency on incidence of a fundamental field can be inhibited or enhanced independently of the SH field intensity stored between the nonlinear layer and the mirror. We have shown that this apparent contradiction can be fully understood only if the quadratic nonlinear interaction includes terms with a momentum mismatch equal to the magnitude of the SH field wave vector, such as the term that accounts for transfer of energy from the reflected SH field back to the incident fundamental.     

Phase space action for minimal surfaces of any dimension in curved spacetime

The phase space action, depending on coordinates, momenta and Lagrange multipliers (which turn out to be components of the induced metric), has been written down for a world sheet of arbitary dimension (a string generalized to membranes) in a curved embedding spacetime. Canonical and hamiltonian formalisms have been formulated in a covariant and general way with the true dynamical variables being separated from the redundant ones. The membrane constraints follow directly from the variation of our action; their suitable superposition gives a hamiltonian from which we derive the equations of motion for a membrane via the Poisson brackets. The same hamiltonian we obtain also in a different way from a variation of the action. For n = 2 all equations coincide with those of strings.     

Gauge covariant local formulation of bosonic strings

A free bosonic string field action is constructed that is local and invariant under the infinite set of gauge transformations corresponding to the conformal group of the two-dimensional world sheet. This allows for a straightforward gauge covariant method of second-quantizing string field theory. The method of extension to the interacting case is presented.     

Twistor description of world surfaces and the action integral of strings

The Cartan-Penrose twistor representation for light-like vectors is generalized to the case of isotropic bivectors describing the world sheets of null-strings. A new twistor formulation of the action of a string is constructed as a sheet integral of a differential 2-form which is quadratic in the twistor variables. The geometric nature of the mechanism for generating string tension is discussed.     

应用于水下能分辨粒径10 μm～500 μm尾流气泡的成像系统

针对尾流气泡成像存在的难点,采用片光源切片扫描与高速摄影相结合的技术手段,研制了一套水下激光成像系统。该系统采用激光片光照明,避免了尾流区气泡图像层叠;设计了3组倍率可切换镜头,实现了对大动态范围（10 m～500 m）粒径小气泡的成像;将镜头分成前后组,以平行光中继,通过片光与前镜组的同步移动,可实现尾流区一定体积内气泡图像的采样,同时还能保证扫描过程中始终成像清晰。此系统通过在海域进行试验,放置深度为5 m,气泡由目标船产生,产生气泡粒径范围10 m～2 000 m,结果表明,系统成像效果良好,满足项目技术要求。     

Chern-Simons topological Lagrangians in odd dimensions and their Kaluza-Klein reduction

By clarifying the behavior of generic Chern-Simons secondary invariants under infinitesimal variation and finite gauge transformation, it is proved that they are eligible to be a candidate term in the Lagrangian in odd dimensions (2k ? 1 for gauge theories and 4k ? 1 for gravity). The coefficients in front of these terms may be quantized because of topological reasons. As a possible application, the dimensional reduction of such actions in Kaluza-Klein theory is discussed. The difficulty in defining the Chern-Simons action for topologically nontrivial field configurations is pointed out and resolved.     

Geometric phase in Bohmian mechanics

Using the quantum kinematic approach of Mukunda and Simon, we propose a geometric phase in Bohmian mechanics. A reparametrization and gauge invariant geometric phase is derived along an arbitrary path in configuration space. The single valuedness of the wave function implies that the geometric phase along a path must be equal to an integer multiple of 2π. The nonzero geometric phase indicates that we go through the branch cut of the action function from one Riemann sheet to another when we locally travel along the path. For stationary states, quantum vortices exhibiting the quantized circulation integral can be regarded as a manifestation of the geometric phase. The bound-state Aharonov-Bohm effect demonstrates that the geometric phase along a closed path contains not only the circulation integral term but also an additional term associated with the magnetic flux. In addition, it is shown that the geometric phase proposed previously from the ensemble theory is not gauge invariant.     

Nonperturbative deformation of D-brane states by the world sheet noncommutativity

By introducing the noncommutativity in the world sheet, we discuss a modification of the D-brane states in the closed string theory. In particular we show how the world sheet noncommutativity induces a nonperturbative effect to the D-brane states.     

Field theory of interacting open superstrings in fermionic ghost representation

The field theory of interacting open superstring in the fermionic ghost representation based on anticommuting and commuting ghosts, corresponding respectively to world sheet bosonic x_μ and fermionic ψ_μ coordinates, is presented. We have to revise once more the field theory of the free Ramond (R) string and starting from a general algebraic point of view we obtain that the number of degrees of freedom in the R and NS (Neveu-Schwarz) sectors are equal, permitting us to construct a supersymmetric operator. We propose to solve a specific equation guaranteeing superinvariance in order to find the R-R-NS and NS-R-R vertices in the term of the NS-NS-NS vertex.