String Type Research Articles

Quantum energies of strings in a ( [formula omitted])-dimensional gauge theory

We study classically unstable string type configurations and compute the renormalized vacuum polarization energies that arise from fermion fluctuations in a ( 2 + 1 )-dimensional analog of the standard model. We then search for a minimum of the total energy (classical plus vacuum polarization energies) by varying the profile functions that characterize the string. We find that typical string configurations bind numerous fermions and that populating these levels is beneficial to further decrease the total energy. Ultimately our goal is to explore the stabilization of string type configurations in the standard model through quantum effects. We compute the vacuum polarization energy within the phase shift formalism which identifies terms in the Born series for scattering data and Feynman diagrams. This approach allows us to implement standard renormalization conditions of perturbation theory and thus yields the unambiguous result for this non-perturbative contribution to the total energy.

The effect of liquid environment on size and aggregation of gold nanoparticles prepared by pulsed laser ablation

The effects of liquid environment on nucleation, growth and aggregation of gold nanoparticles were studied. Gold nanoparticles were prepared by pulsed laser ablation in deionised water with various concentrations of ethanol and also in pure ethanol. UV/visible extinction and TEM observations were employed for characterization of optical properties and particle sizes respectively. Preparation in water results in smaller size, shorter wavelength of maximum extinction and stable solution with an average size of 6 nm. Nanoparticles in solution with low concentration ethanol up to 20 vol% are very similar to those prepared in water. In the mixture of deionised water and 40 up to 80 vol% ethanol, wavelength of maximum extinction shows a red shift and mean size of nanoparticles was increased to 8.2 nm. Meanwhile, in this case, nanoparticles cross-linked each other and formed string type structures. In ethanol, TEM experiments show a mean size of 18 nm and strong aggregation of nanoparticles. The data were discussed qualitatively by considering effects of polarity of surrounding molecules on growth mechanism and aggregation. This study provided a technique to control size, cross-linking and aggregation of gold nanoparticles via changing the nature of liquid carrier medium.

Are preons dyons? Naturalness of three generations

In the present paper a model of preons and their composites is constructed in the framework of the superstring-inspired `flipped' E_6\times \widetilde{E_6} gauge symmetry group which reveals a generalized dual symmetry. Here E_6 and \widetilde{E_6} are non-dual and dual sectors of the theory with hyper-electric g and hyper-magnetic \tilde g charges, respectively. We follow the old idea by J. Pati presuming that preons are dyons, which in our model are confined by hyper-magnetic strings -- composite {\bf N}=1 supersymmetric non-Abelian flux tubes created by the condensation of spreons near the Planck scale. Considering preons belonging to the 27-plet of E_6, we have investigated the breakdown of E_6 (and \widetilde{E_6}) near the Planck scale into the SU(6)\times U(1) (and \widetilde{SU(6)}\times \widetilde{U(1)}) gauge group and shown that the six types of strings having fluxes \Phi_n=n\Phi_0 (n=\pm 1,\pm 2,\pm 3) produce three (and only three) generations of composite quark-leptons and bosons. The model predicts the existence of the Family replicated gauge group [E_6]^3 near the Planck scale. The runnings of the corresponding fine structure constants are investigated, and the critical coupling constants at the two phase transition points near the Planck scale are calculated. The model explains the hierarchies of masses in the Standard Model naturally. The compactification in a space-time with five dimensions and its influence on form-factors of composite objects are also briefly discussed.

Mechanism of Racket Spin Performance in Tennis(Spin Performance Improvement by Lubrication of String Intersections with Super High Speed Video Analysis)

Players often say that some strings provide a better grip and more spin than others, but ball spin did not depend on string type, gauge or tension in the past laboratory experiment. There was no research work on the spin to uncover what is really happening during actual tennis impact owing to difficult experiment. This paper made clear the mechanism of top spin and its improvement by lubrication of strings according to the high speed video analysis. It also provided the more detailed explanations of spin behavior by comparison between a lubricant string racket and a famous 'Spaghetti strings racket' which was banned in 1978 by the International Tennis Federation since it used plastic spaghetti tubing over the strings to reduce friction resulting in the excessive spin on the ball. As the main strings stretch and slide side ways more, the ball is given more spin due to restoring force parallel to the string face when the main strings spring back and the ball is released from the strings. Furthermore, it showed that the more spin results in the reduction of shock vibrations of the wrist joint during impact.

On the evolution of multi string networks

We model the behaviour of a network of interacting (p,q) strings from IIB string theory by considering a field theory containing multiple species of string, allowing us to study the effect of non-intercommuting events due to two different species crossing each other. This then has the potential for a string dominated Universe with the network becoming so tangled that it freezes. We give numerical evidence, explained by a one-scale model, that such freezing does not take place, with the network reaching a scaling limit where its density relative to the background increases with N, the number of string types.

Classification of cohomogeneity-one strings

We define the cohomogeneity one string, string with continuous symmetries, as its world surface is tangent to a Killing vector field of a target space. We classify the Killing vector fields by an equivalence relation using isometries of the target space. We find that the equivalence classes of Killing vectors in Minkowski spacetime are partitioned into seven families. It is clarified that there exist seven types of strings with spacelike symmetries and four types of strings with timelike symmetries, stationary strings.

Erratum: Scaling of multitension cosmic superstring networks [Phys. Rev. DPRVDAQ0556-282171, 103508 (2005)

Brane inflation in superstring theory ends when branes collide, initiating the hot big bang. Cosmic superstrings are produced during the brane collision. The cosmic superstrings produced in a D3-brane-antibrane inflationary scenario have a spectrum: $(p,q)$ bound states of $p$ fundamental (F) strings and $q$ D-strings, where $p$ and $q$ are coprime. By extending the velocity-dependent one-scale network evolution equations for abelian Higgs cosmic strings to allow a spectrum of string tensions, we construct a coupled (infinite) set of equations for strings that interact through binding and self-interactions. We apply this model to a network of $(p,q)$ superstrings. Our numerical solutions show that $(p,q)$ networks rapidly approach a stable scaling solution. We also extract the relative densities of each string type from our solutions. Typically, only a small number of the lowest tension states are populated substantially once scaling is reached. The model we study also has an interesting new feature: the energy released in $(p,q)$ string binding is by itself adequate to allow the network to reach scaling. This result suggests that the scaling solution is robust. To demonstrate that this result is not trivial, we show that choosing a different form for string interactions can lead to network frustration.

Scaling of multitension cosmic superstring networks

Brane inflation in superstring theory ends when branes collide, initiating the hot big bang. Cosmic superstrings are produced during the brane collision. The cosmic superstrings produced in a $D3$-brane-antibrane inflationary scenario have a spectrum: $(p,q)$ bound states of $p$ fundamental ($F$) strings and $q$ $D$-strings, where $p$ and $q$ are coprime. By extending the velocity-dependent one-scale network evolution equations for Abelian Higgs cosmic strings to allow a spectrum of string tensions, we construct a coupled (infinite) set of equations for strings that interact through binding and self-interactions. We apply this model to a network of $(p,q)$ superstrings. Our numerical solutions show that $(p,q)$ networks rapidly approach a stable scaling solution. We also extract the relative densities of each string type from our solutions. Typically, only a small number of the lowest tension states are populated substantially once scaling is reached. The model we study also has an interesting new feature: the energy released in $(p,q)$ string binding is by itself adequate to allow the network to reach scaling. This result suggests that the scaling solution is robust. To demonstrate that this result is not trivial, we show that choosing a different form for string interactions can lead to network frustration.

Controlled synthesis of target strings in a class of splicing systems

This article presents an approach for synthesizing target strings in a class of computational models of DNA recombination. The computational models are formalized as splicing systems in the context of formal languages. Given a splicing system (of a restricted type) and a target string to be synthesized, we construct (i) a rule-embedded splicing automaton that recognizes languages containing strings embedded with symbols representing splicing rules, and (ii) an automaton that implicitly recognizes the target string. By manipulating these two automata, we extract all rule sequences that lead to the production of the target string (if that string belongs to the splicing language). An algorithm for synthesizing a certain type of target strings based on such rule sequences is presented.

Speech synthesis with prosodic model data and accent type

A speech synthesizing method includes determining the accent type of the input character string, selecting the prosodic model data from a prosody dictionary for storing typical ones of the prosodic models representing the prosodic information for the character strings in a word dictionary, based on the input character string and the accent type, transforming the prosodic information of the prosodic model when the character string of the selected prosodic model is not coincident with the input character string, selecting the waveform data corresponding to each character of the input character string from a waveform dictionary, based on the prosodic model data after transformation, and connecting the selected waveform data with each other. Therefore, a difference between an input character string and a character string stored in a dictionary is absorbed, then it is possible to synthesize a natural voice.

Publisher’s Note: Six-dimensional localized black holes: Numerical solutions [Phys. Rev. D69, 104019 (2004)

To test the strong-gravity regime in Randall-Sundrum braneworlds, we consider black holes bound to a brane. In a previous paper, we studied numerical solutions of localized black holes whose horizon radii are smaller than the AdS curvature radius. In this paper, we improve the numerical method and discuss properties of the six dimensional (6D) localized black holes whose horizon radii are larger than the AdS curvature radius. At a horizon temperature $\mathcal{T} \approx 1/2\pi \ell$, the thermodynamics of the localized black hole undergo a transition with its character changing from a 6D Schwarzschild black hole type to a 6D black string type. The specific heat of the localized black holes is negative, and the entropy is greater than or nearly equal to that of the 6D black strings with the same thermodynamic mass. The large localized black holes show flattened horizon geometries, and the intrinsic curvature of the horizon four-geometry becomes negative near the brane. Our results indicate that the recovery mechanism of lower-dimensional Einstein gravity on the brane works even in the presence of the black holes.

Six-dimensional localized black holes: Numerical solutions

To test the strong-gravity regime in Randall-Sundrum braneworlds, we consider black holes bound to a brane. In a previous paper, we studied numerical solutions of localized black holes whose horizon radii are smaller than the AdS curvature radius. In this paper, we improve the numerical method and discuss properties of the six-dimensional (6D) localized black holes whose horizon radii are larger than the AdS curvature radius. At a horizon temperature $\mathcal{T}\ensuremath{\approx}1/2\ensuremath{\pi}\mathcal{l},$ the thermodynamics of the localized black hole undergo a transition with its character changing from a 6D Schwarzschild black hole type to a 6D black string type. The specific heat of the localized black holes is negative, and the entropy is greater than or nearly equal to that of the 6D black strings with the same thermodynamic mass. The large localized black holes show flattened horizon geometries, and the intrinsic curvature of the horizon four-geometry becomes negative near the brane. Our results indicate that the recovery mechanism of lower-dimensional Einstein gravity on the brane works even in the presence of the black holes.

Classical and quantum strings in compactifiedppwaves and Gödel type universes

We consider Neveu-Schwarz pp-waves with spacetime supersymmetry. Upon compactification of a spacelike direction, these backgrounds develop Closed Null Curves (CNCs) and Closed Timelike Curves (CTCs), and are U-dual to supersymmetric Godel type universes. We study classical and quantum strings in this background, with emphasis on the strings winding around the compact direction. We consider two types of strings: long strings stabilized by NS flux and rotating strings which are stabilized against collapse by angular momentum. Some of the latter strings wrap around CNCs and CTCs, and are thus a potential source of pathology. We analyze the partition function, and in particular discuss the effects of these string states. Although our results are not conclusive, the partition function seems to be dramatically altered due to the presence of CNCs and CTCs. We discuss some interpretations of our results, including a possible sign of unitary violation.

Cosmic D-term Strings as Wrapped D3 Branes

We describe cosmic D--term strings as D3 branes wrapped on a resolved conifold. The matter content that gives rise to D--term strings is shown to describe the world--volume theory of a space--filling D3 brane transverse to the conifold which itself is a wrapped D5 brane. We show that, in this brane theory, the tension of the wrapped D3 brane mathces that of the D--term string. We argue that there is a new type of cosmic string which arises from fractional D1 branes on the world--volume of a fractional D3 brane.

Tachyon condensation in open-closed p-adic string theory

We study a simple model of p-adic closed and open strings. It sheds some light on the dynamics of tachyon condensation for both types of strings. We calculate the effect of static and decaying D-brane configurations on the closed string background. For closed string tachyons we find lumps analogous to D-branes. By studying their fluctuation spectrum and the D-branes they admit, we argue that closed string lumps should be interpreted as spacetimes of lower dimensionality described by some noncritical p-adic string theory.

Quantum order from string-net condensations and the origin of light and massless fermions

Recently, it was pointed out that quantum orders and the associated projective symmetry groups can produce and protect massless gauge bosons and massless fermions in local bosonic models. In this paper, we demonstrate that a state with such kind of quantum orders can be viewed as a string-net condensed state. The emerging gauge bosons and fermions in local bosonic models can be regarded as a direct consequence of string-net condensation. The gauge bosons are fluctuations of nets of large closed strings which are condensed in the ground state. The ends of condensed open strings are the charged particles of the corresponding gauge field. For certain types of strings, the ends of strings can even be fermions. According to the string-net picture, fermions always carry gauge charges. This suggests the existence of a new discrete gauge field that couples to neutrinos and neutrons. We also discuss how chiral symmetry that protects massless Dirac fermions can emerge from the projective symmetry of quantum order.

Relation Between Frictional Characteristics and the Strings' Ability to Make a Tennis Ball Spin

The spin of a tennis ball during play is an important factor. There are two kinds of racket strings, one that causes the ball to spin, and the other makes spinning difficult. The relationship between the spin behavior of a tennis ball and the mechanical properties of the strings is discussed. Rotations of the ball after impact are observed by high-speed photography. The rotational speed of the ball increases with the impact speed, and the speed depends greatly on string type. The frictional characteristics of the strings and ball are measured by an apparatus that reveals a good correlation between the static coefficient of friction of the strings and the spin of the ball when the impact speed is low. Spinning behavior is predicted by measuring the coefficient of friction for the strings. The tenden cies of the measured frictional characteristics agree with sensitivity evaluations by users.

The production, spectrum and evolution of cosmic strings in brane inflation

Brane inflation in superstring theory predicts that cosmic strings (but not domain walls or monopoles) are produced towards the end of the inflationary epoch. Here, we discuss the production, the spectrum and the evolution of such cosmic strings, properties that differentiate them from those coming from an abelian Higgs model. As D-branes in extra dimensions, some type of cosmic strings will dissolve rapidly in spacetime, while the stable ones appear with a spectrum of cosmic string tensions. Moreover, the presence of the extra dimensions reduces the interaction rate of the cosmic strings in some scenarios, resulting in an order of magnitude enhancement of the number/energy density of the cosmic string network when compared to the field theory case.

A combinatorial optimization problem arising from text classification

Abstract We study a combinatorial optimization problem related to the automatic classification of texts. The problem consists of covering a given text using strings from a given set, where a cost is incurred for each type of string used. We give a 0-1 linear programming formulation and we report on computational experiences on very large instances using two different Lagrangean relaxations and heuristic algorithms based on simulated annealing and threshold accepting.

Regular Expression Types for Strings in a Text Processing Language

We present λre, a minimal functional calculus with regular expression types for strings, in order to establish a theoretical foundation of using regular expressions as types of strings in text processing languages. The major technical novelties in this paper (with respect to other work such as XDuce) are (1) the use of regular expression effects to statically analyze the shape of the output of an even diverging program and (2) the treatment of as-patterns in non-tail positions. We expect that our approach will be of help for bringing the merits of static typing into scripting languages such as Perl, Python, and Ruby without sacrificing too much of their expressiveness and flexibility.