Probing string fragmentation in nuclear matter: Lepton-nucleus scattering

We introduce a new model for the fragmentation of strings in a “medium” of hadronic objects. These objects may be hadrons, resonances, or string pieces from the fragmentation of other strings. As a first application we treat the fragmentation of a string inside a nuclear medium, taking into account interactions of the fragmenting string with spectator nucleons (spectators of the hard process which created the string in the first place). We compare with neutrino-neon data.     

Physics-based modeling techniques of a twelve-string Portuguese guitar: A non-linear time-domain computational approach for the multiple-strings/bridge/soundboard coupled dynamics

The Portuguese guitar is a pear-shaped instrument with twelve metal strings which is widely used in Portuguese traditional music. Unlike most common guitars, it has a curved top-plate and a specific violin-like bridge which is not rigidly fixed to the soundboard of the instrument. From the dynamical point of view, if the bridge transmits the strings vibrations to the instrument body in order to maximize the radiated energy, it also couples all the component parts of the instrument which therefore interact by structural coupling. This can originate various audible effects such as beating behavior and the excitation of numerous sympathetic resonances enhanced by the large number of strings of the instrument, and this is certainly why the Portuguese guitar has such distinct sound compared to other guitars. In this paper, a fully coupled time-domain model of the Portuguese guitar is developed and a series of simulations are presented to emphasize the various coupling phenomena involved in sound production. To reproduce the main musical features, the model includes the coupled dynamics of the twelve strings supported by a bridge which interact with the body of the instrument, described through Finite-Element modeling of the soundboard of a typical Portuguese guitar. Further simple models have been devised for the string/fret interaction and the pluck excitation. Since nonlinear effects are quite apparent in the behavior of string musical instruments, the string dynamics is modeled by the Kirchhoff–Carrier equations which describe large-amplitude string vibrations, and includes the coupling between both polarizations of string motion. The coupling between the strings and the soundboard at the bridge is provided by a model of the bridge kinematics, built on the basis of simple geometrical rationale, so that the two perpendicular string motions can exchange energy back and forth. By a close examination of the energy transfers between the various subsystems of the model, we first assess the correct behavior of the physical model and then examine the respective influence of the string nonlinearity and the bridge on the nonplanar motion of the string. The fully coupled model which pertains to the restricted group of studies which deals with the complete physical-based modeling of a multi-stringed instrument, captures many important phenomena observed in practice, among which the pitch glide effect and the mutual excitation of sympathetic vibrations.     

Statistical properties of strings

We investigate numerically the configurational statistics of strings. The algorithm models an ensemble of global U(1) cosmic strings, or equivalently vortices in superfluid ⁴He. We use a new method which avoids the specification of boundary conditions on the lattice. We therefore do not have the artificial distinction between short and long string loops or a “second phase” in the string network statistics associated with strings winding around a toroidal lattice. Our lattice is also tetrahedral, which avoids ambiguities associated with the cubic lattices of previous work. We find that the percentage of infinite string is somewhat lower than on cubic lattices, 63% instead of 80%. We also investigate the Hagedorn transition, at which infinite string percolate, controlling the string density by rendering one of the equilibrium states more probable. We measure the percolation threshold, the critical exponent associated with the divergence of a suitably defined susceptibility of the string loops, and that associated with the divergence of the correlation length.     

Nonsupersymmetric string solitons

We begin a search for nonsupersymmetric/supersymmetric dual string pairs by constructing candidate critical nonsupersymmetric strings as solitons in supersymmetric string theories. Using orbifold techniques, one can construct cosmic string solutions which lie in supersymmetric vacua but which do not fall in supermultiplets. We discuss two three-dimensional examples in detail. The effective worldsheet actions for the soliton strings have (0,2) and (1,1) supersymmetry and the correct numbers of massless bosons and fermions to be critical heterotic and type II strings, respectively.     

Compactifications of F-theory on Calabi-Yau threefolds (II)

We continue our study of compactifications of F-theory on Calabi-Yau threefolds. We gain more insight into F-theory duals of heterotic strings and provide a recipe for building F-theory duals for arbitrary heterotic compactifications on elliptically fibered manifolds. As a byproduct we find that string/string duality in six dimensions gets mapped to fiber/base exchange in F-theory. We also construct a number of new N = 1, d = 6 examples of F-theory vacua and study transitions among them. We find that some of these transition points correspond upon further compactification to 4 dimensions to transitions through analogues of Argyres-Douglas points of N = 2 moduli. A key idea in these transitions is the notion of classifying (0,4) fivebranes of heterotic strings.     

Static criteria for the existence of Coulomb strings in storage rings

We derive four rigorous conditions for the stability of Coulomb strings in circular storage rings. These criteria are well met by the existing data from experiments in SIS, ESR, and CRYring but not by the NAP-M experiment. We calculate the potential of the joint transverse zigzag excitation and the longitudinal motion against each other of a string of charged particles as a function of their amplitudes and with the linear density as parameter. This potential exhibits a saddle point in amplitude space which, if overcome, destroys the order of the string. The conditions of stability are derived from the position and height of the saddle point which are fairly independent of the linear density. Our findings confirm the supposition that only the Coulomb interaction in the immediate vicinity of very close encounters of particles is important for the existence of strings.     

The gravitational interaction of conical strings

Up to now calculations of the interaction of cosmic strings have neglected gravity. We consider the purely gravitational interactions that occur at large distances, using the conical line singularity for the gravitational field of a string. We construct spaces with multiple intersecting conical strings, that are exactly consistent with General Relativity, and which can be covered in a single Minkowski coordinate patch, using a Regge calculus type construction. We show that after two such strings pass through each other they remain connected by another string, and we derive the branching rules which govern the junction of three strings. These rules apply to conical type strings in any smoothly curved background, whether they are straight or curved, moving or stationary, and they show that, at the junction, the three strings must be as coplanar as is possible in such a space. For these results to be matched onto the short range results of Field Theory calculations, it is suggested that gravitational radiation must be introduced. This would mean that gravitation is not negligible in these interactions.     

Possible influence of the two string events on the hadron formation in a nuclear environment

One of the basic assumptions of the string model is that as a result of a DIS in nucleus a single string arises, which then breaks into hadrons. However the pomeron exchange considered in this work, leads to the production of two strings in the one event. The hadrons produced in these events have smaller formation lengths, than those with the same energy produced in the single string events. As a consequence, they undergo more substantial absorption in the nuclear matter. PACS 13.87.Fh; 13.60.-r; 14.20.-c; 14.40.-n     

Cosmic strings and domains in unified theories

Unified theories predict that the Universe passes through a sequence of phase transitions as it cools after the big bang. Topological structures (domain walls, strings and monopoles) may be created in these transitions. The production of domains of different zero-temperature vacua (separately by massive walls) excludes some popular scenarios for the breaking of SU(5) and SO(10).Massive strings appear in other schemes. They may be open strings or closed loops. We exhibit an SO(10) example with string formation. SO(8) supergravity may deliver an effective SU(5)× SU(2) unified theory below the Planck mass scale. This can also lead to string production. We present the rather restrictive conditions under which string producing theories are harmless to conventional cosmology. Even then, strings do not seem to provide the initial density perturbations that evolved into galaxies.     

Self-organization in a system of binary strings with spatial interactions

We consider an artificial reaction system whose components are binary strings. Upon encounter, two binary strings produce a third string which competes for storage space with the originators. String types or species can only survive when produced in sufficient numbers. Spatial interactions through introduction of a topology and rules for distance-dependent reactions are discussed. We observe various kinds of survival strategies of binary strings.     

String theories and millisecond pulsars

We discuss the two ways of connecting string theories (cosmic, fundamental and the connection between them) to the observational reality: (i) radioastronomy observations (millisecond pulsar timing), and (ii) elementary particle phenomenology (compactification schemes). We study the limits imposed on the string parameter Gμ by recent millisecond pulsar timings. Cosmic strings derived from GUTs agree with (i). For cosmic strings derived from fundamental strings themselves there is contradiction between (i) and (ii). One of these scenarios connecting string theory to reality must be revised (or the transition from fundamental into cosmic strings rejected). Meanwhile, millisecond pulsar can select one scenario, or reject both of them.     

The Role of Magnetic Field in Anisotropic String Cosmological Model

In this paper we consider a spatially homogenous and anisotropic Bianchi type-V space-time model to investigate the effects of a magnetic field in string cosmology. We assume that the string’s direction and magnetic field are along x-axis. The field equations are solved by using the equation of state for a cloud of strings and variable magnetic permeability. We derive exact solutions for three types of strings: (i) Nambu strings, (ii) string model where the sum of energy density and string tension density is zero and (iii) Takabayasi strings. We examine the behaviour of scale factors and other physical parameters with and without magnetic field and it is found that the magnetic field effects the dynamics of the universe at early time. During late time the universe becomes isotropic even in the presence of magnetic field. The universe expands with decelerated rate during early stages of the evolution of the universe but it goes to marginal inflation at late times.     

Strong Field Gravitational Lensing in a Magnetic Charged Reissner-Nordstr?m Black Hole Pierced by a Cosmic String

The principal focus of this paper is to study the strong field gravitational lensing in a magnetic charged Reissner-Nordstr?m black hole based on the method of cosmic string. We obtain the new coefficients including the tension of the cosmic strings, the strong field deflection limit coefficients, the deflection angle and the magnification, and obtain the relationship between the cosmic string parameter and the new coefficients. The result shows that the cosmic strings have some important effect on the gravitational lensing in a black hole when they pierce it.     

Open-closed string duality at tree level

We study the decay of unstable D-branes in string theory in the presence of an electric field, and show that the classical open string theory results for various properties of the final state agree with the properties of closed string states into which the system is expected to decay. This suggests a duality between tree level open string theory on unstable D-branes and closed strings at high density.     

CONSTRUCTION OF INTERACTING ACTIONS OF BOSONIC OPEN STRINGS AND CLOSED STRINGS BY SYMMETRY PRINCIPLES

Following Kaku's way, various interacting actions of bosonic open strings as well as closed strings are constructed, which are invariant under. local reparametrization transformations, string group and global transformations of a Lie group. Similar to open string, a multiplication rule of closed string fields is given which also satisfies associative law as in open string case.     

T-duality for string in Hořava–Lifshitz gravity

We continue our study of the Lorentz-breaking string theories. These theories are defined as string theory with modified Hamiltonian constraint which breaks the Lorentz symmetry of target space-time. We analyze the properties of this theory in the target space-time that possesses isometry along one direction. We also derive the T-duality rules for Lorentz-breaking string theories and show that they are the same as that of Buscher’s T-duality for the relativistic strings.     

Structural dynamics of chiral strings

It is demonstrated that a microscopic model of an antiferroelectric elementary string makes it possible to explain the specifics of the structural macrokinetics and macroscopic dynamics of chiral strings. It is established that the formation of strings is controlled by diffusion, whereas the supercoiling of strings, by Van der Waals interactions between them. Three modes of strings formation were identified: the uniform growth of cylindrical strings, π-assembly of an inverted cone of thin strings, and π-decay. The π-assembly is accompanied by the rotation of the string about its axis, which can cause instability, leading first to a bending of the string and then to the formation of loops.     

Two mass relations for mesons from string-quark duality

We generalize a self-consistency equation derived previously by us for the Nambu string to strings carrying SU(6) quantum numbers.The self-consistency equations are derived by considering the propagation of a string with the quantum numbers of the physical vacuum. Since we can map the world sheet that the string sweeps out onto rectangles, and the wave function of the physical vacuum is a constant, the boundary conditions are the same on all four sides of the rectangles. We can then calculate the propagator in two ways and this leads to the self-consistency equations. For the strings carrying SU(6) quantum numbers we consider the propagator o strings with the quantum numbers of the physical vacuum all along the string except for having quark quantum numbers either attached or removed from the ends. We can solve these self-consistency equations in a certain approximation and for this case they lead to mass formulae for mesons that are well satisfied in nature.     

Evolution of Nielsen-Olesen''''s String from Chern-Simons Field Theory

We study the topology of Nielsen-Olesen's local field theory of single dual string. Based on the Chern-Simons field theory in three dimensons, we find many strings that can form world sheets in four dimensions. These strings have important relation to the zero point of the complex scalar field. These world sheets of strings can be expressed by the topological invariant number, Hopf index, and Brower degree. Nambu-Goto's action is obtained from the Nielsen's action definitely by using o-mapping theory.