Configuration of Z2 strings

Vachaspati and Vilenkin's numerical simulation of the configuration of strings produced at a U(1)-breaking phase transition is extended to the Z₂ strings appearing in the breaking of SO(3). The results are similar, but the overall proportion of closed loops is only about a third as large. This may have important implications for the evolution of cosmic strings.     

All free string theories are theories of BRST cohomology

The fully gauge-invariant theory of the free open (super) strings is generalized to treat closed (super) strings in the BRST formalism. It is shown that the actions for all theories can be written in the form (Φ,Q_BΦ) using the BRST charge Q_B and the string functional Φ, if the inner product is interpreted appropriately with necessary ghost insertions. Also is shown that consistent truncations of our actions recover all known covariant formulations of (super) strings.     

String cosmology in Bianchi type-VI0 dusty Universe with electromagnetic field

In this paper, the effect of electromagnetic field in the string Bianchi type-VI₀ Universe is investigated. Einstein’s field equations have been solved exactly with suitable physical assumptions for two types of strings: (i) massive strings and (ii) Nambu strings. It is found that when the Universe is dominated by massive strings, the existence of electromagnetic field is necessary as it accelerates the expansion of the Universe. But when our Universe is dominated by Nambu strings, the electromagnetic field does not have significant effect on the evolution of the Universe. We have also shown that the early massive string-dominated Universe got converted to Nambu string-dominated Universe later. Our models are derived from an early deceleration phase to an accelerating phase which is consistent with the recent observations of supernovae type-Ia. The physical and geometrical behaviour of these models are also discussed.     

Interactions of non-Abelian global strings

Non-Abelian global strings are expected to form during the chiral phase transition. They have orientational zero modes in the internal space, associated with the vector-like symmetry SU_(N)L+R$\mathit{SU}{(N)}_{\mathrm{L}+\mathrm{R}}$ broken in the presence of strings. The interaction among two parallel non-Abelian global strings is derived for general relative orientational zero modes, giving a non-Abelian generalization of the Magnus force. It is shown that when the orientations of the strings are the same, the repulsive force reaches the maximum, whereas when the relative orientation becomes the maximum, no force exists between the strings. For the Abelian case we find a finite volume correction to the known result. The marginal instability of the previously known Abelian η^′${\eta }^{\prime }$ strings is discussed.     

In situ Video-STM study of the potential-induced (1 × 1) → “hex” transition on Au(1 0 0) electrode surfaces in Cl containing solution

The potential-induced (1 × 1) → “hex” transition on Au(1 0 0) electrodes in 0.01 M Na₂SO₄ + 1 mM HCl was studied by in situ scanning tunneling microscopy at high time resolution (Video-STM). According to these observations the elementary units of the “hex” surface reconstruction, hexagonally-ordered strings in the Au surface layer, are highly dynamic nanoscale objects. Isolated “hex” strings exhibit dynamic fluctuations in structure and position on the millisecond timescale. These fluctuations exceed the mobility of multistring “hex” domains by several orders of magnitude and can be explained by collective dynamic processes within the strings. Furthermore, the observations reveal a novel 1D mass transport mechanism along the strings, details on the nucleation and growth of “hex” strings and complex string restructuring processes, facilitating “hex” domain ripening.     

Review of AdS/CFT Integrability,Chapter II.2: Quantum Strings in AdS<Subscript>5</Subscript> × S<Superscript>5</Superscript>

We review the semiclassical analysis of strings in AdS₅ × S⁵ with a focus on the relationship to the underlying integrable structures. We discuss the perturbative calculation of energies for strings with large charges, using the folded string spinning in AdS₃ ? AdS₅ as our main example. Furthermore, we review the perturbative light-cone quantisation of the string theory and the calculation of the worldsheet S-matrix.     

Bianchi Types V and VI<Subscript>0</Subscript> Cosmic Strings Coupled with Maxwell Fields in Bimetric Theory

Spatially homogeneous Bianchi types V and VI₀ cosmological models are studied with source cosmic cloud strings coupled with electromagnetic field in Rosen’s (Gen. Relativ. Gravit. 4:435, 1973) bimetric theory of relativity. It is observed that Bianchi type V space time is feasible whereas Bianchi type VI₀ is not feasible. In the feasible case different equations of state for cosmic strings with Maxwell fields do not survive in this theory and the space-time turns out to be flat.     

Universal behavior of transverse momentum distributions of baryons and mesons in the framework of percolation of strings

In the framework of percolation of strings, the transverse momentum distributions in AA and hh collisions at all centralities and energies show a universal behavior. The width of these distributions is related to the width of the distribution of the size of the clusters formed by the overlapping of the strings produced. The difference between the distributions for baryons and mesons originates in the fragmentation of clusters of several strings, which enhances the particles with a higher number of constituents. The results agree with SPS and RHIC data. The predictions for LHC show differences for baryons compared with RHIC. At LHC energies we obtain also a high p_T suppression for pp high multiplicity events compared with the pp minimum bias. PACS 25.75.Nq; 12.38.Mh; 24.85.+p     

A non-perturbative study of regularized bosonic string amplitudes

The Wick-rotated, light-cone gauge U(n) Veneziano model of open and closed strings is examined in the limit as n → ∞, with g₀²n fixed. The amplitudes in both the “pomeron sector” (whose graphs are cylinders with holes punched out) and the “reggeon sector” (whose graphs are rectangles with holes punched out) are regularized using the lattice method of Giles and Thorn, as well as an alternative method. It is found that this string model is trivial. When the cut-off is removed, the pomeron and reggeon sector spectra are those of the free closed and open strings, respectively. This result is independent of the choice of g₀²n. A possible extension to fermionic strings, and the implications for large-n gauge theories are briefly discussed.     

A physical interpretation of the Jacobi imaginary transformation and the critical dimension in dual models

It is shown that the Jacobi imaginary transformation occuring in dual loop calculations may be interpreted as a self-consistency condition obtained by assuming a complicated planar Feynman diagram formulation for strings. The self-consistency condition is derived from the intuitive condition that a “fishnet-diagram” does not change if a free side of the diagram is replaced by the wave function for a string with vacuum quantum numbers. When applying the self-consistency condition to strings for which the spectrum is built up by harmonic oscillators it is seen that the condition is only fulfilled when the number of coupling dimensions is 24 · α₀ where α₀ is the intercept.     

Strings in Gravity with Torsion

A theory of gravitation in 4D is presented with strings used in the material action in U ₄ spacetime. It is shown that the string naturally gives rise to torsion. It is also shown that the equation of motion a string follows from the Bianchi identity, gives the identical result as the Noether conservation laws, and follows a geodesic only in the lowest order approximation. In addition, the conservation laws show that strings naturally have spin, which arises not from their motion but from their one dimensional structure.     

Self-gravitating general-relativistic cosmic strings

We examine the coupled Einstem-Euler-Lagrange equations for nonstationary cosmic strings. Self-consistent solutions to all the equations are found under the assumption that the energy-momentum tensor is of the formT _t ^t =T _z ^z while all other components vanish. It is shown that the strings are necessarily static in this case and that the scalar field potential must be of the usual quartic form with the coupling constants satisfying e²=8.     

Axion cosmology in automatic E6 × U(1) models

An automatic E₆ × U(1) axion model is constructed which is cosmologically consistent, predicts three families of fermions at low energies, and admits cosmic strings capable of seeding galaxy formation.     

Homotopy Algebras Inspired by Classical Open-Closed String Field Theory

We define a homotopy algebra associated to classical open-closed strings. We call it an open-closed homotopy algebra (OCHA). It is inspired by Zwiebach's open-closed string field theory and also is related to the situation of Kontsevich's deformation quantization. We show that it is actually a homotopy invariant notion; for instance, the minimal model theorem holds. Also, we show that our open-closed homotopy algebra gives us a general scheme for deformation of open string structures (A_∞-algebras) by closed strings (L_∞-algebras). H. K is supported by JSPS Research Fellowships for Young Scientists. J. S. is supported in part by NSF grant FRG DMS-0139799 and US-Czech Republic grant INT-0203119.     

The ferroelectric phase transition in tridymite type BaAL2O4 studied by electron microscopy

The paraelectric-ferroelectric (PE-FE) phase transition in stuffed tridymite BaAl₂O₄ was studied in situ by transmission electron microscopy. Electron diffraction revealed that the PE and FE phases have hexagonal symmetry. The PE-FE phase transition is accompanied by a doubling of the cell dimensions in the a-b plane. The transition is reversible, takes place over a wide temperature range (400–670 K.) and the interfaces related to the transition have a fluctuating character. The crystal structure of the high temperature PE phase was determined by high resolution electron microscopy. The structures of the PE phase (space group P6₃22, a≈ 5.22 Å, c ≈ 8.8 Å) and of the FE phase (space group P6₃, a= 10.4469(1)Å, c = 8.7927(1)Å) differ mainly by the configuration of the Al-O strings oriented along the c-axis. In the PE phase all the strings are equivalent whereas straight and corrugated strings alternate in an ordered manner in the FE phase resulting in doubling of the a and b cell parameters. Translation and orientation domains due to the decrease of the translation and point symmetry were frequently observed.     

String-like topological excitations of the electromagnetic field

In order to analyze the topological properties of an arbitrary configuration of the electromagnetic field, its strength F_μν is expressed in terms of new auxiliary fields which replace the gauge potential A_μ. These new fields have only physical singularities even in the presence of monopoles (no Dirac strings) and exhibit a new local O(1, 1) symmetry which replaces the gauge invariance. Boundary conditions on these fields may induce localized string-like singularities or topological defects which act as sources of magnetic field. A typical defect which emerges is a sort of tadpole formed by a non-quantized monopole attached to one or more magnetic strings of finite length. For topological reasons the total magnetic charge is quantized.     

Entanglement entropy in Abelian gauge theories

The definition of geometric entanglement entropy associated with some region in space is discussed for the case of gauge theories. It is argued that since in gauge theories elementary excitations look like loops (closed electric strings) rather than points (particles), the boundaries of the regions should also carry some nonzero entropy. This entropy counts the number of strings which cross these boundaries. Explicit calculations of such entropy are carried out in the limits of infinitely strong and weak couplings of three- and four-dimensional Z _N gauge theories. In three dimensions we find that the entropy is a constant which does not depend on the region, while in four dimensions the familiar area law for the entropy is recovered.     

On the evolution of global strings in the early universe

We find that a bent global string straightens itself out by dissipation into Nambu-Goldstone (NG) bosons in the order of one oscillation time and that the spectrum of radiated NG bosons is 1/k. In the early universe, the assumption that there is one global string per causal horizon is justified after an initial period during which the effect of the primordial plasma on the motion of the strings is non-negligible. We find that the upper bound that axion radiation by strings places on the axion decay constant is comparable to, but not more stringent than the one derived from coherent oscillations of the axion field, i.e. ∫_a ≲ 10¹²GeV. We also discuss the model-dependence of this bound.     

Dynamics of vacuum excitations and quark confinement in quantum field theories

A unified approach to interacting vacuum excitations and quark confinement is formulated in quantum field theories with symmetry breakdown. Vacuum excitations are shown to be coherent clouds of Goldstone bosons or gauge bosons and are interpreted as new asymptotic extended particle states. They correspond to all dynamically possible space-time dependent Bose condensations of the Goldstone bosons in a given theory. Different configurations of vacuum excitations are connected to one another by a family of invariant boson transformations. As an example, the Nambu theory of interacting vortex strings is derived from a Nambu-Heisenberg quark-gluon field theory. The quarks can be completely confined to the strings while the gluons cluster in quantized magnetic flux bundles of penetration width m_v^?1 and provide a short range interaction force.     

Critical String Wave Equations and the QCD(U(Nc)) String. (Some Comments)

We present a simple proof that self-avoiding fermionic strings solutions solve formally (in a Quantum Mechanical Framework) the QCD(U(N _c )) Loop Wave Equation written in terms of random loops.