Bosonic string theories with new boundary conditions

We show that the classical Nambu-Goto string inD dimensions admits Poincaré invariance ind dimensions (d⩽D) if (i)d − 2 of the transverse co-ordinatesx ⁱ are periodic and the rest quasi-periodic involving a real orthogonal matrix with (D − d) (D − d − 1)/2 free parameters, or if (ii)d − 2 ofx ⁱ obey Neumann and the rest obey a boundary condition involvingN free parameters, whereN=(D − d)²/2 ifD − d is even, andN=[(D − d)² − 1]/2 ifD − d is odd.     

Schwarzschild geometry,once more

Schwarzschild geometry exhibits interesting features when the field equations are decomposed with respect to a system of freely falling observers. We only use quantities behaving like tensors under a restricted group of transformations of the reference system. Moreover Lorentz transformations with non-constant velocities drastically change the physical picture of the theory.     

Conformal scalar propagation on the Schwarzschild black-hole geometry

The vacuum activity generated by the curvature of the Schwarzschild black-hole geometry close to the event horizon is studied for the case of a massless, conformal scalar field. The associated approximation to the unknown, exact propagator in the Hartle–Hawking vacuum state for small values of the radial coordinate above r = 2M results in an analytic expression which manifestly features its dependence on the background space–time geometry. This approximation to the Hartle–Hawking scalar propagator on the Schwarzschild black-hole geometry is, for that matter, distinct from all other. It is shown that the stated approximation is valid for physical distances which range from the event horizon to values which are orders of magnitude above the scale within which quantum and backreaction effects are comparatively pronounced. An expression is obtained for the renormalised \({ \langle\phi^2(x)\rangle}\) in the Hartle–Hawking vacuum state which reproduces the established results on the event horizon and in that segment of the exterior geometry within which the approximation is valid. In contrast to previous results the stated expression has the superior feature of being entirely analytic. The effect of the manifold’s causal structure to scalar propagation is also studied.     

Optical appearance of the Schwarzschild black hole in the string cloud context

The image of a black hole(BH) consists of direct and secondary images that depend on the observer position. We investigate the optical appearance of a Schwarzschild BH in the context of a string cloud to reveal how the BH’s observable characteristics are influenced by the inclination angle, string cloud parameter, and impact parameter. Following Luminet’s work [Astron. Astrophys. 75, 228(1979)], we adopt a semi-analytic method to calculate the total bending angle of the light ray and derive the ...     

Lorentz invariance of lightcone string field theory: (I). Bosonic closed string

We construct the Lorentz generators for bosonic closed lightcone string field theory with cubic interactions, and prove that the Lorentz algebra closes if the spacetime dimension is 26.     

Geodesic motions in extraordinary string geometry

The geodesic properties of the stationary vacuum string solution in (4+1) dimensions with momentum flow along the string direction are analyzed by using Hamilton-Jacobi method. The geodesic motions show distinct properties from those of the static one. Especially, any freely falling particle can not arrive at the horizon or singularity. To get into the horizon, a particle need to follow a non-geodesic trajectory. There exist stable null circular orbits and bouncing timelike and null geodesics. In the asymptotic geometry, some geodesics will be repelled by the string contrary to the case of Kerr-Neumann black hole. The light bending effect will be minimized at an impact parameter determined by the angular momentum and energy.     

Higher-dimensional string theory in Lyra geometry

In this paper, a study on string theory has been done in five-dimensional space-time based on Lyra geometry. Also a polynomial relation between the two scale factors is assumed. The equations of state for strings have been used for different solutions     

Superconformal geometry and string theory

We give a formula for the determinant of the super Laplace operator in a holomorphic hermitian line bundle over a superconformal manifold. This is then used to obtain an expression for the fermion string measure.     

Non-commutative geometry and the closed bosonic string

We propose an action for an interacting closed bosonic string. Our formalism relies heavily on ideas discussed by Witten for the open bosonic string. We also obtain the gauge fixed quantum action for the fully interacting open bosonic string.     

The gravitational searchlight effect from synchrotron radiation in the Schwarzschild geometry

Gravitational synchrotron radiation is studied using the techniques of geometrical optics. It is found that the geometry of the Schwarzschild black hole creates a rotating searchlight effect, even for a source particle which radiates only during an infinitesimally brief interval of coordinate time. The period of rotation of the searchlight is shown to provide a measurement of the mass of the blackhole, since the period T is related to the mass M by T = 2π27^1/2 M for the Schwarzschild geometry and by T = 4πM for the extreme (a = M) Kerr geometry.     

An approximation scheme for scalar waves in a Schwarzschild geometry

The Schwarzschild geometry is approximated by a certain set of conformally flat shells. As an example of the use of this approximation, the transmission coefficientT for spherical waves of monochromatic scalar radiation imploding on the black hole is calculated by solving the scalar wave equation within each conformally flat space and matching across the interfaces. The results agree with those of other authors for low and high frequencies and give values ofT at all intermediate frequencies.This work was supported by the National Research Council of Canada.     

Bianchi-IX string cosmological model in Lyra geometry

A class of cosmological solutions of massive strings for the Bianchi-IX space-time are obtained within the framework of Lyra geometry. Various physical and kinematical properties of the models are discussed     

Conformal geometry and string field theory

The covariant perturbation theory rules that should arise from any gauge invariant string field theory, such as those proposed on the basis of BRST formalism, are set forth. The resulting path integral expressions naturally produce coordinate invariant densities on the moduli space of Riemann surfaces; these include the Koba-Nielsen amplitudes. The connection between string field theory and modular invariance is discussed, and it is proposed that future explorations in string field theory focus on coordinate invariant quantities on moduli space.     

Non-commutative geometry and string field theory

An attempt is made to interpret the interactions of bosonic open strings as defining a non-cummulative, associative algebra, and to formulate the classical non-linear field theory of such strings in the language of non-commulative geometry. The point of departure is the BRST approach to string field theory. A setting is given in which there is a unique gauge invariant action, whose linearized approximation reproduces the conventional Veneziano spectrum. A derivation of conventional Veneziano model amplitudes from this gauge invariant action is sketched. Some brief comments are made about attempts to extend these results to open superstrings and to closed strings.     

Classical geometry of bosonic string dynamics

We develop a treatment of bosonic strings on a general curved background in which the volume element and the coordinates of the worldsheet are related in a similar way as canonically conjugate quantities in mechanics. The resultant formalism is a particular variant of the multi-phase-space approach to classical field theory put forward by Kijowski, Tulczyjew, and others. We study conservation laws within this framework and find that all conserved quantities are related to point symmetries, i.e., isometries of the underlying spacetime. Thus, the symmetries of relativistic mechanics coming from Killing tensors have no analogue here. We furthermore deduce from the present scheme the covariant version of the usual phase space.