Kalb-Ramond Background Research Articles

Tensionless strings in a Kalb-Ramond background

We investigate tensionless (or null) bosonic string theory with a Kalb-Ramond background turned on. In analogy with the tensile case, we find that the Kalb-Ramond field has a non-trivial effect on the spectrum only when the theory is compactified on an (S1)⊗d background with d ≥ 2. We discuss the effect of this background field on the tensionless spectrum constructed on three known consistent null string vacua. We elucidate further on the intriguing fate of duality symmetries in these classes of string theories when the background field is turned on.

Nonrelativistic Expansion of Closed Bosonic Strings.

We develop a novel approach to nonrelativistic closed bosonic string theory that is based on a string 1/c^{2} expansion of the relativistic string, where c is the speed of light. This approach has the benefit that one does not need to take a limit of a string in a near-critical Kalb-Ramond background. The 1/c^{2}-expanded Polyakov action at next-to-leading order reproduces the known action of nonrelativistic string theory provided that the target space obeys an appropriate foliation constraint. We compute the spectrum in a flat target space, with one circle direction that is wound by the string, up to next-to-leading order and show that it reproduces the spectrum of the Gomis-Ooguri string.

Curvature and thermal corrections in tree-level CPT-Violating Leptogenesis

In a model for leptogenesis based on spontaneous breaking of Lorentz and mathcal {CPT} symmetry [1–3], we examine the consistency of using the approximation of plane-wave solutions for a free spin-frac{1}{2} Dirac (or Majorana) fermion field propagating in a Friedmann–Lemahat{mathrm{i}}tre–Robertson–Walker space time augmented with a cosmic time-dependent (or, equivalently, a temperature-dependent) Kalb–Ramond (KR) background. For the range of parameters relevant for leptogenesis, our analysis fully justifies the use of plane-wave solutions in our study of leptogenesis with Boltzmann equations; any corrections induced by space-time-curvature are negligible. We also elaborate further on how the lepton asymmetry is communicated to the Baryon sector. We demonstrate that the KR background (KRB) does not contribute to the anomaly equations that determine the baryon asymmetry (a) through an explicit evaluation of a triangle Feynman graph and (b) indirectly, on topological grounds, by identifying the KRB as torsion (in the effective string-inspired low energy gravitational field theory).

Effective action of a dynamical Dp-brane with background fluxes

We shall construct the Dirac-Born-Infeld like and the Wess–Zumino like actions for a dynamical Dp-brane with the U(1) gauge potential and the Kalb–Ramond background field. The brane dynamics simultaneously has both tangential and transverse components. Our calculations will be in the context of the type II superstring theory, via the boundary state formalism.

Pseudoscalar Fields in Torsionful Geometries of the Early Universe, the Baryon Asymmetry and Majorana Neutrino Mass Generation

We discuss here a specific field-theory model, inspired from string theory, in which the generation of a matter-antimatter asymmetry in the Cosmos is due to the propagation of fermions in a non-trivial, spherically asymmetric (and hence Lorentz violating) gravitational background that may characterise the epochs of the early universe. The background induces different dispersion relations, hence populations, between fermions and antifermions, and thus CPT Violation (CPTV) already in thermal equilibrium. Species populations may freeze out leading to leptogenesis and baryogenesis. More specifically, after reviewing some generic models of background-induced CPTV in early epochs of the Universe, we consider a string- inspired scenario, in which the CPTV is associated with a cosmological background with torsion provided by the Kalb-Ramond (KR) antisymemtric tensor field of the string gravitational multiplet. In a four-dimensional space time this field is dual to a pseudoscalar “axion-like” field. The thermalising processes in this model are (right-handed) Majorana neutrino-antineutrino oscillations, which are induced in the presence of the KR axion background. These processes freeze out at a (high) temperature Tc ≫ m, where m is the Majorana neutrino mass, at which the KR background goes to zero or is diminished significantly, through appropriate phase transitions of the (string) universe. An additional, but equally important, role, of the KR field is that its quantum fluctuations and mixing with an ordinary axion, which couples to the Majorana neutrinos via appropriate Yukawa couplings, can also lead to the generation of a Majorana neutrino mass through quantum anomalies. This provides a novel way for generating neutrino masses, independent of the traditional seesaw mechanism.

Open and closed string vertices for branes with magnetic field and T-duality

We discuss carefully the vertices which describe the dipole open strings and closed strings on a D-brane with magnetic flux on a torus. Translation invariance along closed cycles forces surprisingly closed string vertices written in open string formalism to acquire Chan-Paton like matrices. Moreover the one loop amplitudes have a single trace for the part of gauge group with the magnetic flux. These peculiarities are also required by consistency of the action of T-duality in the open string sector. In this way we can show to all orders in perturbation theory the equivalence of the T-dual open string theories, gravitational interactions included. We provide also a new and direct derivation of the bosonic boundary state in presence of constant magnetic and Kalb-Ramond background based on Sciuto-Della Selva-Saito vertex formalism.

A comment on discrete Kalb–Ramond field on orientifold and rank reduction

We show that the rank reduction of the gauge group on orientifolds in presence of non-vanishing discrete Kalb–Ramond field can be explained by the presence of an induced field strength in a non-trivial bundle on the branes. This field strength is also necessary for the tadpole cancellation and the number of branes is left unchanged by the presence of the discrete Kalb–Ramond background. We moreover give a derivation of the normalization of the Möbius amplitude in presence of a non-vanishing Kalb–Ramond field from first principles.

Kalb-Ramond field interactions in a braneworld scenario

Electromagnetic and (linearized) gravitational interactions of the Kalb-Ramond (KR) field, derived from an underlying ten dimensional heterotic string in the zero slope limit, are studied in a five dimensional background Randall-Sundrum I spacetime with standard model fields confined to the visible brane having negative tension. The warp factor responsible for generating the gauge hierarchy in the Higgs sector is seen to appear inverted in the KR field couplings, when reduced to four dimensions. This leads to dramatically enhanced rotation, {\it far beyond observational bounds}, of the polarization plane of electromagnetic and gravitational waves, when scattered by a homogeneous KR background. Possible reasons for the conflict between theory and observation are discussed.

A Study of a Global Monopole in Kalb–Ramond Background

An exact solution around a global monopole resulting from the breaking of a global S0(3) symmetry in Kalb–Ramond background is found. The monopole exerts no gravitational force on non-relativistic matter, but the space around it has a deficit solid angle.

Semi classical gravitational effects around global monopole in Kalb-Ramond background

The problem of semiclassical gravitational effects of globalmonopole in Kalb-Ramond backgroundinvestigated. It is shown that the monopoleexerts repulsive gravitational force on nonrelativistic matter and space around it hasa deficit solid angle.

GRAVITATIONAL FIELD OF A GLOBAL MONOPOLE IN KALB–RAMOND BACKGROUND

The problem of global monopole in Kalb–Ramond background is investigated. A comparison is made with the corresponding results predicted by general relativity.

Global Monopole in Kalb–Ramond Background

In recent, S. SenGupta and S. Sur [Phys. Lett. B 502 (2001) 350] have obtained static vacuum solutions of the gravitational field equations in back ground space time with torsion. The torsion is identified with the field strength of a second-rank anti-symmetric tensor field, namely Kalb-Ramond field. In this work, we present the solutions for the metric outside a monopole resulting from the breaking of a global 0(3) symmetry in Kalb-Ramond background. A comparison is made with the corresponding results predicted by general relativity.

Exact string solutions in nontrivial backgrounds

We show how the classical string dynamics in a D-dimensional gravity background can be reduced to the dynamics of a massless particle constrained on a certain surface whenever there exists at least one Killing vector for the background metric. We obtain a number of sufficient conditions, which ensure the existence of exact solutions to the equations of motion and constraints. These results are extended to include the Kalb-Ramond background. The $D1$-brane dynamics is also analyzed and exact solutions are found. Finally, we illustrate our considerations with several examples in different dimensions. All of this also applies to the tensionless strings.

Spherically symmetric solutions of gravitational field equations in Kalb–Ramond background

Static spherically symmetric solutions in a background spacetime with torsion is derived explicitly. The solutions are shown to possess interesting features like ‘wormholes’ or ‘naked singularity’ in spacetime. The torsion considered here is identified with the field strength of a second rank antisymmetric tensor field namely the Kalb–Ramond field and the proposed solution therefore has much significance in a string inspired gravitational field theory.

P-BRANES, POISSON-SIGMA MODELS AND EMBEDDING APPROACH TO (p+1)-DIMENSIONAL GRAVITY

A generalization of the embedding approach for d-dimensional gravity based upon p-brane theories is proposed. We prove that the D-dimensional p-brane coupled to an antisymmetric tensor field of rank (p+1) provides the dynamical basis for the description of d=(p+1)-dimensional gravity in the isometric embedding formalism. By that we mean that the equations of motion following from this action describe any (p+1)-dimensional space–time (at least locally) once the antisymmetric tensor field is chosen appropriately. "Physical" matter appears in such an approach as a manifestation of a D-dimensional antisymmetric tensor (generalized Kalb–Ramond) background. For the simplest case, the Lorentz harmonic formulation of the bosonic string in a Kalb–Ramond background and its relation to a first order Einstein–Cartan approach for (d=2)-dimensional gravity is analyzed in some detail. We show that a general Poisson-sigma model structure emerges in this case. For the minimal choice of a free D=3 string an interesting "dual" formulation is found which has the structure of a Jackiw–Teitelboim theory, coupled minimally to a massive scalar field. Our approach is intended to serve as a preparation for the study of d-dimensional supergravity theory, either starting from the generalized action of free supersymmetric (d-1)-branes or D(d-1)-branes, or from the corresponding geometric equations ("rheotropic" conditions).