Graviton Field Research Articles

Gravitational waves in open de Sitter space

We compute the spectrum of primordial gravitational wave perturbations in open de Sitter spacetime. The background spacetime is taken to be the continuation of an O(5) symmetric instanton saddle point of the Euclidean no boundary path integral. The two-point tensor fluctuations are computed directly from the Euclidean path integral. The Euclidean correlator is then analytically continued into the Lorentzian region where it describes the quantum mechanical vacuum fluctuations of the graviton field. Unlike the results of earlier work, the correlator is shown to be unique and well behaved in the infrared. We show that the infrared divergence found in previous calculations is due to the contribution of a discrete gauge mode inadvertently included in the spectrum.

Cosmological solutions,p-branes, and the Wheeler-DeWitt equation

The low energy effective actions which arise from string theory or $M$-theory are considered in the cosmological context, where the graviton, dilaton and antisymmetric tensor field strengths depend only on time. We show that previous results can be extended to include cosmological solutions that are related to the ${E}_{N}$ Toda equations. The solutions of the Wheeler-DeWitt equation in minisuperspace are obtained for some of the simpler cosmological models by introducing intertwining operators that generate canonical transformations which map the theories into free theories. We study the cosmological properties of these solutions, and also briefly discuss generalized Brans-Dicke models in our framework. The cosmological models are closely related to $p$-brane solitons, which we discuss in the context of the ${E}_{N}$ Toda equations. We give the explicit solutions for extremal multi-charge $(D\ensuremath{-}3)$-branes in the truncated system described by the ${D}_{4}=O(4,4)$ Toda equations.

Primordial gravitational waves from open inflation

We calculate the spectrum of gravitational waves generated during inflation in open $({\ensuremath{\Omega}}_{0}<1)$ inflationary models. In such models an initial epoch of old inflation solves the horizon and flatness problems, and during this first epoch of inflation the quantum state of the graviton field rapidly approaches the Bunch-Davies vacuum. Then the old inflation ends by the nucleation of a single bubble, inside of which there is a shortened epoch of slow-roll inflation giving ${\ensuremath{\Omega}}_{0}<1$ today. In this paper we reexpress the Bunch-Davies vacuum for the graviton field in terms of the hyperbolic modes inside the bubble and propagate these modes forward in time into the present era. We derive the expression for the contribution from these gravity waves to the cosmic microwave background anisotropy including the effect of a finite-energy difference across the bubble wall.

Supervisor ICs monitor battery-powered equipment

It has been shown that the quantum state of the graviton field outside a black hole horizon carries information about the internal state of the hole. We explain how this allows unitary evaporation: the final radiation state is a complex superposition which depends linearly on the initial black hole state. Under time reversal, the radiation state evolves back to the original black hole quantum state. Formulations of the information paradox on a fixed semiclassical geometry describe only a small subset of the evaporation Hilbert space, and do not exclude overall unitarity.

Structure of the anomaly in the canonical quantization of bosonic strings in background fields

We consider the anomaly problem in the generalized canonical quantization of a bosonic string interacting with background graviton and antisymmetric tensor fields. We derive an equation for the symbol of the anomaly operator, find a solution to that equation, and establish a general form for the anomaly operator allowed by the quantization procedure.

Quantum theory of nonrelativistic particles interacting with gravity.

We investigate the effects of the gravitational field on the quantum dynamics of non-relativistic particles. We consider N non-relativistic particles, interacting with the linearized gravitational field. Using the Feynman - Vernon influence functional technique, we trace out the graviton field, to obtain a master equation for the system of particles to first order in $G$. The effective interaction between the particles, as well as the self-interaction is non-local in time and in general non-markovian. We show that the gravitational self-interaction cannot be held responsible for decoherence of microscopic particles due to the fast vanishing of the diffusion function. For macroscopic particles though, it leads to diagonalization to the energy eigenstate basis, a desirable feature in gravity induced collapse models. We finally comment on possible applications.

Quantum fluctuations, decoherence of the mean field, and structure formation in the early Universe.

We examine from first principles one of the basic assumptions of modern quantum theories of structure formation in the early Universe, i.e., the conditions upon which fluctuations of a quantum field may transmute into classical stochastic perturbations, which grew into galaxies. Our earlier works have discussed the quantum origin of noise in stochastic inflation and quantum fluctuations as measured by particle creation in semiclassical gravity. Here we focus on decoherence and the relation of quantum and classical fluctuations. Instead of using the rather ad hoc splitting of a quantum field into long and short wavelength parts, the latter providing the noise which decoheres the former, we treat a nonlinear theory and examine the decoherence of a quantum mean field by its own quantum fluctuations, or that of other fields it interacts with. This is an example of how a quantum system can be viewed as effectively open and decoheres through its own dynamics. The model we use to discuss fluctuation generation has the inflaton field coupled to the graviton field. We show that when the quantum to classical transition is propertly treated, with due consideration of the relation of decoherence, noise, fluctuation, and dissipation, the amplitude of density contrast predicted falls in the acceptable range without requiring a fine-tuning of the coupling constant of the inflaton field. The conventional treatment which requires an unnaturally small \ensuremath{\lambda}\ensuremath{\approxeq}${10}^{\mathrm{\ensuremath{-}}12}$ in a \ensuremath{\lambda}${\mathrm{\ensuremath{\Phi}}}^{4}$ inflaton field stems from a basic flaw in naively identifying classical perturbations with quantum fluctuations. \textcopyright{} 1995 The American Physical Society.

Infrared behaviour of the closed bosonic thermal string

The dynamical mass generation of the dilaton, graviton and antisymmetric tensor field is enunciated at any finite temperature in connection with the tachyon self-energy in proper reference to the infrared behaviour of the one-loop thermal cosmological constant in the dimensionally regularized,D=26 closed bosonic thermal string theory within the framework of the thermofield dynamics.

Hidden symmetries of two-dimensional string effective action.

The ten-dimensional heterotic string effective action with graviton, dilaton, and antisymmetric tensor fields is dimensionally reduced to two spacetime dimensions. The resulting theory, with some constraints on backgrounds, admits infinite sequence of conserved nonlocal currents. It is shown that generators of the infinitesimal transformations associated with these currents satisfy the Kac-Moody algebra.

DUALITY OF THE SUPERSTRING IN SUPERSPACE

The evolution of a closed NSR string is considered in the background of constant graviton and antisymmetric fields. The σ-model action is written in a manifestly supersymmetric form in terms of superfields. The first order formalism adopted for the closed bosonic string is generalized to implement duality transformations and the constant dual backgrounds are obtained for the dual theory. We recover the G→G−1 duality for the case when antisymmetric tensor field is set to zero. Next, the case when the backgrounds depend on one superfield, is also analyzed. This scenario is similar to the cosmological case envisaged for the bosonic string. The explicit form of the duality transformation is given for this case.

Thermal matter and radiation in a gravitational field.

We study the one-loop contributions of matter and radiation to the gravitational polarization tensor at finite temperatures. Using the analytically continued imaginary-time formalism, the contribution of matter is explicitly given to next-to-leading ($T^2$) order. We obtain an exact form for the contribution of radiation fields, expressed in terms of generalized Riemann zeta functions. A general expression is derived for the physical polarization tensor, which is independent of the parametrization of graviton fields. We investigate the effective thermal masses associated with the normal modes of the corresponding graviton self-energy.

Graviton self-energy in thermal quantum gravity.

We show generally that in thermal gravity, the one-particle irreducible 2-point function depends on the choice of the basic graviton fields. We derive the relevant properties of a physical graviton self-energy, which is independent of the parametrization of the graviton field. An explicit expression for the graviton self-energy at high-temperature is given to one-loop order.

Macroscopic charged heterotic string

Classical solutions of equations of motion in low-energy effective field theory, describing fundamental charged heterotic string, are found. These solutions automatically carry an electric current equal to the charge per unit length, and hence are accompanied by both electric and magnetic fields. Force between two parallel strings vanishes due to cancellation between electric and magnetic forces, and also between graviton, dilaton and antisymmetric tensor field induced forces. Multi-string solutions describing configuration of parallel strings are also found. Finally, the solutions are shown to possess partially broken space-time supersymmetry.

The effective action for wormholes

There is a strong similarity between space-time wormholes and the multiply connected topology that occurs in one- and two-dimensional quantum field theories, like Feynman diagrams and string theory. Integrating out such topological fluctuations gives rise to a quantum field theory on a topologically trivial manifold with effective interactions whose couplings are given by a-parameters. It is shown that these α-parameters are the moments of a single quantum field α on the superspace of the original theory. In the one-dimensional case, this superspace is space-time, but in higher-dimensional field theories, it will be infinite dimensional. However, the superspace for the string contains space-time as a mini-superspace. The single α-field on superspace can be dimensionally reduced to an infinite tower of fields on space-time. If the tachyon is projected out, the lowest members of this tower are the dilaton, graviton and anti-symmetric tensor fields. In the case of space-time wormholes, the α-field is defined on the superspace of General Relativity. There is a discussion of the implications of this for the suggestion that wormholes uniquely fix the values of the physical constants.

Dynamical mass generation of massless string excitations at zero and finite temperature

We investigate the genus 1 mass shift of the dilaton, graviton, and antisymmetric tensor (Kalb-Ramond) field in the zero temperature closed bosonic string and the type II superstring at finite temperature. We find diltion and antisymmetric tensor field mass generation at the one-loop level. The dynamically generated masses are proportional to the cosmological constant or the free energy at finite temperature. Contrary to previous assertions, the graviton remains massless.

Infrared Behaviour of the Open Bosonic Thermal String

The dynamical mass generation of the dilaton, graviton and antisymmetric tensor field is enunciated at any finite temperature in connection with the tachyon self-energy in proper reference to the infrared behaviour of the one-loop thermal cosmological constant in the dimensionally regularized,D=26 closed bosonic thermal string theory within the framework of the thermofield dynamics.

Confining phase of superstrings and axionic strings.

In the four-dimensional effective field theory of the heterotic superstring compactified on a C.alabi- Yau manifold, we find a new class of spacetime string instantons in the gravity sector that involves graviton, dilaton, and Kalb-Ramond (axion) fields. The instantons satisfy generalized (anti)self-duality equations, and saturate a Bogomolnyi bound provided by the underlying supersymmetry. The instantons lead to several intriguing nonperturbative phenomena to low-energy string theory. A mass gap is generated to the Kalb-Ramond gauge fields, and results in the confinement of superstrings into Kalb-Ramond domain walls below the compactification scale. More interestingly, they provide a new example of the nonperturbative breakdown of the superpotential nonrenormalization theorem. Together with the world-sheet string instantons, this implies that all would-be Peccei-Quinn symmetries that arise in four-dimensional string theories are completely broken around the string compactification scale. Being self-dual, the instantons provide precisely two gravitino zero modes, thus might induce dynamical supersymmetry breaking. We also point out an underlying analogy with the invisible-axionic domain walls bounded by axionic strings.

Renormalization of Polyakov’s two-dimensional quantum gravity

Polyakov’s two-dimensional quantum gravity is analysed in the perturbative approach. The two-dimensional general invariance of the effective action is preserved using the background-field method. Renormalization of the gravitational coupling and redefinition of the graviton field are performed explicitly at the one-loop order. Some interesting aspects (renormalizability, gauge condition, renormalization and β-function of the gravitational coupling, redefinition of the graviton field) are found.

Effective one-loop scalar Lagrangian in no-scale supergravity models.

The total one-loop effective scalar Lagrangian is given in an explicitly field-redefinition-invariant form for a general model with derivative self-couplings of the scalars and scalar couplings to graviton, gauge, and fermion fields. This result is then specialized to no-scale models, with a form of the K\ahler potential that is suggested by the zero-slope limit of superstring theories.

Quantization of reimannian gravity: interaction representation

A Riemann-covariant expression of Schwinger's procedure, leading from a Heisenberg to an interaction representation, completes here our quantization of the coupling of a massive graviton field and a spin-zero Kemmer field.