摘要:

Following recent results from the Super-Kamiokande experiment, we reexamine the decaying neutrino hypothesis of Sciama, including for the first time the effects of absorption by intergalactic dust. We find that the theory can (likely) be ruled out on observational grounds. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301588

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Although many people have thought that the difference between the Copenhagen and many-worlds versions of quantum theory was merely metaphysical, quantum cosmology may allow us to make a physical test to distinguish between them empirically. The difference between the two versions shows up when the various components of the wavefunction have different numbers of observers and observations. In the Copenhagen version, a random observation is selected from the sample within the component that is selected by wavefunction collapse, but in the many-worlds version, a random observation is selected from those in all components. Because of the difference in the samples, probable observations in one version can be very improbable in the other version. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301589

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

It is well known that in four or more dimensions, there exist exotic manifolds; manifolds that are homeomorphic but not diffeomorphic to each other. This is in contrast to the uniqueness of the differentiable structure on manifolds in one, two and three dimensions. As exotic manifolds are not diffeomorphic, one can argue that functional integrals for gravity should include a sum over not only physically distinct geometries and topologies but also inequivalent differentiable structures. But can the inclusion of exotic manifolds in such sums make a significant contribution to these quantum amplitudes? In a word, yes. Simply connected exotic Einstein manifolds with positive curvature exist in seven dimensions. Their metrics are found numerically; they are shown to have volumes of the same order of magnitude. Their contribution to the semiclassical evaluation of the partition function for Euclidean quantum gravity in seven dimensions is evaluated and found to be nontrivial. Consequently, inequivalent differentiable structures should be included in the formulation of sums over histories for quantum gravity. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301590

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

A fundamental problem with attempting to quantize general relativity is its perturbative non-renormalizability. However, this fact does not rule out the possibility that non-perturbative effects can be computed, at least in some approximation. We outline a quantum field theory calculation, based on general relativity as the classical theory, which implies a phase transition in quantum gravity. The order parameters are composite fields derived from spacetime metric functions. These are massless below a critical energy scale and become massive above it. There is a corresponding breaking of classical symmetry. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301591

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

A process of operator replacement leads to a generalization of Schrodinger’s equation to curved space-time, linking general relativity and quantum mechanics in a natural way. This fourth-order equation, which reduces and specializes to the Klein-Gordon equation in the flat space limit, must be solved in tandem with the Einstein field equations with suitable stress-energy. The flat space propagator, for large momenta, varies as1/p4,meaning that divergences should be less problematic than in standard theories. Approximate solutions can be obtained for static, spherically-symmetric scalar fields. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301592

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

After discussing the role of time in both General Relativity and Quantum Gravity, it is argued that even in ordinary Quantum Mechanics, the role of time is ambiguous. A rather surprising result is that measurements of the time-of-arrival of a free particle must always be more inaccurate than1/EwhereEis the kinetic energy of the particle. This inaccuracy is not related to the Heisenberg uncertainty relations. It is a dynamical relation which applies to individual measurements of a single quantity. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301593

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We define gravitational mass in asymptotically de Sitter space-times with compactified dimension. We give simple examples with negative energy in higher dimensions. They do not have the lower bound on the mass. We also give a positive energy argument in higher dimensions and realize that elementary fermion cannot exist in our examples. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301594

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

In a wide class of four-dimensional spacetimes which are direct or semidirect products of a homogeneousn-dimensional space and a(4−n)-dimensional space, a field can be decomposed into modes. As a result of this mode decomposition, the main objects which characterize the free quantum field, such as Green functions and heat kernels, can effectively be reduced to objects in a(4−n)-dimensional spacetime with an external dilaton field. We study the problem of the dimensional reduction of the effective action for such spacetimes. While before renormalization the original four-dimensional object can be presented as a “sum over modes” of(4−n)-dimensional objects, this property is violated after renormalization. We calculate the corresponding anomalous terms and relate their origin with the effect of the multiplicative anomaly. This effect is demonstrated with some simple examples. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1303047

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The definition of particle rest mass in a 5D space, like the definition of mass in 4D general relativity, is difficult. We review 6 alternatives. It is plausible that the mass of a particle derives from the geometry of a 4D space embedded in a 5D space, and that the Klein-Gordon equation of 4D quantum theory is a wave equation in a conformal factor of 5D Kaluza-Klein theory. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301595

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We show that the assumption of 5D null particle trajectories in five-dimensional Kaluza-Klein gravity can correspond to either four-dimensional massive or null trajectories when the parameterization is chosen properly. We retain the extra-coordinate dependence in the metric and show the possibility of a cosmological variation in the rest masses of particles, and a consequent departure from 4D geodesic motion by a fifth force. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301596

出版商:AIP    

年代:1999

数据来源: AIP