摘要:

This is the first of a two-part contribution devoted to the evolution of a massless scalar field in various black-hole spacetimes; the second part follows this one and is authored by William G. Laarakkers. In this contribution we consider the evolution of a scalar field propagating in Schwarzschild-de Sitter spacetime. The field is non-minimally coupled to curvature through a coupling constant &xgr;. The spacetime possesses a cosmological horizon in addition to the usual event horizon. The presence of this new horizon affects the late-time evolution of the scalar field: The usual inverse power-law decay of pure Schwarzschild spacetime is replaced by a faster, exponential decay. The decay constant is proportional to the surface gravity of the cosmological horizon, and depends on the field’s multipole orderland the constant &xgr;. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301578

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

In part II of this talk the evolution of a massless scalar field in Schwarzschild-Einstein-de Sitter spacetime is studied numerically. The spacetime has two distinct regions: an inner black-hole region and an outer cosmological region. Early on in the evolution the field behaves as if it were in pure Schwarzschild spacetime, with each multipole of the field first exhibiting quasi-normal ringing followed by a power-law decay. However, later in the evolution the field learns of the existence of the cosmological region and changes behavior. For thel=0mode, the field first changes sign due to the discontinuous negative potential at the boundary. The field then decays again with a power-law falloff, but with a slower decay rate than in the pure Schwarzschild case. For thel>0modes of the field the potential at the boundary is discontinuous and positive. The field therefore encounters a potential barrier at the boundary, and the part of the field that is reflected back from the barrier gives rise to an echo of its earlier quasi-normal oscillations. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301579

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Spherically symmetric Black Holes of the Vaidya type are examined in an asymptotically de Sitter, higher dimensional spacetime. The various horizons are identified and located. The structure and dynamics of such horizons are studied. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301580

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301581

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Boundary conditions defining anon-rotating isolated horizonare given in Einstein-Maxwell theory. A spacetime representing a black hole which itself is in equilibrium but whose exterior contains radiation admits such a horizon. Inspired by Hamiltonian mechanics, a (quasi-)local definition of isolated horizon mass is formulated. Although its definition does not refer to infinity, this mass takes the standard value in a Reissner-Nordstro¨m solution. Furthermore, under certain technical assumptions, the mass of an isolated horizon is shown to equal the future limit of the Bondi energy. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301582

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We extend the Brown and York notion of quasilocal energy to include coupled electromagnetic and dilaton fields and also allow for spatial boundaries that are not orthogonal to the foliation of the spacetime. We investigate how the quasilocal quantities measured by sets of observers transform with respect to boosts. As a natural application of this work we investigate the naked black holes of Horowitz and Ross calculating the quasilocal energies measured by static versus infalling observers. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301583

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

In this talk recent developments of the theory of preheating after inflation are briefly reviewed. In inflationary cosmology, the particles constituting the Universe are created after inflation due to their interaction with moving inflaton field(s) in the process of reheating. In inflationary models motivated by supergravity, both bosons and fermions are created. In the bosonic sector, the leading channel of particle production is the non-perturbative regime of parametric resonance dominated by those bosons which are created exponentially fast with the largest characteristic exponent. In the fermionic sector, the leading channel corresponds to the regime of parametric excitation of fermions, which respects Pauli blocking but differs significantly from the perturbative expectation. In supergravity we also have to consider production of gravitinos and moduli fields, which are cosmologically dangerous relics. We discuss the derivation of the gravitino equations in curved space-time with moving background scalars. We describe recent results on the production of gravitinos from preheating, which may put strong constraints on the inflationary models. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301584

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The possibility of mass in the context of scale-invariant, generally covariant theories, is discussed. Scale invariance is considered in the context of a gravitational theory where the action, in the first order formalism, is of the formS=∫L1&Fgr;d4x+∫L2−gd4xwhere &Fgr; is a density built out of degrees of freedom independent of the metric. For global scale invariance, a “dilaton” &fgr; has to be introduced, with non-trivial potentialsV(&fgr;)=f1e&agr;&fgr;inL1andU(&fgr;)=f2e2&agr;&fgr;inL2.This leads to non-trivial mass generation and a potential for &fgr; which is interesting for new inflation. Scale invariant mass terms for fermions lead to a possible explanation of the present day accelerated universe and of cosmic coincidences. Although the scale symmetry is spontaneously broken there is no Goldstone boson. This surprising effect is due to the fact that in spite of the fact that there is a locally conserved current, no globally conserved dilatation charge exists due to the singular infrared behavior of the spatial components of such a current. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301585

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We show that it is not possible in the absence of dark matter to construct a four-dimensional metric that explains galactic observations. In particular, by working with an effective potential it is shown that a metric which is constructed to fit flat rotation curves in spiral galaxies leads to the wrong sign for the bending of light i.e. repulsion instead of attraction. Hence, without dark matter the motion of particles on galactic scales cannot be explained in terms of geodesic motion on a four-dimensional metric. This reveals a new bright side to dark matter: it is indispensable if we wish to retain the cherished equivalence principle. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301586

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We consider the idea of replacing the gravitational constantGby a function depending on the surrounding medium and whose variation would be noticeable on the galactic scale. Such a function in newtonian dynamics allows one to explain the flat region of the rotation velocity curves of many galaxies, without the dark matter hypothesis. This study is done within a unified field theory of the Kaluza-Klein type where we give an interpretation of gravitation which includes general relativity. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1301587

出版商:AIP    

年代:1999

数据来源: AIP