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R. B. Mann

Publications and source records attributed to R. B. Mann.

At least 163 records · Page 9Linked to original sources
arXiv1996

Canonical reduction of two-dimensional gravity for Particle Dynamics

We develop the formalism for canonical reduction of $(1+1)$--dimensional gravity coupled with a set of point particles by eliminating constraints and imposing coordinate conditions. The formalism itself is quite analogous to the $(3+1)$--dimensional case; however in $(1+1)$ dimensions an auxiliary scalar field is shown to have an important role. The reduced Hamiltonian is expressed as a form of spatial integral of the second derivative of the scalar field. Since in $(1+1)$ dimensions there exists no dynamical degree of freedom of the gravitational field ({\it i.e.} the transverse-traceless part of the metric tensor is zero), the reduced Hamiltonian is completely determined in terms of the particles' canonical variables (coordinates and momenta). The explicit form of the Hamiltonian is calculated both in post-linear and post-Newtonian approximations.

gr-qc↗
arXiv1996

Conserved masses in GHS Einstein and string black holes

We analyze the relationship between quasilocal masses calculated for solutions of conformally related theories. We show that the ADM mass of a static, spherically symmetric solution is conformally invariant (up to a constant factor) only if the background action functional is conformally invariant. Thus, the requirement of conformal invariance places restrictions on the choice of reference spacetimes. We calculate the mass of the black hole solutions obtained by Garfinkle, Horowitz, and Strominger (GHS) for both the string and the Einstein metrics. In addition, the quasilocal thermodynamic quantities in the string metrics are computed and discussed.

gr-qc↗
arXiv1996

Three Flavour Gravitationally Induced Neutrino Oscillations and the Solar Neutrino Problem

Some implications of the proposal that flavor nondiagonal couplings of neutrinos to gravity might resolve the solar neutrino problem are considered in the context of three neutrino flavors. The two--flavor model is discussed as a limiting case of the full three-generation mechanism, and the behavior of the $\nue$ survival probability for various values of the three--flavor parameters is studied. Overlapping allowed SNU regions are obtained for the neutrinos which most likely contribute to the observed solar neutrino deficiency, and the effects of the addition of a third flavor are discussed. The extension to a three--generation framework is found to yield a greater allowed region of parameter space, suggesting that gravitationally--induced neutrino oscillations remain a viable explanation of the Solar Neutrino Problem.

hep-ph↗
arXiv1995

Thermodynamics of Dilatonic Black Holes in $n$ Dimensions

We present a formalism for studying the thermodynamics of black holes in dilaton gravity. The thermodynamic variables are defined on a quasilocal surface surrounding the black hole system and are obtained from a general class of Lagrangians involving a dilaton. The formalism thus accommodates a large number of possible theories and black hole spacetimes. Many of the thermodynamic quantities are identified from the contribution of the action on the quasilocal boundary. The entropy is found using path integral techniques, and a first law of thermodynamics is obtained. As an illustration, we calculate the thermodynamic quantities for two black hole solutions in $(1+1)$ dimensions: one obtained from a string inspired theory and the other being a Liouville black hole in the ``$R=κT$'' theory with a Liouville field.

gr-qc↗
arXiv1995

Mass or Gravitationally Induced Neutrino Oscillations? -- A Comparison of $\B$ Neutrino Flux Spectra in a Three--Generation Framework

Both gravitational and mass induced neutrino oscillation mechanisms provide possible resolutions to the Solar Neutrino Problem. The distinguishing feature between the two mechanisms is their dependence on the neutrino energy. We investigate the implications of this by computing the $\B$ neutrino spectrum as determined from each mechanism using a realistic three--flavor evolution model. We find that in the limit of small $\tetau$ mixing angle, the differences are significant enough to observe in future solar neutrino experiments.

hep-ph↗
arXiv1995

The Equivalence Principle and g-2 Experiments

We consider the possibility of using measurements of anomalous magnetic moments of elementary particles as a possible test of the Einstein Equivalence Principle (EEP). For the class non-metric theories of gravity described by the \tmu formalism we find several novel mechanisms for breaking the EEP, and discuss the possibilities of setting new empirical constraints on such effects.

gr-qc↗
arXiv1995

Gravitationally--Induced Three--Flavor Neutrino Oscillations as a Possible Solution to the Solar Neutrino Problem

Neutrinos can undergo flavor--oscillations if they possess flavor--dependent couplings to the surrounding gravitational field (the VEP mechanism). The neutrino fields can be massless, in accord with the Minimal Standard Model, but at the expense of the Einstein Equivalence Principle. We show that it is possible to explain the observed Solar Neutrino data from the various experiments using the VEP solution in a realistic three--generation framework, and further note how the three--flavor model can offer larger allowed regions of parameter space over the two--flavor models.

hep-ph↗
arXiv1995

Test of the Equivalence Principle from Neutrino Oscillation Experiments

We consider the hypothesis that neutrino oscillation data can be explained if the gravitational couplings of (massless or degenerate mass) neutrinos are flavour non--diagonal, in violation of the equivalence principle. We analyze the various neutrino oscillation laboratory experimental data including the recent LSND observations to constrain the relevant parameter space. We find that there is no allowed region of parameter space which can explain the existing data, implying that the LSND result cannot be explained by oscillations of degenerate-mass neutrinos due to equivalence principle violations.

hep-ph↗
arXiv1995

Cosmological production of charged black hole pairs

We investigate the pair creation of charged black holes in a background with a positive cosmological constant. We consider $C$ metrics with a cosmological constant, and show that the conical singularities in the metric only disappear when it reduces to the Reissner-Nordström de Sitter metric. We construct an instanton describing the pair production of extreme black holes and an instanton describing the pair production of non-extreme black holes from the Reissner-Nordström de Sitter metric, and calculate their actions. There are a number of striking similarities between these instantons and the Ernst instantons, which describe pair production in a background electromagnetic field. We also observe that the type I instanton in the ordinary $C$ metric with zero cosmological constant is actually the Reissner-Nordström solution.

gr-qc↗
arXiv1995

Quasilocal Thermodynamics of Dilaton Gravity coupled to Gauge Fields

We consider an Einstein-Hilbert-Dilaton action for gravity coupled to various types of Abelian and non-Abelian gauge fields in a spatially finite system. These include Yang-Mills fields and Abelian gauge fields with three and four-form field strengths. We obtain various quasilocal quantities associated with these fields, including their energy and angular momentum, and develop methods for calculating conserved charges when a solution possesses sufficient symmetry. For stationary black holes, we find an expression for the entropy from the micro-canonical form of the action. We also find a form of the first law of black hole thermodynamics for black holes with the gauge fields of the type considered here.

gr-qc↗
arXiv1995

Exact Black Hole and Cosmological Solutions in a Two-Dimensional Dilaton-Spectator Theory of Gravity

Exact black hole and cosmological solutions are obtained for a special two-dimensional dilaton-spectator ($ϕ-ψ$) theory of gravity. We show how in this context any desired spacetime behaviour can be determined by an appropriate choice of a dilaton potential function $V(ϕ)$ and a ``coupling function'' $l(ϕ)$ in the action. We illustrate several black hole solutions as examples. In particular, asymptotically flat double- and multiple- horizon black hole solutions are obtained. One solution bears an interesting resemblance to the $2D$ string-theoretic black hole and contains the same thermodynamic properties; another resembles the $4D$ Reissner-Nordstrom solution. We find two characteristic features of all the black hole solutions. First the coupling constants in $l(ϕ)$ must be set equal to constants of integration (typically the mass). Second, the spectator field $ψ$ and its derivative $ψ^{'}$ both diverge at any event horizon. A test particle with ``spectator charge" ({\it i.e.} one coupled either to $ψ$ or $ψ^{'}$), will therefore encounter an infinite tidal force at the horizon or an ``infinite potential barrier'' located outside the horizon respectively. We also compute the Hawking temperature and entropy for our solutions. In $2D$ $FRW$ cosmology, two non-singular solutions which resemble two exact solutions in $4D$ string-motivated cosmology are obtained. In addition, we construct a singular model which describes the $4D$ standard non-inflationary big bang cosmology ($big-bang\rightarrow radiation\rightarrow dust$). Motivated by the similaritiesbetween $2D$ and $4D$ gravitational field equations in $FRW$ cosmology, we briefly discuss a special $4D$ dilaton-spectator action constructed from the bosonic part of the low energy heterotic string action and

gr-qc↗
arXiv1995

Adiabatic Analysis of Gravitationally-Induced Three-Flavor Neutrino Oscillations

Some implications of the proposal that flavor nondiagonal couplings of neutrinos to gravity might resolve the solar neutrino problem are considered in the context of three neutrino flavours. Using an adiabatic approximation iso-SNU curves are calculated for the neutrinos which most likely contribute to the observed solar neutrino deficiency. We show that results obtained with two-flavor models can be recovered, and discuss the effects of the addition of a third flavor. Some results are obtained for this case, and these values are compared with recent experimental data.

hep-ph↗
arXiv1994

Inflationary Behaviour in Axial-symmetric Gravitational Collapse

We show that the interior of a charged, spinning black hole formed from a general axially symmetric gravitational collapse is unstable to inflation of both its mass and angular momentum parameters. Although our results are formulated in the context of $(2+1)$-dimensional black holes, we argue that they are applicable to $(3+1)$ dimensions.

gr-qc↗
arXiv1994

Infinite Blueshift of Charged Null Particles

We demonstrate that charged null particles can be infinitely blue\-shifted in a Kerr-Newman spacetime. The surface of infinite blueshift can be outside of the ergosphere in a Kerr-Newman spacetime, and outside of the outer event horizon for a Reissner-Nordstrom spacetime. Implications for extensions of the standard model which incorporate charged neutrinos are discussed.

gr-qc↗
arXiv1994

Black Holes in Three Dimensional Topological Gravity

We investigate the black hole solution to (2+1)-dimensional gravity coupled to topological matter, with a vanishing cosmological constant. We calculate the total energy, angular momentum and entropy of the black hole in this model and compare with results obtained in Einstein gravity. We find that the theory with topological matter reverses the identification of energy and angular momentum with the parameters in the metric, compared with general relativity, and that the entropy is determined by the circumference of the inner rather than the outer horizon. We speculate that this results from the contribution of the topological matter fields to the conserved currents. We also briefly discuss two new possible (2+1)-dimensional black holes.

gr-qc↗
arXiv1994

Inside a Spinning Black String

We show that mass inflation occurs inside spinning black cosmic string, which is a solution of a low-energy effective string theory in $(3+1)$-dimensions. This confirms Poisson and Israel's conjecture that the inner mass parameter diverges even if spacetime is not spherically symmetric.

gr-qc↗
arXiv1994

Gravitation and Cosmology in Generalized (1+1)-dimensional dilaton gravity

The actions of the ``$R=T$'' and string-inspired theories of gravity in (1+1) dimensions are generalized into one single action which is characterized by two functions. We discuss differing interpretations of the matter stress-energy tensor, and show how two such different interpretations can yield two different sets of field equations from this action. The weak-field approximation, post-Newtonian expansion, hydrostatic equilibrium state of star and two-dimensional cosmology are studied separately by using the two sets of field equations. Some properties in the ``$R=T$'' and string-inspired theories are shown to be generic in the theory induced by the generalized action.

gr-qc↗