20398756
Comment on "Conformal transformations single out a unique measure of distance"
We discuss the consequences of the incorrectness [see the Erratum Phys. Rev. D 49, 1145(E) (1994)] of Cotsakis' paper and add two related remarks. The scope of this Comment is to encourage further research on ``which of the conformally equivalent metrics is the physical one.''
1345747
Inhomogeneous Cosmological Models Containing Homogeneous Inner Hypersurface Geometry. Changes of the BIANCHI Type.
There are investigated such cosmological models which instead of the usual spatial homogeneity property only fulfil the condition that in a certain synchronized system of reference all spacelike sections t = const. are homogeneous manifolds. This allows time-dependent changes of the BIANCHI type. Discussing differential-geometrical theorems it is shown which of them are permitted. Besides the trivial case of changing into type I there exist some possible changes between other types. However, physical reasons like energy inequalities partially exclude them. 
 
 
 
Es werden kosmologische Modelle betrachtet, die anstelle der ublichen raumlichen Homogenitatseigenschaft nur die Bedingung erfullen, das in einem gewissen synchronisierten Bezugssystem alle Raumschnitte t = const. homogene Mannigfaltigkeiten sind. Neben dem trivialen Fall des Wechsels zu Typ I gibt es einige mogliche Anderungen zwischen anderen Typen. Physikalische Grunde wie Energieungleichungen schliesen diese jedoch teilweise aus.
96453795
Isotropic universe with almost scale-invariant fourth-order gravity
We study a class of isotropic cosmologies in fourth-order gravity with Lagrangians of the form L = f(R)+k(G) where R and G are the Ricci and Gauss-Bonnet scalars respectively. A general discussion is given on the conditions under which this gravitational Lagrangian is scale-invariant or almost scale-invariant. We then apply this general background to the specific case L = �R 2 + � GlnG with constants �,�. We find closed form cosmological solutions for this case. One interesting feature of this choice of f(R) and k(G) is that for very small
16295955
Tunneling of the Closed Friedmann Universe with Generation of Scalar Waves
The evolution of the closed Friedmann Universe with a packet of short scalar waves is considered with the help of the Wheeler–DeWitt equation. The packet ensures conservation of homogeneity and isotropy of the metric on average. It is shown that during tunneling the amplitudes of short waves of a scalar field can increase catastrophically promptly if their influence to the metric is not taken into account. This effect is similar to the Rubakov-effect of catastrophic particle creation calculated already in 1984.In our approach to the problem it is possible to consider a self-consistent dynamics of the expansion of the Universe and amplification of short waves. It results in a decrease of the barrier and interruption of of amplification of waves, and we get an exit of the wave function from the quantum to the classically available region.
15973668
On static spherical symmetric solutions of the Bach‐Einstein gravitational field equations
For field equations of 4th order, follwing from a Lagrangian “Ricci scalar plus Weyl scalar”, it is shown (using methods of non-standard analysis) that in a neighbourhood of Minkowski space there do not exist regular static spherically symmetric solutions. With that (besides the known local expansions about r = o nad r = ∞ resp.) for the first time a global statement on the existence of such solutions is given. Finally, this result will be discussed in connection with Einstein's particle programme. 
 
 
 
Fur die Feldgleichungen 4. Ordnung, die aus einem Lagrangeausdruck „Ricci-Skalar plus Weyl-Skalar” folgen, wird unter Zuhilfenahme von Methoden der Nicht-Standard-Analysis gezeigt, das in einer Umgebung des Minkowskiraumes keine statischen kugeslymmetrischen Losungen existeieren. Damit wird erstmals neben den bekannten lokalen Entwicklungen um r = o und r = ∞ eine globale Aussage uber die Existenz solcher Losungen getroffen. Anschliesend wird dies Ergebnis im Zusammenhang mit Einstein's Teilchenprogramm diskutiert.
122236194
The Singularity Problem of Gravitation
We review the present status of the singularity problem in gravitation theory. First we repeat the known results for Einstein's theory. After this, different other gravitation theories are considered under the following aspect: Which of the presumptions leading to singularities in Einstein's theory are not fulfilled, and can this prevent the singularities? In detail: scalar matter fields do not fulfil the positive energy condition, bimetric theories change the gravitational vacuum, theories with torsion and fourth order gravity add new geometric terms. It turns out that the answer is never simply no or yes, but requires new conditions, and new types of singularities occur. Otherwise there exist essential situations where the alternative theories satisfactorily prevent the singular behaviour known from Einstein's theory. Finally, we review on chaotic singularities.
18789561
Is the chiral angle related to the vacuum charge? A study in one dimension.
A resolution of ambiguities that arise in relating the chiral angle to the vacuum charge is presented; their relationship is studied and clarified. A recently developed formulation is applied to a simple one-dimensional example with fractional charge. This example provides a setting in which the breakdown of the adiabatic approximation and the winding of the chiral angle by multiples of 2\ensuremath{\pi} can be studied. We find that the above situations do not a priori imply a change in the vacuum charge nor any ambiguity in its definition. However, a mathematical and physical criterion for the occurrence of level crossing, leading to an integer change in the charge of the vacuum, is provided. The results are given and analyzed from a physical point of view and their generality is discussed.
39321472
Size and scaling of the double-helicity-flip hadronic structure function.
Recently, Jaffe and Manohar identified a new leading-twist structure function {Delta}({ital x},{ital Q}{sup 2}), which can be measured in deep-inelastic scattering from polarized targets with spin {ge}1. We calculate the scaling behavior of {Delta}({ital x},{ital Q}{sup 2}) in QCD, both by computing the anomalous dimensions of the associated operators and by finding the splitting function for the appropriate parton density. We also estimate the size of the lowest moment of {Delta}({ital x},{ital Q}{sup 2}) in the bag model. In an appendix we give the complete cross section for electroproduction from a spin-1 target of arbitrary polarization.
8062504
Dijet production at large rapidity intervals.
Santa Cruz Institute for Particle PhysicsUniversity of California, Santa Cruz, CA 95064, USAAbstractWe examine dijet production at large rapidity intervals at Tevatron energies, by usingthe theory of Lipatov and collaborators which resums the leading powers of the rapidityinterval. We analyze the growth of the Mueller-Navelet K-factor in this context and ﬁndit to be negligible. However, we do ﬁnd a considerable enhancement of jet productionat large transverse momenta. In addition, we show that the correlation in transversemomentum and azimuthal angle of the tagging jets fades away as the rapidity intervalis increased.
12149672
Production of relativistic antihydrogen atoms by pair production with positron capture.
A beam of relativistic antihydrogen atoms, the bound state ([ital [bar p]e][sup +]), can be created by circulating the beam of an antiproton storage ring through an internal gas target. An antiproton that passes through the Coulomb field of a nucleus of charge [ital Z] will create [ital e][sup +][ital e[minus]] pairs, and antihydrogen will form when a positron is created in a bound rather than a continuum state about the antiproton. The cross section for this process is calculated to be [similar to]4[ital Z][sup 2] pb for antiproton momenta above 6 GeV/[ital c]. The gas target of Fermilab Accumulator experiment E760 has already produced [similar to]34 unobserved antihydrogen atoms, and a sample of [similar to]760 is expected in 1995 from the successive experiment E835. No other source of antihydrogen exists. A simple method for detecting relativistic antihydrogen is proposed and a method outlined of measuring the antihydrogen Lamb shift to [similar to]1%.
38541143
Equivalence theorem redux.
The equivalence theorem states that amplitudes involving longitudinal vector bosons are equal to those with the corresponding unphysical scalars in the limit {ital M}{sub {ital W}}{sup 2}/s{r arrow}0. There are two ways to approach this limit, depending on whether {ital M}{sub {ital W}}/{ital M}{sub {ital H}}{r arrow}0 or {ital M}{sub {ital H}}{sup 2}/s{r arrow}0. We show that the theorem has a different physical interpretation in each limit, but its validity in both depends only on the wave-function renormalization of the unphysical Goldstone bosons. We derive a condition that the renormalization parameters must satisfy in order for the theorem to hold. We show that this condition is satisfied in the first limit, appropriate to the heavy-Higgs-boson regime, if momentum subtraction at a scale {ital m}{much lt}{ital M}{sub {ital H}} is used. With this prescription, the theorem is true to lowest nonzero order in {ital g} and to all orders in the Higgs-boson coupling.