Dynamic wormholes

A new framework is proposed for general dynamic wormholes, unifying them with black holes. Both are generically defined locally by outer trapping horizons, temporal for wormholes and spatial or null for black and white holes. Thus wormhole horizons are two-way traversible, while black-hole and white-hole horizons are only one-way traversible. It follows from the Einstein equation that the null energy condition is violated everywhere on a generic wormhole horizon. It is suggested that quantum inequalities constraining negative energy break down at such horizons. Wormhole dynamics can be developed as for black-hole dynamics, including a reversed second law and a first law involving a definition of wormhole surface gravity. Since the causal nature of a horizon can change, being spatial under positive energy and temporal under sufficient negative energy, black holes and wormholes are interconvertible. In particular, if a wormhole's negative-energy source fails, it may collapse into a black hole. Conversely, irradiating a black-hole horizon with negative energy could convert it into a wormhole horizon. This also suggests a possible final state of black-hole evaporation: a stationary wormhole. The new framework allows a fully dynamical description of the operation of a wormhole for practical transport, including the back-reaction of the transported matter on the wormhole. As an example of a matter model, a Klein-Gordon field with negative gravitational coupling is a source for a static wormhole of Morris & Thorne.Comment: 5 revtex pages, 4 eps figures. Minor change which did not reach publisher

Patent collateral, investor commitment, and the market for venture lending

This paper investigates the market for lending to technology startups (i.e., venture lending) and examines two mechanisms that may facilitate trade within it: (1) the ‘salability’ of patent collateral; and (2) the credible commitment of existing equity investors. We find that intensified trading in the secondary patent market is strongly related to the annual rate of startup lending, particularly for startups with more redeployable patent assets. Moreover, we show that the credibility of venture capitalist commitments to reinvest in their startups’ next round of financing can be critical for startup debt provision. Utilizing the crash of 2000 as a severe and unexpected capital supply shock for VCs, we show that lenders continue to finance startups with recently funded investors better able to credibly commit to refinance their portfolio companies, but withdraw from otherwise-promising projects that may have needed their funds the most. The findings are consistent with predictions of incomplete contracting and financial intermediation theory.Accepted manuscrip

Institutions, Structures and Topics of Grassland Research in Germany - From Science to Practice

In Germany, grassland covers some 30% of the agriculturally used land. It forms the basis of forage production in dairy and beef cattle husbandry as well as sheep and horse feeding. The intensification of grassland farming during the last fifty years was made possible through extended basic and applied research in all fields of grassland management. This included the improvement of forage species and varieties by plant breeding, the adaptation of botanical knowledge for the control of the botanical composition of permanent grass swards, the application of regular fertilisation, the improvement of the grazing management, the increased frequency of utilisation or herbage conservation by ensiling. In addition to the general improvement of forage production, the refinement of production measures in animal husbandry has led to a marked increase of efficiency in dairy and beef cattle farming. Production-orientated research was well funded until the late 1980\u27s. Since then, the awareness of adverse side effects of the intensification of grassland farming, such as the loss of biodiversity, the pollution of the environment mainly by excess nitrogen and phosphorus, and the emission of greenhouse gases has grown. In addition, with the reform of the European Union Agricultural Policy in 1992, the rental costs for grassland decreased as did the stocking rates. On marginal sites, grassland is now at risk of being abandoned from agricultural use. Thus, increasing forage production and refining production measures have lost priority in grassland research and multiple function grasslands have become the main target of research

Silicon Waveguides and Ring Resonators at 5.5 {\mu}m

We demonstrate low loss ridge waveguides and the first ring resonators for the mid-infrared, for wavelengths ranging from 5.4 to 5.6 {\mu}m. Structures were fabricated using electron-beam lithography on the silicon-on-sapphire material system. Waveguide losses of 4.0 +/- 0.7 dB/cm are achieved, as well as Q-values of 3.0 k.Comment: 4 pages, 4 figures, includes supplemental material

Energy Density of Non-Minimally Coupled Scalar Field Cosmologies

Scalar fields coupled to gravity via $\xi R {\Phi}^2$ in arbitrary Friedmann-Robertson-Walker backgrounds can be represented by an effective flat space field theory. We derive an expression for the scalar energy density where the effective scalar mass becomes an explicit function of $\xi$ and the scale factor. The scalar quartic self-coupling gets shifted and can vanish for a particular choice of $\xi$. Gravitationally induced symmetry breaking and de-stabilization are possible in this theory.Comment: 18 pages in standard Late

Heat kernel regularization of the effective action for stochastic reaction-diffusion equations

The presence of fluctuations and non-linear interactions can lead to scale dependence in the parameters appearing in stochastic differential equations. Stochastic dynamics can be formulated in terms of functional integrals. In this paper we apply the heat kernel method to study the short distance renormalizability of a stochastic (polynomial) reaction-diffusion equation with real additive noise. We calculate the one-loop {\emph{effective action}} and its ultraviolet scale dependent divergences. We show that for white noise a polynomial reaction-diffusion equation is one-loop {\emph{finite}} in $d=0$ and $d=1$, and is one-loop renormalizable in $d=2$ and $d=3$ space dimensions. We obtain the one-loop renormalization group equations and find they run with scale only in $d=2$.Comment: 21 pages, uses ReV-TeX 3.

Tolman wormholes violate the strong energy condition

For an arbitrary Tolman wormhole, unconstrained by symmetry, we shall define the bounce in terms of a three-dimensional edgeless achronal spacelike hypersurface of minimal volume. (Zero trace for the extrinsic curvature plus a "flare-out" condition.) This enables us to severely constrain the geometry of spacetime at and near the bounce and to derive general theorems regarding violations of the energy conditions--theorems that do not involve geodesic averaging but nevertheless apply to situations much more general than the highly symmetric FRW-based subclass of Tolman wormholes. [For example: even under the mildest of hypotheses, the strong energy condition (SEC) must be violated.] Alternatively, one can dispense with the minimal volume condition and define a generic bounce entirely in terms of the motion of test particles (future-pointing timelike geodesics), by looking at the expansion of their timelike geodesic congruences. One re-confirms that the SEC must be violated at or near the bounce. In contrast, it is easy to arrange for all the other standard energy conditions to be satisfied.Comment: 8 pages, ReV-TeX 3.

Wormhole Cosmology and the Horizon Problem

We construct an explicit class of dynamic lorentzian wormholes connecting Friedmann-Robertson-Walker (FRW) spacetimes. These wormholes can allow two-way transmission of signals between spatially separated regions of spacetime and could permit such regions to come into thermal contact. The cosmology of a network of early Universe wormholes is discussed.Comment: 13 pages, in RevTe

Brans-Dicke wormholes in the Jordan and Einstein frames

We examine the possibility of static wormhole solutions in the vacuum Brans-Dicke theory both in the original (Jordan) frame and in the conformally rescaled (Einstein) frame. It turns out that, in the former frame, wormholes exist only in a very narrow interval of the coupling parameter, viz., -3/2<omega<-4/3. It is shown that these wormholes are not traversable in practice. In the latter frame, wormhole solutions do not exist at all unless energy conditions are violated by hand.Comment: Minor errors corrected, uploaded for the benefit of the researcher

<Tνμ>ren<T^{\mu}_{\nu}>_{ren} of the quantized fields in the Unruh state in the Schwarzschild spacetime

The renormalized expectation value of the stress energy tensor of the conformally invariant massless fields in the Unruh state in the Schwarzschild spacetime is constructed. It is achieved through solving the conservation equation in conformal space and utilizing the regularity conditions in the physical metric. The relations of obtained results to the existing approximations are analysed.Comment: 17 pages, REVTE