Dynamics of a string coupled to gravitational waves - Gravitational wave scattering by a Nambu-Goto straight string

We study the perturbative dynamics of an infinite gravitating Nambu-Goto string within the general-relativistic perturbation framework. We develop the gauge invariant metric perturbation on a spacetime containing a self-gravitating straight string with a finite thickness and solve the linearized Einstein equation. In the thin string case, we show that the string does not emit gravitational waves by its free oscillation in the first order with respect to its oscillation amplitude, nevertheless the string actually bends when the incidental gravitational waves go through it.Comment: Published in Physical Review D. Some explanations are changed to clarify our point

Canonical theory of spherically symmetric spacetimes with cross-streaming null dusts

The Hamiltonian dynamics of two-component spherically symmetric null dust is studied with regard to the quantum theory of gravitational collapse. The components--the ingoing and outgoing dusts--are assumed to interact only through gravitation. Different kinds of singularities, naked or "clothed", that can form during collapse processes are described. The general canonical formulation of the one-component null-dust dynamics by Bicak and Kuchar is restricted to the spherically symmetric case and used to construct an action for the two components. The transformation from a metric variable to the quasilocal mass is shown to simplify the mathematics. The action is reduced by a choice of gauge and the corresponding true Hamiltonian is written down. Asymptotic coordinates and energy densities of dust shells are shown to form a complete set of Dirac observables. The action of the asymptotic time translation on the observables is defined but it has been calculated explicitly only in the case of one-component dust (Vaidya metric).Comment: 15 pages, 3 figures, submitted to Phys. Rev.

On Thermodynamical Properties of Some Coset CFT Backgrounds

We investigate the thermodynamical features of two Lorentzian signature backgrounds that arise in string theory as exact CFTs and possess more than two disconnected asymptotic regions: the 2-d charged black hole and the Nappi-Witten cosmological model. We find multiple smooth disconnected Euclidean versions of the charged black hole background. They are characterized by different temperatures and electro-chemical potentials. We show that there is no straightforward analog of the Hartle-Hawking state that would express these thermodynamical features. We also obtain multiple Euclidean versions of the Nappi-Witten cosmological model and study their singularity structure. It suggests to associate a non-isotropic temperature with this background.Comment: 1+39 pages, harvmac, 8 eps figure

Method to compute the stress-energy tensor for the massless spin 1/2 field in a general static spherically symmetric spacetime

A method for computing the stress-energy tensor for the quantized, massless, spin 1/2 field in a general static spherically symmetric spacetime is presented. The field can be in a zero temperature state or a non-zero temperature thermal state. An expression for the full renormalized stress-energy tensor is derived. It consists of a sum of two tensors both of which are conserved. One tensor is written in terms of the modes of the quantized field and has zero trace. In most cases it must be computed numerically. The other tensor does not explicitly depend on the modes and has a trace equal to the trace anomaly. It can be used as an analytic approximation for the stress-energy tensor and is equivalent to other approximations that have been made for the stress-energy tensor of the massless spin 1/2 field in static spherically symmetric spacetimes.Comment: 34 pages, no figure

Concept of temperature in multi-horizon spacetimes: Analysis of Schwarzschild-De Sitter metric

In case of spacetimes with single horizon, there exist several well-established procedures for relating the surface gravity of the horizon to a thermodynamic temperature. Such procedures, however, cannot be extended in a straightforward manner when a spacetime has multiple horizons. In particular, it is not clear whether there exists a notion of global temperature characterizing the multi-horizon spacetimes. We examine the conditions under which a global temperature can exist for a spacetime with two horizons using the example of Schwarzschild-De Sitter (SDS) spacetime. We systematically extend different procedures (like the expectation value of stress tensor, response of particle detectors, periodicity in the Euclidean time etc.) for identifying a temperature in the case of spacetimes with single horizon to the SDS spacetime. This analysis is facilitated by using a global coordinate chart which covers the entire SDS manifold. We find that all the procedures lead to a consistent picture characterized by the following features: (a) In general, SDS spacetime behaves like a non-equilibrium system characterized by two temperatures. (b) It is not possible to associate a global temperature with SDS spacetime except when the ratio of the two surface gravities is rational (c) Even when the ratio of the two surface gravities is rational, the thermal nature depends on the coordinate chart used. There exists a global coordinate chart in which there is global equilibrium temperature while there exist other charts in which SDS behaves as though it has two different temperatures. The coordinate dependence of the thermal nature is reminiscent of the flat spacetime in Minkowski and Rindler coordinate charts. The implications are discussed.Comment: 12 page

Isotopic evidence for palaeowaters in the British Isles

Before the 20th century, groundwater circulation in the aquifers of the British Isles had largely adjusted to the temperate maritime climate and sea levels established over the past 10 ka since the end of the Pleistocene. However, in the last 100 a this natural regime has been disturbed by abstraction of water for public supply and industrial use, and palaeowaters from earlier recharge episodes are now becoming a factor to be considered in water balance estimates. This paper presents a synthesis of the existing palaeowater distribution in the British Isles, based on isotopic evidence (δ18O, δ2H and and14C). As such, it has relevance to palaeoclimatic studies in addition to the water resource implications. The Triassic basins of England and Northern Ireland contain saline waters beyond the range14C dating (>; 40 ka). Stable isotopic ratios show enrichment in some basins and depletion in others, without an overall pattern that would explain all the observed compositions. The results for the Wessex basin suggest recharge in pre-Quaternary times, but for the other basins some flushing by Pleistocene or Holocene meteoric waters is indicated. Isolated occurrences of apparently long-residence waters are found elsewhere throughout the British Isles, for example from Carboniferous and Lower Palaeozoic strata. In such cases, environmental isotopes are more useful as constraints on hydrogeological models than as indicators of palaeoconditions. Major water supply aquifers are restricted almost entirely to England. The two sandstone formations (Triassic Sherwood Sandstone and Cretaceous Lower Greensand) have a greater range of stable isotopic values between phreatic and confined conditions than the two carbonate formations (Jurassic Lincolnshire Limestone and Cretaceous Chalk). This indicates that the sandstone aquifers are better archives of information on palaeoconditions than the carbonate aquifers. They show that atmospheric circulation patterns over Britain have probably remained the same since the late Pleistocene. However,14C data from all four of the major aquifers emphasise the hiatus in recharge during periglacial conditions which occurred between the late Pleistocene and early Holocene