95 research outputs found
Detecting a stochastic background of gravitational waves by correlating n detectors
We discuss the optimal detection strategy for a stochastic background of
gravitational waves in the case n detectors are available. In literature so
far, only two cases have been considered: 2- and n-point correlators. We
generalize these analysises to m-point correlators (with m<n) built out of the
n detector signals, obtaining the result that the optimal choice is to combine
2-point correlators. Correlating n detectors in this optimal way will improve
the (suitably defined) signal-to-noise ratio with respect to the n=2 case by a
factor equal to the fourth root of n(n-1)/2. Finally we give an estimation of
how this could improve the sensitivity for a network of multi-mode spherical
antennas.Comment: 12 pages, version accepted by Class. & Quant. Gra
The fine tuning problem in pre-big-bang inflation
We examine the effect of spatial curvature in the pre-big-bang inflationary
model suggested by string theory. We study corrections and we
show that, independently of the initial curvature, they lead to a phase of
exponential inflation. The amount of inflation in this phase is long enough to
solve the horizon and flatness problems if the evolution starts deeply into the
weak coupling regime. There is a region of the parameter space of the model
where such a long inflationary phase at the string scale is consistent with
COBE anisotropies, millisecond pulsar timing and nucleosynthesis constraints.
We discuss implications for the spectrum of relic gravitational waves at the
frequencies of LIGO and Virgo.Comment: revised Sept. 97; the new version includes a discussion of the
compatibility between a long inflationary phase at the string scale and the
experimental bounds on the gravitational wave spectru
Supersymmetric Vacuum Configurations in String Cosmology
We examine in a cosmological context the conditions for unbroken
supersymmetry in N=1 supergravity in D=10 dimensions. We show that the
cosmological solutions of the equations of motion obtained considering only the
bosonic sector correspond to vacuum states with spontaneous supersymmetry
breaking. With a non vanishing gravitino-dilatino condensate we find a solution
of the equations of motion that satisfies necessary conditions for unbroken
supersymmetry and that smoothly interpolates between Minkowski space and
DeSitter space with a linearly growing dilaton, thus providing a possible
example of a supersymmetric and non-singular pre-big-bang cosmology.Comment: 4 pages, Latex, 2 figure
On the frequency of gravitational waves
We show that there are physically relevant situations where gravitational
waves do not inherit the frequency spectrum of their source but its wavenumber
spectrum.Comment: 4 pages, 2 figures. In v2 minor corrections and a full sentence
changed in section III in the paragraph about turbulence. Version accepted
for publication by PR
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