152 research outputs found
Superluminality in the Bi- and Multi- Galileon
We re-explore the Bi- and Multi-Galileon models with trivial asymptotic
conditions at infinity and show that propagation of superluminal fluctuations
is a common and unavoidable feature of these theories, unlike previously
claimed in the literature. We show that all Multi-Galileon theories containing
a Cubic Galileon term exhibit superluminalities at large distances from a point
source, and that even if the Cubic Galileon is not present one can always find
sensible matter distributions in which there are superluminal modes at large
distances. In the Bi-Galileon case we explicitly show that there are always
superluminal modes around a point source even if the Cubic Galileon is not
present. Finally, we briefly comment on the possibility of avoiding
superluminalities by modifying the asymptotic conditions at infinity.Comment: 32 pages, minor changes, few references adde
Frequentist versus Bayesian analyses: Cross-correlation as an (approximate) sufficient statistic for LIGO-Virgo stochastic background searches
Sufficient statistics are combinations of data in terms of which the
likelihood function can be rewritten without loss of information. Depending on
the data volume reduction, the use of sufficient statistics as a preliminary
step in a Bayesian analysis can lead to significant increases in efficiency
when sampling from posterior distributions of model parameters. Here we show
that the frequency integrand of the cross-correlation statistic and its
variance are approximate sufficient statistics for ground-based searches for
stochastic gravitational-wave backgrounds. The sufficient statistics are
approximate because one works in the weak-signal approximation and uses
measured estimates of the auto-correlated power in each detector. Using
analytic and numerical calculations, we prove that LIGO-Virgo's hybrid
frequentist-Bayesian parameter estimation analysis is equivalent to a fully
Bayesian analysis. This work closes a gap in the LIGO-Virgo literature, and
suggests directions for additional searches.Comment: 17 pages, 5 figure
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