occasional meanderings in physics' brave new world

Name:
Location: New Zealand

Marni D. Sheppeard

## Friday, August 21, 2009

### Gravity Goose

Recall that, at GRG18, the LIGO collaboration reported null results for GRB 070201, which was coincident with the spiral arms of the Andromeda galaxy. That is, if this burst was located in Andromeda, it could not have been generated by a compact binary under the usual theoretical assumptions, most notably the assumption that gravitons (if they exist, which I suspect not) travel at speed $c$.

Nature reports on LIGO's latest null results with the heading: Gravity waves 'around the corner'. You gotta love those quotation marks. The new paper, for those fortunate enough (including me, at present) to have access, is here. Part of the abstract reads:
Our result constrains the energy density of the stochastic gravitational wave background normalized by the critical energy density of the Universe, in the frequency band around $100$ Hz, to be < $6.9 \times 10^{-6}$ at $95$% confidence. The data rule out models of early Universe evolution with relatively large equation of state parameter, as well as cosmic (super)string models with relatively small string tension that are favoured in some string theory models.