105,535 research outputs found
Manipulating lightcone fluctuations in an analogue cosmic string
We study the flight time fluctuations in an anisotropic medium inspired by a
cosmic string with an effective fluctuating refractive index caused by
fluctuating vacuum electric fields, which are analogous to the lightcone
fluctuations due to fluctuating spacetime metric when gravity is quantized. The
medium can be realized as a metamaterial that mimics a cosmic string in the
sense of transformation optics. For a probe light close to the analogue string,
the flight time variance is times that in a normal homogeneous and
isotropic medium, where is a parameter characterizing the deficit angle
of the spacetime of a cosmic string. The parameter , which is always
greater than unity for a real cosmic string, is determined by the dielectric
properties of the metamaterial for an analogue string. Therefore, the flight
time fluctuations of a probe light can be manipulated by changing the electric
permittivity and magnetic permeability of the analogue medium. We argue that it
seems possible to fabricate a metamaterial that mimics a cosmic string with a
large in laboratory so that a currently observable flight time variance
might be achieved.Comment: 13 pages, 1 figur
Quantum gravitational interaction between a polarizable object and a boundary
We investigate the interaction caused by quantum gravitational vacuum
fluctuations between a gravitationally polarizable object and a gravitational
boundary, and find a position-dependent energy shift of the object, which
induces a force in close analogy to the Casimir-Polder force in the
electromagnetic case. For a Dirichlet boundary, the explicit form of the
quantum gravitational potential for the polarizable object in its ground-state
is worked out and is found to behave like in the near regime, and
in the far regime, where is the distance to the boundary. Taking a
Bose-Einstein condensate as a gravitationally polarizable object, we find that
the relative correction to the radius caused by fluctuating quantum
gravitational waves in vacuum is of order . Although far too small to
observe in comparison with its electromagnetic counterpart, it is nevertheless
of the order of the gravitational strain caused by a recently detected black
hole merger on the arms of the LIGO.Comment: 11 pages, no figure
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