428 research outputs found
Unitary S Matrices With Long-Range Correlations and the Quantum Black Hole
We propose an S matrix approach to the quantum black hole in which causality,
unitarity and their interrelation play a prominent role. Assuming the 't Hooft
S matrix ansatz for a gravitating region surrounded by an asymptotically flat
space-time we find a non-local transformation which changes the standard
causality requirement but is a symmetry of the unitarity condition of the S
matrix. This new S matrix then implies correlations between the in and out
states of the theory with the involvement of a third entity which in the case
of a quantum black hole, we argue is the horizon S matrix. Such correlations
are thus linked to preserving the unitarity of the S matrix and to the fact
that entangling unitary operators are nonlocal. The analysis is performed
within the Bogoliubov S matrix framework by considering a spacetime consisting
of causal complements with a boundary in between. No particular metric or
lagrangian dynamics need be invoked even to obtain an evolution equation for
the full S matrix. Constraints imposed by the new causality requirement and
implications for the effectiveness of field theoretical descriptions and for
complementarity are also discussed. We find that the tension between
information preservation and complementarity may be resolved provided the full
quantum gravity theory either through symmetries or fine tuning forbids the
occurrence of closed time like curves of information flow. Then, even if
causality is violated near the horizon at any intermediate stage, a standard
causal ordering may be preserved for the observer away from the horizon. In the
context of the black hole, the novelty of our formulation is that it appears
well suited to understand unitarity at any intermediate stage of black hole
evaporation. Moreover, it is applicable generally to all theories with long
range correlations including the final state projection models.Comment: 47 pages Latex, 1 figure.Corrected typos. Some section titles
changed. Minor clarifying additions to all sections. Conclusions unchanged.
Accepted for publication in JHE
BMS Supertranslation Symmetry Implies Faddeev-Kulish Amplitudes
We show explicitly that, among the scattering amplitudes constructed from
eigenstates of the BMS supertranslation charge, the ones that conserve this
charge, are equal to those constructed from Faddeev-Kulish states. Thus,
Faddeev-Kulish states naturally arise as a consequence of the asymptotic
symmetries of perturbative gravity and all charge conserving amplitudes are
infrared finite. In the process we show an important feature of the
Faddeev-Kulish clouds dressing the external hard particles: these clouds can be
moved from the incoming states to the outgoing ones, and vice-versa, without
changing the infrared finiteness properties of S matrix elements. We also apply
our discussion to the problem of the decoherence of momentum configurations of
hard particles due to soft boson effects.Comment: 22 pages, 3 figure
On the Possibility of Super-luminal Propagation in a Gravitational Background
We argue that superluminal propagation in a gravitational field discovered by
Drummond and Hathrell in the lowest order of perturbation theory remains intact
in higher orders. The criticism of this result based on an exact calculation of
the one loop correction to the photon polarization operator in the Penrose
plane wave approximation is not tenable. The statement that quantum causality
is automatically imposed by classical causality is possibly invalid due to the
infrared nature of the same triangle diagram which also contributes to the
quantum trace anomaly.Comment: 11 page
- …