Abstract
The c=1 matrix model, with or without a type 0 hat, has an exact quantum solution corresponding to closed string tachyon condensation along a null surface. The condensation occurs, and spacetime dissolves, at a finite retarded time on I^+. The outgoing quantum state of tachyon fluctuations in this time-dependent background is computed using both the collective field and exact fermion pictures. Perturbative particle production induced by the moving tachyon wall is shown to be similar to that induced by a soft moving mirror. Hence, despite the fact that I^+ for the tachyon is geodesicaly incomplete, quantum correlations in the incoming state are unitarily transmitted to the outgoing state in perturbation theory. It is also shown that, non-perturbatively, information can leak across the tachyon wall, and tachyon scattering is not unitary. Exact unitarity remains intact only in the free fermion picture.
Highlights
The c = 1 matrix model, with or without a type 0 hat, has an exact quantum solution corresponding to closed string tachyon condensation along a null surface
This paper considers the exact quantum description of closed string tachyon condensation along a null hypersurface
In this process the Fermi sea – together with the spacetime described by its fluctuating surface – comes to an end at a finite retarded time t−end on I+
Summary
This is a moving hyperbola centered at. The second interaction term (which is a weight (1,1) operator) is an exponential potential wall, albeit less steep than the standard one This wall moves with time, effectively cutting off the universe at a time-varying distance. Any observer moving along a timelike trajectory will eventually move into a region where the tachyon field becomes arbitrarily large This solution is a form of closed string tachyon condensation [11]
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