49,114 research outputs found
Quantum Fields in a Big Crunch/Big Bang Spacetime
We consider quantum field theory on a spacetime representing the Big
Crunch/Big Bang transition postulated in the ekpyrotic or cyclic cosmologies.
We show via several independent methods that an essentially unique matching
rule holds connecting the incoming state, in which a single extra dimension
shrinks to zero, to the outgoing state in which it re-expands at the same rate.
For free fields in our construction there is no particle production from the
incoming adiabatic vacuum. When interactions are included the total particle
production for fixed external momentum is finite at tree level. We discuss a
formal correspondence between our construction and quantum field theory on de
Sitter spacetime.Comment: 30 pages, RevTex file, five postscript figure file
Dictionary matching in a stream
We consider the problem of dictionary matching in a stream. Given a set of
strings, known as a dictionary, and a stream of characters arriving one at a
time, the task is to report each time some string in our dictionary occurs in
the stream. We present a randomised algorithm which takes O(log log(k + m))
time per arriving character and uses O(k log m) words of space, where k is the
number of strings in the dictionary and m is the length of the longest string
in the dictionary
Vacuum energy in conical space with additional boundary conditions
Total vacuum energy of some quantized fields in conical space with additional
boundary conditions is calculated. These conditions are imposed on a
cylindrical surface which is coaxial with the symmetry axis of conical space.
The explicit form of the matching conditions depends on the field under
consideration. In the case of electromagnetic field, the perfectly conducting
boundary conditions or isorefractive matching conditions are imposed on the
cylindrical surface. For a massless scalar field, the semi-transparent
conditions (-potential) on the cylindrical shell are investigated. As a
result, the total Casimir energy of electromagnetic field and scalar field, per
a unit length along the symmetry axis, proves to be finite unlike the case of
an infinitely thin cosmic string. In these studies the spectral zeta functions
are widely used. It is shown briefly how to apply this technique for obtaining
the asymptotics of the relevant thermodynamical functions in the high
temperature limit.Comment: 29 pages, 2 figures, the title was changed for a more adequate one,
the abstract was rewritten, a few typos and minor grammar mistakes were
correcte
Dual String Pairs With N=1 And N=2 Supersymmetry In Four Dimensions
Based on a simple adiabatic argument and by considering the heterotic string
counterpart of certain symmetries of Type II superstrings such as
and orientation reversal, we construct orbifold candidates for dual pairs of
heterotic and Type II string theories with and supersymmetry. We
also analyze from a similar point of view the fibrations that enter
in recently proposed candidates and use this structure together with
certain orientation-reversing symmetries to construct dual pairs. These
pairs involve generalizations of Type I vacua which can be equivalent to
heterotic strings, while standard Type I vacua are related to
.Comment: 40 page
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