11,189 research outputs found
Birth of Closed Strings and Death of Open Strings during Tachyon Condensation
The tremendous progress achieved through the study of black holes and branes
suggests that their time dependent generalizations called Spacelike branes
(S-branes) may prove similarly useful. An example of an established approach to
S-branes is to include a string boundary interaction and we first summarize
evidence for the death of open string degrees of freedom for the homogeneous
rolling tachyon on a decaying brane. Then, we review how to extract the flat
S-brane worldvolumes describing the homogeneous rolling tachyon and how large
deformations correspond to creation of lower dimensional strings and branes.
These S-brane worldvolumes are governed by S-brane actions which are on equal
footing to D-brane actions, since they are derived by imposing conformality on
the string worldsheet, as well as by analyzing fluctuations of time dependent
tachyon configurations. As further examples we generalize previous solutions of
the S-brane actions so as to describe multiple decaying and nucleating closed
fundamental strings. Conceptually S-brane actions are therefore different from
D-brane actions and can provide a description of time dependent strings/branes
and possibly their interactions.Comment: 15 pages, 7 eps figures; invited review for Modern Physics Letters A,
including new solutions for S-brane actions. v2 published version, minor
typos correcte
Stationary quantum Markov process for the Wigner function
As a stochastic model for quantum mechanics we present a stationary quantum
Markov process for the time evolution of the Wigner function on a lattice phase
space Z_N x Z_N with N odd. By introducing a phase factor extension to the
phase space, each particle can be treated independently. This is an improvement
on earlier methods that require the whole distribution function to determine
the evolution of a constituent particle. The process has branching and
vanishing points, though a finite time interval can be maintained between the
branchings. The procedure to perform a simulation using the process is
presented.Comment: 12 pages, no figures; replaced with version accepted for publication
in J. Phys. A, title changed, an example adde
Growth of single-crystal columns of CoSi2 embedded in epitaxial Si on Si(111) by molecular beam epitaxy
The codeposition of Si and Co on a heated Si(111) substrate is found to result in epitaxial columns of CoSi2 if the Si:Co ratio is greater than approximately 3:1. These columns are surrounded by a Si matrix which shows bulk-like crystalline quality based on transmission electron microscopy and ion channeling. This phenomenon has been studied as functions of substrate temperature and Si:Co ratio. Samples with columns ranging in average diameter from approximately 25 to 130 nm have been produced
Stringy Derivation of Nahm Construction of Monopoles
We derive the Nahm construction of monopoles from exact tachyon condensation
on unstable D-branes. The Dirac operator used in the Nahm construction is
identified with the tachyon profile in our D-brane approach, and we provide
physical interpretation of the procedures Nahm gave. Crucial is the
introduction of infinite number of brane-antibranes from which arbitrary
D-brane can be constrcuted, exhibitting a unified view of various D-branes. We
explicitly show the equivalence of the D3-brane boundary state with the
monopole profile and the D1-brane boundary state with the Nahm data as
transverse scalars.Comment: 18 pages, 4 eps figures, JHEP style, comments about low energy limits
added, references adde
Vortex-boson duality in four space-time dimensions
A continuum version of the vortex-boson duality in (3+1) dimensions is
formulated and its implications studied in the context of a pair Wigner crystal
in underdoped cuprate superconductors. The dual theory to a phase fluctuating
superconductor (or superfluid) is shown to be a theory of bosonic strings
interacting through a Kalb-Ramond rank-2 tensorial gauge field. String
condensation produces Higgs mass for the gauge field and the expected Wigner
crystal emerges as an interesting space-time analog of the Abrikosov lattice.Comment: 4 pages REVTeX; for related work and info visit
http://www.physics.ubc.ca/~fran
Complete solution for unambiguous discrimination of three pure states with real inner products
Complete solutions are given in a closed analytic form for unambiguous
discrimination of three general pure states with real mutual inner products.
For this purpose, we first establish some general results on unambiguous
discrimination of n linearly independent pure states. The uniqueness of
solution is proved. The condition under which the problem is reduced to an
(n-1)-state problem is clarified. After giving the solution for three pure
states with real mutual inner products, we examine some difficulties in
extending our method to the case of complex inner products. There is a class of
set of three pure states with complex inner products for which we obtain an
analytical solution.Comment: 13 pages, 3 figures, presentation improved, reference adde
Black Hole Geometries in Noncommutative String Theory
We obtain a generalized Schwarzschild (GS-) and a generalized
Reissner-Nordstrom (GRN-) black hole geometries in (3+1)-dimensions, in a
noncommutative string theory. In particular, we consider an effective theory of
gravity on a curved -brane in presence of an electromagnetic (EM-) field.
Two different length scales, inherent in its noncommutative counter-part, are
exploited to obtain a theory of effective gravity coupled to an U(1)
noncommutative gauge theory to all orders in . It is shown that the
GRN-black hole geometry, in the Planckian regime, reduces to the GS-black hole.
However in the classical regime it may be seen to govern both
Reissner-Nordstrom and Schwarzschild geometries independently. The emerging
notion of 2D black holes evident in the frame-work are analyzed. It is argued
that the -string in the theory may be described by the near horizon 2D black
hole geometry, in the gravity decoupling limit. Finally, our analysis explains
the nature of the effective force derived from the nonlinear EM-field and
accounts for the Hawking radiation phenomenon in the formalism.Comment: 30 pages, 2 figure
Reexamination of optimal quantum state estimation of pure states
A direct derivation is given for the optimal mean fidelity of quantum state
estimation of a d-dimensional unknown pure state with its N copies given as
input, which was first obtained by M. Hayashi in terms of an infinite set of
covariant positive operator valued measures (POVM's) and by Bruss and
Macchiavello establishing a connection to optimal quantum cloning. An explicit
condition for POVM measurement operators for optimal estimators is obtained, by
which we construct optimal estimators with finite POVM using exact quadratures
on a hypersphere. These finite optimal estimators are not generally universal,
where universality means the fidelity is independent of input states. However,
any optimal estimator with finite POVM for M(>N) copies is universal if it is
used for N copies as input.Comment: v3(journal version): title changed, presentation improve
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