587 research outputs found
Optimal parameter estimation of a depolarizing channel
We investigate strategies for estimating a depolarizing channel for a finite dimensional system. Our analysis addresses the double optimization problem of selecting the best input probe state and the measurement strategy that minimizes the Bayes cost of a quadratic function. In the qubit case, we derive the Bayes optimal strategy for any finite number of input probe particles when bipartite entanglement can be formed in the probe particles
Open Virtual Structure Constants and Mirror Computation of Open Gromov-Witten Invariants of Projective Hypersurfaces
In this paper, we generalize Walcher's computation of the open Gromov-Witten
invariants of the quintic hypersurface to Fano and Calabi-Yau projective
hypersurfaces. Our main tool is the open virtual structure constants. We also
propose the generalized mirror transformation for the open Gromov-Witten
invariants, some parts of which are proven explicitly. We also discuss possible
modification of the multiple covering formula for the case of higher
dimensional Calabi-Yau manifolds. The generalized disk invariants for some
Calabi-Yau and Fano manifolds are shown and they are certainly integers after
re-summation by the modified multiple covering formula. This paper also
contains the direct integration method of the period integrals for higher
dimensional Calabi-Yau hypersurfaces in the appendix.Comment: 24pages, 5figure
Time variation of proton-electron mass ratio and fine structure constant with runaway dilaton
Recent astrophysical observations indicate that the proton-electron mass
ratio and the fine structure constant have gone through nontrivial time
evolution. We discuss their time variation in the context of a dilaton runaway
scenario with gauge coupling unification at the string scale . We
show that the choice of adjustable parameters allows them to fit the same order
magnitude of both variations and their (opposite) signs in such a scenario.Comment: 16 pages, 1 figure, to appear in Phys. Rev.
Black Strings in Our World
The brane world scenario is a new approach to resolve the problem on how to
compactify the higher dimensional spacetime to our 4-dimensional world. One of
the remarkable features of this scenario is the higher dimensional effects in
classical gravitational interactions at short distances. Due to this feature,
there are black string solutions in our 4-dimensional world. In this paper,
assuming the simplest model of complex minimally coupled scalar field with the
local U(1) symmetry, we show a possibility of black-string formation by merging
processes of type I long cosmic strings in our 4-dimensional world. No fine
tuning for the parameters in the model might be necessary.Comment: 11pages, no figur
Primordial Non-Gaussianity in Models with Dark Matter Isocurvature Fluctuations
We investigate primordial non-Gaussianity and dark matter isocurvature
fluctuations in the modulated reheating and the curvaton scenarios. In these
scenarios, large non-Gaussianity can be generated, on the other hand, depending
on how dark matter is produced, too large isocurvature fluctuations can also
arise, which is inconsistent with current observations. In this paper, we study
this issue in a mixed scenario where the curvature fluctuations can also be
produced from the inflaton fluctuations as well as those from a light scalar
field such as the modulus and the curvaton. We show that primordial
fluctuations can be highly non-Gaussian without conflicting the current
constraint on isocurvature fluctuations for such mixed scenarios. However, if
the constraint on isocurvature fluctuations becomes severer as expected by the
Planck satellite, , a nonlinearity parameter for adiabatic
fluctuations, should be very small as , which would give
interesting implications for the generation mechanism of dark matter.
Non-Gaussianity from isocurvature fluctuations is also discussed in these
scenarios.Comment: 26 pages, 4 figures, accepted for publication in PR
Cosmological evolution of cosmic strings with time-dependent tension
We discuss the cosmological evolution of cosmic strings with time-dependent
tension. We show that, in the case that the tension changes as a power of time,
the cosmic string network obeys the scaling solution: the characteristic scale
of the string network grows with the time. But due to the time dependence of
the tension, the ratio of the energy density of infinite strings to that of the
background universe is {\it not} necessarily constant.Comment: 9 pages, to appear in Phys. Rev.
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