13,349 research outputs found
Dyon Spectrum in Generic N=4 Supersymmetric Z_N Orbifolds
We find the exact spectrum of a class of quarter BPS dyons in a generic N=4
supersymmetric Z_N orbifold of type IIA string theory on K3\times T^2 or T^6.
We also find the asymptotic expansion of the statistical entropy to first
non-leading order in inverse power of charges and show that it agrees with the
entropy of a black hole carrying same set of charges after taking into account
the effect of the four derivative Gauss-Bonnet term in the effective action of
the theory.Comment: LaTeX file, 39 pages; minor change
5D Black Holes and Strings with Higher Derivatives
We find asymptotically flat black hole and string solutions to 5D
supergravity in the presence of higher derivative terms. In some cases,
including the fundamental heterotic string solution, the higher derivative
terms smooth out naked singularities into regular geometries carrying zero
entropy. We also compute corrections to the entropy of 5D Calabi-Yau black
holes, and discuss the relation to previous results.Comment: 33 pages, 2 figs., harvmac; v2: typos corrected, references added v3:
refs correcte
Black Hole Microstates and Attractor Without Supersymmetry
Due to the attractor mechanism, the entropy of an extremal black hole does
not vary continuously as we vary the asymptotic values of various moduli
fields. Using this fact we argue that the entropy of an extremal black hole in
string theory, calculated for a range of values of the asymptotic moduli for
which the microscopic theory is strongly coupled, should match the statistical
entropy of the same system calculated for a range of values of the asymptotic
moduli for which the microscopic theory is weakly coupled. This argument does
not rely on supersymmetry and applies equally well to nonsupersymmetric
extremal black holes. We discuss several examples which support this argument
and also several caveats which could invalidate this argument.Comment: 50 pages; references adde
Limits on the integration constant of the dark radiation term in Brane Cosmology
We consider the constraints from primordial Helium abundances on the constant
of integration of the dark radiation term of the brane-world generalized
Friedmann equation derived from the Randall-Sundrum Single brane model. We
found that -- using simple, approximate and semianalytical Method -- that the
constant of integration is limited to be between -8.9 and 2.2 which limits the
possible contribution from dark radiation term to be approximately between -27%
to 7% of the background photon energy density.Comment: 8 page
Fundamental Superstrings as Holograms
The worldsheet of a macroscopic fundamental superstring in the Green-Schwarz
light-cone gauge is viewed as a possible boundary hologram of the near horizon
region of a small black string. For toroidally compactified strings, the
hologram has global symmetries of AdS_3 \times S^{d-1} \times T^{8-d}, (d
=3,..,8), only some of which extend to local conformal symmetries. We construct
the bulk string theory in detail for the particular case of d=3. The symmetries
of the hologram are correctly reproduced from this exact worldsheet description
in the bulk. Moreover, the central charge of the boundary Virasoro algebra
obtained from the bulk agrees with the Wald entropy of the associated small
black holes. This construction provides an exact CFT description of the near
horizon region of small black holes both in Type-II and heterotic string theory
arising from multiply wound fundamental superstrings.Comment: 46 pages, JHEP style. v2: Comments, references adde
Analysis of complete positivity conditions for quantum qutrit channels
We present an analysis of complete positivity (CP) constraints on qutrit
quantum channels that have a form of affine transformations of generalized
Bloch vector. For diagonal (damping) channels we derive conditions analogous to
the ones that in qubit case produce tetrahedron structure in the channel
parameter space.Comment: 12 pages, 8 figures (.eps), minor changes in the text and formula
Spacelike localization of long-range fields in a model of asymptotic electrodynamics
A previously proposed algebra of asymptotic fields in quantum electrodynamics
is formulated as a net of algebras localized in regions which in general have
unbounded spacelike extension. Electromagnetic fields may be localized in
`symmetrical spacelike cones', but there are strong indications this is not
possible in the present model for charged fields, which have tails extending in
all space directions. Nevertheless, products of appropriately `dressed' fermion
fields (with compensating charges) yield bi-localized observables.Comment: 29 pages, accepted for publication in Annales Henri Poincar\'
Quantum decoherence in noninertial frames
Quantum decoherence, which appears when a system interacts with its
environment in an irreversible way, plays a fundamental role in the description
of quantum-to-classical transitions and has been successfully applied in some
important experiments. Here, we study the decoherence in noninertial frames for
the first time. It is shown that the decoherence and loss of the entanglement
generated by the Unruh effect will influence each other remarkably. It is
interesting to note that in the case of the total system under decoherence, the
sudden death of entanglement may appear for any acceleration. However, in the
case of only Rob's qubit underging decoherence sudden death may only occur when
the acceleration parameter is greater than a "critical point."Comment: 4 pages, 3 figure
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