217 research outputs found
Entangling power and operator entanglement in qudit systems
We establish the entangling power of a unitary operator on a general
finite-dimensional bipartite quantum system with and without ancillas, and give
relations between the entangling power based on the von Neumann entropy and the
entangling power based on the linear entropy. Significantly, we demonstrate
that the entangling power of a general controlled unitary operator acting on
two equal-dimensional qudits is proportional to the corresponding operator
entanglement if linear entropy is adopted as the quantity representing the
degree of entanglement. We discuss the entangling power and operator
entanglement of three representative quantum gates on qudits: the SUM, double
SUM, and SWAP gates.Comment: 8 pages, 1 figure. Version 3: Figure was improved and the MS was a
bit shortene
A solution of the coincidence problem based on the recent galactic core black hole mass density increase
A mechanism capable to provide a natural solution to two major cosmological
problems, i.e. the cosmic acceleration and the coincidence problem, is
proposed. A specific brane-bulk energy exchange mechanism produces a total dark
pressure, arising when adding all normal to the brane negative pressures in the
interior of galactic core black holes. This astrophysically produced negative
dark pressure explains cosmic acceleration and why the dark energy today is of
the same order to the matter density for a wide range of the involved
parameters. An exciting result of the analysis is that the recent rise of the
galactic core black hole mass density causes the recent passage from cosmic
deceleration to acceleration. Finally, it is worth mentioning that this work
corrects a wide spread fallacy among brane cosmologists, i.e. that escaping
gravitons result to positive dark pressure.Comment: 14 pages, 3 figure
Drag Force in a Charged N=4 SYM Plasma
Following recent developments, we employ the AdS/CFT correspondence to
determine the drag force exerted on an external quark that moves through an N=4
super-Yang-Mills plasma with a non-zero R-charge density (or, equivalently, a
non-zero chemical potential). We find that the drag force is larger than in the
case where the plasma is neutral, but the dependence on the charge is
non-monotonic.Comment: 16 pages, 1 eps figure; v2: references added, typos fixed; v3: more
general ansatz, new nontrivial solution obtained, nonmonotonicity of the drag
force made explicit in new figure, version to appear in JHE
From Fundamental Strings to Small Black Holes
We give evidence in favour of a string/black hole transition in the case of
BPS fundamental string states of the Heterotic string. Our analysis goes beyond
the counting of degrees of freedom and considers the evolution of dynamical
quantities in the process. As the coupling increases, the string states
decrease their size up to the string scale when a small black hole is formed.
We compute the absorption cross section for several fields in both the black
hole and the perturbative string phases. At zero frequency, these cross
sections can be seen as order parameters for the transition. In particular, for
the scalars fixed at the horizon the cross section evolves to zero when the
black hole is formed.Comment: 36 pages, 4 figures, argument about minimally coupled scalar
absorption cross section clarifie
Stretched Horizon and Entropy of Superstars
Amongst the class of supergravity solutions found by Lin, Lunin and
Maldacena, we consider pure and mixed state configurations generated by phase
space densities in the dual fermionic picture. A one-to-one map is constructed
between the phase space densities and piecewise monotonic curves, which
generalize the Young diagrams corresponding to pure states. Within the
fermionic phase space picture, a microscopic formula for the entropy of mixed
states is proposed. Considering thermal ensembles, agreement is found between
the thermodynamic and the proposed microscopic entropies. Furthermore, we study
fluctuations in thermodynamic ensembles for the superstar and compare the
entropy of these ensembles with the area of stretched horizons predicted by the
mean fluctuation size.Comment: 21 pages, 3 figures, 2 references adde
Typicality versus thermality: An analytic distinction
In systems with a large degeneracy of states such as black holes, one expects
that the average value of probe correlation functions will be well approximated
by the thermal ensemble. To understand how correlation functions in individual
microstates differ from the canonical ensemble average and from each other, we
study the variances in correlators. Using general statistical considerations,
we show that the variance between microstates will be exponentially suppressed
in the entropy. However, by exploiting the analytic properties of correlation
functions we argue that these variances are amplified in imaginary time,
thereby distinguishing pure states from the thermal density matrix. We
demonstrate our general results in specific examples and argue that our results
apply to the microstates of black holes.Comment: 22 pages + appendices, 3 eps figure
The calibration of the Sudbury Neutrino Observatory using uniformly distributed radioactive sources
The production and analysis of distributed sources of 24Na and 222Rn in the
Sudbury Neutrino Observatory (SNO) are described. These unique sources provided
accurate calibrations of the response to neutrons, produced through
photodisintegration of the deuterons in the heavy water target, and to low
energy betas and gammas. The application of these sources in determining the
neutron detection efficiency and response of the 3He proportional counter
array, and the characteristics of background Cherenkov light from trace amounts
of natural radioactivity is described.Comment: 24 pages, 13 figure
Note on New Massive Gravity in
In this note we study the properties of linearized gravitational excitations
in the new massive gravity theory in asymptotically spacetime and find
that there is also a critical point for the mass parameter at which massive
gravitons become massless as in topological massive gravity in .
However, at this critical point in the new massive gravity the energy of all
branches of highest weight gravitons vanish and the central charges also vanish
within the Brown-Henneaux boundary conditions. The new massive gravity in
asymptotically spacetime seems to be trivial at this critical point
under the Brown-Henneaux boundary conditions if the Brown-Henneaux boundary
conditions can be consistent with this theory. At this point, the boundary
conditions of log gravity may be preferred.Comment: v3 typos corrected, refs added, version to appear in JHE
Chiral Gravity in Three Dimensions
Three dimensional Einstein gravity with negative cosmological constant
-1/\ell^2 deformed by a gravitational Chern-Simons action with coefficient
1/\mu is studied in an asymptotically AdS_3 spacetime. It is argued to violate
unitary or positivity for generic \mu due to negative-energy massive gravitons.
However at the critical value \mu\ell=1, the massive gravitons disappear and
BTZ black holes all have mass and angular momentum related by \ell M=J. The
corresponding chiral quantum theory of gravity is conjectured to exist and be
dual to a purely right-moving boundary CFT with central charges
(c_L,c_R)=(0,3\ell /G).Comment: 21 pages, published version, typos corrected, more reference adde
Spinning Strings as Small Black Rings
Certain supersymmetric elementary string states with spin can be viewed as
small black rings whose horizon has the topology of S^1 \times S^{d-3} in a
d-dimensional string theory. By analyzing the singular black ring solution in
the supergravity approximation, and using various symmetries of the \alpha'
corrected effective action we argue that the Bekenstein-Hawking-Wald entropy of
the black string solution in the full string theory agrees with the statistical
entropy of the same system up to an overall normalization constant. While the
normalization constant cannot be determined by the symmetry principles alone,
it can be related to a similar normalization constant that appears in the
expression for small black holes without angular momentum in one less
dimension. Thus agreement between statistical and macroscopic entropy of
(d-1)-dimensional non-rotating elementary string states would imply a similar
agreement for a d-dimensional elementary string state with spin. Our analysis
also determines the structure of the near horizon geometry and provides us with
a geometric derivation of the Regge bound. These studies give further evidence
that a ring-like horizon is formed when large angular momentum is added to a
small black hole.Comment: LaTeX file, 31 pages; v2: references to earlier work adde
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