21,862 research outputs found
Additivity of Entangled Channel Capacity for Quantum Input States
An elementary introduction into algebraic approach to unified quantum
information theory and operational approach to quantum entanglement as
generalized encoding is given. After introducing compound quantum state and two
types of informational divergences, namely, Araki-Umegaki (a-type) and of
Belavkin-Staszewski (b-type) quantum relative entropic information, this paper
treats two types of quantum mutual information via entanglement and defines two
types of corresponding quantum channel capacities as the supremum via the
generalized encodings. It proves the additivity property of quantum channel
capacities via entanglement, which extends the earlier results of V. P.
Belavkin to products of arbitrary quantum channels for quantum relative entropy
of any type.Comment: 17 pages. See the related papers at
http://www.maths.nott.ac.uk/personal/vpb/research/ent_com.htm
Identification of Candidate Millisecond Pulsars from Fermi LAT Observations II
Following our work presented in Dai et al. (2016), we report our detailed
data analysis for another 38 Fermi gamma-ray un-associated sources. These
sources are selected from the Fermi Large Area Telescope (LAT) third source
catalog on the basis of the properties of known gamma-ray millisecond pulsars
(MSPs) and for the purpose of finding likely candidate MSPs. From our analysis
of the LAT data, we identify that among the 38 sources, 28 of them are single
point-like sources with clean background and their spectra show significant
curvature. We also conduct analysis of archival X-ray data available for 24 of
the 28 sources. In the fields of 10 sources, there are at least one X-ray
object, and in those of the other 14 sources, no X-ray object is detected but
probably due to the X-ray observations being short. We discuss the possible MSP
nature for these sources. Six of them(J0514.6-4406, J1035.7-6720, J1624.2-4041,
J1744.1-7619, J1946.4-5403, and J2039.6-5618) are most likely associated with
pulsars because of multi-wavelength identifications including direct radio or
gamma-ray detection of pulsations. To firmly establish the associations or
verify the MSP nature for other sources, deep X-ray and/or optical observations
are needed.Comment: 18 pages, 4 figure
Environment and Energy Injection Effects in GRB Afterglows
In a recent paper (Dai & Lu 1999), we have proposed a simple model in which
the steepening in the light curve of the R-band afterglow of the gamma-ray
burst (GRB) 990123 is caused by the adiabatic shock which has evolved from an
ultrarelativistic phase to a nonrelativistic phase in a dense medium. We find
that such a model is quite consistent with observations if the medium density
is about . Here we discuss this model in more
details. In particular, we investigate the effects of synchrotron self
absorption and energy injection. A shock in a dense medium becomes
nonrelativistic rapidly after a short relativistic phase. The afterglow from
the shock at the nonrelativistic stage decays more rapidly than at the
relativistic stage. Since some models for GRB energy sources predict that a
strongly magnetic millisecond pulsar may be born during the formation of GRB,
we discuss the effect of such a pulsar on the evolution of the nonrelativistic
shock through magnetic dipole radiation. We find that after the energy which
the shock obtains from the pulsar is much more than the initial energy of the
shock, the afterglow decay will flatten significantly. When the pulsar energy
input effect disappears, the decay will steepen again. These features are in
excellent agreement with the afterglows of GRB 980519, GRB 990510 and GRB
980326. Furthermore, our model fits very well all the observational data of GRB
980519 including the last two detections.Comment: 21 pages, LaTeX, accepted for publication in ApJ, one paragraph adde
Production of black holes and their angular momentum distribution in models with split fermions
In models with TeV-scale gravity it is expected that mini black holes will be
produced in near-future accelerators. On the other hand, TeV-scale gravity is
plagued with many problems like fast proton decay, unacceptably large
neutron-antineutron oscillations, flavor changing neutral currents, large
mixing between leptons, etc. Most of these problems can be solved if different
fermions are localized at different points in the extra dimensions. We study
the cross-section for the production of black holes and their angular momentum
distribution in these models with "split" fermions. We find that, for a fixed
value of the fundamental mass scale, the total production cross section is
reduced compared with models where all the fermions are localized at the same
point in the extra dimensions. Fermion splitting also implies that the bulk
component of the black hole angular momentum must be taken into account in
studies of the black hole decay via Hawking radiation.Comment: accepted for publication in Phys. Rev.
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