217 research outputs found
“With a View to Speech”
The Beast & the Sovereign, by Jacques Derrida, 2 volumes, translated by Geoffrey Bennington, edited by Geoffrey Bennington and Peggy Kamuf. The Seminars of Jacques Derrida. Chicago: University of Chicago Press, 2009 and 2011. Volume 1, 349 pp. 38.00 cloth. Volume 2, 293 pp. 35.00 cloth
Gamma-Ray Burst without Baryonic and Magnetic Load?
We show that, contrary to common belief, internal shocks can arise in an
accelerating radiation-dominated jet if it is confined even weakly to a
converging opening angle because the acceleration declines. The
radiation-dominated internal shock (RDIS) enables a very efficient yet highly
nonthermal emission by Fermi-like photon acceleration, keeping the
electron-positron () pair photosphere and inertia up to a high Lorentz
factor >1000. In gamma-ray bursts (GRBs), a weak confinement would persist
beyond the progenitor star or surrounding matter because of the fast cocoon
accompanying the breakout jet. The simplest model predicts few high-energy
cosmic rays and neutrinos, and a correlation between the early afterglow and
the GeV-TeV prompt emission. The central engine allows a less fine-tuned baryon
load than previously thought, even including pure-leptonic unmagnetized
outflows.Comment: 10 pages, 3 figures, final version to be published in Progress of
Theoretical Physic
Hydrodynamical effects in internal shock of relativistic outflows
We study both analytically and numerically hydrodynamical effects of two
colliding shells, the simplified models of the internal shock in various
relativistic outflows such as gamma-ray bursts and blazars. We pay particular
attention to three interesting cases: a pair of shells with the same rest mass
density (``{\it equal rest mass density}''), a pair of shells with the same
rest mass (``{\it equal mass}''), and a pair of shells with the same bulk
kinetic energy (``{\it equal energy}'') measured in the intersteller medium
(ISM) frame. We find that the density profiles are significantly affected by
the propagation of rarefaction waves. A split-feature appears at the contact
discontinuity of two shells for the ``equal mass'' case, while no significant
split appears for the ``equal energy'' and ``equal rest mass density'' cases.
The shell spreading with a few ten percent of the speed of light is also shown
as a notable aspect caused by rarefaction waves. The conversion efficiency of
the bulk kinetic energy to internal one is numerically evaluated. The time
evolutions of the efficiency show deviations from the widely-used inellastic
two-point-mass-collision model.Comment: 29 pages, 16 figures, accepted by Ap
Deterministic quantum teleportation of photonic quantum bits by a hybrid technique
Quantum teleportation allows for the transfer of arbitrary, in principle,
unknown quantum states from a sender to a spatially distant receiver, who share
an entangled state and can communicate classically. It is the essence of many
sophisticated protocols for quantum communication and computation. In order to
realize flying qubits in these schemes, photons are an optimal choice, however,
teleporting a photonic qubit has been limited due to experimental
inefficiencies and restrictions. Major disadvantages have been the
fundamentally probabilistic nature of linear-optics Bell measurements as well
as the need for either destroying the teleported qubit or attenuating the input
qubit when the detectors do not resolve photon numbers. Here we experimentally
realize fully deterministic, unconditional quantum teleportation of photonic
qubits. The key element is to make use of a "hybrid" technique:
continuous-variable (CV) teleportation of a discrete-variable, photonic qubit.
By optimally tuning the receiver's feedforward gain, the CV teleporter acts as
a pure loss channel, while the input dual-rail encoded qubit, based on a single
photon, represents a quantum error detection code against amplitude damping and
hence remains completely intact for most teleportation events. This allows for
a faithful qubit transfer even with imperfect CV entangled states: the overall
transfer fidelities range from 0.79 to 0.82 for four distinct qubits, all of
them exceeding the classical limit of teleportation. Furthermore, even for a
relatively low level of the entanglement, qubits are teleported much more
efficiently than in previous experiments, albeit post-selectively (taking into
account only the qubit subspaces), with a fidelity comparable to the previously
reported values
Thermal Radiation from GRB Jets
In this study, the light curves and spectrum of the photospheric thermal
radiation from ultrarelativistic gamma-ray burst (GRB) jets are calculated
using 2D relativistic hydrodynamic simulations of jets from a collapsar. As the
jet advances, the density around the head of the jet decreases, and its Lorentz
factor reaches as high as 200 at the photosphere and 400 inside the
photosphere. For an on-axis observer, the photosphere appears concave shaped
due to the low density and high beaming factor of the jet. The luminosity
varies because of the abrupt change in the position of the photosphere due to
the internal structure of the jet. Comparing our results with GRB090902B, the
flux level of the thermal-like component is similar to our model, although the
peak energy looks a little bit higher (but still within a factor of 2). From
the comparison, we estimate that the bulk Lorentz factor of GRB090902B is
) where is the radius of the
photosphere. The spectrum for an on-axis observer is harder than that for an
off-axis observer. There is a time lag of a few seconds for high energy bands
in the light curve. This may be the reason for the delayed onset of GeV
emission seen in GRB080916C. The spectrum below the peak energy is a power law
and the index is which is softer than that of single temperature
plank distribution but still harder than that of typical value of observed one.Comment: 15 pages, 5 figures, revised to Ap
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