11,318 research outputs found
Towards a Coulomb gas of instantons in the SO(4)xU(1) Higgs model on R_4
The Higgs model on is extended by a term so
that the action receives a nonvanishing contribution from the interactions of
2-instantons and 3-instantons, and can be expressed as the inverse of the
Laplacian on in terms of the mutual distances of the instantons. The
one-instanton solutions of both the basic and the extended models have been
studied in detail numerically.Comment: 29 pages LaTeX, 4 Figures available from authors on reques
Evidence for nonlinear diffusive shock acceleration of cosmic-rays in the 2006 outburst of the recurrent nova RS Ophiuchi
Spectroscopic observations of the 2006 outburst of the recurrent nova RS
Ophiuchi at both infrared (IR) and X-ray wavelengths have shown that the blast
wave has decelerated at a higher rate than predicted by the standard
test-particle adiabatic shock-wave model. Here we show that the observed
evolution of the nova remnant can be explained by the diffusive shock
acceleration of particles at the blast wave and the subsequent escape of the
highest energy ions from the shock region. Nonlinear particle acceleration can
also account for the difference of shock velocities deduced from the IR and
X-ray data. The maximum energy that accelerated electrons and protons can have
achieved in few days after outburst is found to be as high as a few TeV. Using
the semi-analytic model of nonlinear diffusive shock acceleration developed by
Berezhko & Ellison, we show that the postshock temperature of the shocked gas
measured with RXTE/PCA and Swift/XRT imply a relatively moderate acceleration
efficiency.Comment: Accepted for publication in ApJ
High-Fidelity Z-Measurement Error Correction of Optical Qubits
We demonstrate a quantum error correction scheme that protects against
accidental measurement, using an encoding where the logical state of a single
qubit is encoded into two physical qubits using a non-deterministic photonic
CNOT gate. For the single qubit input states |0>, |1>, |0>+|1>, |0>-|1>,
|0>+i|1>, and |0>-i|1> our encoder produces the appropriate 2-qubit encoded
state with an average fidelity of 0.88(3) and the single qubit decoded states
have an average fidelity of 0.93(5) with the original state. We are able to
decode the 2-qubit state (up to a bit flip) by performing a measurement on one
of the qubits in the logical basis; we find that the 64 1-qubit decoded states
arising from 16 real and imaginary single qubit superposition inputs have an
average fidelity of 0.96(3).Comment: 4 pages, 4 figures, comments welcom
Changing social contracts in climate-change adaptation
Risks from extreme weather events are mediated through
state, civil society and individual action
1
,
2
. We propose evolving
social contracts as a primary mechanism by which adaptation
to climate change proceeds. We use a natural experiment
of policy and social contexts of the UK and Ireland affected
by the same meteorological event and resultant flooding in
November 2009. We analyse data from policy documents and
from household surveys of 356 residents in western Ireland and
northwest England. We find significant differences between
perceptions of individual responsibility for protection across
the jurisdictions and between perceptions of future risk from
populations directly affected by flooding events. These explain
differences in stated willingness to take individual adaptive
actions when state support retrenches. We therefore show
that expectations for state protection are critical in mediating
impacts and promoting longer-term adaptation. We argue
that making social contracts explicit may smooth pathways to
effective and legitimate adaptation
XMM-Newton observations of Nova Sgr 1998
We report on X-ray observations of Nova Sagittarius 1998 (V4633 Sgr),
performed with XMM-Newton at three different epochs, 934, 1083 and 1265 days
after discovery. The nova was detected with the EPIC cameras at all three
epochs, with emission spanning the whole energy range from 0.2 to 10 keV.
The X-ray spectra do not change significantly at the different epochs, and
are well fitted for the first and third observations with a multi-temperature
optically thin thermal plasma, while lower statistics in the second
observations lead to a poorer fit. The thermal plasma emission is most probably
originated in the shock heated ejecta, with chemical composition similar to
that of a CO nova. However, we can not completely rule out reestablished
accretion as the origin of the emission. We also obtain upper limits for the
temperature and luminosity of a potential white dwarf atmospheric component,
and conclude that hydrogen burning had already turned-off by the time of our
observations.Comment: 18 pages, 3 figures. Accepted in Astrophysical Journa
An All Optical Fibre Quantum Controlled-NOT Gate
We report the first experimental demonstration of an optical controlled-NOT
gate constructed entirely in fibre. We operate the gate using two heralded
optical fibre single photon sources and find an average logical fidelity of 90%
and an average process fidelity of 0.83<F<0.91. On the basis of a simple model
we are able to conclude that imperfections are primarily due to the photon
sources, meaning that the gate itself works with very high fidelity.Comment: 4 pages, 4 figures, comments welcom
Quantum gate characterization in an extended Hilbert space
We describe an approach for characterizing the process of quantum gates using
quantum process tomography, by first modeling them in an extended Hilbert
space, which includes non-qubit degrees of freedom. To prevent unphysical
processes from being predicted, present quantum process tomography procedures
incorporate mathematical constraints, which make no assumptions as to the
actual physical nature of the system being described. By contrast, the
procedure presented here ensures physicality by placing physical constraints on
the nature of quantum processes. This allows quantum process tomography to be
performed using a smaller experimental data set, and produces parameters with a
direct physical interpretation. The approach is demonstrated by example of
mode-matching in an all-optical controlled-NOT gate. The techniques described
are non-specific and could be applied to other optical circuits or quantum
computing architectures.Comment: 4 pages, 2 figures, REVTeX (published version
Finite energy/action solutions of Yang-Mills equations on Schwarzschild and deSitter backgrounds for dimension
Physically relevant gauge and gravitational theories can be seen as special
members of hierarchies of more elaborate systems. The Yang-Mills (YM) system is
the first member of a hierarchy of Lagrangians which we will index by ,
and the Einstein-Hilbert (EH) system of general relativity is the first member
of another hierarchy which we index by . In this paper, we study the
classical equations of the YM hierarchy considered in the
background of special geometries (Schwarzschild, deSitter,anti-deSitter) of the
EH hierarchy. Solutions are obtained in various dimensions and lead
to several examples of non-self-dual YM fields. When self-dual
solutions exist in addition. Their action is equal to the Chern-Pontryagin
charge and can be compared with that of the non-self-dual solutions.Comment: LaTeX, 25 pages, 2 figures, new title, minor change
Swift observations of the 2006 outburst of the recurrent nova RS Ophiuchi: I. Early X-ray emission from the shocked ejecta and red giant wind
RS Ophiuchi began its latest outburst on 2006 February 12. Previous outbursts
have indicated that high velocity ejecta interact with a pre-existing red giant
wind, setting up shock systems analogous to those seen in Supernova Remnants.
However, in the previous outburst in 1985, X-ray observations did not commence
until 55 days after the initial explosion. Here we report on Swift observations
covering the first month of the 2006 outburst with the Burst Alert (BAT) and
X-ray Telescope (XRT) instruments. RS Oph was clearly detected in the BAT 14-25
keV band from t=0 to days. XRT observationsfrom 0.3-10 keV, started at
3.17 days after outburst. The rapidly evolving XRT spectra clearly show the
presence of both line and continuum emission which can be fitted by thermal
emission from hot gas whose characteristic temperature, overlying absorbing
column, , and resulting unabsorbed total flux decline monotonically
after the first few days. Derived shock velocities are in good agreement with
those found from observations at other wavelengths. Similarly, is in
accord with that expected from the red giant wind ahead of the forward shock.
We confirm the basic models of the 1985 outburst and conclude that standard
Phase I remnant evolution terminated by days and the remnant then
rapidly evolved to display behaviour characteristic of Phase III. Around t=26
days however, a new, luminous and highly variable soft X-ray source began to
appear whose origin will be explored in a subsequent paper.Comment: 20 pages, 4 figures (2 updated), accepted by Ap
Infrared afterglow of GRB041219 as a result of reradiation on dust in a circumstellar cloud
Observations of gamma ray bursts (GRB) afterglows in different spectral bands
provide a most valuable information about their nature, as well as about
properties of surrounding medium. Powerful infrared afterglow was observed from
the strong GRB041219. Here we explain the observed IR afterglow in the model of
a dust reradiation of the main GRB signal in the envelope surrounding the GRB
source. In this model we do not expect appearance of the prompt optical
emission which should be absorbed in the dust envelope. We estimate the
collimation angle of the gamma ray emission, and obtain restrictions on the
redshift (distance to GRB source), by fitting the model parameters to the
observational data.Comment: 6 pages, 2 figures, Submited to Astrofizik
- …