2,013 research outputs found
Evidence for the PSL(22) Wess-Zumino-Novikov-Witten model as a model for the plateau transition in Quantum Hall effect: Evaluation of numerical simulations
In this paper I revise arguments in favour of the PSL(22)
Wess-Zumino-Novikov-Witten (WZNW) model as a theory of the plateau transition
in Integer Quantum Hall effect. I show that all available numerical data
(including the correlation length exponent ) are consistent with the
predictions of such WZNW model with the level .Comment: 11 pages, no figure
Asymptotic Symmetries of String Theory on AdS3 X S3 with Ramond-Ramond Fluxes
String theory on AdS3 space-times with boundary conditions that allow for
black hole states has global asymptotic symmetries which include an infinite
dimensional conformal algebra. Using the conformal current algebra for
sigma-models on PSU(1,1|2), we explicitly construct the R-symmetry and Virasoro
charges in the worldsheet theory describing string theory on AdS3 X S3 with
Ramond-Ramond fluxes. We also indicate how to construct the full boundary
superconformal algebra. The boundary superconformal algebra plays an important
role in classifying the full spectrum of string theory on AdS3 with
Ramond-Ramond fluxes, and in the microscopic entropy counting in D1-D5 systems.Comment: 30 page
Optimized Dynamical Decoupling for Time Dependent Hamiltonians
The validity of optimized dynamical decoupling (DD) is extended to
analytically time dependent Hamiltonians. As long as an expansion in time is
possible the time dependence of the initial Hamiltonian does not affect the
efficiency of optimized dynamical decoupling (UDD, Uhrig DD). This extension
provides the analytic basis for (i) applying UDD to effective Hamiltonians in
time dependent reference frames, for instance in the interaction picture of
fast modes and for (ii) its application in hierarchical
DD schemes with pulses about two perpendicular axes in spin space. to
suppress general decoherence, i.e., longitudinal relaxation and dephasing.Comment: 5 pages, no figure
Co-sputtered MoRe thin films for carbon nanotube growth-compatible superconducting coplanar resonators
Molybdenum rhenium alloy thin films can exhibit superconductivity up to
critical temperatures of . At the same time, the films are
highly stable in the high-temperature methane / hydrogen atmosphere typically
required to grow single wall carbon nanotubes. We characterize molybdenum
rhenium alloy films deposited via simultaneous sputtering from two sources,
with respect to their composition as function of sputter parameters and their
electronic dc as well as GHz properties at low temperature. Specific emphasis
is placed on the effect of the carbon nanotube growth conditions on the film.
Superconducting coplanar waveguide resonators are defined lithographically; we
demonstrate that the resonators remain functional when undergoing nanotube
growth conditions, and characterize their properties as function of
temperature. This paves the way for ultra-clean nanotube devices grown in situ
onto superconducting coplanar waveguide circuit elements.Comment: 8 pages, 6 figure
Unveiling Soft Gamma-Ray Repeaters with INTEGRAL
Thanks to INTEGRAL's long exposures of the Galactic Plane, the two brightest
Soft Gamma-Ray Repeaters, SGR 1806-20 and SGR 1900+14, have been monitored and
studied in detail for the first time at hard-X/soft gamma rays.
This has produced a wealth of new scientific results, which we will review
here. Since SGR 1806-20 was particularly active during the last two years, more
than 300 short bursts have been observed with INTEGRAL. and their
characteristics have been studied with unprecedented sensitivity in the 15-200
keV range. A hardness-intensity anticorrelation within the bursts has been
discovered and the overall Number-Intensity distribution of the bursts has been
determined. In addition, a particularly active state, during which ~100 bursts
were emitted in ~10 minutes, has been observed on October 5 2004, indicating
that the source activity was rapidly increasing. This eventually led to the
Giant Flare of December 27th 2004, for which a possible soft gamma-ray (>80
keV) early afterglow has been detected.
The deep observations allowed us to discover the persistent emission in hard
X-rays (20-150 keV) from 1806-20 and 1900+14, the latter being in a quiescent
state, and to directly compare the spectral characteristics of all Magnetars
(two SGRs and three Anomalous X-ray Pulsars) detected with INTEGRAL.Comment: 8 pages, 7 figures, Presented at the conference "Isolated Neutron
Stars: from the Surface to the Interior", London, UK, 24-28 April 200
Spin-down rate and inferred dipole magnetic field of the soft gamma-ray repeater SGR 1627-41
Using Chandra data taken on 2008 June, we detected pulsations at 2.59439(4) s
in the soft gamma-ray repeater SGR 1627-41. This is the second measurement of
the source spin period and allows us to derive for the first time a long-term
spin-down rate of (1.9 +/- 0.4)E-11 s/s. From this value we infer for SGR
1627-41 a characteristic age of 2.2 kyr, a spin-down luminosity of 4E+34 erg/s
(one of the highest among sources of the same class), and a surface dipole
magnetic field strength of 2E+14 G. These properties confirm the magnetar
nature of SGR 1627-41; however, they should be considered with caution since
they were derived on the basis of a period derivative measurement made using
two epochs only and magnetar spin-down rates are generally highly variable. The
pulse profile, double-peaked and with a pulsed fraction of (13 +/- 2)% in the
2-10 keV range, closely resembles that observed by XMM-Newton in 2008
September. Having for the first time a timing model for this SGR, we also
searched for a pulsed signal in archival radio data collected with the Parkes
radio telescope nine months after the previous X-ray outburst. No evidence for
radio pulsations was found, down to a luminosity level 10-20 times fainter (for
a 10% duty cycle and a distance of 11 kpc) than the peak luminosity shown by
the known radio magnetars.Comment: 5 pages, 2 figures; accepted for publication in MNRAS Letter
On Symmetry Enhancement in the psu(1,1|2) Sector of N=4 SYM
Strong evidence indicates that the spectrum of planar anomalous dimensions of
N=4 super Yang-Mills theory is given asymptotically by Bethe equations. A
curious observation is that the Bethe equations for the psu(1,1|2) subsector
lead to very large degeneracies of 2^M multiplets, which apparently do not
follow from conventional integrable structures. In this article, we explain
such degeneracies by constructing suitable conserved nonlocal generators acting
on the spin chain. We propose that they generate a subalgebra of the loop
algebra for the su(2) automorphism of psu(1,1|2). Then the degenerate
multiplets of size 2^M transform in irreducible tensor products of M
two-dimensional evaluation representations of the loop algebra.Comment: 35 pages, v2: references added, sign inconsistency resolved in
(5.5,5.6), v3: Section 3.4 on Hamiltonian added, minor improvements, to
appear in JHE
The dust-scattering X-ray rings of the anomalous X-ray pulsar 1E 1547.0-5408
On 2009 January 22 numerous strong bursts were detected from the anomalous
X-ray pulsar 1E 1547.0-5408. Swift/XRT and XMM-Newton/EPIC observations carried
out in the following two weeks led to the discovery of three X-ray rings
centered on this source. The ring radii increased with time following the
expansion law expected for a short impulse of X-rays scattered by three dust
clouds. Assuming different models for the dust composition and grain size
distribution, we fit the intensity decay of each ring as a function of time at
different energies, obtaining tight constrains on the distance of the X-ray
source. Although the distance strongly depends on the adopted dust model, we
find that some models are incompatible with our X-ray data, restricting to 4-8
kpc the range of possible distances for 1E 1547.0-5408. The best-fitting dust
model provides a source distance of 3.91 +/- 0.07 kpc, which is compatible with
the proposed association with the supernova remnant G 327.24-0.13, and implies
distances of 2.2 kpc, 2.6 kpc and 3.4 kpc for the dust clouds, in good
agreement with the dust distribution inferred by CO line observations towards
1E 1547.0-5408. However, dust distances in agreement with CO data are also
obtained for a set of similarly well-fitting models that imply a source
distance of about 5 kpc. A distance of about 4-5 kpc is also favored by the
fact that these dust models are already known to provide good fits to the
dust-scattering halos of bright X-ray binaries.Comment: Accepted for publication in The Astrophysical Journal; 10 pages in
emulate-apj style, 3 tables, 5 color figures. Note: abstract truncated; full
abstract in the pape
Efficient Coherent Control by Optimized Sequences of Pulses of Finite Duration
Reliable long-time storage of arbitrary quantum states is a key element for
quantum information processing. In order to dynamically decouple a spin or
quantum bit from a dephasing environment, we introduce an optimized sequence of
control pulses of finite durations \tau\pp and finite amplitudes. The
properties of this sequence of length stem from a mathematically rigorous
derivation. Corrections occur only in order and \tau\pp^3 without
mixed terms such as T^N\tau\pp or T^N\tau\pp^2. Based on existing
experiments, a concrete setup for the verification of the properties of the
advocated realistic sequence is proposed.Comment: 8 pages, 1 figur
The conformal current algebra on supergroups with applications to the spectrum and integrability
We compute the algebra of left and right currents for a principal chiral
model with arbitrary Wess-Zumino term on supergroups with zero Killing form. We
define primary fields for the current algebra that match the affine primaries
at the Wess-Zumino-Witten points. The Maurer-Cartan equation together with
current conservation tightly constrain the current-current and current-primary
operator product expansions. The Hilbert space of the theory is generated by
acting with the currents on primary fields. We compute the conformal dimensions
of a subset of these states in the large radius limit. The current algebra is
shown to be consistent with the quantum integrability of these models to
several orders in perturbation theory.Comment: 45 pages. Minor correction
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