375 research outputs found
Correlation Functions in -Deformed N=6 Supergravity
Gauged N=8 supergravity in four dimensions is now known to admit a
deformation characterized by a real parameter lying in the interval
. We analyse the fluctuations about its anti-de Sitter
vacuum, and show that the full N=8 supersymmetry can be maintained by the
boundary conditions only for . For non-vanishing , and
requiring that there be no propagating spin s>1 fields on the boundary, we show
that N=3 is the maximum degree of supersymmetry that can be preserved by the
boundary conditions. We then construct in detail the consistent truncation of
the N=8 theory to give -deformed SO(6) gauged N=6 supergravity, again
with in the range . We show that this theory
admits fully N=6 supersymmetry-preserving boundary conditions not only for
, but also for . These two theories are related by a
U(1) electric-magnetic duality. We observe that the only three-point functions
that depend on involve the coupling of an SO(6) gauge field with the
U(1) gauge field and a scalar or pseudo-scalar field. We compute these
correlation functions and compare them with those of the undeformed N=6 theory.
We find that the correlation functions in the theory
holographically correspond to amplitudes in the U(N)_k x U(N)_{-k} ABJM model
in which the U(1) Noether current is replaced by a dynamical U(1) gauge field.
We also show that the -deformed N=6 gauged supergravities can be
obtained via consistent reductions from the eleven-dimensional or
ten-dimensional type IIA supergravities.Comment: 38 pages, one figur
Phase-dependent absorption features in X-ray spectra of X-ray Dim Isolated Neutron Stars
A detailed phase-resolved spectroscopy of archival XMM-Newton observations of X-ray Dim Isolated Neutron Stars (XDINSs) led to the discovery of narrow and strongly phase-dependent absorption features in two of these sources. The first was discovered in the X-ray spectrum of RX J0720.4-3125, followed by a new possible candidate in RX J1308.6+2127. Both spectral lines have similar properties: they are detected for only ∼ 20% of the rotational cycle and appear to be stable over the timespan covered by the observations. We performed Monte Carlo simulations to test the significance of these phase-variable features and in both cases the outcome has confirmed the detection with a confidence level > 4.6σ. Because of the narrow width and the strong dependence on the pulsar rotational phase, the most likely interpretation for these spectral features is in terms of resonant proton cyclotron absorption scattering in a confined high-B structure close to the stellar surface. Within the framework of this interpretation, our results provide evidence for deviations from a pure dipole magnetic field on small scales for highly magnetized neutron stars and support the proposed scenario of XDINSs being aged magnetars, with a strong non-dipolar crustal B-field component
Renewed activity from the magnetar CXOU J164710.2-455216
On 2018 February 5 at 19:27:11 UT, Swift BAT detected a new burst from a direction consistent with the magnetar CXOU J164710.2-455216 (trigger=808755; Barthelmy et al. 2018, GCN #22389)
Minimal Stability in Maximal Supergravity
Recently, it has been shown that maximal supergravity allows for
non-supersymmetric AdS critical points that are perturbatively stable. We
investigate this phenomenon of stability without supersymmetry from the
sGoldstino point of view. In particular, we calculate the projection of the
mass matrix onto the sGoldstino directions, and derive the necessary conditions
for stability. Indeed we find a narrow window allowing for stable SUSY breaking
points. As a by-product of our analysis, we find that it seems impossible to
perturb supersymmetric critical points into non-supersymmetric ones: there is a
minimal amount of SUSY breaking in maximal supergravity.Comment: 27 pages, 1 figure. v2: two typos corrected, published versio
Using Virtual Reality to Rehabilitate Neglect
Purpose: Virtual Reality (VR) platforms gained a lot of attention in the rehabilitation field due to their ability to engage patients and the opportunity they offer to use real world scenarios. As neglect is characterized by an impairment in exploring space that greatly affects daily living, VR could be a powerful tool compared to classical paper and pencil tasks and computer training. Nevertheless, available platforms are costly and obstructive. Here we describe a low cost platform for neglect rehabilitation, that using consumer equipments allows the patient to train at home in an intensive fashion.
Method: We tested the platform on IB, a chronic neglect patient, who did not benefit from classical rehabilitation.
Results: Our results show that IB improved both in terms of neglect and attention. Importantly, these ameliorations lasted at a follow up evaluation 5 months after the last treatment session and generalized to everyday life activities.
Conclusions: VR platforms built using equipment technology and following theoretical principles on brain functioning may induce greater ameliorations in visuo-spatial deficits than classical paradigms possibly thanks to the real world scenarios in association with the "visual feedback" of the patient's own body operating in the virtual environmen
The X-ray outburst of the Galactic Center magnetar over six years of Chandra observations
The magnetar SGR J1745-2900 discovered at parsecs distance from the Milky Way
central black hole, Sagittarius A*, represents the closest pulsar to a
supermassive black hole ever detected. Furthermore, its intriguing radio
emission has been used to study the environment of the black hole, as well as
to derive a precise position and proper motion for this object. The discovery
of SGR J1745-2900 has opened interesting debates about the number, age and
nature of pulsars expected in the Galactic center region. In this work, we
present extensive X-ray monitoring of the outburst of SGR J1745-2900 using the
Chandra X-ray Observatory, the only instrument with the spatial resolution to
distinguish the magnetar from the supermassive black hole (2.4" angular
distance). It was monitored from its outburst onset in April 2013 until August
2019, collecting more than fifty Chandra observations for a total of more than
2.3 Ms of data. Soon after the outburst onset, the magnetar emission settled
onto a purely thermal emission state that cooled from a temperature of about
0.9 to 0.6 keV over 6 years. The pulsar timing properties showed at least two
changes in the period derivative, increasing by a factor of about 4 during the
outburst decay. We find that the long-term properties of this outburst
challenge current models for the magnetar outbursts.Comment: 11 pages, 6 figures. Accepted by Ap
The X-ray evolution and geometry of the > 2018 outburst of XTE J1810-197
After 15 years, in late 2018, the magnetar XTE J1810–197 underwent a second recorded X-ray outburst event and reactivated as a radio pulsar. We initiated an Xray monitoring campaign to follow the timing and spectral evolution of the magnetar as its flux decays using Swift, XMM–Newton, NuSTAR, and NICER observations. During the year-long campaign, the magnetar reproduced similar behaviour to that found for the first outburst, with a factor of two change in its spin-down rate from ∼ 7.2 × 10−12 s s−1 to ∼ 1.5 × 10−11 s s−1 after two months. Unique to this outburst, we confirm the peculiar energy-dependent phase shift of the pulse profile. Following the initial outburst, the spectrum of XTE J1810–197 is well-modelled by multiple blackbody components corresponding to a pair of non-concentric, hot thermal caps surrounded by a cooler one, superposed to the colder star surface. We model the energy-dependent pulse profile to constrain the viewing and surface emission geometry and find that the overall geometry of XTE J1810–197 has likely evolved relative to that found for the 2003 event
- …