25,317 research outputs found
Probing Fuzzballs with Particles, Waves and Strings
We probe D1D5 micro-state geometries with massless particles, waves and
strings. To this end, we study geodetic motion, Klein-Gordon equation and
string scattering in the resulting gravitational background. Due to the reduced
rotational symmetry, even in the simple case of a circular fuzzball, the system
cannot be integrated elementarily. Yet, for motion in the plane of the string
profile or in the orthogonal plane to it, one can compute the deflection angle
or the phase shift and identify the critical impact parameter, at which even a
massless probe is captured by the fuzzball if its internal momentum is properly
tuned. We find agreement among the three approaches, thus giving further
support to the fuzzball proposal at the dynamical level.Comment: 35 pages. Extended and improved discussions on the integrability of
the geodetic equations and on the critical impact parameter
D-brane Instantons on the T^6/Z_3 orientifold
We give a detailed microscopic derivation of gauge and stringy instanton
generated superpotentials for gauge theories living on D3-branes at
Z_3-orientifold singularities. Gauge instantons are generated by D(-1)-branes
and lead to Affleck, Dine and Seiberg (ADS) like superpotentials in the
effective N=1 gauge theories with three generations of bifundamental and
anti/symmetric matter. Stringy instanton effects are generated by Euclidean
ED3-branes wrapping four-cycles on T^6/\Z_3. They give rise to Majorana masses
in one case and non-renormalizable superpotentials for the other cases. Finally
we determine the conditions under which ADS like superpotentials are generated
in N=1 gauge theories with adjoints, fundamentals, symmetric and antisymmetric
chiral matter.Comment: 31 pages, no figure
The emotional contagion in children with autism spectrum disorder
Studies of the last decade have demonstrated that children with Autism
Spectrum Disorder (ASD) showed difficulties in language, social and relational
areas, but they had also impairment in the mechanisms of embodied simulation,
namely the imitative behaviors that allow the body to give an experiential
meaning to own and other’s emotions. The identification of this specific emotional
response in ASD children, also defined as emotional contagion, allows to move
the therapeutic focus from reducing the behavioral symptomatic expressions of
the child to promoting the expression of his ability of emotional regulation. The
aim of this study was to investigate the presence of emotional contagion in 53
ASD children aged between 22 and 66 months, through the Test of emotional
contagion and verify the presence of compromised emotional contagion areas.
Our findings have shown that the severity of the disorder is closely related to
the inability of the child to respond to the emotional stimuli, regardless from
cognitive abilities, and that emotion to which children responded most frequently
was happiness, while the one who responded less was anger
Wilson-'t Hooft operators and the theta angle
We consider -dimensional Yang-Mills theory on a
space-time with a compact spatial direction, and prove the following result:
Under a continuous increase of the theta angle , a 't
Hooft operator associated with a closed spatial curve that
winds around the compact direction undergoes a monodromy . The new 't Hooft operator transforms
under large gauge transformations in the same way as the product , where is the Wilson operator associated with the curve
and the fundamental representation of SU(N).Comment: 7 page
Massive higher spins and holography
We review recent progress towards the understanding of higher spin gauge
symmetry breaking in AdS space from a holographic vantage point. According to
the AdS/CFT correspondence, N=4 SYM theory at vanishing coupling constant
should be dual to a theory in AdS which exhibits higher spin gauge symmetry
enhancement. When the SYM coupling is non-zero, all but a handful of HS
currents are violated by anomalies, and correspondingly local higher spin
symmetry in the bulk gets spontaneously broken. In agreement with previous
results and holographic expectations, we find that, barring one notable
exception (spin 1 eating spin 0), the Goldstone modes responsible for HS
symmetry breaking in AdS have non-vanishing mass even in the limit in which the
gauge symmetry is restored. We show that spontaneous breaking a' la
Stueckelberg implies that the mass of the relevant spin s'=s-1 Goldstone field
is exactly the one predicted by the correspondence.Comment: 8 pages, talk presented by M.B. at the "Fourth Meeting on Constrained
Dynamics and Quantum gravity" held in Cala Gonone (Sardinia, Italy),
September 12-16, 200
A search for changing-look AGN in the Grossan catalog
We observed with XMM-Newton 4 objects selected from the Grossan catalog, with
the aim to search for new 'changing-look' AGN. The sample includes all the
sources which showed in subsequent observations a flux much lower than the one
measured with HEAO A-1: NGC 7674, NGC 4968, IRAS 13218+0552 and NGC 1667. None
of the sources was caught in a high flux state during the XMM-Newton
observations, whose analysis reveal they are all likely Compton-thick objects.
We suggest that, for all the sources, potential problems with the HEAO A-1
source identification and flux measurement prevent us from being certain that
the HEAO A-1 data represent a putative 'high' state for these objects.
Nonetheless, based on the high flux state and Compton-thin spectrum of its
GINGA observation, NGC 7674 represents probably the sixth known case of a
'changing-look' Seyfert 2 galaxy. From the X-ray variability pattern, we can
estimate a likely lower limit of a few parsec to the distance of the inner
walls of the torus in this object. Remarkably, IRAS 13218+0552 was not detected
by XMM-Newton, despite being currently classified as a Seyfert 1 with a large
[OIII] flux. However, the original classification was likely to be affected by
an extreme velocity outflow component in the emission lines. The object likely
harbors an highly obscured AGN and should be re-classified as a Type 2 source.Comment: 11 pages, 12 figures, accepted for publication in A&
From the emotional integration to the cognitive construction: the developmental approach of Turtle Project in children with autism spectrum disorder
Background: Children with autism spectrum disorder show a deficit in neurobiological processes. This deficit
hinders the development of intentional behavior and appropriate problem-solving, leading the child to implement
repetitive and stereotyped behaviors and to have difficulties in reciprocal interactions, empathy and in the
development of a theory of mind. The objective of this research is to verify the effectiveness of a relationship-based
approach on the positive evolution of autistic symptoms.
Method: A sample of 80 children with autism spectrum disorder was monitored during the first four years of
therapy, through a clinical diagnostic assessment at the time of intake and then in two follow-up.
Results: The results showed that through the Autism Diagnostic Observation Schedule it is possible to
assess the socio-relational key elements on which the therapy is based. There was evidence, in fact, of significant
improvements after two and four years of therapy, both for children with severe autistic symptoms and for those in
autistic spectrum.
Conclusions: Socio-relational aspects represent the primary element on which work in therapy with autistic
children and can be considered as indicators of a positive evolution and prognosis that will produce improvements
even in the cognitive are
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