18,203 research outputs found
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
On Exact Symmetries and Massless Vectors in Holographic Flows and other Flux Vacua
We analyze the isometries of Type IIB flux vacua based on the
Papadopolous-Tseytlin ansatz and identify the related massless bulk vector
fields. To this end we devise a general ansatz, valid in any flux
compactification, for the fluctuations of the metric and p-forms that
diagonalizes the coupled equations. We then illustrate the procedure in the
simple case of holographic flows driven by the RR 3-form flux only.
Specifically we study the fate of the isometries of the Maldacena-Nunez
solution associated to wrapped D5-branes.Comment: 23 page
On the driver of relativistic effects strength in Seyfert galaxies
Spectroscopy of X-ray emission lines emitted in accretion discs around
supermassive black holes is one of the most powerful probes of the accretion
flow physics and geometry, while also providing in principle observational
constraints on the black hole spin.[...] We aim at determining the ultimate
physical driver of the strength of this relativistic reprocessing feature. We
first extend the hard X-ray flux-limited sample of Seyfert galaxies studied so
far (FERO, de la Calle Perez et al. 2010) to obscured objects up to a column
density N_H=6x10^23 atoms/cm/cm. We verify that none of the line properties
depends on the AGN optical classification, as expected from the Seyfert
unification scenarios. There is also no correlation between the accretion disc
inclination, as derived from formal fits of the line profiles, and the optical
type or host galaxy aspect angle, suggesting that the innermost regions of the
accretion disc and the host galaxy plane are not aligned. [...]. Data are not
sensitive enough to the detailed ionisation state of the line-emitting disc.
However, the lack of dependency of the line EW on either the luminosity or the
rest-frame centroid energy rules out that disc ionisation plays an important
role on the EW dynamical range in Seyferts. The dynamical range of the
relativistically broadened K-alpha iron line EW in nearby Seyferts appears to
be mainly determined by the properties of the innermost accretion flow. We
discuss several mechanisms (disc ionisation, disc truncation, aberration due to
a mildly relativistic outflowing corona) which can explain this. [...]
Observational data are still not in contradiction with scenarios invoking
different mechanisms for the spectral complexity around the iron line, most
notably the "partial covering" absorption scenario. (abridged).Comment: Accepted for publication on Astronomy & Astrophysics. 14 pages, 9
figure
New HErschel Multi-wavelength Extragalactic Survey of Edge-on Spirals (NHEMESES)
Edge-on spiral galaxies offer a unique perspective on the vertical structure
of spiral disks, both stars and the iconic dark dustlanes. The thickness of
these dustlanes can now be resolved for the first time with Herschel in
far-infrared and sub-mm emission. We present NHEMESES, an ongoing project that
targets 12 edge-on spiral galaxies with the PACS and SPIRE instruments on
Herschel. These vertically resolved observations of edge-on spirals will impact
on several current topics.
First and foremost, these Herschel observations will settle whether or not
there is a phase change in the vertical structure of the ISM with disk mass.
Previously, a dramatic change in dustlane morphology was observed as in massive
disks the dust collapses into a thin lane. If this is the case, the vertical
balance between turbulence and gravity dictates the ISM structure and
consequently star-formation and related phenomena (spiral arms, bars etc.). We
specifically target lower mass nearby edge-ons to complement existing Herschel
observations of high-mass edge-on spirals (the HEROES project).
Secondly, the combined data-set, together with existing Spitzer observations,
will drive a new generation of spiral disk Spectral Energy Distribution models.
These model how dust reprocesses starlight to thermal emission but the dust
geometry remains the critical unknown.
And thirdly, the observations will provide an accurate and unbiased census of
the cold dusty structures occasionally seen extending out of the plane of the
disk, when backlit by the stellar disk. To illustrate the NHEMESES project, we
present early results on NGC 4244 and NGC 891, two well studies examples of a
low and high-mass edge-on spiral.Comment: 3 pages, 4 figures, to appear in the proceedings of IAU 284, "The
Spectral Energy Distribution of Galaxies", (SED2011), 5-9 September 2011,
Preston, UK, editors, R.J. Tuffs & C.C.Popescu (v2 updated metadata
Prematurity and low birth weight baby at birth: from research to intervention
Este artigo apresenta uma revisão bibliográfica dos estudos que, no âmbito da psicologia, se dedicaram ao parto prematuro e ao baixo peso do bebé à nascença. Debruça-se especialmente sobre as causas e consequências, a curto e a longo prazo, apresentadas na investigação actual, contemplando os pais e o bebé. Discute ainda a intervenção, no que se refere às estratégias preventivas e remediativas úteis nesta situação.This article is a review of various studies
that, within the range of psychology,
have researched premature
labor and low birth weight at birth. It
focuses mostly on the causes and
consequences, both short and long
term, that are presented within the
line of research nowadays, considering
both parents and baby. It also
discusses intervention, concerning
preventive and remeditative strategies
that are suitable for this situation
On the spectrum of AdS/CFT beyond supergravity
We test the spectrum of string theory on AdS_5 x S^5 derived in
hep-th/0305052 against that of single-trace gauge invariant operators in free
N=4 super Yang-Mills theory. Masses of string excitations at critical tension
are derived by extrapolating plane-wave frequencies at g_{YM}=0 down to finite
J. On the SYM side, we present a systematic description of the spectrum of
single-trace operators and its reduction to PSU(2,2|4) superconformal primaries
via a refined Eratostenes' supersieve. We perform the comparison of the
resulting SYM/string spectra of charges and multiplicities order by order in
the conformal dimension \Delta up to \Delta=10 and find perfect agreement.
Interestingly, the SYM/string massive spectrum exhibits a hidden symmetry
structure larger than expected, with bosonic subgroup SO(10,2) and thirty-two
supercharges.Comment: 28 pages, LaTeX2
New Results on Holographic Three-Point Functions
We exploit a gauge invariant approach for the analysis of the equations
governing the dynamics of active scalar fluctuations coupled to the
fluctuations of the metric along holographic RG flows. In the present approach,
a second order ODE for the active scalar emerges rather simply and makes it
possible to use the Green's function method to deal with (quadratic)
interaction terms. We thus fill a gap for active scalar operators, whose
three-point functions have been inaccessible so far, and derive a general,
explicitly Bose symmetric formula thereof. As an application we compute the
relevant three-point function along the GPPZ flow and extract the irreducible
trilinear couplings of the corresponding superglueballs by amputating the
external legs on-shell.Comment: v2: reference added, typos corrected v3: sign convention for
background changed, agrees with version published in JHE
Photoabsorption on nuclei
We calculate the total photoabsorption cross section on nuclei in the energy
range from 300 MeV to 1 GeV within the framework of a semi-classical phase
space model. Besides medium modifications like Fermi motion and Pauli blocking
we focus on the collision broadening of the involved resonances. The resonance
contributions to the elementary cross section are fixed by fits to partial wave
amplitudes of pion photoproduction. The cross sections for ,
needed for the calculation of collision broadening, are obtained by detailed
balance from a fit to cross sections. We show that a
reasonable collision broadening is not able to explain the experimentally
observed disappearance of the -resonance in the photoabsorption
cross section on nuclei.Comment: 26 pages Latex including 9 postscript figure
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