26,862 research outputs found
A perturbative re-analysis of N=4 supersymmetric Yang--Mills theory
The finiteness properties of the N=4 supersymmetric Yang-Mills theory are
reanalyzed both in the component formulation and using N=1 superfields, in
order to discuss some subtleties that emerge in the computation of gauge
dependent quantities. The one-loop corrections to various Green functions of
elementary fields are calculated. In the component formulation it is shown that
the choice of the Wess-Zumino gauge, that is standard in supersymmetric gauge
theories, introduces ultraviolet divergences in the propagators at the one-loop
level. Such divergences are exactly cancelled when the contributions of the
fields that are put to zero in the Wess-Zumino gauge are taken into account. In
the description in terms of N=1 superfields infrared divergences are found for
every choice of gauge different from the supersymmetric generalization of the
Fermi-Feynman gauge. Two-, three- and four-point functions of N=1 superfields
are computed and some general features of the infrared problem are discussed.
We also examine the effect of the introduction of mass terms for the (anti)
chiral superfields in the theory, which break supersymmetry from N=4 to N=1. It
is shown that in the mass deformed model no ultraviolet divergences appear in
two-point functions. It argued that this result can be generalized to n-point
functions, supporting the proposal of a possible of use of this modified model
as a supersymmetry-preserving regularization scheme for N=1 theories.Comment: 41 pages, LaTeX2e, uses feynMP package to draw Feynman diagram
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
Pansharpening techniques to detect mass monument damaging in Iraq
The recent mass destructions of monuments in Iraq cannot be monitored with the terrestrial survey methodologies, for obvious reasons
of safety. For the same reasons, it’s not advisable the use of classical aerial photogrammetry, so it was obvious to think to the use of
multispectral Very High Resolution (VHR) satellite imagery. Nowadays VHR satellite images resolutions are very near airborne
photogrammetrical images and usually they are acquired in multispectral mode. The combination of the various bands of the images
is called pan-sharpening and it can be carried on using different algorithms and strategies. The correct pansharpening methodology,
for a specific image, must be chosen considering the specific multispectral characteristics of the satellite used and the particular
application. In this paper a first definition of guidelines for the use of VHR multispectral imagery to detect monument destruction in
unsafe area, is reported.
The proposed methodology, agreed with UNESCO and soon to be used in Libya for the coastal area, has produced a first report
delivered to the Iraqi authorities. Some of the most evident examples are reported to show the possible capabilities of identification of
damages using VHR images
Precision Spectroscopy and Higher Spin symmetry in the ABJM model
We revisit Kaluza-Klein compactification of 11-d supergravity on S^7/Z_k
using group theory techniques that may find application in other flux vacua
with internal coset spaces. Among the SO(2) neutral states, we identify
marginal deformations and fields that couple to the recently discussed
world-sheet instanton of Type IIA on CP^3. We also discuss charged states, dual
to monopole operators, and the Z_k projection of the Osp(4|8) singleton and its
tensor products. In particular, we show that the doubleton spectrum may account
for N=6 higher spin symmetry enhancement in the limit of vanishing 't Hooft
coupling in the boundary Chern-Simons theory.Comment: 44 page
SL(2,Z) Multiplets in N=4 SYM Theory
We discuss the action of SL(2,Z) on local operators in D=4, N=4 SYM theory in
the superconformal phase. The modular property of the operator's scaling
dimension determines whether the operator transforms as a singlet, or
covariantly, as part of a finite or infinite dimensional multiplet under the
SL(2,Z) action. As an example, we argue that operators in the Konishi multiplet
transform as part of a (p,q) PSL(2,Z) multiplet. We also comment on the
non-perturbative local operators dual to the Konishi multiplet.Comment: 14 pages, harvmac; v2: published version with minor change
Simplifying one-loop amplitudes in superstring theory
We show that 4-point vector boson one-loop amplitudes, computed in ref.[1] in
the RNS formalism, around vacuum configurations with open unoriented strings,
preserving at least N=1 SUSY in D=4, satisfy the correct supersymmetry Ward
identities, in that they vanish for non MHV configurations (++++) and (-+++).
In the MHV case (--++) we drastically simplify their expressions. We then study
factorisation and the limiting IR and UV behaviour and find some unexpected
results. In particular no massless poles are exposed at generic values of the
modular parameter. Relying on the supersymmetric properties of our bosonic
amplitudes, we extend them to manifestly supersymmetric super-amplitudes and
compare our results with those obtained in the D=4 hybrid formalism, pointing
out difficulties in reconciling the two approaches for contributions from N=1,2
sectors.Comment: 38 pages plus appendice
Cooperative damping mechanism of the resonance in the nuclear photoabsorption
We propose a resonance damping mechanism to explain the disappearance of the
peaks around the position of the resonances higher than the resonance
in the nuclear photoabsorption. This phenomenon is understood by taking into
account the cooperative effect of the collision broadening of and
, the pion distortion and the interference in the two-pion
photoproduction processes in the nuclear medium.Comment: 11 pages, uses revtex.sty. To appear in Phys. Rev. Let
The metal and dust yields of the first massive stars
We quantify the role of Population (Pop) III core-collapse supernovae (SNe)
as the first cosmic dust polluters. Starting from a homogeneous set of stellar
progenitors with masses in the range [13 - 80] Msun, we find that the mass and
composition of newly formed dust depend on the mixing efficiency of the ejecta
and the degree of fallback experienced during the explosion. For standard Pop
III SNe, whose explosions are calibrated to reproduce the average elemental
abundances of Galactic halo stars with [Fe/H] < -2.5, between 0.18 and 3.1 Msun
(0.39 - 1.76 Msun) of dust can form in uniformly mixed (unmixed) ejecta, and
the dominant grain species are silicates. We also investigate dust formation in
the ejecta of faint Pop III SN, where the ejecta experience a strong fallback.
By examining a set of models, tailored to minimize the scatter with the
abundances of carbon-enhanced Galactic halo stars with [Fe/H ] < -4, we find
that amorphous carbon is the only grain species that forms, with masses in the
range 2.7 10^{-3} - 0.27 Msun (7.5 10^{-4} - 0.11 Msun) for uniformly mixed
(unmixed) ejecta models. Finally, for all the models we estimate the amount and
composition of dust that survives the passage of the reverse shock, and find
that, depending on circumstellar medium densities, between 3 and 50% (10 - 80%)
of dust produced by standard (faint) Pop III SNe can contribute to early dust
enrichment.Comment: Accepted by MNRAS, 22 pages, 12 figures, 12 table
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
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