1,675 research outputs found
Constituent gluon interpretation of glueballs and gluelumps
Arguments are given that support the interpretation of the lattice QCD
glueball and gluelump spectra in terms of bound states of massless constituent
gluons with helicity-1. In this scheme, the mass hierarchy of the currently
known gluelumps and glueballs is mainly due to the number of constituent gluons
and can be understood within a simple flux tube model. It is also argued that
the lattice QCD glueball should be seen as a four-gluon bound state.
The flux tube model allows for a parameter-free computation of its mass, which
is in good agreement with lattice QCD.Comment: 3 figures, use of package youngta
Gravitational cubic interactions for a massive mixed symmetry gauge field
In a recent paper arXiv:1107.1872 cubic gravitational interactions for a
massless mixed symmetry field in AdS space have been constructed. In the
current paper we extend these results to the case of massive field. We work in
a Fradkin-Vasiliev approach and use frame-like gauge invariant description for
massive field which works in (A)dS spaces with arbitrary values of cosmological
constant including flat Minkowski space. In this, massless limit in AdS space
coincides with the results of arXiv:1107.1872 while we show that it is
impossible to switch on gravitational interaction for massless field in dS
space.Comment: 13 page
Gauge fields and infinite chains of dualities
We show that the particle states of Maxwell's theory, in dimensions, can
be represented in an infinite number of ways by using different gauge fields.
Using this result we formulate the dynamics in terms of an infinite set of
duality relations which are first order in space-time derivatives. We derive a
similar result for the three form in eleven dimensions where such a possibility
was first observed in the context of E11. We also give an action formulation
for some of the gauge fields. In this paper we give a pedagogical account of
the Lorentz and gauge covariant formulation of the irreducible representations
of the Poincar\'e group, used previously in higher spin theories, as this plays
a key role in our constructions. It is clear that our results can be
generalised to any particle.Comment: 37 page
Dust models post-Planck: constraining the far-infrared opacity of dust in the diffuse interstellar medium
We compare the performance of several dust models in reproducing the dust
spectral energy distribution (SED) per unit extinction in the diffuse
interstellar medium (ISM). We use our results to constrain the variability of
the optical properties of big grains in the diffuse ISM, as published by the
Planck collaboration.
We use two different techniques to compare the predictions of dust models to
data from the Planck HFI, IRAS and SDSS surveys. First, we fit the far-infrared
emission spectrum to recover the dust extinction and the intensity of the
interstellar radiation field (ISRF). Second, we infer the ISRF intensity from
the total power emitted by dust per unit extinction, and then predict the
emission spectrum. In both cases, we test the ability of the models to
reproduce dust emission and extinction at the same time.
We identify two issues. Not all models can reproduce the average dust
emission per unit extinction: there are differences of up to a factor
between models, and the best accord between model and observation is obtained
with the more emissive grains derived from recent laboratory data on silicates
and amorphous carbons. All models fail to reproduce the variations in the
emission per unit extinction if the only variable parameter is the ISRF
intensity: this confirms that the optical properties of dust are indeed
variable in the diffuse ISM.
Diffuse ISM observations are consistent with a scenario where both ISRF
intensity and dust optical properties vary. The ratio of the far-infrared
opacity to the band extinction cross-section presents variations of the
order of ( in extreme cases), while ISRF intensity varies
by ( in extreme cases). This must be accounted for in
future modelling.Comment: A&A, in pres
The Energetics of Molecular Gas in NGC 891 from H_2 and Far-infrared Spectroscopy
We have studied the molecular hydrogen energetics of the edge-on spiral galaxy NGC 891, using a 34 position map in the lowest three pure rotational H_2 lines observed with the Spitzer Infrared Spectrograph. The S(0), S(1), and S(2) lines are bright with an extinction-corrected total luminosity of ~2.8 × 10^7 L_☉, or 0.09% of the total-infrared luminosity of NGC 891. The H_2 line ratios are nearly constant along the plane of the galaxy—we do not observe the previously reported strong drop-off in the S(1)/S(0) line intensity ratio in the outer regions of the galaxy, so we find no evidence for the very massive cold CO-free molecular clouds invoked to explain the past observations. The H_2 level excitation temperatures increase monotonically indicating that there is more than one component to the emitting gas. More than 99% of the mass is in the lowest excitation (T_(ex) ~ 125 K) "warm" component. In the inner galaxy, the warm H_2 emitting gas is ~16% of the CO(1-0)-traced cool molecular gas, while in the outer regions the fraction is twice as high. This large mass of warm gas is heated by a combination of the far-UV photons from stars in photodissociation regions (PDRs) and the dissipation of turbulent kinetic energy. Including the observed far-infrared [O I] and [C II] fine-structure line emission and far-infrared continuum emission in a self-consistent manner to constrain the PDR models, we find essentially all of the S(0) and most (70%) of the S(1) line arise from low excitation PDRs, while most (80%) of the S(2) and the remainder of the S(1) line emission arise from low-velocity microturbulent dissipation
Adiabatic invariants drive rhythmic human motion in variable gravity
Natural human movements are stereotyped. They minimise cost functions that
include energy, a natural candidate from mechanical and physiological points of
view. In time-changing environments, however, motor strategies are modified
since energy is no longer conserved. Adiabatic invariants are relevant
observables in such cases, although they have not been investigated in human
motor control so far. We fill this gap and show that the theory of adiabatic
invariants explains how humans move when gravity varies
Mixed-symmetry tensor conserved currents and AdS/CFT correspondence
We present the full list of conserved currents built of two massless spinor
fields in Minkowski space and their derivatives multiplied by Clifford algebra
elements. The currents have particular mixed-symmetry type described by Young
diagrams with one row and one column of arbitrary lengths and heights. Along
with Yukawa-like totally antisymmetric currents the complete set of constructed
currents exactly matches the spectrum of AdS mixed-symmetry fields arising in
the generalized Flato-Fronsdal theorem for two spinor singletons. As a
by-product, we formulate and study general properties of primary fields and
conserved currents of mixed-symmetry type.Comment: 17 pages; v2: typos corrected, clarifications and refs added; v3:
more explanations and refs added; contribution to the J.Phys.A special volume
on "Higher Spin Theories and AdS/CFT" edited by Matthias Gaberdiel and
Mikhail Vasilie
High surface area activated carbon prepared from wood-based spent mushroom substrate for supercapacitors and water treatment
Edible white-rot fungi are commonly cultivated on wood-based substrates and selectively degrade lignin to a larger extent during their growth. Spent mushroom substrate (SMS) is produced in huge amounts by the mushroom industry and today there is a lack of proven methods to valorize this kind of biomass waste, which in most cases is landfilled or used as fuel. This study demonstrates that birch wood-based SMS from the cultivation of oyster mushrooms can be converted into high-quality activated carbon (AC) with an extremely high surface area of about 3000 m2 /g. These activated carbons showed good performance when used in electrodes for supercapacitors, with energy storage parameters nearly identical to AC produced from high-quality virgin birch wood. Moreover, AC produced from SMS showed high potential as an adsorbent for cleaning reactive orange-16 azo dye from aqueous solutions as well as contaminants from synthetic effluents and from real sewage water. The kinetics of adsorption were well represented by the Avrami fractional order model and isotherms of adsorption by the Liu model. The theoretical maximum reactive orange-16 adsorption capacities were approximately 519 mg/g (SMS-based carbon) and 553 mg/g (virgin birch-based carbon). The removal of contaminants from synthetic effluents made of different dyes and inorganic compounds was around 95% and 83% depending on the effluent composition. The removal of contaminants from raw sewage water was around 84%, and from treated sewage water was around 68%. Overall, the results showed that activated carbon prepared from waste generated during cultivation of white-rot fungi is as good as activated carbon prepared from high-quality virgin wood
A Higgs Mechanism for Gravity. Part II: Higher Spin Connections
We continue the work of hep-th/0503024 in which gravity is considered as the
Goldstone realization of a spontaneously broken diffeomorphism group. We
complete the discussion of the coset space Diff(d,R)/SO(1,d-1) formed by the
d-dimensional group of analytic diffeomorphisms and the Lorentz group. We find
that this coset space is parameterized by coordinates, a metric and an infinite
tower of higher-spin-like or generalized connections. We then study effective
actions for the corresponding symmetry breaking which gives mass to the higher
spin connections. Our model predicts that gravity is modified at high energies
by the exchange of massive higher spin particles.Comment: 17 pages; discussion on local Poincare invariance and matter currents
added; references adde
Magnetic field morphology in nearby molecular clouds as revealed by starlight and submillimetre polarization
Within four nearby (d < 160 pc) molecular clouds, we statistically evaluate
the structure of the interstellar magnetic field, projected on the plane of the
sky and integrated along the line of sight, as inferred from the polarized
thermal emission of Galactic dust observed by Planck at 353 GHz and from the
optical and NIR polarization of background starlight. We compare the dispersion
of the field orientation directly in vicinities with an area equivalent to that
subtended by the Planck effective beam at 353 GHz (10') and using the
second-order structure functions of the field orientation angles. We find that
the average dispersion of the starlight-inferred field orientations within
10'-diameter vicinities is less than 20 deg, and that at these scales the mean
field orientation is on average within 5 deg of that inferred from the
submillimetre polarization observations in the considered regions. We also find
that the dispersion of starlight polarization orientations and the polarization
fractions within these vicinities are well reproduced by a Gaussian model of
the turbulent structure of the magnetic field, in agreement with the findings
reported by the Planck collaboration at scales greater than 10' and for
comparable column densities. At scales greater than 10', we find differences of
up to 14.7 deg between the second-order structure functions obtained from
starlight and submillimetre polarization observations in the same positions in
the plane of the sky, but comparison with a Gaussian model of the turbulent
structure of the magnetic field indicates that these differences are small and
are consistent with the difference in angular resolution between both
techniques.Comment: 15 pages, 10 figures, submitted to A&
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