10,070 research outputs found
Nontrivial classes in from nontrivalent graph cocycles
We construct nontrivial cohomology classes of the space of
imbeddings of the circle into , by means of Feynman diagrams. More
precisely, starting from a suitable linear combination of nontrivalent
diagrams, we construct, for every even number , a de Rham cohomology
class on . We prove nontriviality of these classes by evaluation
on the dual cycles.Comment: 10 pages, 11 figures. V2: minor changes, typos correcte
Correlations and enlarged superconducting phase of - chains of ultracold molecules on optical lattices
We compute physical properties across the phase diagram of the -
chain with long-range dipolar interactions, which describe ultracold polar
molecules on optical lattices. Our results obtained by the density-matrix
renormalization group (DMRG) indicate that superconductivity is enhanced when
the Ising component of the spin-spin interaction and the charge component
are tuned to zero, and even further by the long-range dipolar interactions.
At low densities, a substantially larger spin gap is obtained. We provide
evidence that long-range interactions lead to algebraically decaying
correlation functions despite the presence of a gap. Although this has recently
been observed in other long-range interacting spin and fermion models, the
correlations in our case have the peculiar property of having a small and
continuously varying exponent. We construct simple analytic models and
arguments to understand the most salient features.Comment: published version with minor modification
IMPACT OF IONOSPHERIC HORIZONTAL ASYMMETRY ON ELECTRON DENSITY PROFILES DERIVED BY GNSS RADIO OCCULTATION
The âOnion-peeling' algorithm is a very common technique used to invert Radio Occultation (RO) data in the ionosphere. Because of the implicit assumption of spherical symmetry for the electron density distribution in the ionosphere, the standard Onion-peeling algorithm could give erroneous concentration values in the retrieved electron density profile. In particular, this happens when strong horizontal ionospheric electron density gradients are present, like for example in the Equatorial Ionization Anomaly (EIA) region during high solar activity periods. In this work, using simulated RO TEC data computed by means of the NeQuick2 ionospheric electron density model and ideal RO geometries, we tried to formulate and evaluate an asymmetry level indicator for quasi-horizontal radio occultation observations. This asymmetry index is based on the electron density variation that a ray may experience along its propagation path (satellite to satellite link) in a RO event. Our previous qualitative assessment based on ideal simulations of RO events shows very high correlation between our asymmetry index and Onion-peeling retrieval errors (Shaikh M.M. et al 2013): errors produced by Onion-peeling in the retrieval of NmF2 and VTEC are larger at the geographical locations where our asymmetry index indicates high asymmetry in the ionosphere. In this contribution, an analysis of the asymmetry index has been carried out for the first time using real radio occultation geometries taken from COSMIC mission. This has been done for COSMIC events for which, considering the same RO geometry, simulated Limb-TEC (LTEC) under NeQuick2 background were quite close to the real LTEC observations (providing âquasi' co-located vertical profiles of electron density after inversion). On the basis of the outcomes of our work, for a given geometry of a real RO event and using a suitable ionospheric model, we will try to investigate the possibility to predict ionospheric asymmetry expected for the particular RO geometry considered. We could also try to evaluate, in advance, its impact on the inverted electron density profile, providing an indication of the expected product quality, if standard Onion-peelingalgorithm will be adopted to invert the observables. Results presented in this paper are initial outcomes based on our asymmetry evaluation algorith
Re-evaluation of the Gottfried sum using neural networks
We provide a determination of the Gottfried sum from all available data,
based on a neural network parametrization of the nonsinglet structure function
F_2. We find S_G=0.244 +- 0.045, closer to the quark model expectation S_G=1/3
than previous results. We show that the uncertainty from the small x region is
somewhat underestimated in previous determinations.Comment: 4 pages, 3 figures, latex with revte
The orientation of galaxy dark matter haloes around cosmic voids
Using the Millennium N-body Simulation we explore how the shape and angular momentum of galaxy dark matter haloes surrounding the largest cosmological voids are oriented. We find that the major and intermediate axes of the haloes tend to lie parallel to the surface of the voids, whereas the minor axis points preferentially in the radial direction. We have quantified the strength of these alignments at different radial distances from the void centres. The effect of these orientations is still detected at distances as large as 2.2 Rvoid from the void centre. Taking a subsample of haloes expected to contain disc-dominated galaxies at their centres we detect, at the 99.9 per cent confidence level, a signal that the angular momentum of those haloes tends to lie parallel to the surface of the voids. Contrary to the alignments of the inertia axes, this signal is only detected in shells at the void surface (1 < R < 1.07 Rvoid) and disappears at larger distances. This signal, together with the similar alignment observed using real spiral galaxies, strongly supports the prediction of the Tidal Torque theory that both dark matter haloes and baryonic matter have acquired, conjointly, their angular momentum before the moment of turnaround
Thermodynamic consistency of energy and virial routes: An exact proof within the linearized Debye-H\"uckel theory
The linearized Debye-H\"uckel theory for liquid state is shown to provide
thermodynamically consistent virial and energy routes for any potential and for
any dimensionality. The importance of this result for bounded potentials is
discussed.Comment: 4 pages, 1 figure; v2: minor change
The Higgs boson from an extended symmetry
The variety of ideas put forward in the context of a "composite" picture for
the Higgs boson calls for a simple and effective description of the related
phenomenology. Such a description is given here by means of a "minimal" model
and is explicitly applied to the example of a Higgs-top sector from an SO(5)
symmetry. We discuss the spectrum, the ElectroWeak Precision Tests, B-physics
and naturalness. We show the difficulty to comply with the different
constraints. The extended gauge sector relative to the standard SU(2)xU(1), if
there is any, has little or no impact on these considerations. We also discuss
the relation of the "minimal" model with its "little Higgs" or "holographic"
extensions based on the same symmetry.Comment: 22 pp; v3: Small corrections, version to be published in Phys. Rev.
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