25,466 research outputs found
Of Higgs, Unitarity and other Questions
On the verge of conclusive checks on the Standard Model by the LHC, we
discuss some of the basic assumptions. The reason for this analysis stems from
a recent proposal of an Electroweak Model based on a nonlinearly realized gauge
group SU(2) X U(1), where, in the perturbative approximation, there is no Higgs
boson. The model enjoys the Slavnov-Taylor identities and therefore the
perturbative unitarity. On the other hand, it is commonly believed that the
existence of the Higgs boson is entangled with the property of unitarity, when
high energy processes are considered. The argument is based mostly on the
Froissart bound and on the Equivalence Theorem. In this talk we briefly review
some of our objections on the validity of such arguments. Some open questions
are pointed out, in particular on the limit of zero mass for the vector mesons
and on the fate of the longitudinal polarizations.Comment: 23 pages, 1 figure, presented by Ruggero Ferrari at the International
Conference "Gauge Fields. Yesterday, Today, Tomorrow" in honor of A.A.
Slavnov. Moscow, January 19-24 201
Chern-Simons Field Theories with Non-semisimple Gauge Group of Symmetry
Subject of this work is a class of Chern-Simons field theories with
non-semisimple gauge group, which may well be considered as the most
straightforward generalization of an Abelian Chern-Simons field theory. As a
matter of fact these theories, which are characterized by a non-semisimple
group of gauge symmetry, have cubic interactions like those of non-abelian
Chern-Simons field theories, but are free from radiative corrections. Moreover,
at the tree level in the perturbative expansion,there are only two connected
tree diagrams, corresponding to the propagator and to the three vertex
originating from the cubic interaction terms. For such theories it is derived
here a set of BRST invariant observables, which lead to metric independent
amplitudes. The vacuum expectation values of these observables can be computed
exactly. From their expressions it is possible to isolate the Gauss linking
number and an invariant of the Milnor type, which describes the topological
relations among three or more closed curves.Comment: 16 pages, 1 figure, plain LaTeX + psfig.st
Nonlinear Multi-Frequency Converter Array for Vibration Energy Harvesting in Autonomous Sensorsâ
Abstract This work proposes and experimentally validates a vibration energy harvester which combines the multi-frequency and nonlinear approaches into a converter array. The converter array consists of four piezoelectric cantilevers composed of ferromagnetic substrates with screen-printed lead zirconate titanate (PZT) layers coupled with a single permanent magnet elastically suspended on the array base in order to create a nonlinear behaviour. The presence of a moving magnet and the possibility to realize cantilevers with different potential curves can be useful to obtain a collective nonlinear behaviour due to strong coupling irrespective of the amplitude of the mechanical excitation, therefore increasing the overall effectiveness of the converter array. The experimental results confirm that combining cantilevers with different potential curves can be useful to obtain a collective bistable behaviour, therefore increasing the overall effectiveness of the converter array
The Wide-field High-resolution Infrared TElescope (WHITE)
The Wide-field High-resolution Infrared TElescope (WHITE) will be dedicated
in the first years of its life to carrying out a few (well focused in terms of
science objectives and time) legacy surveys.
WHITE would have an angular resolution of ~0.3'' homogeneous over ~0.7 sq.
deg. in the wavelength range 1 - 5 um, which means that we will very
efficiently use all the available observational time during night time and day
time. Moreover, the deepest observations will be performed by summing up
shorter individual frames. We will have a temporal information that can be used
to study variable objects.
The three key science objectives of WHITE are : 1) A complete survey of the
Magellanic Clouds to make a complete census of young stellar objects in the
clouds and in the bridge and to study their star formation history and the link
with the Milky Way. The interaction of the two clouds with our Galaxy might the
closest example of a minor merging event that could be the main driver of
galaxy evolution in the last 5 Gyrs. 2) The building of the first sample of
dusty supernovae at z<1.2 in the near infrared range (1-5 um) to constrain the
equation of state from these obscured objects, study the formation of dust in
galaxies and build the first high resolution sample of high redshift galaxies
observed in their optical frame 3) A very wide weak lensing survey over that
would allow to estimate the equation of state in a way that would favourably
compete with space projects.Comment: Invited talk to the 2nd ARENA Conference : "The Astrophysical Science
Cases at Dome C" Potsdam 17-21 September, 200
Diffusive shock acceleration in extragalactic jets
We calculate the temporal evolution of distributions of relativistic
electrons subject to synchrotron and adiabatic processes and Fermi-like
acceleration in shocks. The shocks result from Kelvin-Helmholtz instabilities
in the jet. Shock formation and particle acceleration are treated in a
self-consistent way by means of a numerical hydrocode. We show that in our
model the number of relativistic particles is conserved during the evolution,
with no need of further injections of supra-thermal particles after the initial
one. From our calculations, we derive predictions for values and trends of
quantities like the spectral index and the cutoff frequency that can be
compared with observations.Comment: 12 pages containing 7 postscript figures; uses A&A macros. Accepted
for publication in Astronomy and Astrophysic
On Abelian Multi-Chern-Simons Field Theories
In this paper a class of multi-Chern-Simons field theories which is relevant
to the statistical mechanics of polymer systems is investigated. Motivated by
the problems which one encounters in the treatment of these theories, a general
procedure is presented to eliminate the Chern-Simons fields from their action.
In this way it has been possible to derive an expression of the partition
function of topologically linked polymers which depends explicitly on the
topological numbers and does not have intractable nonlocal terms as it happened
in previous approaches. The new formulation of multi-Chern-Simons field
theories is then used to remove and clarify some inconsistencies and
ambiguities which apparently affect field theoretical models of topologically
linked polymers. Finally, the limit of disentangled polymers is discussed.Comment: 18 pages, plain LaTe
Interference in interacting quantum dots with spin
We study spectral and transport properties of interacting quantum dots with
spin. Two particular model systems are investigated: Lateral multilevel and two
parallel quantum dots. In both cases different paths through the system can
give rise to interference. We demonstrate that this strengthens the multilevel
Kondo effect for which a simple two-stage mechanism is proposed. In parallel
dots we show under which conditions the peak of an interference-induced orbital
Kondo effect can be split.Comment: 8 pages, 8 figure
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