11,449 research outputs found
Reconfigurable photonic integrated mode (de)multiplexer for SDM fiber transmission
A photonic integrated circuit for mode multiplexing and demultiplexing in a
few-mode fiber is presented and demonstrated. Two 10 Gbit/s channels at the
same wavelength and polarization are simultaneously transmitted over modes LP01
and LP11a of a few-mode fiber exploiting the integrated mode MUX and DEMUX. The
proposed Indium-Phosphide-based circuits have a good coupling efficiency with
fiber modes with mode-dependant loss smaller than 1 dB. Measured mode
excitation cross-talk is as low as -20 dB and a channel cross-talk after
propagation and demultiplexing of -15 dB is achieved. An operational bandwidth
of the full transmission system of at least 10 nm is demonstrated. Both mode
MUX and DEMUX are fully reconfigurable and allow a dynamic switch of channel
routing in the transmission system
The MINI mixed finite element for the Stokes problem: An experimental investigation
Super-convergence of order 1.5 in pressure and velocity has been
experimentally investigated for the two-dimensional Stokes problem discretised
with the MINI mixed finite element. Even though the classic mixed finite
element theory for the MINI element guarantees linear convergence for the total
error, recent theoretical results indicate that super-convergence of order 1.5
in pressure and of the linear part of the computed velocity to the piecewise
linear nodal interpolation of the exact velocity is in fact possible with
structured, three-directional triangular meshes. The numerical experiments
presented here suggest a more general validity of super-convergence of order
1.5, possibly to automatically generated and unstructured triangulations. In
addition, the approximating properties of the complete computed velocity have
been compared with the approximating properties of the piecewise-linear part of
the computed velocity, finding that the former is generally closer to the exact
velocity, whereas the latter conserves mass better
Social Aggregation as a Cooperative Game
A new approach for the description of phenomena of social aggregation is
suggested. On the basis of psychological concepts (as for instance social norms
and cultural coordinates), we deduce a general mechanism for the social
aggregation in which different clusters of individuals can merge according to
the cooperation among the agents. In their turn, the agents can cooperate or
defect according to the clusters distribution inside the system. The fitness of
an individual increases with the size of its cluster, but decreases with the
work the individual had to do in order to join it. In order to test the
reliability of such new approach, we introduce a couple of simple toy models
with the features illustrated above. We see, from this preliminary study, how
the cooperation is the most convenient strategy only in presence of very large
clusters, while on the other hand it is not necessary to have one hundred
percent of cooperators for reaching a totally ordered configuration with only
one megacluster filling the whole system.Comment: 18 pages, 10 figure
Off-shell renormalization in the presence of dimension 6 derivative operators. II. UV coefficients
The full off-shell one loop renormalization for all divergent amplitudes up
to dimension 6 in the Abelian Higgs-Kibble model, supplemented with a maximally
power counting violating higher-dimensional gauge-invariant derivative
interaction , is
presented. This allows one to perform the complete renormalization of
radiatively generated dimension 6 operators in the model at hand. We describe
in details the technical tools required in order to disentangle the
contribution to UV divergences parameterized by (generalized) non-polynomial
field redefinitions. We also discuss how to extract the dependence of the
-function coefficients on the non-renormalizable coupling in one
loop approximation, as well as the cohomological techniques (contractible
pairs) required to efficiently separate the mixing of contributions associated
to different higher-dimensional operators in a spontaneously broken effective
field theory.Comment: 33 pages; revised version including the derivation of the one-loop
beta function
Polya-Szego inequality and Dirichlet -spectral gap for non-smooth spaces with Ricci curvature bounded below
We study decreasing rearrangements of functions defined on (possibly
non-smooth) metric measure spaces with Ricci curvature bounded below by
and dimension bounded above by in a synthetic sense, the so
called spaces. We first establish a Polya-Szego type inequality
stating that the -Sobolev norm decreases under such a rearrangement
and apply the result to show sharp spectral gap for the -Laplace operator
with Dirichlet boundary conditions (on open subsets), for every . This extends to the non-smooth setting a classical result of
B\'erard-Meyer and Matei; remarkable examples of spaces fitting out framework
and for which the results seem new include: measured-Gromov Hausdorff limits of
Riemannian manifolds with Ricci, finite dimensional Alexandrov spaces
with curvature, Finsler manifolds with Ricci. In the second
part of the paper we prove new rigidity and almost rigidity results attached to
the aforementioned inequalities, in the framework of spaces, which
seem original even for smooth Riemannian manifolds with Ricci.Comment: 33 pages. Final version published in Journal de Math\'ematiques Pures
et Appliqu\'ee
Off-shell renormalization in the presence of dimension 6 derivative operators. I. General theory
The consistent recursive subtraction of UV divergences order by order in the
loop expansion for spontaneously broken effective field theories with
dimension-6 derivative operators is presented for an Abelian gauge group. We
solve the Slavnov-Taylor identity to all orders in the loop expansion by
homotopy techniques and a suitable choice of invariant field coordinates (named
bleached variables) for the linearly realized gauge group. This allows one to
disentangle the gauge-invariant contributions to off-shell 1-PI amplitudes from
those associated with the gauge-fixing and (generalized) non-polynomial field
redefinitions (that do appear already at one loop). The tools presented can be
easily generalized to the non-Abelian case.Comment: 37 pages, 3 figures; updated version to match the published on
Off-shell renormalization in Higgs effective field theories
The off-shell one-loop renormalization of a Higgs effective field theory
possessing a scalar potential
with arbitrary is presented. This is achieved by renormalizing the theory
once reformulated in terms of two auxiliary fields , which, due to the
invariance under an extended Becchi-Rouet-Stora-Tyutin symmetry, are tightly
constrained by functional identities. The latter allow in turn the explicit
derivation of the mapping onto the original theory, through which the
(divergent) multi-Higgs amplitude are generated in a purely algebraic fashion.
We show that, contrary to naive expectations based on the loss of power
counting renormalizability, the Higgs field undergoes a linear Standard Model
like redefinition, and evaluate the renormalization of the complete set of
Higgs self-coupling in the case.Comment: 33 pages, no figures. v3: complete one-loop off-shell renormalization
for a BSM potential involving arbitrary powers of
presented; Higgs wavefunction
renormalization shown to be SM like; renormalization of the complete set of
Higgs self-coupling in the case discussed. v3 matches the
published on
Canonical transformations in gauge theories with non-trivial backgrounds
We show how to implement the background field method by means of canonical
transformations and comment on the applications of the method to
non-perturbative techniques in non-Abelian gauge theories. We discuss the case
of the lattice in some details.Comment: 6 pages. Prepared for the Sixth International Conference on Quarks
and Nuclear Physics QNP2012, April 16-20, 2012, Ecole Polytechnique,
Palaiseau, Pari
Magneto-transport from momentum dissipating holography
We obtain explicit expressions for the thermoelectric transport coefficients
of a strongly coupled, planar medium in the presence of an orthogonal magnetic
field and momentum-dissipating processes. The computations are performed within
the gauge/gravity framework where the momentum dissipation mechanism is
introduced by including a mass term for the bulk graviton. Relying on the
structure of the computed transport coefficients and promoting the parameters
to become dynamical functions, we propose a holography inspired phenomenology
open to a direct comparison with experimental data from the cuprates.Comment: 23 page
Send in the clowns. Humor and power in Italian political, social and cultural life
No abstract available
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