2,067 research outputs found
On the ground state of gapless two flavor color superconductors
This paper is devoted to the study of some aspects of the instability of two
flavor color superconductive quark matter. We find that, beside color
condensates, the Goldstone boson related to the breaking of suffers of
a velocity instability. We relate this wrong sign problem, which implies the
existence of a Goldstone current in the ground state or of gluonic
condensation, to the negative squared Meissner mass of the gluon in
the g2SC phase. Moreover we investigate the Meissner masses of the gluons and
the squared velocity of the Goldstone in the multiple plane wave LOFF states,
arguing that in such phases both the chromo-magnetic instability and the
velocity instability are most probably removed. We also do not expect Higgs
instability in such multiple plane wave LOFF. The true vacuum of gapless two
flavor superconductors is thus expected to be a multiple plane wave LOFF state.Comment: 16 pages, RevTe3X4 styl
A New Fast Silicon Photomultiplier Photometer
The realization of low-cost instruments with high technical performance is a
goal which deserves some efforts in an epoch of fast technological
developments: indeed such instruments can be easily reproduced and therefore
allow to open new research programs in several Observatories. We realized a
fast optical photometer based on the SiPM technology, using commercially
available modules. Using low-cost components we have developed a custom
electronic chain to extract the signal produced by a commercial MPPC module
produced by Hamamatsu, in order to obtain sub millisecond sampling of the light
curve of astronomical sources, typically pulsars. In the early February 2011 we
observed the Crab Pulsar at the Cassini telescope with our prototype
photometer, deriving its period, power spectrum and shape of its light curve in
very good agreement with the results obtained in the past with other
instruments.Comment: Accepted for Publications of the Astronomical Society of Pacific
(PASP), 8 pages, 8 figure
Evaluating the phase diagram of superconductors with asymmetric spin populations
The phase diagram of a non-relativistic fermionic system with imbalanced
state populations interacting via a short-range S-wave attractive interaction
is analyzed in the mean field approximation. We determine the energetically
favored state for different values of the mismatch between the two Fermi
spheres in the weak and strong coupling regime considering both homogeneous and
non-homogeneous superconductive states. We find that the homogeneous
superconductive phase persists for values of the population imbalance that
increase with increasing coupling strength. In the strong coupling regime and
for large population differences the energetically stable homogeneous phase is
characterized by one gapless mode. We also find that the inhomogeneous
superconductive phase characterized by the condensate is energetically favored in a range of values
of the chemical potential mismatch that shrinks to zero in the strong coupling
regime.Comment: 9 pages, 5 figure
Superfluid and Pseudo-Goldstone Modes in Three Flavor Crystalline Color Superconductivity
We study the bosonic excitations in the favorite cubic three flavor
crystalline LOFF phases of QCD. We calculate in the Ginzburg-Landau
approximation the masses of the eight pseudo Nambu-Goldstone Bosons (NGB)
present in the low energy theory. We also compute the decay constants of the
massless NGB Goldstones associated to superfluidity as well as those of the
eight pseudo NGB. Differently from the corresponding situation in the
Color-Flavor-Locking phase, we find that meson condensation phases are not
expected in the present scenario.Comment: 10 pages, RevTeX4 class. Section IIIA enlarged, to appear on Phys.
Rev.
Chiral magnetic effect in the PNJL model
We study the two-flavor Nambu--Jona-Lasinio model with the Polyakov loop
(PNJL model) in the presence of a strong magnetic field and a chiral chemical
potential which mimics the effect of imbalanced chirality due to QCD
instanton and/or sphaleron transitions. Firstly we focus on the properties of
chiral symmetry breaking and deconfinement crossover under the strong magnetic
field. Then we discuss the role of on the phase structure. Finally the
chirality charge, electric current, and their susceptibility, which are
relevant to the Chiral Magnetic Effect, are computed in the model.Comment: Some reference added. Minor revisions. One figure added. To appear on
Phys. Rev.
Magnetic Susceptibility of the Quark Condensate and Polarization from Chiral Models
We compute the magnetic susceptibility of the quark condensate and the
polarization of quarks at zero temperature and in a uniform magnetic
background. Our theoretical framework consists of two chiral models that allow
to treat self-consistently the spontaneous breaking of chiral symmetry: the
linear model coupled to quarks, dubbed quark-meson model, and the
Nambu-Jona-Lasinio model. We also perform analytic estimates of the same
quantities within the renormalized quark-meson model, both in the regimes of
weak and strong fields. Our numerical results are in agreement with the recent
literature; moreover, we confirm previous Lattice findings, related to the
saturation of the polarization at large fields.Comment: 13 pages, 4 figure
Chiral magnetic effect in the PNJL model
We study the two-flavor Nambu--Jona-Lasinio model with the Polyakov loop
(PNJL model) in the presence of a strong magnetic field and a chiral chemical
potential which mimics the effect of imbalanced chirality due to QCD
instanton and/or sphaleron transitions. Firstly we focus on the properties of
chiral symmetry breaking and deconfinement crossover under the strong magnetic
field. Then we discuss the role of on the phase structure. Finally the
chirality charge, electric current, and their susceptibility, which are
relevant to the Chiral Magnetic Effect, are computed in the model.Comment: Some reference added. Minor revisions. One figure added. To appear on
Phys. Rev.
Porting Decision Tree Algorithms to Multicore using FastFlow
The whole computer hardware industry embraced multicores. For these machines,
the extreme optimisation of sequential algorithms is no longer sufficient to
squeeze the real machine power, which can be only exploited via thread-level
parallelism. Decision tree algorithms exhibit natural concurrency that makes
them suitable to be parallelised. This paper presents an approach for
easy-yet-efficient porting of an implementation of the C4.5 algorithm on
multicores. The parallel porting requires minimal changes to the original
sequential code, and it is able to exploit up to 7X speedup on an Intel
dual-quad core machine.Comment: 18 pages + cove
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