3,270 research outputs found
Microscopic eigenvalue correlations in QCD with imaginary isospin chemical potential
We consider the chiral limit of QCD subjected to an imaginary isospin
chemical potential. In the epsilon-regime of the theory we can perform precise
analytical calculations based on the zero-momentum Goldstone modes in the
low-energy effective theory. We present results for the spectral correlation
functions of the associated Dirac operators.Comment: 13 pages, 2 figures, RevTe
Response of an atomic Bose-Einstein condensate to a rotating elliptical trap
We investigate numerically the response of an atomic Bose-Einstein condensate
to a weakly-elliptical rotating trap over a large range of rotation
frequencies. We analyse the quadrupolar shape oscillation excited by rotation,
and discriminate between its stable and unstable regimes. In the latter case,
where a vortex lattice forms, we compare with experimental observations and
find good agreement. By examining the role of thermal atoms in the process, we
infer that the process is temperature-independent, and show how terminating the
rotation gives control over the number of vortices in the lattice. We also
study the case of critical rotation at the trap frequency, and observe large
centre-of-mass oscillations of the condensate.Comment: 14 pages, 8 figure
Renormalization Group and Infinite Algebraic Structure in D-Dimensional Conformal Field Theory
We consider scalar field theory in the D-dimensional space with nontrivial
metric and local action functional of most general form. It is possible to
construct for this model a generalization of renormalization procedure and
RG-equations. In the fixed point the diffeomorphism and Weyl transformations
generate an infinite algebraic structure of D-Dimensional conformal field
theory models. The Wilson expansion and crossing symmetry enable to obtain sum
rules for dimensions of composite operators and Wilson coefficients.Comment: 16 page
On the effective conductivity of composite materials
A composite conductive material, which consists of fibers of a high
conductivity in a matrix of low conductivity, is discussed. The effective
conductivity of the system considered is calculated in Clausius-Mossotti
approximation. Obtained relationships can be used to calculate the conductivity
of a matrix, using experimentally measured parameters. Electric fields in the
matrix and the inclusions are calculated. It is shown that the field in a
low-conductivity matrix can be much higher than the external applied one.Comment: Russian version is include
Are the school prevention programmes - aimed at de-normalizing smoking among youths - beneficial in the long term? An example from the Smoke Free Class Competition in Italy
Tobacco smoking by young people is of great concern because it usually leads to regular smoking, nicotine addiction and quitting difficulties. Young people "hooked" by tobacco maintain the profits of the tobacco industry by replacing smokers who quit or die. If new generations could be tobacco-free, as supported by tobacco endgame strategies, the tobacco epidemic could end within decades. Smoking prevention programmes for teens are offered by schools with the aim to prevent or delay smoking onset. Among these, the Smoke Free Class Competition (SFC) was widely implemented in Europe. Its effectiveness yielded conflicting results, but it was only evaluated at short/medium term (6 - 18 months). The aim of this study is to evaluate its effectiveness after a longer follow-up (3 to 5 years) in order to allow enough time for the maturing of the students and the internalization of the experience and its contents. Fifteen classes were randomly sampled from two Italian high schools of Bologna province that regularly offered the SFC to first year students; 382 students (174 participating in the SFC and 208 controls) were retrospectively followed-up and provided their "smoking histories". At the end of their last year of school (after 5 years from the SFC), the percentage of students who stated that they were regular smokers was lower among the SFC students than in controls: 13.5% vs 32.9% (p=0.03). From the students' "smoking histories", statistically significant protective ORs were observed for SFC students at the end of 1st and 5th year: 0.42 (95% CI 0.19-0.93) and 0.32 (95% CI 0.11-0.91) respectively. Absence of smokers in the family was also a strongly statistically significant factor associated with being a non-smoker student. These results suggest that SFC may have a positive impact on lowering the prevalence of smoking in the long term (5 years)
Decoupling a Cooper-pair box to enhance the lifetime to 0.2 ms
We present a circuit QED experiment in which a separate transmission line is
used to address a quasi-lumped element superconducting microwave resonator
which is in turn coupled to an Al/AlO/Al Cooper-pair box (CPB) charge
qubit. In our measurements we find a strong correlation between the measured
lifetime of the CPB and the coupling between the qubit and the transmission
line. By monitoring perturbations of the resonator's 5.44 GHz resonant
frequency, we have measured the spectrum, lifetime (), Rabi, and Ramsey
oscillations of the CPB at the charge degeneracy point while the CPB was
detuned by up to 2.5 GHz . We find a maximum lifetime of the CPB was s for to 4.5 GHz. Our measured 's are consistent with
loss due to coupling to the transmission line, spurious microwave circuit
resonances, and a background decay rate on the order of
s of unknown origin, implying that the loss tangent in the AlO
junction barrier must be less than about at 4.5 GHz, about 4
orders of magnitude less than reported in larger area Al/AlO/Al tunnel
junctions
Chiral phase transition in lattice QCD as a metal-insulator transition
We investigate the lattice QCD Dirac operator with staggered fermions at
temperatures around the chiral phase transition. We present evidence of a
metal-insulator transition in the low lying modes of the Dirac operator around
the same temperature as the chiral phase transition. This strongly suggests the
phenomenon of Anderson localization drives the QCD vacuum to the chirally
symmetric phase in a way similar to a metal-insulator transition in a
disordered conductor. We also discuss how Anderson localization affects the
usual phenomenological treatment of phase transitions a la Ginzburg-Landau.Comment: 7 pages, 6 figures, references added, typos corrected, journal
versio
Hamiltonian type Lie bialgebras
We first prove that, for any generalized Hamiltonian type Lie algebra ,
the first cohomology group is trivial. We then show that
all Lie bialgebra structures on are triangular.Comment: LaTeX, 16 page
Decoherence in Josephson Qubits from Dielectric Loss
Dielectric loss from two-level states is shown to be a dominant decoherence
source in superconducting quantum bits. Depending on the qubit design,
dielectric loss from insulating materials or the tunnel junction can lead to
short coherence times. We show that a variety of microwave and qubit
measurements are well modeled by loss from resonant absorption of two-level
defects. Our results demonstrate that this loss can be significantly reduced by
using better dielectrics and fabricating junctions of small area . With a redesigned phase qubit employing low-loss
dielectrics, the energy relaxation rate has been improved by a factor of 20,
opening up the possibility of multi-qubit gates and algorithms.Comment: shortened version submitted to PR
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