187 research outputs found
Study of High Beta Optics Solution for TOTEM
The TOTEM experiment requires special high beta optics solutions. We report on studies of optics for an intermediate β* = 90m, as well as a solutions for a very high β* of 1535 m, which respect all known constraints. These optics are rather different from the normal physics optics and will require global tune changes or adjustments
Simulation of Beam-Gas Scattering in the LHC
We report on background studies for the LHC with detailed simulations. The simulations now include generation of beam-gas scattering in combination with multiturn tracking of protons. Low beta optics and available aperture files for this configuration make it possible to generate loss maps according to the pressure distribution in the LHC
Proximity DC squids in the long junction limit
We report the design and measurement of
Superconducting/normal/superconducting (SNS) proximity DC squids in the long
junction limit, i.e. superconducting loops interrupted by two normal metal
wires roughly a micrometer long. Thanks to the clean interface between the
metals, at low temperature a large supercurrent flows through the device. The
dc squid-like geometry leads to an almost complete periodic modulation of the
critical current through the device by a magnetic flux, with a flux periodicity
of a flux quantum h/2e through the SNS loop. In addition, we examine the entire
field dependence, notably the low and high field dependence of the maximum
switching current. In contrast with the well-known Fraunhoffer-type
oscillations typical of short wide junctions, we find a monotonous gaussian
extinction of the critical current at high field. As shown in [15], this
monotonous dependence is typical of long and narrow diffusive junctions. We
also find in some cases a puzzling reentrance at low field. In contrast, the
temperature dependence of the critical current is well described by the
proximity effect theory, as found by Dubos {\it et al.} [16] on SNS wires in
the long junction limit. The switching current distributions and hysteretic IV
curves also suggest interesting dynamics of long SNS junctions with an
important role played by the diffusion time across the junction.Comment: 12 pages, 16 figure
Properties of the strongly paired fermionic condensates
We study a gas of fermions undergoing a wide resonance s-wave BCS-BEC
crossover, in the BEC regime at zero temperature. We calculate the chemical
potential and the speed of sound of this Bose-condensed gas, as well as the
condensate depletion, in the low density approximation. We discuss how higher
order terms in the low density expansion can be constructed. We demonstrate
that the standard BCS-BEC gap equation is invalid in the BEC regime and is
inconsistent with the results obtained here. We indicate how our theory can in
principle be extended to nonzero temperature. The low density approximation we
employ breaks down in the intermediate BCS-BEC crossover region. Hence our
theory is unable to predict how the chemical potential and the speed of sound
evolve once the interactions are tuned towards the BCS regime. As a part of our
theory, we derive the well known result for the bosonic scattering length
diagrammatically and check that there are no bound states of two bosons.Comment: 16 pages, 15 figures. References added and typos correcte
Spectra of pinned charge density waves with background current
We develop techniques which allow us to calculate the spectra of pinned
charge density waves with background current
Causality and universality in low-energy quantum scattering
We generalize Wigner's causality bounds and Bethe's integral formula for the
effective range to arbitrary dimension and arbitrary angular momentum.
Moreover, we discuss the impact of these constraints on the separation of low-
and high-momentum scales and universality in low-energy quantum scattering.Comment: 9 pages, 1 figure, published versio
Stability of mode-locked kinks in the ac driven and damped sine-Gordon lattice
Kink dynamics in the underdamped and strongly discrete sine-Gordon lattice
that is driven by the oscillating force is studied. The investigation is
focused mostly on the properties of the mode-locked states in the {\it
overband} case, when the driving frequency lies above the linear band. With the
help of Floquet theory it is demonstrated that the destabilizing of the
mode-locked state happens either through the Hopf bifurcation or through the
tangential bifurcation. It is also observed that in the overband case the
standing mode-locked kink state maintains its stability for the bias amplitudes
that are by the order of magnitude larger than the amplitudes in the
low-frequency case.Comment: To appear in Springer Series on Wave Phenomena, special volume
devoted to the LENCOS'12 conference; 6 figure
Stability of the fermionic gases close to a p-wave Feshbach resonance
We study the stability of the paired fermionic p-wave superfluid made out of
identical atoms all in the same hyperfine state close to a p-wave Feshbach
resonance. First we reproduce known results concerning the lifetime of a 3D
superfluid, in particular, we show that it decays at the same rate as its
interaction energy, thus precluding its equilibration before it decays. Then we
proceed to study its stability in case when the superfluid is confined to 2D by
means of an optical harmonic potential. We find that the relative stability is
somewhat improved in 2D in the BCS regime, such that the decay rate is now
slower than the appropriate interaction energy scale. The improvement in
stability, however, is not dramatic and one probably needs to look for other
mechanisms to suppress decay to create a long lived 2D p-wave fermionic
superfluid
Causality and the effective range expansion
We derive the generalization of Wigner's causality bounds and Bethe's
integral formula for the effective range parameter to arbitrary dimension and
arbitrary angular momentum. We also discuss the impact of these constraints on
the separation of low- and high-momentum scales and universality in low-energy
scattering. Some of our results were summarized earlier in a letter
publication. In this work, we present full derivations and several detailed
examples.Comment: 27 pages, 5 figures, explicit examples added, typos corrected, final
versio
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