182,474 research outputs found
Comments on the observation of high multiplicity events at the LHC
We analyze the structure of the high multiplicity events observed by the CMS
collaboration at the LHC. We argue that the bulk of the observed correlations
is due to the production of a pair of jets with p_t > 15 GeV/c. We also suggest
that high multiplicity events are due to a combination of three effects: high
underlying multiplicity for collisions at small impact parameters, upward
fluctuations of the gluon density in the colliding protons, and production of
hadrons in the fragmentation of dijets. The data analysis is suggested which
may clarify the underlying dynamics of the high multiplicity events and probe
fluctuations of the gluon field as a function of x.Comment: 8 pages, final version published in Phys.Rev. D rapid communications
includes note added in proof
Formation of a condensed state with macroscopic number of phonons in ultracold Bose gases
A mechanism for the formation of a new type of stationary state with
macroscopical number of phonons in condensed atomic gases is proposed. This
mechanism is based on generating longitudinal phonons as a result of parametric
resonance caused by a permanent modulation of the transverse trap frequency in
an elongated trap. The phonon-phonon interaction predetermines the
self-consistent evolution which is completed with macroscopic population of one
from all levels within the energy interval of parametric amplification. This
level proves to be shifted to the edge of this interval. All other levels end
the evolution with zero population.Comment: 9 pages, 8 figure
Nonequilibrium spin-dependent phenomena in mesoscopic superconductor-normal metal tunnel structures
We analyze the broad range of spin-dependent nonequilibrium transport
properties of hybrid systems composed of a normal region tunnel coupled to two
superconductors with exchange fields induced by the proximity to thin
ferromagnetic layers and highlight its functionalities. By calculating the
quasiparticle distribution functions in the normal region we find that they are
spin-dependent and strongly sensitive to the relative angle between exchange
fields in the two superconductors. The impact of inelastic collisions on their
properties is addressed. As a result, the electric current flowing through the
system is found to be strongly dependent on the relative angle between exchange
fields, giving rise to a huge value of magnetoresistance. Moreover, the current
presents a complete spin-polarization in a wide range of bias voltages, even in
the quasiequilibrium case. In the nonequilibrium limit we parametrize the
distributions with an ``effective`` temperature, which turns out to be strongly
spin-dependent, though quite sensitive to inelastic collisions. By tunnel
coupling the normal region to an additional superconducting electrode we show
that it is possible to implement a spin-polarized current source of both spin
species, depending on the bias voltages applied.Comment: Published version: 12 pages, 14 figures; new text added and one
figure modifie
Gate-controlled superconductivity in diffusive multiwalled carbon nanotube
We have investigated electrical transport in a diffusive multiwalled carbon
nanotube contacted using superconducting leads made of Al/Ti sandwich
structure. We find proximity-induced superconductivity with measured critical
currents up to I_cm = 1.3 nA, tunable by gate voltage down to 10 pA. The
supercurrent branch displays a finite zero bias resistance which varies as R_0
proportional to I_cm^-alpha with alpha=0.74. Using IV-characteristics of
junctions with phase diffusion, a good agreement is obtained with Josephson
coupling energy in the long, diffusive junction model of A.D Zaikin and G.F.
Zharkov (Sov. J. Low Temp. Phys. 7, 184 (1981)).Comment: 5 pages, 4 figure
General two-order-parameter Ginzburg-Landau model with quadratic and quartic interactions
Ginzburg-Landau model with two order parameters appears in many
condensed-matter problems. However, even for scalar order parameters, the most
general U(1)-symmetric Landau potential with all quadratic and quartic terms
contains 13 independent coefficients and cannot be minimized with
straightforward algebra. Here, we develop a geometric approach that circumvents
this computational difficulty and allows one to study properties of the model
without knowing the exact position of the minimum. In particular, we find the
number of minima of the potential, classify explicit symmetries possible in
this model, establish conditions when and how these symmetries are
spontaneously broken, and explicitly describe the phase diagram.Comment: 36 pages, 7 figures; v2: added additional clarifications and a
discussion on how this method differs from the MIB-approac
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