64,166 research outputs found
Dynamics of a rod in a homogeneous/inhomogeneous frozen disordered medium: Correlation functions and non-Gaussian effects
We present molecular dynamics simulations of the motion of a single rigid rod
in a disordered static 2d-array of disk-like obstacles. Two different
configurations have been used for the latter: A completely random one, and
which thus has an inhomogeneous structure, and an homogeneous ``glassy'' one,
obtained from freezing a liquid of soft disks in equilibrium. Small differences
are observed between both structures for the translational dynamics of the rod
center-of-mass. In contrast to this, the rotational dynamics in the glassy host
medium is strongly slowed down in comparison with the random one. We calculate
angular correlation functions for a wide range of rod length and density of
obstacles as control parameters. A two-step decay is observed for large
values of and , in analogy with supercooled liquids at temperature
close to the glass transition. In agreement with the prediction of the Mode
Coupling Theory, a time-length and time-density scaling is obtained. In order
to get insight on the relation between the heterogeneity of the dynamics and
the structure of the host medium, we determine the deviations from Gaussianity
at different length scales. Strong deviations are obtained even at spatial
scales much larger than the rod length. The magnitude of these deviations is
independent of the nature of the host medium. This result suggests that the
large scale translational dynamics of the rod is affected only weakly by the
presence of inhomogeneities in the host medium.Comment: Published in AIP Conference Proceedings 708 (2004) 576-58
Logarithmic Relaxation in a Kinetically Constrained Model
We present Monte Carlo simulations in a modification of the
north-or-east-or-front model recently investigated by Berthier and Garrahan [J.
Phys. Chem. B 109, 3578 (2005)]. In this coarse-grained model for relaxation in
supercooled liquids, the liquid structure is substituted by a three-dimensional
array of cells. A spin variable is assigned to each cell, with values 0 or 1
denoting respectively unexcited and excited local states in a mobility field.
Change in local mobility (spin flip) for a given cell is permitted according to
kinetic constraints determined by the mobilities of neighboring cells. In this
work we keep the same kinetic constraints of the original model, but we
introduce two types of cells (denoted as "fast'' and "slow'') with very
different rates for spin flip. As a consequence, fast and slow cells exhibit
very different relaxation times for spin correlators. While slow cells exhibit
standard relaxation, fast cells display anomalous relaxation, characterized by
a concave-to-convex crossover in spin correlators by changing temperature or
composition. At intermediate state points logarithmic relaxation is observed
over three time decades. These results display striking analogies with dynamic
correlators reported in recent simulations on a bead-spring model for polymer
blends.Comment: Major changes. To be published in Journal of Chemical Physic
Unveiling the Effect of Magnetic Noise in the Coherence of Single-Molecule Quantum Processors
Quantum bits (qubits) constitute the most elementary building-blocks of any quantum technology, where information is stored and processed in the form of quantum superpositions between discrete energy levels. In particular, the fabrication of quantum processors is a key long-term goal that will allow us conducting specific tasks much more efficiently than the most powerful classical computers can do. Motivated by recent experiments in which three addressable spin qubits are defined on a potential single-molecule quantum processor, namely the [Gd(H2O)P5W30O110]12− polyoxometalate, we investigate the decohering effect of magnetic noise on the encoded quantum information. Our state-of-the-art model, which provides more accurate results than previous estimates, show a noticeable contribution of magnetic noise in limiting the survival timescale of the qubits. Yet, our results suggest that it might not be the only dephasing mechanism at play but other mechanisms, such as lattice vibrations and physical movement of magnetic nuclei, must be considered to understand the whole decoherence process
The 750 GeV Diphoton Excess as a First Light on Supersymmetry Breaking
One of the most exciting explanations advanced for the recent diphoton excess
found by ATLAS and CMS is in terms of sgoldstino decays: a signal of low-energy
supersymmetry-breaking scenarios. The sgoldstino, a scalar, couples directly to
gluons and photons, with strength related to gaugino masses, that can be of the
right magnitude to explain the excess. However, fitting the suggested resonance
width, Gamma ~ 45 GeV, is not so easy. In this paper we explore efficient
possibilities to enhance the sgoldstino width, via the decay into two Higgses,
two Higgsinos and through mixing between the sgoldstino and the Higgs boson. In
addition, we present an alternative and more efficient mechanism to generate a
mass splitting between the scalar and pseudoscalar components of the
sgoldstino, which has been suggested as an interesting alternative explanation
to the apparent width of the resonance.Comment: 14 pages, 3 figure
Domain walls in supersymmetric QCD
We consider domain walls that appear in supersymmetric SU(N) with one massive
flavour. In particular, for N > 3 we explicitly construct the elementary domain
wall that interpolates between two contiguous vacua. We show that these
solutions are BPS saturated for any value of the mass of the matter fields. We
also comment on their large N limit and their relevance for supersymmetric
gluodynamics.Comment: 4 pages, 1 figure, uses latex with hep99 class files. Presented at
the International Europhysics Conference in High Energy Physics, Tampere
(Finland) 15-21 July 199
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