1,653 research outputs found
Universal far-from-equilibrium Dynamics of a Holographic Superconductor
Symmetry breaking phase transitions are an example of non-equilibrium
processes that require real time treatment, a major challenge in strongly
coupled systems without long-lived quasiparticles. Holographic duality provides
such an approach by mapping strongly coupled field theories in D dimensions
into weakly coupled quantum gravity in D+1 anti-de Sitter spacetime. Here, we
use holographic duality to study formation of topological defects -- winding
numbers -- in the course of a superconducting transition in a strongly coupled
theory in a 1D ring. When the system undergoes the transition on a given quench
time, the condensate builds up with a delay that can be deduced using the
Kibble-Zurek mechanism from the quench time and the universality class of the
theory, as determined from the quasinormal mode spectrum of the dual model.
Typical winding numbers deposited in the ring exhibit a universal fractional
power law dependence on the quench time, also predicted by the Kibble-Zurek
Mechanism.Comment: 33 pages; 8 figure
Assisted finite-rate adiabatic passage across a quantum critical point: Exact solution for the quantum Ising model
The dynamics of a quantum phase transition is inextricably woven with the
formation of excitations, as a result of the critical slowing down in the
neighborhood of the critical point. We design a transitionless quantum driving
through a quantum critical point that allows one to access the ground state of
the broken-symmetry phase by a finite-rate quench of the control parameter. The
method is illustrated in the one-dimensional quantum Ising model in a
transverse field. Driving through the critical point is assisted by an
auxiliary Hamiltonian, for which the interplay between the range of the
interaction and the modes where excitations are suppressed is elucidated.Comment: 2 figures, 5 page
R^2-corrections to Chaotic Inflation
Scalar density cosmological perturbations, spectral indices and reheating in
a chaotic inflationary universe model, in which a higher derivative term is
added, are investigated. This term is supposed to play an important role in the
early evolution of the Universe, specifically at times closer to the Planck
era.Comment: 14 pages, accepted for publication in MPL
Atom cooling by non-adiabatic expansion
Motivated by the recent discovery that a reflecting wall moving with a
square-root in time trajectory behaves as a universal stopper of classical
particles regardless of their initial velocities, we compare linear in time and
square-root in time expansions of a box to achieve efficient atom cooling. For
the quantum single-atom wavefunctions studied the square-root in time expansion
presents important advantages: asymptotically it leads to zero average energy
whereas any linear in time (constant box-wall velocity) expansion leaves a
non-zero residual energy, except in the limit of an infinitely slow expansion.
For finite final times and box lengths we set a number of bounds and cooling
principles which again confirm the superior performance of the square-root in
time expansion, even more clearly for increasing excitation of the initial
state. Breakdown of adiabaticity is generally fatal for cooling with the linear
expansion but not so with the square-root expansion.Comment: 4 pages, 4 figure
Fluxoid formation: size effects and non-equilibrium universality
Simple causal arguments put forward by Kibble and Zurek suggest that the
scaling behaviour of condensed matter at continuous transitions is related to
the familiar universality classes of the systems at quasi-equilibrium. Although
proposed 25 years ago or more, it is only in the last few years that it has
been possible to devise experiments from which scaling exponents can be
determined and in which this scenario can be tested. In previous work, an
unusually high Kibble-Zurek scaling exponent was reported for spontaneous
fluxoid production in a single isolated superconducting Nb loop, albeit with
low density. Using analytic approximations backed up by Langevin simulations,
we argue that densities as small as these are too low to be attributable to
scaling, and are conditioned by the small size of the loop. We also reflect on
the physical differences between slow quenches and small rings, and derive some
criteria for these differences, noting that recent work on slow quenches does
not adequately explain the anomalous behaviour seen here.Comment: 7 pages, 4 figures, presentation given at CMMP 201
False vacuum decay in a brane world cosmological model
The false vacuum decay in a brane world model is studied in this work. We
investigate the vacuum decay via the Coleman-de Luccia instanton, derive
explicit approximative expressions for the Coleman-de Luccia instanton which is
close to a Hawking-Moss instanton and compare the results with those already
obtained within Einstein's theory of relativity.Comment: minor changes done, references added, version to appear in GR
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