491 research outputs found
How to Run Through Walls: Dynamics of Bubble and Soliton Collisions
It has recently been shown in high resolution numerical simulations that
relativistic collisions of bubbles in the context of a multi-vacua potential
may lead to the creation of bubbles in a new vacuum. In this paper, we show
that scalar fields with only potential interactions behave like free fields
during high-speed collisions; the kick received by them in a collision can be
deduced simply by a linear superposition of the bubble wall profiles. This
process is equivalent to the scattering of solitons in 1+1 dimensions. We
deduce an expression for the field excursion (shortly after a collision), which
is related simply to the field difference between the parent and bubble vacua,
i.e. contrary to expectations, the excursion cannot be made arbitrarily large
by raising the collision energy. There is however a minimum energy threshold
for this excursion to be realized. We verify these predictions using a number
of 3+1 and 1+1 numerical simulations. A rich phenomenology follows from these
collision induced excursions - they provide a new mechanism for scanning the
landscape, they might end/begin inflation, and they might constitute our very
own big bang, leaving behind a potentially observable anisotropy.Comment: 15pgs, 14 figures, v2, thanks for the feedback
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Unexpected benefits of deciding by mind wandering
The mind wanders, even when people are attempting to make complex decisions. We suggest that mind wanderingâallowing one's thoughts to wander until the âcorrectâ choice comes to mindâcan positively impact people's feelings about their decisions. We compare post-choice satisfaction from choices made by mind wandering to reason-based choices and randomly assigned outcomes. Participants chose a poster by mind wandering or deliberating, or were randomly assigned a poster. Whereas forecasters predicted that participants who chose by mind wandering would evaluate their outcome as inferior to participants who deliberated (Experiment 1), participants who used mind wandering as a decision strategy evaluated their choice just as positively as did participants who used deliberation (Experiment 2). In some cases, it appears that people can spare themselves the effort of deliberation and instead âdecide by wind wandering,â yet experience no decrease in satisfaction
Time-Scales for Nonlinear Processes in Preheating after Multifield Inflation with Nonminimal Couplings
We have conducted extensive lattice simulations to study the post-inflation
dynamics of multifield models involving nonminimal couplings. We explore the
parameter dependence of preheating in these models and describe the various
time-scales that control such nonlinear processes as energy transfer,
re-scattering, and the approach to radiation-domination and thermalization. In
the limit of large nonminimal couplings (), we find that
efficient transfer of energy from the inflaton condensate to radiative degrees
of freedom, emergence of a radiation-dominated equation of state, and the onset
of thermalization each consistently occur within
-folds after the end of inflation, largely independent of the values of the
other couplings in the models. The exception is the case of negative
ellipticity, in which there is a misalignment between the dominant direction in
field-space along which the system evolves and the larger of the nonminimal
couplings . In those cases, the field-space-driven parametric resonance
is effectively shut off. More generally, the competition between the scalar
fields' potential and the field-space manifold structure can yield interesting
phenomena such as two-stage resonances. Despite the explosive particle
production, which can lead to a quick depletion of the background energy
density, the nonlinear processes do not induce any super-horizon correlations
after the end of inflation in these models, which keeps predictions for CMB
observables unaffected by the late-time amplification of isocurvature
fluctuations. Hence the excellent agreement between primordial observables and
recent observations is preserved for this class of models, even when we
consider post-inflation dynamics.Comment: 32 pages (plus appendices), 17 figures. References added and minor
edits to match published versio
Precession of a Freely Rotating Rigid Body. Inelastic Relaxation in the Vicinity of Poles
When a solid body is freely rotating at an angular velocity ,
the ellipsoid of constant angular momentum, in the space , has poles corresponding to spinning about the minimal-inertia and
maximal-inertia axes. The first pole may be considered stable if we neglect the
inner dissipation, but becomes unstable if the dissipation is taken into
account. This happens because the bodies dissipate energy when they rotate
about any axis different from principal. In the case of an oblate symmetrical
body, the angular velocity describes a circular cone about the vector of
(conserved) angular momentum. In the course of relaxation, the angle of this
cone decreases, so that both the angular velocity and the maximal-inertia axis
of the body align along the angular momentum. The generic case of an asymmetric
body is far more involved. Even the symmetrical prolate body exhibits a
sophisticated behaviour, because an infinitesimally small deviation of the
body's shape from a rotational symmetry (i.e., a small difference between the
largest and second largest moments of inertia) yields libration: the precession
trajectory is not a circle but an ellipse. In this article we show that often
the most effective internal dissipation takes place at twice the frequency of
the body's precession. Applications to precessing asteroids, cosmic-dust
alignment, and rotating satellites are discussed.Comment: 47 pages, 1 figur
High-resolution error detection in the capture process of a single-electron pump
The dynamic capture of electrons in a semiconductor quantum dot (QD) by raising a potential
barrier is a crucial stage in metrological quantized charge pumping. In this work, we use a quantum
point contact (QPC) charge sensor to study errors in the electron capture process of a QD formed in
a GaAs heterostructure. Using a two-step measurement protocol to compensate for 1/f noise in the
QPC current, and repeating the protocol more than 106 times, we are able to resolve errors with
probabilities of order 106. For the studied sample, one-electron capture is affected by errors in
30 out of every million cycles, while two-electron capture was performed more than 106 times
with only one error. For errors in one-electron capture, we detect both failure to capture an electron
and capture of two electrons. Electron counting measurements are a valuable tool for investigating
non-equilibrium charge capture dynamics, and necessary for validating the metrological accuracy
of semiconductor electron pumps
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