1,804 research outputs found
Dark energy fifth forces in torsion pendulum experiments
The chameleon scalar field is a matter-coupled dark energy candidate whose
nonlinear self-interaction partially screens its fifth force at laboratory
scales. Nevertheless, small-scale experiments such as the torsion pendulum can
provide powerful constraints on chameleon models. Here we develop a simple
approximation for computing chameleon fifth forces in torsion pendulum
experiments such as Eot-Wash. We show that our approximation agrees well with
published constraints on the quartic chameleon, and we use it to extend these
constraints to a much wider range of models. Finally, we forecast the
constraints which will result from the next-generation Eot-Wash experiment, and
show that this experiment will exclude a wide range of quantum-stable models.Comment: 15 pages, 17 figures; matches version accepted by PR
Constraints on Light Pseudoscalars Implied by Tests of the Gravitational Inverse-Square Law
The exchange of light pseudoscalars between fermions leads to a
spin-independent potential in order g^4, where g is the Yukawa
pseudoscalar-fermion coupling constant. This potential gives rise to detectable
violations of both the weak equivalence principle (WEP) and the gravitational
inverse-square law (ISL), even if g is quite small. We show that when
previously derived WEP constraints are combined with those arisingfrom ISL
tests, a direct experimental limit on the Yukawa coupling of light
pseudoscalars to neutrons can be inferred for the first time (g_n^2/4pi < 1.6
\times 10^-7), along with a new (and significantly improved) limit on the
coupling of light pseudoscalars to protons.Comment: 12 pages, Revtex, with 1 Postscript figure (submitted to Physical
Review Letters
G77-340 Scheduling Irrigation by Electrical Resistance Blocks
Delay of irrigation for a few days during a critical part of the growing season can be expensive. A week\u27s delay in supplying irrigation water to corn or grain sorghum can reduce potential yield more than 30 bushels per acre.
Several methods are available to help you schedule the right amount of water at the right time. One of these methods uses electrical resistance blocks discussed in this NebGuide
Is violation of Newton's second law possible?
Astrophysical observations (usually explained by dark matter) suggest that
classical mechanics could break down when the acceleration becomes extremely
small (the approach known as modified Newtonian dynamics, or MOND). I present
the first analysis of MOND manifestations in terrestrial (rather than
astrophysical) settings. A new effect is reported: around each equinox date, 2
spots emerge on the Earth where static bodies experience spontaneous
acceleration due to the possible violation of Newton's second law. Preliminary
estimates indicate that an experimental search for this effect can be feasible.Comment: 10 pages; minor changes to match the published versio
Quantized Casimir Force
We investigate the Casimir effect between two-dimensional electron systems
driven to the quantum Hall regime by a strong perpendicular magnetic field. In
the large separation (d) limit where retardation effects are essential we find
i) that the Casimir force is quantized in units of 3\hbar c \alpha^2/(8\pi^2
d^4), and ii) that the force is repulsive for mirrors with same type of
carrier, and attractive for mirrors with opposite types of carrier. The sign of
the Casimir force is therefore electrically tunable in ambipolar materials like
graphene. The Casimir force is suppressed when one mirror is a charge-neutral
graphene system in a filling factor \nu=0 quantum Hall state.Comment: 4.2 page
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