32 research outputs found
Spin-Dependent Macroscopic Forces from New Particle Exchange
Long-range forces between macroscopic objects are mediated by light particles
that interact with the electrons or nucleons, and include spin-dependent static
components as well as spin- and velocity-dependent components. We parametrize
the long-range potential between two fermions assuming rotational invariance,
and find 16 different components. Applying this result to electrically neutral
objects, we show that the macroscopic potential depends on 72 measurable
parameters. We then derive the potential induced by the exchange of a new gauge
boson or spinless particle, and compare the limits set by measurements of
macroscopic forces to the astrophysical limits on the couplings of these
particles.Comment: 37 page
Tests of the Gravitational Inverse-Square Law
We review recent experimental tests of the gravitational inverse-square law
and the wide variety of theoretical considerations that suggest the law may
break down in experimentally accessible regions.Comment: 81 pages, 10 figures, submitted by permission of the Annual Review of
Nuclear and Particle Science. Final version of this material is scheduled to
appear in the Annual Review of Nuclear and Particle Science Vol. 53, to be
published in December 2003 by Annual Reviews, http://AnnualReviews.or
A liquid helium target system for a measurement of parity violation in neutron spin rotation
A liquid helium target system was designed and built to perform a precision
measurement of the parity-violating neutron spin rotation in helium due to the
nucleon-nucleon weak interaction. The measurement employed a beam of low energy
neutrons that passed through a crossed neutron polarizer--analyzer pair with
the liquid helium target system located between them. Changes between the
target states generated differences in the beam transmission through the
polarizer--analyzer pair. The amount of parity-violating spin rotation was
determined from the measured beam transmission asymmetries. The expected
parity-violating spin rotation of order rad placed severe constraints
on the target design. In particular, isolation of the parity-odd component of
the spin rotation from a much larger background rotation caused by magnetic
fields required that a nonmagnetic cryostat and target system be supported
inside the magnetic shielding, while allowing nonmagnetic motion of liquid
helium between separated target chambers. This paper provides a detailed
description of the design, function, and performance of the liquid helium
target system.Comment: V2: 29 pages, 14 figues, submitted to Nucl. Instrum. Meth. B. Revised
to address reviewer comment
Ghost Condensation and a Consistent Infrared Modification of Gravity
We propose a theoretically consistent modification of gravity in the
infrared, which is compatible with all current experimental observations. This
is an analog of Higgs mechanism in general relativity, and can be thought of as
arising from ghost condensation--a background where a scalar field \phi has a
constant velocity, = M^2. The ghost condensate is a new kind of
fluid that can fill the universe, which has the same equation of state, \rho =
-p, as a cosmological constant, and can hence drive de Sitter expansion of the
universe. However, unlike a cosmological constant, it is a physical fluid with
a physical scalar excitation, which can be described by a systematic effective
field theory at low energies. The excitation has an unusual low-energy
dispersion relation \omega^2 \sim k^4 / M^2. If coupled to matter directly, it
gives rise to small Lorentz-violating effects and a new long-range 1/r^2 spin
dependent force. In the ghost condensate, the energy that gravitates is not the
same as the particle physics energy, leading to the possibility of both sources
that can gravitate and antigravitate. The Newtonian potential is modified with
an oscillatory behavior starting at the distance scale M_{Pl}/M^2 and the time
scale M_{Pl}^2/M^3. This theory opens up a number of new avenues for attacking
cosmological problems, including inflation, dark matter and dark energy.Comment: 42 pages, LaTeX 2
Spectral action for torsion with and without boundaries
We derive a commutative spectral triple and study the spectral action for a
rather general geometric setting which includes the (skew-symmetric) torsion
and the chiral bag conditions on the boundary. The spectral action splits into
bulk and boundary parts. In the bulk, we clarify certain issues of the previous
calculations, show that many terms in fact cancel out, and demonstrate that
this cancellation is a result of the chiral symmetry of spectral action. On the
boundary, we calculate several leading terms in the expansion of spectral
action in four dimensions for vanishing chiral parameter of the
boundary conditions, and show that is a critical point of the action
in any dimension and at all orders of the expansion.Comment: 16 pages, references adde
Constraining spacetime torsion with LAGEOS
We compute the corrections to the orbital Lense-Thirring effect (or
frame-dragging) in the presence of spacetime torsion. We derive the equations
of motion of a test body in the gravitational field of a rotating axisymmetric
massive body, using the parametrized framework of Mao, Tegmark, Guth and Cabi.
We calculate the secular variations of the longitudes of the node and of the
pericenter. We also show how the LAser GEOdynamics Satellites (LAGEOS) can be
used to constrain torsion parameters. We report the experimental constraints
obtained using both the nodes and perigee measurements of the orbital
Lense-Thirring effect. This makes LAGEOS and Gravity Probe B (GPB)
complementary frame-dragging and torsion experiments, since they constrain
three different combinations of torsion parameters
Powder Compaction: Compression Properties of Cellulose Ethers
Effective development of matrix tablets requires a comprehensive understanding of different raw material attributes and their impact on process parameters. Cellulose ethers (CE) are the most commonly used pharmaceutical excipients in the fabrication of hydrophilic matrices. The innate good compression and binding properties of CE enable matrices to be prepared using economical direct compression (DC) techniques. However, DC is sensitive to raw material attributes, thus, impacting the compaction process. This article critically reviews prior knowledge on the mechanism of powder compaction and the compression properties of cellulose ethers, giving timely insight into new developments in this field