7,798 research outputs found
Q & A Experiment to Search for Vacuum Dichroism, Pseudoscalar-Photon Interaction and Millicharged Fermions
A number of experiments are underway to detect vacuum birefringence and
dichroism -- PVLAS, Q & A, and BMV. Recently, PVLAS experiment has observed
optical rotation in vacuum by a magnetic field (vacuum dichroism). Theoretical
interpretations of this result include a possible pseudoscalar-photon
interaction and the existence of millicharged fermions. Here, we report the
progress and first results of Q & A (QED [quantum electrodynamics] and Axion)
experiment proposed and started in 1994. A 3.5-m high-finesse (around 30,000)
Fabry-Perot prototype detector extendable to 7-m has been built and tested. We
use X-pendulums and automatic control schemes developed by the
gravitational-wave detection community for mirror suspension and cavity
control. To polarize the vacuum, we use a 2.3-T dipole permanent magnet, with
27-mm-diameter clear borehole and 0.6-m field length,. In the experiment, the
magnet is rotated at 5-10 rev/s to generate time-dependent polarization signal
with twice the rotation frequency. Our
ellipsometer/polarization-rotation-detection-system is formed by a pair of
Glan-Taylor type polarizing prisms with extinction ratio lower than 10-8
together with a polarization modulating Faraday Cell with/without a quarter
wave plate. We made an independent calibration of our apparatus by performing a
measurement of gaseous Cotton-Mouton effect of nitrogen. We present our first
experimental results and give a brief discussion of our experimental limit on
pseudo-scalar-photon interaction and millicharged fermions.Comment: 21 pages, 13 figures, submitted to Modern Physics Letter
Second post-Newtonian approximation of scalar-tensor theory of gravity
Deep space laser ranging missions like ASTROD I (Single-Spacecraft
Astrodynamical Space Test of Relativity using Optical Devices) and ASTROD,
together with astrometry missions like GAIA and LATOR will be able to test
relativistic gravity to an unprecedented level of accuracy. More precisely,
these missions will enable us to test relativistic gravity to
, and will require 2nd post-Newtonian approximation of
relevant theories of gravity. The first post-Newtonian approximation is valid
to and the second post-Newtonian is valid to in the solar
system. The scalar-tensor theory is widely discussed and used in tests of
relativistic gravity, especially after the interests in inflation, cosmological
constant and dark energy in cosmology. In the Lagrangian, intermediate-range
gravity term has a similar form as cosmological term. Here we present the full
second post-Newtonian approximation of the scalar-tensor theory including
viable examples of intermediate-range gravity. We use Chandrasekhar's approach
to derive the metric coefficients and the equation of the hydrodynamics
governing a perfect fluid in the 2nd post-Newtonian approximation in
scalar-tensor theory; all terms inclusive of are retained
consistently in the equation of motion.Comment: 20 pages, COSPAR2006 H0.1-
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