2,466 research outputs found
A detector of small harmonic displacements based on two coupled microwave cavities
The design and test of a detector of small harmonic displacements is
presented. The detector is based on the principle of the parametric conversion
of power between the resonant modes of two superconducting coupled microwave
cavities. The work is based on the original ideas of Bernard, Pegoraro, Picasso
and Radicati, who, in 1978, suggested that superconducting coupled cavities
could be used as sensitive detectors of gravitational waves, and on the work of
Reece, Reiner and Melissinos, who, {in 1984}, built a detector of this kind.
They showed that an harmonic modulation of the cavity length l produced an
energy transfer between two modes of the cavity, provided that the frequency of
the modulation was equal to the frequency difference of the two modes. They
achieved a sensitivity to fractional deformations of dl/l~10^{-17} Hz^{-1/2}.
We repeated the Reece, Reiner and Melissinos experiment, and with an improved
experimental configuration and better cavity quality, increased the sensitivity
to dl/l~10^{-20} Hz^{-1/2}. In this paper the basic principles of the device
are discussed and the experimental technique is explained in detail. Possible
future developments, aiming at gravitational waves detection, are also
outlined.Comment: 28 pages, 12 eps figures, ReVteX. \tightenlines command added to
reduce number of pages. The following article has been accepted by Review of
Scientific Instruments. After it is published, it will be found at
http://link.aip.org/link/?rs
The rf control and detection system for PACO the parametric converter detector
In this technical note the rf control and detection system for a detector of
small harmonic displacements based on two coupled microwave cavities (PACO) is
presented. The basic idea underlying this detector is the principle of
parametric power conversion between two resonant modes of the system,
stimulated by the (small) harmonic modulation of one system parameter. In this
experiment we change the cavity length applying an harmonic voltage to a
piezo-electric crystal. The system can achieve a great sensitivity to small
harmonic displacements and can be an interesting candidate for the detection of
small, mechanically coupled, interactions (e.g. high frequency gravitational
waves).Comment: 13 pages, 4 postscript figure
Parametric gravity wave detector
Since 1978 superconducting coupled cavities have been proposed as a sensitive
detector of gravitational waves. The interaction of the gravitational wave with
the cavity walls, and the esulting motion, induces the transition of some
energy from an initially excited cavity mode to an empty one. The energy
transfer is maximum when the frequency of the wave is equal to the frequency
difference of the two cavity modes. In 1984 Reece, Reiner and Melissinos built
a detector of the type proposed, and used it as a transducer of harmonic
mechanical motion, achieving a sensitivity to fractional deformations of the
order dx/x ~ 10^(-18). In this paper the working principles of the detector are
discussed and the last experimental results summarized. New ideas for the
development of a realistic gravitational waves detector are considered; the
outline of a possible detector design and its expected sensitivity are also
shown.Comment: 9 pages, 6 figures. Talk given at the Workshop on Electromagnetic
Probes of Fundamentals Physics, Erice (Italy), October 200
A detector of gravitational waves based on coupled microwave cavities
Since 1978 superconducting coupled cavities have been proposed as sensitive
detector of gravitational waves. The interaction of the gravitational wave with
the cavity walls, and the resulting motion, induces the transition of some
electromagnetic energy from an initially excited cavity mode to an empty one.
The energy transfer is maximum when the frequency of the wave is equal to the
frequency difference of the two cavity modes. In this paper the basic
principles of the detector are discussed. The interaction of a gravitational
wave with the cavity walls is studied in the proper reference frame of the
detector, and the coupling between two electromagnetic normal modes induced by
the wall motion is analyzed in detail. Noise sources are also considered; in
particular the noise coming from the brownian motion of the cavity walls is
analyzed. Some ideas for the developement of a realistic detector of
gravitational waves are discussed; the outline of a possible detector design
and its expected sensitivity are also shown.Comment: 29 pages, 12 eps figures. Typeset by REVTe
Two Coupled Superconducting Cavities as a Gravitational Wave Detector: First Experimental Results
First experimental results of a feasibility study of a gravitational wave
detector based on two coupled superconducting cavities are presented. Basic
physical principles underlying the detector behaviour and sensitivity limits
are discussed. The detector layout is described in detail and its rf properties
are showed. The limit sensitivity to small harmonic displacements at the
detection frequency (around 1 MHz) is showed. The system performance as a
potential g.w. detector is discussed and future developments are foreseen.Comment: 7 pages, 3 figures. Presented at the 9th Workshop on RF
Superconductivity, November 1-5, 1999, Santa Fe, New Mexico, US
Chiral symmetry and the axial nucleon to Delta(1232) transition form factors
We study the momentum and the quark mass dependence of the axial nucleon to
Delta(1232) transition form factors in the framework of non-relativistic chiral
effective field theory to leading-one-loop order. The outcome of our analysis
provides a theoretical guidance for chiral extrapolations of lattice QCD
results with dynamical fermions.Comment: 18 pages, 3 figure
Lattice Calculation of Heavy-Light Decay Constants with Two Flavors of Dynamical Quarks
We present results for , , , and their ratios in
the presence of two flavors of light sea quarks (). We use Wilson light
valence quarks and Wilson and static heavy valence quarks; the sea quarks are
simulated with staggered fermions. Additional quenched simulations with
nonperturbatively improved clover fermions allow us to improve our control of
the continuum extrapolation. For our central values the masses of the sea
quarks are not extrapolated to the physical , masses; that is, the
central values are "partially quenched." A calculation using "fat-link clover"
valence fermions is also discussed but is not included in our final results. We
find, for example,
MeV, , MeV, and , where in each case the first error is
statistical and the remaining three are systematic: the error within the
partially quenched approximation, the error due to the missing strange
sea quark and to partial quenching, and an estimate of the effects of chiral
logarithms at small quark mass. The last error, though quite significant in
decay constant ratios, appears to be smaller than has been recently suggested
by Kronfeld and Ryan, and Yamada. We emphasize, however, that as in other
lattice computations to date, the lattice quark masses are not very light
and chiral log effects may not be fully under control.Comment: Revised version includes an attempt to estimate the effects of chiral
logarithms at small quark mass; central values are unchanged but one more
systematic error has been added. Sections III E and V D are completely new;
some changes for clarity have also been made elsewhere. 82 pages; 32 figure
Implications of an arithmetical symmetry of the commutant for modular invariants
We point out the existence of an arithmetical symmetry for the commutant of
the modular matrices S and T. This symmetry holds for all affine simple Lie
algebras at all levels and implies the equality of certain coefficients in any
modular invariant. Particularizing to SU(3)_k, we classify the modular
invariant partition functions when k+3 is an integer coprime with 6 and when it
is a power of either 2 or 3. Our results imply that no detailed knowledge of
the commutant is needed to undertake a classification of all modular
invariants.Comment: 17 pages, plain TeX, DIAS-STP-92-2
More evidence of localization in the low-lying Dirac spectrum
We have extended our computation of the inverse participation ratio of
low-lying (asqtad) Dirac eigenvectors in quenched SU(3). The scaling dimension
of the confining manifold is clearer and very near 3. We have also computed the
2-point correlator which further characterizes the localization.Comment: presented at Lattice2005(Topology and Confinement), Dublin, July
25-30, 2005, 6 pages, 3 figures, to appear in Proceedings of Scienc
Asymptotic scaling of the gluon propagtor on the lattice
We pursue the study of the high energy behaviour of the gluon propagator on
the lattice in the Landau gauge in the flavorless case (n_f=0). It was shown in
a precedin g paper that the gluon propagator did not reach three-loop
asymptotic scaling at an energy scale as high as 5 GeV.
Our present high statistics analysis includes also a simulation at
( fm), which allows to reach GeV.
Special care has been devoted to the finite lattice-spacing artifacts as well
as to the finite volume effects, the latter being acute at where
the volume is bounded by technical limits. Our main conclusion is a strong
evidence that the gluon propagator has reached three-loop asymptotic scaling,
at ranging from 5.6 GeV to 9.5 GeV. We buttress up this conclusion on
several demanding criteria of asymptoticity, including scheme independence. Our
fit in the 5.6 GeV to 9.5 GeV window yields MeV, in good agreement with our previous result,
MeV, obtained from the three gluon
vertex, but it is significantly above the Schr\"odinger functional method
estimate : MeV. The latter difference is not understood.
Confirming our previous paper, we show that a fourth loop is necessary to fit
the whole () GeV energy window.Comment: latex-file, 19 pgs., 6 fig
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