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L. Conti

Publications and source records attributed to L. Conti.

34 records · Page 2Linked to original sources
arXiv2003

Selective readout and back-action reduction for wideband acoustic gravitational wave detectors

We present the concept of selective readout for broadband resonant mass gravitational wave detectors. This detection scheme is capable of specifically selecting the signal from the contributions of the vibrational modes sensitive to the gravitational waves, and efficiently rejecting the contribution from non gravitationally sensitive modes. Moreover this readout, applied to a dual detector, is capable to give an effective reduction of the back-action noise within the frequency band of interest. The overall effect is a significant enhancement in the predicted sensitivity, evaluated at the standard quantum limit for a dual torus detector. A molybdenum detector, 1 m in diameter and equipped with a wide area selective readout, would reach spectral strain sensitivities 2x10^{-23}/sqrt{Hz} between 2-6 kHz.

gr-qc↗
arXiv2003

Thermal and back-action noises in dual-sphere gravitational-waves detectors

We study the sensitivity limits of a broadband gravitational-waves detector based on dual resonators such as nested spheres. We determine both the thermal and back-action noises when the resonators displacements are read-out with an optomechanical sensor. We analyze the contributions of all mechanical modes, using a new method to deal with the force-displacement transfer functions in the intermediate frequency domain between the two gravitational-waves sensitive modes associated with each resonator. This method gives an accurate estimate of the mechanical response, together with an evaluation of the estimate error. We show that very high sensitivities can be reached on a wide frequency band for realistic parameters in the case of a dual-sphere detector.

gr-qc↗
arXiv2002

Room temperature GW bar detector with opto-mechanical readout

We present the full implementation of a room-temperature gravitational wave bar detector equipped with an opto-mechanical readout. The mechanical vibrations are read by a Fabry--Perot interferometer whose length changes are compared with a stable reference optical cavity by means of a resonant laser. The detector performance is completely characterized in terms of spectral sensitivity and statistical properties of the fluctuations in the system output signal. The new kind of readout technique allows for wide-band detection sensitivity and we can accurately test the model of the coupled oscillators for thermal noise. Our results are very promising in view of cryogenic operation and represent an important step towards significant improvements in the performance of massive gravitational wave detectors.

gr-qc↗
arXiv2002

Experimental measurement of photothermal effect in Fabry-Perot cavities

We report the experimental observation of the photothermal effect. The measurements are performed by modulating the laser power absorbed by the mirrors of two high-finesse Fabry-Perot cavities. The results are very well described by a recently proposed theoretical model [M. Cerdonio, L. Conti, A. Heidmann and M. Pinard, Phys. Rev. D 63 (2001) 082003], confirming the correctness of such calculations. Our observations and quantitative characterization of the photothermal effect demonstrate its critical importance for high sensitivity interferometric displacement measurements, as those necessary for gravitational wave detection.

gr-qc↗
arXiv2001

Wideband dual sphere detector of gravitational waves

We present the concept of a sensitive AND broadband resonant mass gravitational wave detector. A massive sphere is suspended inside a second hollow one. Short, high-finesse Fabry-Perot optical cavities read out the differential displacements of the two spheres as their quadrupole modes are excited. At cryogenic temperatures one approaches the Standard Quantum Limit for broadband operation with reasonable choices for the cavity finesses and the intracavity light power. A molybdenum detector of overall size of 2 m, would reach spectral strain sensitivities of 2x10^-23/Sqrt{Hz} between 1000 Hz and 3000 Hz.

gr-qc↗
arXiv2001

The t->WZb decay in the Standard Model: A Critical Reanalysis

We compute the t->WZb decay rate, in the Standard Model, at the leading order in perturbation theory, with special attention to the effects of the finite widths of the W and Z bosons. These effects are extremely important, since the t->WZb decay occurs near its kinematical threshold. They increase the value of the decay rate by orders of magnitude near threshold or allow it below the nominal threshold. We discuss a procedure to take into account the finite-width effects and compare the results with previous studies of this decay. Within the Standard Model, for a top quark mass in the range between 170 and 180 GeV, we find BR(t->WZb) ~ 2 x 10^{-6}, which makes the observation at the LHC very difficult if at all possible.

hep-ph↗
arXiv2001

Thermoelastic effects at low temperatures and quantum limits in displacement measurements

The displacement fluctuations of mirrors in optomechanical devices, induced via thermal expansion by temperature fluctuations due either to thermodynamic fluctuations or to fluctuations in the photon absorption, can be made smaller than quantum fluctuations, at the low temperatures, high reflectivities and high light powers needed to readout displacements at the standard quantum limit. The result is relevant for the design of quantum limited gravitational-wave detectors, both "interferometers" and "bars", and for experiments to study directly mechanical motion in the quantum regime.

gr-qc↗
arXiv2000

Delta M_K and epsilon_K in SUSY at the Next-to-Leading order

We perform a Next-to-Leading order analysis of Delta S=2 processes beyond the Standard Model. Combining the recently computed NLO anomalous dimensions and the B parameters of the most general Delta S=2 effective Hamiltonian, we give an analytic formula for Delta M_K and epsilon_K in terms of the Wilson coefficients at the high energy scale. This expression can be used for any extension of the Standard Model with new heavy particles. Using this result, we consider gluino-mediated contributions to Delta S=2 transitions in general SUSY models and provide an improved analysis of the constraints on off-diagonal mass terms between the first two generations of down-type squarks. Finally, we improve the constraints on R-violating couplings from Delta M_K and epsilon_K.

hep-ph↗
arXiv2000

Initial operation of the International Gravitational Event Collaboration

The International Gravitational Event Collaboration, IGEC, is a coordinated effort by research groups operating gravitational wave detectors working towards the detection of millisecond bursts of gravitational waves. Here we report on the current IGEC resonant bar observatory, its data analysis procedures, the main properties of the first exchanged data set. Even though the available data set is not complete, in the years 1997 and 1998 up to four detectors were operating simultaneously. Preliminary results are mentioned.

astro-ph↗
arXiv1999

B-parameters for DeltaS = 2 Supersymmetric Operators

We present a calculation of the matrix elements of the most general set of DeltaS=2 dimension-six four-fermion operators. The values of the matrix elements are given in terms of the corresponding B-parameters. Our results can be used in many phenomenological applications, since the operators considered here give important contributions to K^0--K^0bar mixing in several extensions of the Standard Model (supersymmetry, left-right symmetric models, multi-Higgs models etc.). The determination of the matrix elements improves the accuracy of the phenomenological analyses intended to put bounds on basic parameters of the different models, as for example the pattern of the sfermion mass matrices. The calculation has been performed on the lattice, using the tree-level improved Clover action at two different values of the strong coupling constant (beta=6/g_0^2(a)=6.0 and 6.2, corresponding to a^-1= 2.1 and 2.7 GeV respectively), in the quenched approximation. The renormalization constants and mixing coefficients of the lattice operators have been obtained non-perturbatively.

hep-lat↗
arXiv1998

B-parameters for $ΔS = 2$ SUSY Operators

We present the first lattice measurement, using Non Perturbative Renormalization Method, of the B-parameters of the dimension-six four-fermion operators relevant for the supersymmetric corrections to the $ΔS=2$ transitions.

hep-lat↗
arXiv1997

Lattice B-parameters for $ΔS = 2$ and $ΔI = 3/2$ Operators

We compute several matrix elements of dimension-six four-fermion operators and extract their B-parameters. The calculations have been performed with the tree-level Clover action at $β= 6.0$. The renormalization constants and mixing coefficients of the lattice operators have been obtained non-perturbatively. In the $\MSbar$ renormalization scheme, at a renormalization scale $μ\simeq 2$ GeV, we find $B_K (B_9^{3/2}) = 0.66(11), B_7^{3/2} = 0.72(5)$ and $B_8^{3/2} = 1.03(3)$. The result for $B_8^{3/2}$ has important implications for the calculation of $ε^\prime / ε$.

hep-lat↗
arXiv1997

Non-perturbative Renormalization of the Complete Basis of Four-fermion Operators and B-parameters

We present results on the B-parameters $B_K$, $B^{3/2}_7$ and $B^{3/2}_8$, at $β=6.0$, with the tree-level Clover action. The renormalization of the complete basis of dimension-six four-fermion operators has been performed non-perturbatively. Our results for $B_K$ and $B^{3/2}_7$ are in reasonable agreement with those obtained with the (unimproved) Wilson action. This is not the case for $B^{3/2}_8$. We also discuss some subtleties arising from a recently proposed modified definition of the B-parameters.

hep-lat↗
arXiv1997

A High Statistics Lattice Calculation of Heavy-Light Meson Decay Constants

We present a high statistics study of the D- and B-meson decay constants. The results were obtained by using the Clover and Wilson lattice actions at two different values of the lattice spacing $a$, corresponding to $β=6.0$ and 6.2. After a careful analysis of the systematic errors present in the extraction of the physical results, by assuming quite conservative discretization errors, we find $f_{D_s}=237 \pm 16$ MeV, $f_{D} = 221 \pm 17$ MeV ($f_{D_s}/f_D=1.07(4)$), $f_{B_s} = 205 \pm 35$ MeV, $f_{B} = 180 \pm 32$ MeV ($f_{B_s}/f_B=1.14(8)$), in good agreement with previous estimates.

hep-lat↗
arXiv1996

Full QCD with dynamical Wilson fermions on a 24^3 x 40-lattice -- a feasibility study

The investigation of light sea-quark effects in lattice QCD with dynamical Wilson fermions requires both larger physical volumes and finer lattice resolutions than achieved previously. As high-end supercomputers like the 512-node APE Tower provide the compute power to perform a major step towards the chiral limit (T-chi-L), we have launched a feasibility study on a 24^3 x 40 lattice. We approach the chiral limit--while refining the resolution--, using the standard Wilson fermion action. Following previous work, our Hybrid Monte Carlo simulation runs at beta=5.6 and two kappa-values, 0.1575 and 0.158. From our study, we are confident that, for the APE Tower, a realistic working point has been found corresponding to a volume of 2 fm^3, with chirality characterized by 1/(a m_pi) = 5.6.

hep-lat↗