Pipe cooling perspectives for superconducting accelerating cavities

We explore the rf characteristics of pipe cooled superconducting cavities versus bath cooled ones, using different pipe configurations and different liquid helium temperatures. Pipe cooled cavities can perform nearly as well as bath cooled ones, provided a suitable pipe configuration and cavity wall thickness is chosen. Pure thermal estimates and fits with experimental data show that pipe cooling is a viable solution for future cavities

A gravitational wave window on extra dimensions

We report on the possibility of detecting a submillimetre-sized extra dimension by observing gravitational waves (GWs) emitted by pointlike objects orbiting a braneworld black hole. Matter in the `visible' universe can generate a discrete spectrum of high frequency GWs with amplitudes moderately weaker than the predictions of general relativity (GR), while GW signals generated by matter on a `shadow' brane hidden in the bulk are potentially strong enough to be detected using current technology. We know of no other astrophysical phenomena that produces GWs with a similar spectrum, which stresses the need to develop detectors capable of measuring this high-frequency signature of large extra dimensions.Comment: 9 pages, 5 figure

Microwave apparatus for gravitational waves observation

In this report the theoretical and experimental activities for the development of superconducting microwave cavities for the detection of gravitational waves are presented.Comment: 42 pages, 28 figure

Nonlinear coupled Alfv\'{e}n and gravitational waves

In this paper we consider nonlinear interaction between gravitational and electromagnetic waves in a strongly magnetized plasma. More specifically, we investigate the propagation of gravitational waves with the direction of propagation perpendicular to a background magnetic field, and the coupling to compressional Alfv\'{e}n waves. The gravitational waves are considered in the high frequency limit and the plasma is modelled by a multifluid description. We make a self-consistent, weakly nonlinear analysis of the Einstein-Maxwell system and derive a wave equation for the coupled gravitational and electromagnetic wave modes. A WKB-approximation is then applied and as a result we obtain the nonlinear Schr\"{o}dinger equation for the slowly varying wave amplitudes. The analysis is extended to 3D wave pulses, and we discuss the applications to radiation generated from pulsar binary mergers. It turns out that the electromagnetic radiation from a binary merger should experience a focusing effect, that in principle could be detected.Comment: 20 pages, revtex4, accepted in PR

Thermal history of the plasma and high-frequency gravitons

Possible deviations from a radiation-dominated evolution, occurring prior the synthesis of light nuclei, impacted on the spectral energy density of high-frequency gravitons. For a systematic scrutiny of this situation, the $\Lambda$CDM paradigm must be complemented by (at least two) physical parameters describing, respectively, a threshold frequency and a slope. The supplementary frequency scale sets the lower border of a high-frequency domain where the spectral energy grows with a slope which depends, predominantly, upon the total sound speed of the plasma right after inflation. While the infra-red region of the graviton energy spectrum is nearly scale-invariant, the expected signals for typical frequencies larger than 0.01 nHz are hereby analyzed in a model-independent framework by requiring that the total sound speed of the post-inflationary plasma be smaller than the speed of light. Current (e.g. low-frequency) upper limits on the tensor power spectra (determined from the combined analysis of the three large-scale data sets) are shown to be compatible with a detectable signal in the frequency range of wide-band interferometers. In the present context, the scrutiny of the early evolution of the sound speed of the plasma can then be mapped onto a reliable strategy of parameter extraction including not only the well established cosmological observables but also the forthcoming data from wide band interferometers.Comment: 47 pages, 31 included figures, to appear in Classical and Quantum Gravit

Stochastic Gravitational Wave Production After Inflation

In many models of inflation, the period of accelerated expansion ends with preheating, a highly non-thermal phase of evolution during which the inflaton pumps energy into a specific set of momentum modes of field(s) to which it is coupled. This necessarily induces large, transient density inhomogeneities which can source a significant spectrum of gravitational waves. In this paper, we consider the generic properties of gravitational waves produced during preheating, perform detailed calculations of the spectrum for several specific inflationary models, and identify problems that require further study. In particular, we argue that if these gravitational waves exist they will necessarily fall within the frequency range that is feasible for direct detection experiments -- from laboratory through to solar system scales. We extract the gravitational wave spectrum from numerical simulations of preheating after $\lambda \phi^4$ and $m_{\phi}^2 \phi^2$ inflation, and find that they lead to a gravitational wave amplitude of around $\Omega_{gw}h^2\sim 10^{-10}$. This is considerably higher than the amplitude of the primordial gravitational waves produced during inflation. However, the typical wavelength of these gravitational waves is considerably shorter than LIGO scales, although in extreme cases they may be visible at scales accessible to the proposed BBO mission. We survey possible experimental approaches to detecting any gravitational wave background generated during preheating.Comment: 11 pages. Updated references. Minor clarification

New parametric transducer for resonant detectors: Advances and room temperature test

We are developing a prototype of cryogenic parametric converter transducer operating at 5 GHz, for the upgrade of the ROG Collaboration resonant G. W. antennas. This device is built on the experience of the Niobe detector (D. G. Blair et al.), with substantial modifications that should let us achieve better stability and sensitivity. The prototype uses as parametric converter a superconducting coaxial cavity with a 50 micron gap (Q 0 = 5 × 10 8 at 1.5K and 100μW RF power dissipation), and a contacless RF coupling for thermal insulation between the 2K stage and the ultra cryogenic (100mK) antenna. The coupler features a constant transmission loss of 0.2dB over a range of displacements of 5mm in x, y and z around the nominal operating position with a separation of 8mm between the two halves of the coupler. In this way the large, low frequency swings (0.5 and 17 Hz), of the 2 Tons antenna around its suspension point have no influence on the transducer performance. To test all the components of the transducer and the system performance, a room temperature prototype is installed on the TART (Test Antenna at Room Temperature) facility at the INFN labs. Using critical coupling for the RF cavity input coupler we manage to keep to a minimum the leakage of the drive signal to the first RF amplifier. In this way we avoid degradation of the RF amplifier noise figure (0.6 dB at room temperature) produced by the RF amplifier saturation Experimental results agree with the full analysis of the room temperature detector performances. © 2008 IOP Publishing Ltd