How to reduce the suspension thermal noise in LIGO without improving the Q's of the pendulum and violin modes

The suspension noise in interferometric gravitational wave detectors is caused by losses at the top and the bottom attachments of each suspension fiber. We use the Fluctuation-Dissipation theorem to argue that by careful positioning of the laser beam spot on the mirror face it is possible to reduce the contribution of the bottom attachment point to the suspension noise by several orders of magnitude. For example, for the initial and enhanced LIGO design parameters (i.e. mirror masses and sizes, and suspension fibers' lengths and diameters) we predict a reduction of $\sim 100$ in the "bottom" spectral density throughout the band $35-100\hbox{Hz}$ of serious thermal noise. We then propose a readout scheme which suppresses the suspension noise contribution of the top attachment point. The idea is to monitor an averaged horizontal displacement of the fiber of length $l$; this allows one to record the contribution of the top attachment point to the suspension noise, and later subtract it it from the interferometer readout. For enhanced LIGO this would allow a suppression factor about 100 in spectral density of suspension thermal noise.Comment: a few misprints corrected; submitted to Classical and Quantum Gravit

Sub-SQL Sensitivity via Optical Rigidity in Advanced LIGO Interferometer with Optical Losses

The ``optical springs'' regime of the signal-recycled configuration of laser interferometric gravitational-wave detectors is analyzed taking in account optical losses in the interferometer arm cavities. This regime allows to obtain sensitivity better than the Standard Quantum Limits both for a free test mass and for a conventional harmonic oscillator. The optical losses restrict the gain in sensitivity and achievable signal-to-noise ratio. Nevertheless, for parameters values planned for the Advanced LIGO gravitational-wave detector, this restriction is insignificant.Comment: 15 pages, 9 figure

The Personality Traits as Risk Factors for the Development of Cognitive Impairment and Affective Symptomatology in Patients with COVID-19: The Pilot Study

The current pilot study has been carried out in order to find the possible relationships between premorbid personality traits and cognitive impairments and affective symptomatology in patients recovered from COVID-19. Thirty subjects with so-called post-COVID-19 syndrome have been included into study. The diagnosis of COVID-19 has been previously confirmed by laboratory tests in each person. The control group included 30 healthy persons. For the assessment of depression and anxiety, the Hospital Anxiety and Depression Scale has been used. For the assessment of cognitive impairment, Verbal Fluency test, Montreal Cognitive Assessment (MoCA) test, and Wisconsin Card Sorting test (WCST) were used. The Munich Personality Scale and Toronto Alexithymia Scale were used for the assessment of premorbid personality. The multiple stepwise regression analysis has been used for the assessment of relationships between premorbid personality constructs and cognitive tests results and affective and anxiety symptomatology. Obtained results have shown that Frustration Tolerance test decreased the number of wrong answers in WCST and reduced the latency of the answers with positive reinforcement and also reduced the depression level and by that had the positive effects. On the other hand, Extraversion reduced the score of Montreal Cognitive Assessment (MoCA) test and increased the percentage of perseverative wrong answers in WCST-2 test and by that had negative effect on cognitive functions. Similarly, constructs of Adherence to Social Norms and Tendencies to Isolation both reduced the final MOCA score and by that predisposed to post-COVID-19 syndrome development. Esoteric tendencies construct reduced the latencies of answers with positive and negative reinforcement in WCST-3 and WCST-4 and by that had protective influence on cognitive functions. Alexithymia score correlated positively with Depression, while Neuroticism correlated positively with Anxiety

Dual-Resonator Speed Meter for a Free Test Mass

A description and analysis are given of a ``speed meter'' for monitoring a classical force that acts on a test mass. This speed meter is based on two microwave resonators (``dual resonators''), one of which couples evanescently to the position of the test mass. The sloshing of the resulting signal between the resonators, and a wise choice of where to place the resonators' output waveguide, produce a signal in the waveguide that (for sufficiently low frequencies) is proportional to the test-mass velocity (speed) rather than its position. This permits the speed meter to achieve force-measurement sensitivities better than the standard quantum limit (SQL), both when operating in a narrow-band mode and a wide-band mode. A scrutiny of experimental issues shows that it is feasible, with current technology, to construct a demonstration speed meter that beats the wide-band SQL by a factor 2. A concept is sketched for an adaptation of this speed meter to optical frequencies; this adaptation forms the basis for a possible LIGO-III interferometer that could beat the gravitational-wave standard quantum limit h_SQL, but perhaps only by a factor 1/xi = h_SQL/h ~ 3 (constrained by losses in the optics) and at the price of a very high circulating optical power --- larger by 1/xi^2 than that required to reach the SQL.Comment: RevTex: 13 pages with 4 embedded figures (two .eps format and two drawn in TeX); Submitted to Physical Review