Gravitációs hullámkeltési folyamatok vizsgálata az általános relativitáselméletben = Study of gravitational wave production in general relativity

A kutatási terveinknek megfelelően az alábbi nyolc területen értünk el eredményeket: I. A nemlineáris gömbszimmetrikus dinamikai rendszerek időfejlődését hűen leíró numerikus eljárásunkat továbbfejlesztettük úgy, hogy mind az szimmetriafeltételektől mentes rendszerek leírására, mind pedig az „adaptív rácsfinomításos” technikai elemek alkalmazására képes legyen. A fejlesztésekkel párhuzamosan különféle általános relativisztikus dinamikai rendszer időfejlődését határoztuk meg. II. Feltártuk a gravitációs összeomlási folyamatok során kialakuló dinamikai feketelyuk-téridők topológiai tulajdonságait. III. A gravitáció geometrizált elméleteiben megadtuk a szinguláris téridők globális kiterjeszthetőségének szükséges feltételeit. IV. Fizikailag reális állapotegyenletű forgó neutroncsillag-modellek megkonstruálása. V. Gömbszimmetrikus csillagmodellek vizsgálata a nem zérus kozmológiai állandóval jellemzett univerzummodellek esetén. VI. Neutroncsillag-modellek stabilitásvizsgálata, valamint a gömbhéjakba tömörülő anyageloszlások általános dinamikájának leírása. VII. A deformált stacionárius feketelyuk-téridők általános leírása. VIII. Részvétel a Virgo tudományos együttműködés munkájában és a CBwaves nevű programcsomag kidolgozása és a LIGO-Virgo együttműködés által alkalmazott keresőalgoritmusokba történő integrálása. A pályázatban megjelölt feladatokhoz kapcsolódóan 14 elméleti témájú, és 23 kollaborációs, magas impaktfaktorú folyóiratcikkünk jelent meg. | In accordance with our research proposal the new results belong to either of the following eight categories: I. Our numerical method capable to follow the time evolution of generic spherically symmetric dynamical systems was further developed such that both the symmetry assumptions were relaxed and the techniques of adaptive mesh refinements had been implemented. In parallel the developed code had been applied to study the evolution of various general relativistic dynamical systems. II. The topological properties of generic co-dimension two surfaces in black hole spacetime was determined. III. In metric theories of gravity the necessary conditions guaranteeing the global extendibility of singular spacetimes were given. IV. Neutron star models with physically reasonable equation of state were constructed. V. Spherically symmetric stars in models of the universe with non-zero cosmological constant were investigated. VI.The radial stability of neutron star models and the dynamics of matter distribution concentrated on spherical shells were determined. VII. A generic framework of deformed stationary black hole spacetimes was established. VIII. We joined to the Virgo scientific collaboration.The CBwaves software was developed and it was integrated it into various data analyzing algorithms of the LIGO-Virgo collaboration. In relation with the listed achievements 14 theoretical, and 23 experimental papers have been published in high impact scientific journals

First all-sky search for continuous gravitational waves from unknown sources in binary systems

We present the first results of an all-sky search for continuous gravitational waves from unknown spinning neutron stars in binary systems using LIGO and Virgo data. Using a specially developed analysis program, the TwoSpect algorithm, the search was carried out on data from the sixth LIGO science run and the second and third Virgo science runs. The search covers a range of frequencies from 20 Hz to 520 Hz, a range of orbital periods from 2 to ∼2,254h and a frequency- and period-dependent range of frequency modulation depths from 0.277 to 100 mHz. This corresponds to a range of projected semimajor axes of the orbit from ∼0.6×10-3ls to ∼6,500ls assuming the orbit of the binary is circular. While no plausible candidate gravitational wave events survive the pipeline, upper limits are set on the analyzed data. The most sensitive 95% confidence upper limit obtained on gravitational wave strain is 2.3×10-24 at 217 Hz, assuming the source waves are circularly polarized. Although this search has been optimized for circular binary orbits, the upper limits obtained remain valid for orbital eccentricities as large as 0.9. In addition, upper limits are placed on continuous gravitational wave emission from the low-mass x-ray binary Scorpius X-1 between 20 Hz and 57.25 Hz

Improved upper limits on the stochastic gravitational-wave background from 2009-2010 LIGO and Virgo data

Gravitational waves from a variety of sources are predicted to superpose to create a stochastic background. This background is expected to contain unique information from throughout the history of the Universe that is unavailable through standard electromagnetic observations, making its study of fundamental importance to understanding the evolution of the Universe. We carry out a search for the stochastic background with the latest data from the LIGO and Virgo detectors. Consistent with predictions from most stochastic gravitational-wave background models, the data display no evidence of a stochastic gravitational-wave signal. Assuming a gravitational-wave spectrum of ΩGW(f)=Ωα(f/fref)α, we place 95% confidence level upper limits on the energy density of the background in each of four frequency bands spanning 41.5-1726 Hz. In the frequency band of 41.5-169.25 Hz for a spectral index of α=0, we constrain the energy density of the stochastic background to be ΩGW(f)\u3c5.6×10-6. For the 600-1000 Hz band, ΩGW(f)\u3c0.14(f/900Hz)3, a factor of 2.5 lower than the best previously reported upper limits. We find ΩGW(f)\u3c1.8×10-4 using a spectral index of zero for 170-600 Hz and ΩGW(f)\u3c1.0(f/1300Hz)3 for 1000-1726 Hz, bands in which no previous direct limits have been placed. The limits in these four bands are the lowest direct measurements to date on the stochastic background. We discuss the implications of these results in light of the recent claim by the BICEP2 experiment of the possible evidence for inflationary gravitational waves

Constraints on Cosmic Strings from the LIGO-Virgo Gravitational-Wave Detectors

Cosmic strings can give rise to a large variety of interesting astrophysical phenomena. Amongthem, powerful bursts of gravitational waves (GWs) produced by cusps are a promising observationalsignature. In this Letter we present a search for GWs from cosmic string cusps in data collectedby the LIGO and Virgo gravitational wave detectors between 2005 and 2010, with over 625 days oflive time. We find no evidence of GW signals from cosmic strings. From this result, we derive newconstraints on cosmic string parameters, which complement and improve existing limits from previ-ous searches for a stochastic background of GWs from cosmic microwave background measurementsand pulsar timing data. In particular, if the size of loops is given by the gravitational backreactionscale, we place upper limits on the string tension Gμ below 10−8 in some regions of the cosmic stringparameter space

First searches for optical counterparts to gravitational-wave candidate events

Heat conduction experiments are performed in order to identify effects beyond Fourier. Two experimental setups are discussed. First, a simple experiment by a heterogeneous material is investigated from the point of view of generalized heat conduction, then the classical laser flash method is analysed

Application of a Hough search for continuous gravitational waves on data from the fifth LIGO science run

We report on an all–sky search for periodic gravitational waves inthe frequency range 50 − 1000 Hz with the first derivative of frequency in therange −8.9 × 10−10 Hz/s to zero in two years of data collected during LIGO’sfifth science run. Our results employ a Hough transform technique, introducinga χ2 test and analysis of coincidences between the signal levels in years 1 and 2 of observations that offers a significant improvement in the product of strainsensitivity with compute cycles per data sample compared to previously publishedsearches. Since our search yields no surviving candidates, we present resultstaking the form of frequency dependent, 95% confidence upper limits on thestrain amplitude h0. The most stringent upper limit from year 1 is 1.0 × 10−24 in the 158.00 − 158.25 Hz band. In year 2, the most stringent upper limit is 8.9 × 10−25 in the 146.50 − 146.75 Hz band. This improved detection pipeline,which is computationally efficient by at least two orders of magnitude better thanour flagship Einstein@Home search, will be important for “quick-look” searchesin the Advanced LIGO and Virgo detector era

Gravitational waves from known pulsars: results from the initial detector era

We present the results of searches for gravitational waves from a large selection of pulsars using datafrom the most recent science runs (S6, VSR2 and VSR4) of the initial generation of interferometricgravitational wave detectors LIGO (Laser Interferometric Gravitational-wave Observatory) and Virgo.We do not see evidence for gravitational wave emission from any of the targeted sources but produce upper limits on the emission amplitude. We highlight the results from seven young pulsars with largespin-down luminosities. We reach within a factor of five of the canonical spin-down limit for all sevenof these, whilst for the Crab and Vela pulsars we further surpass their spin-down limits. We presentnew or updated limits for 172 other pulsars (including both young and millisecond pulsars). Now thatthe detectors are undergoing major upgrades, and, for completeness, we bring together all of the mostup-to-date results from all pulsars searched for during the operations of the first-generation LIGO,Virgo and GEO600 detectors. This gives a total of 195 pulsars including the most recent resultsdescribed in this paper

Reconstruction of the gravitational wave signal h(t) during the Virgo science runs and independent validation with a photon calibrator

The Virgo detector is a kilometer-scale interferometer for gravitational wave detection located near Pisa (Italy). About 13 months of data were accumulated during four science runs (VSR1, VSR2, VSR3 and VSR4) between May 2007 and September 2011, with increasing sensitivity. In this paper, the method used to reconstruct, in the range 10 Hz–10 kHz, the gravitational wave strain time series h(t) from the detector signals is described. The standard consistency checks of the reconstruction are discussed and used to estimate the systematic uncertainties of the h(t) signal as a function of frequency. Finally, an independent setup, the photon calibrator, is described and used to validate the reconstructed h(t) signal and the associated uncertainties. The systematic uncertainties of the h(t) time series are estimated to be 8% in amplitude. The uncertainty of the phase of h(t) is 50 mrad at 10 Hz with a frequency dependence following a delay of 8 μs at high frequency. A bias lower than 4 μs and depending on the sky direction of the GW is also present