**Authors**: Priyamvada Natarajan, Ezequiel Treister

**Date**: 20 Aug 2008

**Abstract**: We make a case for the existence for ultra-massive black holes (UMBHs) in the Universe, but argue that there exists a likely upper limit to black hole masses of the order of $M \sim 10ˆ{10} \msun$. We show that there are three strong lines of argument that predicate the existence of UMBHs: (i) expected as a natural extension of the observed black hole mass bulge luminosity relation, when extrapolated to the bulge luminosities of bright central galaxies in clusters; (ii) new predictions for the mass function of seed black holes at high redshifts predict that growth via accretion or merger-induced accretion inevitably leads to the existence of rare UMBHs at late times; (iii) the local mass function of black holes computed from the observed X-ray luminosity functions of active galactic nuclei predict the existence of a high mass tail in the black hole mass function at $z = 0$. Consistency between the optical and X-ray census of the local black hole mass function requires an upper limit to black hole masses. This consistent picture also predicts that the slope of the $M_{\rm bh}$-$\sigma$ relation will evolve with redshift at the high mass end. Models of self-regulation that explain the co-evolution of the stellar component and nuclear black holes naturally provide such an upper limit. The combination of multi-wavelength constraints predicts the existence of UMBHs and simultaneously provides an upper limit to their masses. The typical hosts for these local UMBHs are likely the bright, central cluster galaxies in the nearby Universe.

0808.2813
(/preprints)

2008-09-15, 08:55
**[edit]**

**Authors**: M. Rakhmanov, J. D. Romano, J. T. Whelan

**Date**: 28 Aug 2008

**Abstract**: Searches for gravitational waves with km-scale laser interferometers often involve the long-wavelength approximation to describe the detector response. The prevailing assumption is that the corrections to the detector response due to its finite size are small and the errors due to the long-wavelength approximation are negligible. Recently, however, Baskaran and Grishchuk (2004 Class. Quantum Grav. 21 4041) found that in a simple Michelson interferometer such errors can be as large as 10 percent. For more accurate analysis, these authors proposed to use a linear-frequency correction to the long wavelength approximation. In this paper we revisit these calculations. We show that the linear-frequency correction is inadequate for certain locations in the sky and therefore accurate analysis requires taking into account the exact formula, commonly derived from the photon round-trip propagation time. Also, we extend the calculations to include the effect of Fabry-Perot resonators in the interferometer arms. Here we show that a simple approximation which combines the long-wavelength Michelson response with the single-pole approximation to the Fabry-Perot transfer function produces rather accurate results. In particular, the difference between the exact and the approximate formulae is at most 2-3 percent for those locations in the sky where the detector response is greater than half of its maximum value. We analyse the impact of such errors on detection sensitivity and parameter estimation in searches for periodic gravitational waves emitted by a known pulsar, and in searches for an isotropic stochastic gravitational-wave background. At frequencies up to 1 kHz, the effect of such errors is at most 1-2 percent. For higher frequencies, or if more accuracy is required, one should use the exact formula for the response.

0808.3805
(/preprints)

2008-09-04, 12:48
**[edit]**

**Authors**: Luca Baiotti, Sebastiano Bernuzzi, Giovanni Corvino, Roberto De Pietri, Alessandro Nagar

**Date**: 28 Aug 2008

**Abstract**: The main aim of this study is the comparison of gravitational waveforms obtained from numerical simulations which employ different numerical evolution approaches and different wave-extraction techniques. For this purpose, we evolve an oscillating, non-rotating polytropic neutron-star model with two different approaches: a full nonlinear relativistic simulation (in three dimensions) and a linear simulation based on perturbation theory. The extraction of the gravitational-wave signal is performed with three methods: The gauge-invariant curvature-perturbation theory based on the Newman-Penrose scalar $\psi_4$; The gauge-invariant Regge-Wheeler-Zerilli-Moncrief metric-perturbation theory of a Schwarzschild space-time; Some generalization of the quadrupole emission formula.

0808.4002
(/preprints)

2008-09-04, 12:47
**[edit]**

**Authors**: Umberto Cannella, Riccardo Sturani (University of Geneva)

**Date**: 29 Aug 2008

**Abstract**: We apply the Effective-Field-Theory approach to General Relativity introduced by Goldberger and Rothstein to the case of scalar-tensor gravity theories for point-like and string-like sources. Within this framework we compute the energy momentum tensor renormalisation to first Post-Newtonian order which allows to write down the corrections to the standard (Newtonian) gravitational potential and to the extra-scalar potential. In the case of a point particle source with cubic self interactions we reproduce the known result of a potential increasing with distance at "Post-Newtonian" level. In the case of one dimensional-extended source we are able to confirm and extend the result by Buonanno and Damour about the renormalisation of the string tension.

0808.4034
(/preprints)

2008-09-04, 12:47
**[edit]**

**Authors**: Matthew D. Duez, Francois Foucart, Lawrence E. Kidder, Harald P. Pfeiffer, Mark A. Scheel, Saul A. Teukolsky

**Date**: 29 Aug 2008

**Abstract**: We present a code for solving the coupled Einstein-hydrodynamics equations to evolve relativistic, self-gravitating fluids. The Einstein field equations are solved in generalized harmonic coordinates on one grid using pseudospectral methods, while the fluids are evolved on another grid using shock-capturing finite difference or finite volume techniques. We show that the code accurately evolves equilibrium stars and accretion flows. Then we simulate an equal-mass nonspinning black hole-neutron star binary, evolving through the final four orbits of inspiral, through the merger, to the final stationary black hole. The gravitational waveform can be reliably extracted from the simulation.

0809.0002
(/preprints)

2008-09-04, 12:46
**[edit]**

**Authors**: P.Astone, M.Bassan, P.Bonifazi, K.M.Borkowski, R.J.Budzyński, A.Chincarini, E.Coccia, S.D'Antonio, M.Di Paolo Emilio, V.Fafone, S.Frasca, S.Foffa, G.Giordano, P.Jaranowski, W.Kondracki, A.Królak, M.Maggiore, A.Marini, Y.Minenkov, I.Modena, G.Modestino, A.Moleti, G.V.Pallottino, C.Palomba, R.Parodi, M.Pietka, G.Pizzella, H.J.Pletsch, L.Quintieri, F.Ricci, A.Rocchi, F.Ronga, R.Sturani, R.Terenzi, R.Vaccarone, M.Visco

**Date**: 1 Sep 2008

**Abstract**: A search for periodic gravitational-wave signals from isolated neutron stars in the NAUTILUS detector data is presented. We have analyzed half a year of data over the frequency band $<922.2; 923.2>$ Hz, the spindown range $<-1.463\times10ˆ{-8}; 0>$ Hz/s and over the entire sky. We have divided the data into 2 day stretches and we have analyzed each stretch coherently using matched filtering. We have imposed a low threshold for the optimal detection statistic to obtain a set of candidates that are further examined for coincidences among various data stretches. For some candidates we have also investigated the change of the signal-to-noise ratio when we increase the observation time from two to four days. Our analysis has not revealed any gravitational-wave signals. Therefore we have imposed upper limits on the dimensionless gravitational-wave amplitude over the parameter space that we have searched. Depending on frequency, our upper limit ranges from $3.4 \times 10ˆ{-23}$ to $1.3 \times 10ˆ{-22}$. We have attempted a statistical verification of the hypotheses leading to our conclusions. We estimate that our upper limit is accurate to within 18%.

0809.0273
(/preprints)

2008-09-04, 12:46
**[edit]**

**Authors**: Xavier Amador

**Date**: 16 Apr 2006

**Abstract**: This is an updated introductory review of 2 possible gravitational anomalies that has attracted part of the Scientific community: the Allais effect that occur during solar eclipses, and the Pioneer 10 spacecraft anomaly, experimented also by Pioneer 11 and Ulysses spacecrafts. It seems that, to date, no satisfactory conventional explanation exist to these phenomena, and this suggests that possible new physics will be needed to account for them. The main purpose of this review is to announce 3 other new measurements that will be carried on during the 2005 solar eclipses in Panama and Colombia (Apr. 8) and in Portugal (Oct.15).

0604069
(/preprints/gr-qc)

2008-09-04, 12:45
**[edit]**

© M. Vallisneri 2012 — last modified on 2010/01/29

*Tantum in modicis, quantum in maximis*