We present our current best estimate of the plausible observing scenarios for the Advanced LIGO, Advanced Virgo and KAGRA gravitational-wave detectors over the next several years, with the intention of providing information to facilitate planning for multi-messenger astronomy with gravitational waves. We estimate the sensitivity of the network to transient gravitational-wave signals for the third (O3), fourth (O4) and fifth observing (O5) runs, including the planned upgrades of the Advanced LIGO and Advanced Virgo detectors. We study the capability of the network to determine the sky location of the source for gravitational-wave signals from the inspiral of binary systems of compact objects, that is binary neutron star, neutron star–black hole, and binary black hole systems. The ability to localize the sources is given as a sky-area probability, luminosity distance, and comoving volume. The median sky localization area (90% credible region) is expected to be a few hundreds of square degrees for all types of binary systems during O3 with the Advanced LIGO and Virgo (HLV) network. The median sky localization area will improve to a few tens of square degrees during O4 with the Advanced LIGO, Virgo, and KAGRA (HLVK) network. During O3, the median localization volume (90% credible region) is expected to be on the order of $$10^{5}, 10^{6}, 10^{7}\mathrm {\ Mpc}^3$$ 10 5 , 10 6 , 10 7 Mpc 3 for binary neutron star, neutron star–black hole, and binary black hole systems, respectively. The localization volume in O4 is expected to be about a factor two smaller than in O3. We predict a detection count of $$1^{+12}_{-1}$$ 1 - 1 + 12 ($$10^{+52}_{-10}$$ 10 - 10 + 52 ) for binary neutron star mergers, of $$0^{+19}_{-0}$$ 0 - 0 + 19 ($$1^{+91}_{-1}$$ 1 - 1 + 91 ) for neutron star–black hole mergers, and $$17^{+22}_{-11}$$ 17 - 11 + 22 ($$79^{+89}_{-44}$$ 79 - 44 + 89 ) for binary black hole mergers in a one-calendar-year observing run of the HLV network during O3 (HLVK network during O4). We evaluate sensitivity and localization expectations for unmodeled signal searches, including the search for intermediate mass black hole binary mergers.

We study the cosmological evolutions of the equation of state for dark energy w DE in the exponential and logarithmic as well as their combination f (T ) theories. We show that the crossing of the phantom divide line of w DE = −1 can be realized in the combined f (T ) theory even though it cannot be in the exponential or logarithmic f (T ) theory. In particular, the crossing is from w DE > −1 to w DE < −1, in the opposite manner from f (R) gravity models. We also demonstrate that this feature is favored by the recent observational data.Cosmic observations from Supernovae Ia (SNe Ia) [1], cosmic microwave background (CMB) radiation [2][3][4], large scale structure (LSS) [5], baryon acoustic oscillations (BAO) [6], and weak lensing [7] have implied that the expansion of the universe is currently accelerating. This is one of the most important issues in modern physics. Approaches to account for the late time cosmic acceleration fall into two representative categories: One is to introduce "dark energy" in the right-hand side of the Einstein equation in the framework of general relativity (for a review on dark energy, see [8]). The other is to modify the left-hand side of the Einstein equation, called as a modified gravitational theory, e.g., f (R) gravity [9][10][11].As another possible way to examine gravity beyond general relativity, one could use the Weitzenböck connection, which has no curvature but torsion, rather than the curvature defined by the Levi-Civita connection. Such an approach is referred to "teleparallelism" (see, e.g., [12][13][14][15]), which was also taken by Einstein [16]. To explain the late time acceleration of the universe, the teleparallel Lagrangian density described by the torsion scalar T has been extended to a function of T [17, 18] 1 . This idea is equivalent to the concept of f (R) gravity, in which the Ricci scalar R in the Einstein-Hilbert action is promoted to a function of R.Recently, f (T ) gravity has been extensively studied in the literature [20][21][22][23][24][25].In this paper, we explicitly examine the cosmological evolution in the exponential f (T ) theory [18,23] in more detail with the analysis method in Ref. [26]. In particular, we study the equation of state (w DE ) and energy density (ρ DE ) for dark energy. The recent cosmological observational data [27] seems to imply a dynamical dark energy of equation of state with the crossing of the phantom divide line w DE = −1 from the non-phantom phase to phantom phase as the redshift z decreases in the near past. However, we illustrate that the universe with the exponential f (T ) theory always stays in the non-phantom (quintessence) phase or the phantom one, and hence the crossing of the phantom divide cannot be realized [23]. It is interesting to mention that such an exponential type as f (R) gravity models has been investigated in Refs. [28][29][30]. We also present a logarithmic f (T ) theory and show that it has a similar feature as the exponential one. Our motivation in this paper is to build up a realistic f (T ) theor...

We report results of a search for an isotropic gravitational-wave background (GWB) using data from Advanced LIGO's and Advanced Virgo's third observing run (O3) combined with upper limits from the earlier O1 and O2 runs. Unlike in previous observing runs in the advanced detector era, we include Virgo in the search for the GWB. The results of the search are consistent with uncorrelated noise, and therefore we place upper limits on the strength of the GWB. We find that the dimensionless energy density ⌦GW  5.8 ⇥ 10 9 at the 95% credible level for a flat (frequencyindependent) GWB, using a prior which is uniform in the log of the strength of the GWB, with 99% of the sensitivity coming from the band 20-76.6 Hz; ⌦GW(f )  3.4 ⇥ 10 9 at 25 Hz for a power-law GWB with a spectral index of 2/3 (consistent with expectations for compact binary coalescences), in the band 20-90.6 Hz; and ⌦GW(f )  3.9 ⇥ 10 10 at 25 Hz for a spectral index of 3, in the band 20-291.6 Hz. These upper limits improve over our previous results by a factor of 6.0 for a flat GWB, 8.8 for a spectral index of 2/3, and 13.1 for a spectral index of 3. We also search for a GWB arising from scalar and vector modes, which are predicted by alternative theories of gravity; we do not find evidence of these, and place upper limits on the strength of GWBs with these polarizations. We demonstrate that there is no evidence of correlated noise of magnetic origin by performing a Bayesian analysis that allows for the presence of both a GWB and an e↵ective magnetic background arising from geophysical Schumann resonances. We compare our upper limits to a fiducial model for the GWB from the merger of compact binaries, updating the model to use the most recent datadriven population inference from the systems detected during O3a. Finally, we combine our results with observations of individual mergers and show that, at design sensitivity, this joint approach may yield stronger constraints on the merger rate of binary black holes at z & 2 than can be achieved with individually resolved mergers alone.

We report results from searches for anisotropic stochastic gravitational-wave backgrounds using data from the first three observing runs of the Advanced LIGO and Advanced Virgo detectors. For the first time, we include Virgo data in our analysis and run our search with a new efficient pipeline called PyStoch on data folded over one sidereal day. We use gravitational-wave radiometry (broadband and narrow band) to produce sky maps of stochastic gravitational-wave backgrounds and to search for gravitational waves from point sources. A spherical harmonic decomposition method is employed to look for gravitationalwave emission from spatially-extended sources. Neither technique found evidence of gravitational-wave signals. Hence we derive 95% confidence-level upper limit sky maps on the gravitational-wave energy flux from broadband point sources, ranging from F α;Θ < ð0.013-7.6Þ × 10 −8 erg cm −2 s −1 Hz −1 , and on the (normalized) gravitational-wave energy density spectrum from extended sources, ranging from Ω α;Θ < ð0.57-9.3Þ × 10 −9 sr −1 , depending on direction (Θ) and spectral index (α). These limits improve upon previous limits by factors of 2.9-3.5. We also set 95% confidence level upper limits on the frequencydependent strain amplitudes of quasimonochromatic gravitational waves coming from three interesting targets, Scorpius X-1, SN 1987A and the Galactic Center, with best upper limits range from h 0 < ð1.7-2.1Þ × 10 −25 , a factor of ≥ 2.0 improvement compared to previous stochastic radiometer searches.

Where a licence is displayed above, please note the terms and conditions of the licence govern your use of this document.When citing, please reference the published version. Take down policyWhile the University of Birmingham exercises care and attention in making items available there are rare occasions when an item has been uploaded in error or has been deemed to be commercially or otherwise sensitive.