Ears wide open...

... to catch loud and clear the Einstein's symphony in full spectrum



Frequency Classification of Gravitational Waves




The Gravitation-Wave (GW) Spectrum Classification


Characteristic strain hc vs. frequency for various GW detectors and sources. [QA: Quasar Astrometry; QAG: Quasar Astrometry Goal; LVC: LIGOVirgo Constraints; CSDT: Cassini Spacecraft Doppler Tracking; SMBH-GWB: Supermassive Black Hole-GW Background.]

We have presented a complete frequency classification of GWs according to their detection methods. ... several bands are amenable to direct detection... Although the prospect of a launch of space GW is only expected in about 20 years, the detection in the low frequency band may have the largest signal to noise ratios. This will enable the detailed study of black hole co-evolution with galaxies and with the dark energy issue. Foreground separation and correlation detection method need to be investigated to achieve the sensitivities 10-16 -10-17 or beyond in Ωgw to study the primordial GW background for exploring very early universe and possibly quantum gravity regimes. When we look back at the theoretical and experimental development of GW physics and astronomy over the last 100 years, there are many challenges, some pitfalls, and during last 50 years close interactions among theorists and experimentalists. The subject and community have become clearly multidisciplinary. One example is the interaction of the GW community and the Quantum Optics community in the last 40 years to identify standard quantum uncertainties in measurement, to realize that this is not an obstacle of measurement in principle, and to find ways to overcome it. Another example is the interaction of the physics community and the astronomy community to understand and to identify detectable and potentially detectable GW sources. With current technology development and astrophysical understanding, we are in a position using GWs to study more thoroughly galaxies, supermassive black holes and clusters together with cosmology, and to explore deeper into the origin of gravitation and our universe. Next 100 years will be the golden age of GW astronomy and GW physics. The current and coming generations are holding such promises.
(Submitted on 1 Nov 2015)
In the same vein, the interested reader is invited to learn about the multi-band gravitational wave astronomy concepts and its obstacles here.


... and get the pitch of the dark note
With obvious short-comings in our understanding of fundamental principles of nature dangling, e.g. the lack of a dark matter candidate or the observed matter/antimatter asymmetry, and in absence of evidence for new physics at collider experiments, so-called dark sectors become increasingly attractive as add-on to the Standard Model. If uncharged under the Standard Model gauge group, dark sectors could even have a rich particle spectrum without leaving an observable imprint in measurements at particle colliders. Hence, this could leave us in the strenuous situation where we might have to rely exclusively on very feeble possibly only gravitational interactions to infer their existence. 
For dark sectors to address the matter/anti-matter asymmetry via electroweak baryogenesis, usually a strong first-order phase transition is required. It is well known that a first-order phase transition is accompanied by three mechanisms that can give rise to gravitational waves in the early universe [6–13]: collisions of expanding vacuum bubbles, sounds waves, and magnetohydrodynamic turbulence of bubbles in the hot plasma. However, for previously studied models, e.g. (N)MSSM [14], strongly coupled dark sectors [15], or the electroweak phase transition with the Higgs potential modified by a sextic term [16], the resulting GW frequencies after red-shifting are expected to have frequencies of some two or more orders of magnitude below the reach of aLIGO. On the other hand, if electroweak symmetry breaking is triggered in the dark sector at temperatures significantly above the electroweak scale, e.g. by radiatively generating a vev using the Coleman-Weinberg mechanism, GW with frequencies are within the aLIGO reach, i.e. 1-100 Hz. However, we will explain that the overall amplitude of the signal is too small for aLIGO at present sensitivity, but it can be probed by the next generation of interferometers [These future experiments also include the advanced LIGO/VIRGO detectors operating in years 2020+ at the projected final sensitivity]. 
At the same time, already now, aLIGO can probe beyond the standard model physics. We will investigate the consequences of topological defects, such as a domain wall passing through the interferometer. We will model this by introducing a non-vanishing effective photon mass localised on the domain wall, while vanishing elsewhere [this is not a gravitational effect, but effectively it looks like local ripples affecting propagation of photons]. The signatures of passing domain walls can be well separated from black-hole mergers and motivates and extension of ongoing search strategies.

(Submitted on 11 Feb 2016 (v1), last revised 16 Feb 2016 (this version, v2))

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