Soon after matter and antimatter appeared in the cosmos, the universe underwent a phase change where more antimatter converted into heavy anti-neutrinos than matter converted into heavy matter neutrinos. The total charge of the universe remained zero, and the matter-antimatter balance is preserved, but what remained was mostly regular matter and heavy anti-neutrinos.
Recently a team proposed a way to prove this neutrino phase change. If such a phase change occurred, the shift in mass would have created gravitational waves throughout the observable universe. In their recent work, they argue that these gravitational waves should be detectable by future gravity telescopes. If they are right, it could finally solve one of the biggest mysteries in cosmology.
Thermal leptogenesis through the type I seesaw mechanism gives an elegant and minimal explanation for two outstanding puzzles in the standard model. Unfortunately, the scale of physics is naturally well beyond what can be directly test on Earth. Given the fundamental
nature of these puzzles, indirect tests of thermal leptogenesis are of great value and we propose cosmic strings as a powerful probe of the paradigm. Researchers argue that based on the simple observation that the right handed neutrino mass necessary to explain the observed neutrino masses is below the Planck or a possible grand unification scale. This suggests that some symmetry survives below to these scales to protect the right handed neutrino mass. Since successful leptogenesis requires the breaking of this symmetry to be below the scale of inflation, its breaking can be observed through its predicted cosmological defects. Gravitational Wave detectors are a robust probe of thermal leptogenesis.
Gravitational Wave Detectors
(1995) TAMA 300
(1995) GEO 600
(2007) Virgo interferometer
(2010) GEO High Frequency
(2015) Advanced LIGO
(2016) Advanced Virgo
(2019) KAGRA (LCGT)
(2023) IndIGO (LIGO-India)
(2030s) Einstein Telescope
(2030s) Cosmic Explorer
(2030s?) Taiji (gravitational wave observatory)
(2027) Deci-hertz Interferometer Gravitational wave Observatory (DECIGO)
(2034) Laser Interferometer Space Antenna (Lisa Pathfinder, a development mission, was launched December 2015)
Future Gravitational Wave Detectors – Einstein Telescope
Einstein Telescope (ET) or Einstein Observatory, is a proposed third-generation ground-based gravitational wave detector, currently under study by some institutions in the European Union. It will be able to test Einstein’s general theory of relativity in strong field conditions and realize precision gravitational wave astronomy. Although still in the early design study phase, the basic parameters are established. Like KAGRA, it will be located underground to reduce seismic noise and “gravity gradient noise” caused by nearby moving objects. The arms of the Einstein Telescope will be 10 km long (compared to 4 km for LIGO, and 3 km for Virgo and KAGRA), and like LISA, there will be three arms in an equilateral triangle, with two detectors in each corner.
In 2021 or 2022, it will be announced where the Einstein Telescope will eventually be built.
Each of the three detectors would be composed of two interferometers, one optimized for operation below 30 Hz and one optimized for operation at higher frequencies. The low-frequency interferometers (1 to 250 Hz) will use optics cooled to 10 K with a beam power of about 18 kW in each arm cavity. The high-frequency ones (10 Hz to 10 kHz) will use room-temperature optics and a much higher recirculating beam power of 3 MW.
A prototype, or testing facility, called the ET Pathfinder will be built at Maastricht University in the Netherlands.
The evolution of the current gravitational wave detectors Advanced Virgo and Advanced LIGO, as second-generation detectors, is well defined. Currently they have been upgraded to their so-called enhanced level and they are expected to reach their design sensitivity in the next few years.
The Laser Interferometer Space Antenna (LISA) is a mission led by the European Space Agency to detect and accurately measure gravitational waves—tiny ripples in the fabric of space-time—from astronomical sources. LISA would be the first dedicated space-based gravitational wave detector. It aims to measure gravitational waves directly by using laser interferometry. The LISA concept has a constellation of three spacecraft arranged in an equilateral triangle with sides 2.5 million km long, flying along an Earth-like heliocentric orbit.
The Deci-Hertz Interferometer Gravitational wave Observatory (or DECIGO) is a proposed Japanese, space-based, gravitational wave observatory. The laser interferometric gravitational wave detector is so named because it is to be most sensitive in the frequency band between 0.1 and 10 Hz, filling in the gap between the sensitive bands of LIGO and LISA. If funding can be found, its designers hope to launch it in 2027.
The design is similar to LISA, with three zero-drag satellites in a triangular arrangement, but using a smaller separation of only 1000 km. The precursor mission B-DECIGO with 100 km long arms is planned to be launched in the late 2020s, target is an Earth orbit with an average altitude of 2000 km.
Big Bang Observer
The Big Bang Observer (BBO) is a proposed successor to the Laser Interferometer Space Antenna (LISA) by the European Space Agency. The primary scientific goal is the observation of gravitational waves from the time shortly after the Big Bang, but it would also be able to detect younger sources of gravitational radiation, like binary inspirals. BBO would likely be sensitive to all LIGO and LISA sources, and others. Its extreme sensitivity would come from the higher-power lasers and correlation of signals from several different interferometers that would be placed around the Sun.
The first phase resembles LISA, consisting of three spacecraft flown in a triangular pattern. The second phase adds three more triangles (twelve spacecraft total), spaced 120° apart in solar orbit, with one position having two overlapping triangles in a hexagram formation.
The individual satellites would differ from those in LISA by having far more powerful lasers. In addition each triangle will be much smaller than the triangles in LISA’s pattern, about 50,000 km instead of 1 to 5 million km.
Cosmic Explorer is a proposed third generation ground-based gravitational wave observatory. Cosmic explorer uses the same L-shaped design as the LIGO detectors, except with ten times longer arms of 40 km each. This will significantly increase the sensitivity of the observatory allowing observation of the first black hole mergers in the Universe. In 2019 Cosmic Explorer team published a study about research needed over 2020s decade to build the observator
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