MSV-2035 Astronomy Document - Inside Design - FINAL - FINAL

Astronomy & Astrophysics 35 optical depth, and the nature of dust particles in our Galaxy. The main goals for the CMBR experiments in the coming decade are: (1) Detection of the signatures of primordial gravitational waves, which, according to the prevalent paradigm of inflation, are expected to have originated in the early universe, leaving imprints as polarisation in the CMB. (2)Accurate measurements of the CMB polarisation. This 16 would also reveal ultra-high energy physics, if inflation operates at the energy scale of 10 GeV (about a trillion times more than that attained in the Large Hadron Collider!) corresponding to Grand Unified Theories and would be the first direct evidence of quantum gravity. Such measurements can also place important constraints on the primordial magnetic fields. (3) Detection of weak gravitational lensing (WL) signal in the CMB polarisation. This would provide a high signal-to-noise map of the integratedmatter distribution in the Universe thought to be dominated by darkmatter of unknown nature, whose presence is detected only through its gravitational effects. (4) Constraining the total mass of neutrinos, that will permit us to fundamentally establish the neutrinomass hierarchy fromastrophysical observations. Some of the international space experiments in different stages of planning include the Lite satellite for B-mode polarisation and Inflation from cosmic background Radiation Detection (LiteBIRD by JAXA+NASA), the Primordial Inflation Explorer (PIXIE: by NASA) and the Cosmic Origins Explorer (CoRE by ESA). Indian scientists have also proposed a spacemission, CMBBharat, to study the CMBR. There are also an enormous amount of CMB science that can be done using the ground based detectors. Experiments like the BICEP 3 (Background Imaging of Cosmic Extragalactic Polarization) aim to measure the CMB B-mode polarisation, that is likely to carry the signature of primordial gravitational waves. The primary challenge however is to separate the B-mode caused by the galactic dust from the cosmological signal. To reduce this contamination, the ground based detectors focus on those patches of the sky which are relatively clean from galactic dust.While the space based detectors, being able to probe both small and large angular scales simultaneously may have a better chance of detecting the B-mode, the ground based detectors are quite significantly inexpensive, and hence firmly hold their place. 3.6 GravitationalWaveObservatories Gravitational waves are emitted when there are sudden changes in the curvature of space-time and these often result from catastrophic events like mergers of compact objects like black holes, neutron stars, or, supernova explosions. Low intensity gravitational waves are also emitted frompulsars and, in principle, signal from these can be added over a long period to improve signal to noise ratio. Lastly, there is interest in detecting the stochastic gravitational background that results from cosmic inflation phase transitions in the early universe, and also from a combination of a very large number of sources of gravitational waves. After initial attempts to observe gravitational waves with bar detectors in 1960s, focus shifted to L-shaped interferometers. The first generation LIGO (Laser Interferometer Gravitational-wave Observatory) demonstrated the possibility to detect and measure extremely tiny distance fluctuations caused by the passage of gravitational waves. This was followed by the next generation GW LIGO detectors in the USA, VIRGO detector in Europe and the most recent KAGRA detector in Japan. Gradual developments in technology over four decades finally resulted in the first detection of gravitational waves by LIGO in 2015. Then in 2017, the electromagnetic (EM) follow-up of the binary neutron star merger discovered by the network of the LIGO-Virgo detectors, showcased a remarkable international MEGA SCIENCE VISION-2035