Astrophysics

Cosmology has seen great progress thanks to precision measurements and is bound to greatly benefit from upcoming Large Scale Structure and Cosmic Microwave Background data. I will point out a number of interesting directions. In particular, I discuss how the microphysics of inflation may be tested in galaxy surveys through “fossil” signatures originating from squeezed primordial correlations. I further elaborate on the constraining power of CMB spectral distortions on small-scale cosmological fluctuations and on particle decays in the very early Universe in relation to reheating. I also describe some of the possible constraints on inflation and reheating from future B-mode observations.

I will describe the Dark Energy Spectroscopic Instrument (DESI), an instrument currently being built to carry out a large galaxy redshift survey.  DESI is the next step beyond the SDSS and BOSS surveys, mapping over 30 million galaxies.  I will focus in particular on the amazing engineering challenges of the DESI instrument itself, which includes a 5,000-robot army and 250 kilometers of fiber optics.  I will conclude by briefly describing the work I am personally involved in: a large imaging survey that will measure the galaxies from which DESI will select targets for follow-up spectroscopic observation.

Modified gravitation known as Scalar-Tensor- Vector-Gravity (STVG) and MOG and its consequences for dark matter and dark energy in astrophysics and cosmology and black holes is reviewed. A variable speed of light (VSL) cosmology is compared to inflation. MOG predictions for gravitational waves are compared to the LIGO/Virgo collaboration data. MOG – black hole predictions for the sizes of the Sagittarius A* shadow are compared to the sizes predicted by the Schwarzschild and Kerr solutions. A possible void cosmology is compared to the standard cosmology based on dark energy and the cosmological constant.

Current constraints on spatial curvature demonstrate it to be dynamically negligible at late times. However, neglecting it as a cosmological parameter would be premature, as it offers a valuable test of eternal inflation models and probes novel large-scale structure phenomena. I will discuss a recent project in which a broad and conservative approach was employed to systematically forecast spatial curvature constraints from a suite of upcoming cosmology surveys, while also examining important degeneracies with cosmological parameters and potential sources of systematic error.

Pulsars are some of physics and astrophysics’ most exotic objects, and they have already earned two Nobel Prizes. We currently know of about 2500 of them in our Galaxy, but a small subset, the millisecond pulsars (MSPs), are truly remarkable. These systems are notoriously hard to detect, yet their numbers have more than doubled in the past 5 years via surveys using the world’s most sensitive
telescopes, new instrumentation, and huge amounts of computing. Specialized “timing” observations of these systems, accounting for each and every one of the billions of rotations of the stars, are providing fantastic results in basic physics. In this talk I’ll focus on the efforts to directly detect gravitational waves from super-massive black hole binaries, make strong-field tests of general relativity, and determine the nature of the densest form of matter known in the universe.

Despite varying speed of light theories (VSL) should be considered as another type of alternative gravity theories with an extra scalar degree of freedom, their formulation causes the problems in view of breaking the light principle and relativity principle. Besides, there are a couple of physical contexts in which c plays the crucial role and it is uncertain that it has the same meaning everywhere. During my talk I will discuss some basic theoretical formulations of varying c theories and discuss their benefits as well as problems. Then, I will review some cosmological tests of VSL theories making also a comparative statistical analysis of the basic theoretical frameworks. Among them, the recent Moffat's varying c approach. 

We are currently entering the era of precision CMB polarization observations. The most exciting scientific targets are a possible detection of primordial gravitational waves and a measurement of the sum of the neutrino masses. The former depends on the extensive landscape of early Universe models, while the latter has been forecasted to present a clear, and reachable, scientific target. First, if large angular B modes are detected, we should firmly establish that these are sourced by primordial gravitational waves. I will discuss that cross correlating the B-mode signal with the curl-lensing field could help establish the nature of the detected B-modes. Second, I will propose to look beyond Gaussianity in the tensor sector. Scalar non-Gaussianities are tightly constrained by Planck, but couplings between tensors and scalars are currently not constrained and future CMB polarization surveys could open a new window into the early Universe, by searching for tensor non-Gaussianites. Finally, a detection of the normal hierarchy of the neutrino mass requires an excellent measurement of the amplitude of primordial fluctuations. The required measurement can only be achieved if we are able to measure the large angle E-mode polarization spectrum, which currently lies beyond reach, at least within the foreseeable future. I will present a possible solution and show how this simple methodology can be used to constrain exotic primordial physics at the same time.