Singularities in any physical theory are either remarkable indicators of the unknown
underlying fundamental theory, or indicate a change in the description of the physical reality …

Gravitational waves (GWs) have a great potential to probe cosmology. We review early
universe sources that can lead to cosmological backgrounds of GWs. We begin by …

The cosmological principle (CP)—the notion that the Universe is spatially isotropic and
homogeneous on large scales—underlies a century of progress in cosmology. It is …

The European Space Agency's Planck satellite, which was dedicated to studying the early
Universe and its subsequent evolution, was launched on 14 May 2009. It scanned the …

We present cosmological parameter results from the final full-mission Planck measurements
of the cosmic microwave background (CMB) anisotropies, combining information from the …

Axions comprise a broad class of particles that can play a major role in explaining the
unknown aspects of cosmology. They are also well-motivated within high energy physics …

Over recent decades, the role of torsion in gravity has been extensively investigated along
the main direction of bringing gravity closer to its gauge formulation and incorporating spin …

A stochastic background of gravitational waves could be created by the superposition of a
large number of independent sources. The physical processes occurring at the earliest …

We present cosmological parameter results from the final full-mission Planck measurements
of the CMB anisotropies. We find good consistency with the standard spatially-flat 6 …

We review the paradigm of holographic dark energy (HDE), which arises from a theoretical
attempt of applying the holographic principle (HP) to the dark energy (DE) problem. Making …