The simplest ΛCDM model provides a good fit to a large span of cosmological data but
harbors large areas of phenomenology and ignorance. With the improvement of the number …

The Swampland program aims to distinguish effective theories which can be completed into
quantum gravity in the ultraviolet from those which cannot. This article forms an introduction …

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 …

We review applications of string theory to cosmology, from primordial times to the present-
day accelerated expansion. Starting with a brief overview of cosmology and string …

The Swampland program aims to determine the constraints that an effective field theory must
satisfy to be consistent with a UV embedding in a quantum gravity theory. Different …

Among Swampland conditions, the distance conjecture characterizes the geometry of scalar
fields and the de Sitter conjecture constrains allowed potentials on it. We point out a …

The recent result of the Dark Energy Spectroscopic Instrument (DESI) in combination with
other cosmological data shows evidence of the evolving dark energy parametrized by the w …

We study constraints imposed by two proposed string Swampland criteria on cosmology.
These criteria involve an upper bound on the range traversed by scalar fields as well as a …

We conjecture that the quantum complexity of a holographic state is dual to the action of a
certain spacetime region that we call a Wheeler-DeWitt patch. We illustrate and test the …

String theory suggests the simultaneous presence of many ultralight axions, possibly
populating each decade of mass down to the Hubble scale 10-33 eV. Conversely the …